阅读说明：本技术 一种含铜耐腐蚀钢轨的焊接方法 (Welding method of copper-containing corrosion-resistant steel rail ) 是由 白威 李大东 陆鑫 徐飞翔 于 2021-08-09 设计创作，主要内容包括：本发明公开了一种含铜耐腐蚀钢轨的焊接方法。该方法包括以下步骤：步骤1)：制备所述含铜耐腐蚀钢轨母材,其中所述含铜耐腐蚀钢轨母材显微组织控制为包括90-100％的珠光体和0-10％的先共析铁素体,并且所述含铜耐腐蚀钢轨母材的组分中包括质量百分比为0.20-0.60％的Cu；步骤2)：对由步骤1)的含铜耐腐蚀钢轨母材制作的多个钢轨进行焊接,控制钢轨焊接顶锻量保持在8.6-9.8mm,焊接采用4.0-8.2MJ的热输入量,钢轨焊接推瘤完成后采用22-25t的保压压力进行保压。该方法通过对钢轨含铜量、焊接的热输入量、钢轨焊接顶锻量和推瘤阶段的保压操作进行控制,可以挺高铁路服役安全性。(The invention discloses a welding method of copper-containing corrosion-resistant steel rails. The method comprises the following steps: step 1): preparing the copper-containing corrosion-resistant steel rail base metal, wherein the microstructure of the copper-containing corrosion-resistant steel rail base metal is controlled to comprise 90-100% of pearlite and 0-10% of pro-eutectoid ferrite, and the composition of the copper-containing corrosion-resistant steel rail base metal comprises 0.20-0.60% of Cu by mass percentage; step 2): welding a plurality of steel rails made of the copper-containing corrosion-resistant steel rail base material obtained in the step 1), controlling the welding upsetting amount of the steel rails to be kept at 8.6-9.8mm, adopting 4.0-8.2MJ heat input amount for welding, and adopting 22-25t pressure maintaining pressure to maintain pressure after the steel rail welding push tumor is finished. The method can improve the safety of the railway service by controlling the copper content of the steel rail, the heat input amount of welding, the welding upsetting amount of the steel rail and the pressure maintaining operation in the stage of pushing the built-up edge.)

1. A welding method of a copper-containing corrosion-resistant steel rail is characterized by comprising the following steps:

step 1): preparing the copper-containing corrosion-resistant steel rail base metal, wherein the microstructure of the copper-containing corrosion-resistant steel rail base metal is controlled to comprise 90-100% of pearlite and 0-10% of pro-eutectoid ferrite, and the composition of the copper-containing corrosion-resistant steel rail base metal comprises 0.20-0.60% of Cu by mass percentage;

step 2): welding a plurality of steel rails made of the copper-containing corrosion-resistant steel rail base material obtained in the step 1), controlling the welding upsetting amount of the steel rails to be kept at 8.6-9.8mm, adopting 4.0-8.2MJ heat input amount for welding, and adopting 22-25t pressure maintaining pressure to maintain pressure after the steel rail welding push tumor is finished.

2. The method of claim 1, further comprising a post-weld cooling step, wherein the post-weld cooling step comprises natural cooling in air to room temperature after the rail weld joint flash is complete.

3. The method of claim 1, wherein the copper-containing corrosion resistant rail parent metal comprises, in weight percent: 0.65-0.85% of C, 0.32-0.68% of Si, 0.70-1.10% of Mn, 0.2-0.5% of Cr, 0.02-0.06% of V, 0.20-0.40% of Ni, 0.20-0.60% of Cu, and the balance of Fe and inevitable impurities.

4. The method of claim 1, wherein the copper-containing corrosion resistant rail parent material is obtained by a method comprising:

heating and rolling the steel billet into a steel rail, standing and cooling in the air;

when the central temperature of the top surface of the rail head is reduced to 850 ℃ plus 790 ℃, respectively blowing cooling media to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head until the central temperature of the top surface of the rail head is reduced to 420 ℃ plus 350 ℃ plus 420 ℃, and then stopping blowing the cooling media;

continue cooling to room temperature in air.

5. The method of claim 4, wherein the cooling medium is injected by cooling the rail at a cooling rate of 3.0-7.0 ℃/s.

6. The method of claim 1, wherein the welding is performed using mobile flash welding.

7. The method according to claim 1, wherein the Cu content in the Cu-containing corrosion-resistant steel rail base metal is 0.40%, the microstructure of the steel rail base metal is 95% pearlite and 5% pro-eutectoid ferrite, the steel rail welding upset forging amount is maintained at 9.5mm, the steel rail welding is performed with a heat input of 7.0MJ, and the pressure in the pressure holding stage is maintained at 24 t.

8. The method according to claim 1, wherein the Cu content in the Cu-containing corrosion-resistant steel rail base metal is 0.35%, the steel rail base metal microstructure is 99% pearlite and 1% pro-eutectoid ferrite, and the rail welding upset is maintained at 8.9mm, rail welding is performed using a heat input of 6.0MJ, and the pressure during the pressure holding stage is maintained at 23 t.

9. The method according to claim 1, wherein the Cu content in the Cu-containing corrosion-resistant steel rail base metal is 0.45%, the microstructure of the steel rail base metal is pearlite at 100%, the steel rail welding upset amount is maintained at 8mm, the steel rail welding is performed by using a heat input of 9.2MJ, and the holding pressure in the holding pressure push-up stage is maintained at 24 t.

10. The method as claimed in claim 1, wherein the copper-containing corrosion resistant rail parent material has a tensile strength of 1100-1280MPa and an elongation of 12-18%.

Technical Field

The invention relates to the technical field of railway steel rail manufacturing, in particular to a welding method of a copper-containing corrosion-resistant steel rail.

Background

The corrosion of steel rails is a technical problem which troubles railways all over the world, and the cost for replacing the steel rails due to the corrosion is hundreds of millions of yuan each year all over the world. With the rapid development of the railway industry, potential safety hazards and economic losses caused by the corrosion problem of the steel rail become more serious, and scholars at home and abroad conduct various technical exploration and attempts to enhance the corrosion resistance of the steel rail.

Copper is a main alloy element for improving the corrosion resistance of steel, and the steel contains a certain amount of copper, so that the corrosion resistance can be effectively improved. When copper and phosphorus are used in combination, the corrosion resistance of the steel is more remarkable. At present, common copper-containing steel comprises Cu-P series weathering steel, Cu-P-Cr-Ni series weathering steel and the like, and is widely applied to the industries of buildings, vehicles, containers and the like. By adopting a mode of adding micro-alloying of Cu, Cr, Ni and the like, the low-alloy high-strength corrosion-resistant steel rail is developed, has the characteristics of high strength, good corrosion resistance and the like, and can be used for passenger transport or passenger and cargo mixed transport railways.

However, if the heating time of the copper-containing steel is too long and the heating temperature is too high during heating, copper is enriched at the grain boundary of the steel surface and erodes the grain boundary, a surface orange skin tissue (essentially surface fine cracking) is caused during subsequent thermomechanical rolling, and the service performance of the corrosion-resistant steel rail is seriously affected, even the driving safety is endangered. In the welding process of the copper-containing corrosion-resistant steel rail, copper elements generated by heating in the welding operation are enriched and corrode crystal boundaries at the welding seams of the steel rail joint and the crystal boundaries of a superheat area, the crystal boundaries are easy to melt, crystal boundary cracks are formed, the problems that follow-up steel rail joints are peeled off and fall off under the action of stress in the service process of a railway line, fatigue fracture and the like are caused, and the service safety of the railway is influenced.

Disclosure of Invention

Aiming at the problems, the invention provides a welding method of a copper-containing corrosion-resistant steel rail. The method comprehensively controls the copper content of the steel rail, the heat input amount of welding, the welding upsetting amount of the steel rail and the pressure maintaining operation in the stage of pushing the built-up edge, can avoid the problem of melting of a crystal boundary in a welding heat affected zone caused by enrichment of alloy elements in a welding seam and a superheat zone of a steel rail joint, and improves the service safety of a high-speed railway.

According to an aspect of the invention, there is provided a method of welding copper-containing corrosion resistant steel rails, the method comprising the steps of:

step 1): preparing a copper-containing corrosion-resistant steel rail base material, wherein the microstructure of the copper-containing corrosion-resistant steel rail base material is controlled to comprise 90-100% of pearlite and 0-10% of pro-eutectoid ferrite, and the composition of the copper-containing corrosion-resistant steel rail base material comprises 0.20-0.60% of Cu by mass percent;

step 2): welding a plurality of steel rails made of the copper-containing corrosion-resistant steel rail base material obtained in the step 1), controlling the welding upsetting amount of the steel rails to be kept at 8.6-9.8mm, adopting 4.0-8.2MJ heat input amount for welding, and adopting 22-25t pressure maintaining pressure to maintain pressure after the steel rail welding push tumor is finished. The inventor researches and discovers that for steel with the copper content of 0.20-0.60%, if the heat input is too large, the retention time of the welding high temperature is too long, the cooling speed of the joint after welding is slow, and the phenomenon of melting (cracking) of the welding heat affected zone grain boundary caused by enrichment of copper element can occur. Too low or too high holding pressure can adversely affect the stability of the welding quality of the steel rail, resulting in the reduction of the tensile and fatigue properties of the steel rail joint.

According to one embodiment of the invention, the method further comprises a post-weld cooling step, wherein the post-weld cooling step comprises natural cooling to room temperature in air after the push beading of the welded joint of the steel rail is finished.

According to one embodiment of the invention, the copper-containing corrosion-resistant steel rail parent material comprises the following components in percentage by weight: 0.65-0.85% of C, 0.32-0.68% of Si, 0.70-1.10% of Mn, 0.2-0.5% of Cr, 0.02-0.06% of V, 0.20-0.40% of Ni, 0.20-0.60% of Cu, and the balance of Fe and inevitable impurities.

According to one embodiment of the invention, the copper-containing corrosion-resistant steel rail parent material is obtained by a method comprising the following steps:

heating and rolling the steel billet into a steel rail, standing and cooling in the air;

when the central temperature of the top surface of the rail head is reduced to 850 ℃ plus 790 ℃, respectively blowing cooling media to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head until the central temperature of the top surface of the rail head is reduced to 420 ℃ plus 350 ℃ plus 420 ℃, and then stopping blowing the cooling media;

continue cooling to room temperature in air.

According to one embodiment of the invention, the cooling medium is blown in such a way that the rail is cooled at a cooling rate of 3.0-7.0 ℃/s.

According to one embodiment of the invention, the welding is performed by mobile flash welding.

According to one embodiment of the invention, the Cu content in the copper-containing corrosion-resistant steel rail base metal is 0.40%, the microstructure of the steel rail base metal is 95% of pearlite and 5% of pro-eutectoid ferrite, the steel rail welding upsetting amount is kept at 9.5mm, the steel rail welding is carried out by adopting the heat input of 7.0MJ, and the pressure in the pressure maintaining stage is kept at 24 t.

According to one embodiment of the invention, the Cu content in the copper-containing corrosion-resistant steel rail base metal is 0.35%, the microstructure of the steel rail base metal is 99% of pearlite and 1% of pro-eutectoid ferrite, the steel rail welding upsetting amount is kept at 8.9mm, the steel rail welding is carried out by adopting the heat input of 6.0MJ, and the pressure in the pressure maintaining stage is kept at 23 t.

According to one embodiment of the invention, the Cu content in the copper-containing corrosion-resistant steel rail base metal is 0.45%, the microstructure of the steel rail base metal is pearlite of 100%, the steel rail welding upsetting amount is kept at 8mm, the steel rail welding is carried out by adopting the heat input of 9.2MJ, and the pressure keeping pressure in the pressure keeping and tumor pushing stage is kept at 24 t.

According to one embodiment of the invention, the copper-containing corrosion-resistant steel rail parent material has the tensile strength of 1100-1280MPa and the elongation of 12-18%.

The welding method of the copper-containing corrosion-resistant steel rail disclosed by the invention is used for designing a welding process matched with the material components based on the components and the copper content of the steel rail base metal. By adopting the welding method, the phenomenon of crystal boundary melting of a welding heat affected zone caused by the enrichment of alloy elements can be avoided in a zone which is +/-20 mm away from the center of a welding seam, and meanwhile, the generation probability of welding dust spots can be effectively reduced. The full-section tensile strength Rm of the flash welding joint of the corrosion-resistant heat-treated steel rail in a welded state obtained by the method is more than or equal to 900MPa, the average hardness of the longitudinal section of the joint reaches more than 90% of the hardness of a base metal of the steel rail, the fatigue life of the joint reaches more than 300 ten thousand times, and the service safety of the steel rail is obviously improved.

Drawings

FIG. 1 is a schematic view of the various zones of a rail weld joint.

Fig. 2 is a schematic diagram of the positions of the metallographic samples taken in the examples and the comparative examples.

FIG. 3 is a metallographic structure chart of example 1.

FIG. 4 is a metallographic structure chart of example 2.

FIG. 5 is a metallographic structure chart of example 3.

FIG. 6 is a metallographic structure chart of example 4.

FIG. 7 is a metallographic structure chart of example 5.

Fig. 8 is a metallographic structure diagram of comparative example 1.

Fig. 9 is a metallographic structure diagram of comparative example 2.

Fig. 10 is a tensile fracture diagram of comparative example 3.

FIG. 11 is a tensile fracture plot of comparative example 4.

FIG. 12 is a tensile fracture plot of comparative example 5.

FIG. 13 is a fracture metallographic structure chart of comparative example 6.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Copper diffuses most readily between 1100 ℃ and 1200 ℃ during the heating of the copper-containing steel weld, so that the residence time in this zone is minimized. If the high-temperature retention time is too long and the temperature is too high, copper elements are easy to enrich and corrode crystal boundaries at the weld joints of the steel rail joints and the crystal boundaries of the superheat region, the crystal boundaries are easy to melt, crystal boundary cracks are formed, and the problems of stripping and chipping, fatigue fracture and the like of the follow-up steel rail joints under the action of stress in the service process of a railway line are caused, so that the service safety of the railway is influenced. Therefore, the welding heat input amount is strictly controlled based on the structure and the components of the base metal in the steel rail welding process, and the high-temperature residence time of welding is reduced. Meanwhile, the performance control of the steel rail welding joint needs to be matched with proper upsetting amount and pressure maintaining pressure in a tumor pushing stage so as to fully eliminate welding dust spots, welding slag inclusions and other defects possibly formed in a welding seam and reduce the influence of the welding defects on the mechanical property of the steel rail joint.

In the invention, the steel rail welding joint is a region which is obtained after welding and has a length of 60-100 mm including a welding seam. The full section refers to the whole section of the steel rail welding joint, including a welding seam, with the length of about 60-100 mm, and comprises a rail head, a rail web and a rail bottom.

The microstructure of the base material of the copper-containing corrosion-resistant steel rail of the invention is controlled to be pearlite 90-100% and pro-eutectoid ferrite 0-10% (volume percentage). The tensile strength of the base material is 1100-1280MPa, and the elongation is 12-18%. The chemical components of the steel rail base metal for obtaining the microstructure need to meet the following conditions (by mass percent): 0.65-0.85% of C, 0.32-0.68% of Si, 0.70-1.10% of Mn, 0.2-0.5% of Cr, 0.02-0.06% of V, 0.20-0.40% of Ni, 0.20-0.60% of Cu, and the balance of Fe and inevitable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then is kept stand and is cooled in the air, when the central temperature of the top surface of the rail head is reduced to 790-850 ℃, cooling media are respectively sprayed to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws of the two sides of the rail head, so that the cooling speed is 3.0-7.0 ℃/s, and when the central temperature of the top surface of the rail head is reduced to 350-420 ℃, the accelerated cooling is stopped and the air cooling is continued to the room temperature (20-25 ℃). The steel rail rolling of the invention is based on a universal rolling production line, and the steel rail structure performance is controlled based on an on-line heat treatment production line after the steel rail is rolled.

Wherein the welding process controls the welding upset amount to be kept between 8.6 and 9.8 mm. The invention enters the welding process control stage after the steel rail is rolled, and the upset forging amount is specially controlled. If the welding upset forging amount is too small, the welding seam has unremoved dust spots and welding slag, and the mechanical property of the joint is reduced; if the welding upset amount is controlled too much, a cold joint is easily formed, and the mechanical properties of the joint are also reduced. In practice, the optimum upsetting amount needs to be confirmed by carrying out a large number of experiments related to static bending, drop weight, stretching and the like on the rail joint.

The steel rail mobile flash welding machine is used for carrying out a welding test by adopting 4.0-8.2MJ moderate heat input. If the heat input is too large, the retention time of the welding high temperature is too long, the cooling speed of the welded joint is slow, and the problem of melting (cracking) of the welding heat affected zone grain boundary formed by copper element enrichment may occur.

Wherein, the post-welding cooling is controlled to be naturally cooled to room temperature in the air after the push beading of the steel rail welding joint is finished.

And in the pressure maintaining stage after the steel rail welding push button is finished, 22-25t of pressure maintaining pressure is adopted, so that the steel rail welding quality is further stabilized. Too low or too high holding pressure can adversely affect the stability of the welding quality of the steel rail, resulting in the reduction of the tensile and fatigue properties of the steel rail joint.

Fig. 1 shows a schematic view of the various zones of a rail weld joint. In the examples and comparative examples, the positions of the longitudinal section hardness detection points 3 to 5mm below the rail head tread of the welded rail joint are shown in fig. 1, where a is the rail welding heat affected zone, b is the rail head tread of the welded rail joint, and c is the weld center. In fig. 2, the position c is the center of the weld joint, and the position d is the sampling position of the metallographic specimen of the rail head tread of the steel rail welding joint.

Example 1

The microstructure of the steel rail base material is controlled to be 90% of pearlite and 10% of pro-eutectoid ferrite. The tensile strength of the base material was 1150MPa, and the elongation thereof was 13%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: c at a content of 0.65%, Si at a content of 0.32%, Mn at a content of 1.1%, Cr at a content of 0.5%, V at a content of 0.06%, Ni at a content of 0.20%, Cu at a content of 0.60%, and the balance Fe and inevitable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 790 ℃, cooling media with the cooling speed of 3.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 350 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to the room temperature (25 ℃).

The rail is flash welded by a rail mobile flash welding machine with 4.0MJ moderate heat input, the actual welding upset amount is kept at 8.6mm, the pressure in the pressure maintaining stage is kept at 22t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint push-up is finished.

The rail joint obtained in this example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the method, the phenomenon of grain boundary fusion does not occur in the steel rail welding seam and the welding heat affected zone within +/-20 mm from the center of the welding seam. As shown in fig. 3, at an observation magnification of 100X, the weld microstructure was pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone microstructure was fully pearlite. The average value of the tensile strength of the whole section of the steel rail flash welding joint is 910MPa, the average hardness of the longitudinal section of the joint reaches 91 percent of the hardness of the steel rail base metal, the fatigue life of the joint reaches 300 ten thousand times, and the mechanical property of the welding joint meets various requirements of the service safety of the steel rail.

Example 2

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by a movable flash welding machine of the rail and adopting the intermediate heat input of 7.0MJ, the actual welding upset forging quantity is kept at 9.5mm, the pressure in the pressure maintaining stage is kept at 24t, and the steel rail is naturally cooled (air cooled) to the room temperature after the joint push-up is finished.

The rail joint obtained in this example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the method, the phenomenon of grain boundary fusion does not occur in the steel rail welding seam and the welding heat affected zone within +/-20 mm from the center of the welding seam. As shown in fig. 4, at an observation magnification of 100X, the weld structure was pearlite and pro-eutectoid ferrite along the crystal, and the heat-affected zone structure was fully pearlite. The average value of the tensile strength of the whole section of the steel rail flash welding joint is 920MPa, the average hardness of the longitudinal section of the joint reaches 92% of the hardness of a steel rail base metal, the fatigue life of the joint reaches 300 ten thousand times, and the mechanical property of the welding joint meets various requirements of the service safety of the steel rail.

Example 3

The microstructure of the steel rail base material is controlled to be 99% of pearlite and 1% of pro-eutectoid ferrite, the tensile strength is 1220MPa, and the elongation is 15%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.76% by weight of C, 0.60% by weight of Si, 0.85% by weight of Mn, 0.4% by weight of Cr, 0.04% by weight of V, 0.25% by weight of Ni, 0.35% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the rail steel with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 830 ℃, cooling media with the cooling speed of 5.5 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to the room temperature (25 ℃).

The rail is flash welded by using a rail mobile flash welding machine and adopting 6.0MJ moderate heat input, the actual welding upset forging quantity is kept at 8.9mm, the pressure in the pressure maintaining stage is kept at 23t, and when the joint push-up is finished, the steel rail is naturally cooled (air cooled) to the room temperature.

The rail joint obtained in this example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the method, the phenomenon of grain boundary fusion does not occur in the steel rail welding seam and the welding heat affected zone within +/-20 mm from the center of the welding seam. As shown in fig. 5, at an observation magnification of 100X, the weld structure was pearlite and pro-eutectoid ferrite along the crystal, and the heat-affected zone structure was fully pearlite. The average value of the tensile strength of the whole section of the steel rail flash welding joint is 930MPa, the average hardness of the longitudinal section of the joint reaches 93 percent of the hardness of the steel rail base metal, the fatigue life of the joint reaches 300 ten thousand times, and the mechanical property of the welding joint meets various requirements of the service safety of the steel rail.

Example 4

The microstructure of the steel rail base metal is controlled to be 100% of pearlite, the tensile strength of the steel rail base metal is 1270MPa, and the elongation of the steel rail base metal is 12.2%. The chemical components of the steel rail steel for obtaining the microstructure need to meet the following conditions: 0.82% by weight of C, 0.54% by weight of Si, 0.88% by weight of Mn, 0.46% by weight of Cr, 0.025% by weight of V, 0.30% by weight of Ni, 0.45% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the rail steel with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by using a rail mobile flash welding machine and adopting 8.0MJ medium heat input, the actual welding upset forging quantity is kept at 9.2mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 24t, and when the joint bump pushing is finished, the steel rail is naturally cooled (air cooled) to room temperature.

The rail joint obtained in this example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. Performing three-point bending fatigue test on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and taking the condition that the welding joint does not generate fatigue fracture when cyclic load is loaded for 300 ten thousand times as a test target; referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the method, the phenomenon of grain boundary fusion does not occur in the steel rail welding seam and the welding heat affected zone within +/-20 mm from the center of the welding seam. As shown in fig. 6, at an observation magnification of 100X, the weld structure was pearlite and pro-eutectoid ferrite along the crystal, and the heat-affected zone structure was fully pearlite. The average value of tensile strength of the whole section of the steel rail flash welding joint is 925MPa, the average hardness of the longitudinal section of the joint reaches 92% of the hardness of a steel rail base metal, the fatigue life of the joint reaches 300 ten thousand times, and the mechanical property of the welding joint meets various requirements of service safety of the steel rail.

Example 5

The microstructure of the steel rail base material is controlled to be 92% of pearlite and 8% of proeutectoid ferrite. The base material had a tensile strength of 1230MPa and an elongation of 15%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.85% C, 0.68% Si, 0.70% Mn, 0.2% Cr, 0.02% V, 0.40% Ni, 0.20% Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 850 ℃, cooling media with the cooling speed of 7.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 420 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to the room temperature (25 ℃).

The rail is flash welded by using a rail mobile flash welding machine and adopting 8.2MJ medium heat input, the actual welding upset forging quantity is kept at 9.8mm, the pressure in the pressure maintaining stage is kept at 25t, and when the joint push-up is finished, the steel rail is naturally cooled (air cooled) to the room temperature.

The rail joint obtained in this example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the method, the phenomenon of grain boundary fusion does not occur in the steel rail welding seam and the welding heat affected zone within +/-20 mm from the center of the welding seam. As shown in fig. 7, at an observation magnification of 100X, the weld structure was pearlite and pro-eutectoid ferrite along the crystal, and the heat-affected zone structure was fully pearlite. The average value of tensile strength of the whole section of the steel rail flash welding joint is 930MPa, the average hardness of the longitudinal section of the joint reaches 94% of the hardness of the steel rail base metal, the fatigue life of the joint reaches 300 ten thousand times, and the mechanical property of the welding joint meets various requirements of the service safety of the steel rail.

Comparative example 1

The microstructure of the steel rail base metal is controlled to be 95 percent of pearlite and 5 percent of pro-eutectoid ferrite, the tensile strength is 1200MPa, and the elongation is 15 percent. The chemical components of the steel rail steel for obtaining the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.90% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the rail steel with the microstructure needs to meet the following conditions: the processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The steel rail is flash welded by a steel rail mobile flash welding machine with 7MJ medium heat input, the actual welding upset amount is kept at 9.5mm, the pressure in the pressure maintaining stage is kept at 24t, and when the joint beading is finished, the steel rail is naturally cooled (air cooled) to room temperature.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. Performing three-point bending fatigue test on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and taking the condition that the welding joint does not generate fatigue fracture when cyclic load is loaded for 300 ten thousand times as a test target; referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the steel rail welding joint treated by the comparative example, due to the fact that the copper content in the steel rail base metal is too high, the obvious grain boundary melting phenomenon occurs in a steel rail welding heat affected zone within a +/-10 mm area from the center of a welding line in the welding process. As shown in fig. 8, the metallographic photograph shows the presence of grain boundary melting voids. At 100 Xobservation magnification, the weld and heat affected zone were organized normally. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is full pearlite. The average value of the tensile strength of the whole section of the flash welding joint of the steel rail is only 650MPa, the average hardness of the longitudinal section of the joint reaches 91 percent of the hardness of a base metal of the steel rail, but the fatigue life of the joint is 150 ten thousand times due to the occurrence of the phenomenon of melting of a grain boundary of a welding heat affected zone, and the operation safety of the railway is not facilitated.

Comparative example 2

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is welded by a rail mobile flash welding machine with 13.0MJ large heat input, the actual welding upset amount is kept at 9.5mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 24t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint bump pushing is finished.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: with the rail welded joint treated in the comparative example, a partial grain boundary melting phenomenon occurred in the rail welding heat affected zone within ± 15mm from the center of the weld due to excessive welding heat input during welding (as shown in fig. 9). Referring to fig. 9, at 100X observation magnification, the weld and heat affected zone organization were normal. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is pearlite and a small amount of pro-eutectoid ferrite. The average value of the tensile strength of the whole section of the flash welding joint of the steel rail is only 500MPa, the high-temperature retention time is too long due to the overlarge welding heat input, the average hardness of the longitudinal section of the joint only reaches 82% of the hardness of a base metal of the steel rail, and meanwhile, the fatigue life of the joint is 140 ten thousand times due to the occurrence of the phenomenon of melting of a crystal boundary of a welding heat affected zone, so that the flash welding joint of the steel rail is not beneficial to the running safety of the railway.

Comparative example 3

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by a rail mobile flash welding machine with 7.0MJ moderate heat input, the actual welding upset amount is kept at 7.0mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 24t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint bump pushing is finished.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the rail welded joint treated by the comparative example, no grain boundary melting phenomenon occurred in the rail welding heat affected zone within ± 20mm from the center of the weld. At 100 Xobservation magnification, the weld and heat affected zone were organized normally. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is full pearlite. In the welding process, the welding dust spot defect at the welding seam is not eliminated (as shown in figure 10) due to the fact that the welding upsetting amount of the steel rail is too small, the tensile property of the joint is reduced, the average value of the tensile strength of the whole section of the flash welding head of the steel rail is only 850MPa, the average hardness of the longitudinal section of the joint reaches 91% of the hardness of the base metal of the steel rail, the fatigue life of the joint is only 180 ten thousand times due to the existence of the welding dust spot at the welding seam, and the safety of railway operation is not facilitated.

Comparative example 4

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by a rail mobile flash welding machine with 7.0MJ moderate heat input, the actual welding upset amount is kept at 9.5mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 30t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint bump pushing is finished.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the rail welded joint treated by the comparative example, no grain boundary melting phenomenon occurred in the rail welding heat affected zone within ± 20mm from the center of the weld. At 100 Xobservation magnification, the weld and heat affected zone were organized normally. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is pearlite and a small amount of pro-eutectoid ferrite. Excessive weld metal is discharged due to excessive holding pressure in the holding pressure push-up stage, fusion between the metal at the weld is poor, and a cold joint is formed (as shown in figure 11), so that the tensile and fatigue properties of the steel rail joint are reduced. The average value of the tensile strength of the whole section of the steel rail flash welding head is only 800MPa, the average hardness of the longitudinal section of the joint reaches 91 percent of the hardness of the steel rail base metal, and the fatigue life of the joint is only 130 ten thousand times due to the occurrence of cold joints, so that the steel rail flash welding head is not beneficial to the running safety of a railway.

Comparative example 5

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by a rail mobile flash welding machine with 7.0MJ moderate heat input, the actual welding upset amount is kept at 12.5mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 24t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint bump pushing is finished.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: for the rail welded joint treated by the comparative example, no grain boundary melting phenomenon occurred in the rail welding heat affected zone within ± 20mm from the center of the weld. At 100 Xobservation magnification, the weld and heat affected zone were organized normally. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is pearlite and a small amount of pro-eutectoid ferrite. Due to the excessive upset forging, excessive weld metal is discharged, fusion between the metal at the weld is poor, and a cold joint is formed (as shown in fig. 12), so that the tensile and fatigue properties of the steel rail joint are reduced. The average value of the tensile strength of the whole section of the flash welding joint of the steel rail is only 780MPa, the average hardness of the longitudinal section of the joint reaches 91 percent of the hardness of the base metal of the steel rail, and the fatigue life of the joint is only 140 ten thousand times due to the occurrence of cold joints, so that the flash welding joint of the steel rail is not beneficial to the running safety of the railway.

Comparative example 6

The microstructure of the steel rail base metal is controlled to be 95% of pearlite and 5% of proeutectoid ferrite. The base material had a tensile strength of 1250MPa and an elongation of 14%. The chemical components of the steel rail base metal with the microstructure need to meet the following conditions: 0.68% by weight of C, 0.45% by weight of Si, 0.90% by weight of Mn, 0.3% by weight of Cr, 0.04% by weight of V, 0.30% by weight of Ni, 0.40% by weight of Cu, and the balance Fe and unavoidable impurities. The processing technology of the steel rail base metal with the microstructure needs to meet the following conditions: the steel billet is heated and rolled into a 60kg/m single-weight steel rail, then the steel rail is placed in the air for cooling, when the central temperature of the top surface of the rail head is reduced to 820 ℃, cooling media with the cooling speed of 6.0 ℃/s are respectively blown to the top surface of the rail head, the two side surfaces of the rail head and the lower jaws at the two sides of the rail head to 400 ℃, then the accelerated cooling is stopped, and the steel rail is continuously air-cooled to room temperature (25 ℃).

The rail is flash welded by a rail mobile flash welding machine with 10.0MJ moderate heat input, the actual welding upset amount is kept at 9.5mm, the pressure maintaining pressure in the pressure maintaining and bump pushing stage is kept at 24t, and the steel rail is naturally cooled (air cooled) to room temperature after the joint bump pushing is finished.

The rail joint obtained in this comparative example was machined into a longitudinal hardness test specimen. Joint hardness test according to TB/T1632.2-2014 Rail weld part 2: the method is carried out according to GB/T230.1-2009, and adopts HRC scale, and uses Hp to represent the average hardness value of the steel rail base metal, Hj to represent the average hardness value of the joint, and the position of the joint with the hardness lower than 0.9Hp to represent a softening area. A three-point bending fatigue test is carried out on a steel rail welding joint by adopting an MTS-FT310 type fatigue testing machine, and the aim of the test is that the welding joint does not generate fatigue fracture when the cyclic load is loaded for 300 ten thousand times. Referring to the sampling method shown in FIG. 2, metallographic structure examination is carried out on the metallographic structure sample of the steel rail joint according to GB/T13298-2015 metal microstructure examination method, etching is carried out on the metallographic structure sample of the steel rail joint by adopting a 3% nitric acid alcohol solution, and the metallographic structure of the steel rail joint is observed by adopting a German Leica MeF3 optical microscope.

The results show that: with the welded rail joint treated by the present comparative example, a grain boundary melting phenomenon occurred in the weld heat affected zone of the rail within ± 10mm from the center of the weld, as shown in fig. 13. At 100 Xobservation magnification, the weld and heat affected zone were organized normally. Wherein the weld structure is pearlite and pro-eutectoid ferrite along the crystal, and the heat affected zone structure is pearlite and a small amount of pro-eutectoid ferrite. The average value of the tensile strength of the whole section of the flash welding joint of the steel rail is only 560MPa, the high-temperature retention time is long due to large welding heat input, the average hardness of the longitudinal section of the joint only reaches 85% of the hardness of a base material of the steel rail, and meanwhile, the fatigue life of the joint is 160 ten thousand times due to the occurrence of the phenomenon of melting of a grain boundary of a welding heat affected zone, so that the flash welding joint of the steel rail is not beneficial to the running safety of the railway.

As can be seen by comparing examples 1 to 5 with comparative examples 1 to 6: by adopting the welding method of the copper-containing corrosion-resistant steel rail, the phenomenon of crystal boundary melting of a welding heat affected zone caused by enrichment of alloy elements (mainly copper) can be avoided in a region which is +/-20 mm away from the center of a welding seam, the generation probability of welding dust spots can be effectively reduced, and a martensite structure in a steel rail joint heat affected zone is avoided. The full-section tensile strength Rm of the flash welded joint of the corrosion-resistant heat-treated steel rail in the welded state obtained by the method is not less than 900MPa, the average hardness of the longitudinal section of the joint reaches more than 90% of the hardness of the base metal of the steel rail, the fatigue life of the joint reaches more than 300 ten thousand times, and the method is favorable for ensuring the running safety of the railway.

The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.