阅读说明：本技术 消除75kg/m过共析钢轨移动闪光焊接头过烧缺陷的方法 (Method for eliminating overburning defect of mobile flash welding head of hypereutectoid steel rail of 75kg/m ) 是由 李大东 陆鑫 王若愚 邓健 于 2021-07-23 设计创作，主要内容包括：本发明公开了一种消除75kg/m过共析钢轨移动闪光焊接头过烧缺陷的方法,属于铁路钢轨焊接技术领域。消除75kg/m过共析钢轨移动闪光焊接头过烧缺陷的方法通过前期脉动阶段控制焊接热输入、后期烧化阶段的位移控制、以及顶锻量的控制,可消除过共析钢轨移动闪光焊接头轨底出现的点状或条状过烧孔洞缺陷；同时,本发明控制焊后热处理工艺细化钢轨晶粒,提高韧塑性和踏面硬度,使过共析钢轨闪光焊接头满足TB/T1632.2-2014行业标准规定连续15支接头通过落锤检验的技术要求,可有效解决现有过共析钢轨闪光焊接头质量较差,难以通过中国铁道行业TB/T1632标准的问题。(The invention discloses a method for eliminating the overburning defect of a moving flash welding head of a 75kg/m hypereutectoid steel rail, belonging to the technical field of railway steel rail welding. The method for eliminating the overburning defect of the moving flash welding head of the hypereutectoid steel rail of 75kg/m can eliminate the spot or strip-shaped overburning hole defect at the rail bottom of the moving flash welding head of the hypereutectoid steel rail by controlling welding heat input in an early pulsation stage, displacement control in a later burning stage and upset amount control; meanwhile, the invention controls the postweld heat treatment process to refine steel rail crystal grains, improves the toughness and plasticity and the tread hardness, ensures that the hypereutectoid steel rail flash welding head meets the technical requirement that continuous 15 joints pass drop hammer inspection according to the TB/T1632.2-2014 industrial standard, and can effectively solve the problems that the existing hypereutectoid steel rail flash welding head has poor quality and is difficult to pass the TB/T1632 standard of the China railway industry.)

1. The method for eliminating the overburning defect of the moving flash welding head of the hypereutectoid steel rail of 75kg/m is characterized by comprising the following steps of:

a. a welding procedure: controlling the total heat input quantity of welding in the moving flash welding process to be 11.0-13.5MJ, the time of an early pulse heating stage to be 65-70s, the accelerated burning displacement of a later stage to be 10.0-12.0mm, and the actual upset forging quantity of welding to be 11.0-13.0 mm;

b. postweld heat treatment: after the post-welding joint is air-cooled to less than 400 ℃, the joint is heated to the tread temperature of 900-.

2. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 1, wherein: and in the step a, controlling the total heat input quantity of the welding in the mobile flash welding process to be 12.0-13.5 MJ.

3. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 1, wherein: in the step a, the actual upsetting amount of the welding is controlled to be 12.0-13.0 mm.

4. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 1, wherein: in the step b, the heating mode is intermediate frequency heating or flame full-section heating.

5. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 4, wherein: the full-section heating of the flame is that the joint railhead, the rail web and the rail bottom are heated simultaneously, and the temperature difference is less than 50 ℃.

6. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 1, wherein: in the step b, the air cooling is realized by adopting the air pressure of 0.20-0.25MPa to spray air to the tread area of the joint.

7. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 6, wherein: the air pressure adopted for air cooling is 0.20-0.22 MPa.

8. The method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail as claimed in claim 1 or 6, wherein: the tread refers to a contact part of a wheel and a steel rail.

Technical Field

The invention belongs to the technical field of railway steel rail welding, and relates to a method for eliminating the overburning defect of a mobile flash welding head of a hypereutectoid steel rail of 75 kg/m.

Background

At present, railway lines at home and abroad all adopt a welding jointless track technology, fixed and mobile flash welding is a main method and process for welding rails, and according to the standard series standard TB/T1632.2-2014 part 2 of rail welding: the standard technique of flash welding requires that the joint must pass a drop hammer test, that a fixed flash welding process must continuously pass a 25-branch joint drop hammer test, and that a mobile flash welding process must continuously pass a 15-branch joint drop hammer test. 0.85-1.10% of high carbon hypereutectoid steel rails are subjected to drop weight test, and about 80% of broken flash welding heads are subjected to 1-hammer breakage caused by the point or strip-shaped overburning hole defect in a HAZ region with the subsurface depth of 0-2.0mm in the center of the rail bottom, and then are broken due to the gray spot defect. Compared with the existing U71Mn, U75V and U78CrV steel rail flash welding joints which basically have no rail bottom overburning defect due to drop hammer breakage, the difficulty of passing drop hammer inspection of 0.85-1.10% high-carbon hypereutectoid steel rail flash welding is greatly increased.

The reason that 0.85-1.10% of flash welding head of the hypereutectoid steel rail with high carbon content is easy to generate point-shaped or strip-shaped overburning hole defects in an HAZ area with the depth of 0-2.0mm at the subsurface of the center of the rail bottom is that the melting point is reduced due to the increase of the carbon content, and the liquidus temperature T of the hypereutectoid steel rail is_LCompared with U71Mn and U75V steel rails, the temperature of the solidus line Ts is respectively 17-11 ℃ lower and 42-28 ℃ lower, which shows that the hypereutectoid steel rail is particularly easy to cause the overburning defect of the HAZ area of the rail bottom of the steel rail joint due to the lower temperature of the liquid-solid phase line under the same welding heat input condition.

At present, a lot of technologies for welding hypereutectoid steel rails are researched, but no relevant research is provided for improving the defect of rail bottom overburning holes in flash welding of high-carbon hypereutectoid steel rails, so that it is necessary to research how to improve the defect of overburning of a mobile flash welding head of the hypereutectoid steel rails so as to enable the defect to meet the TB/T1632.2-2014 industrial standard.

Disclosure of Invention

The invention aims to solve the technical problem that the existing hypereutectoid steel rail flash welding head has poor quality and is difficult to pass the TB/T1632 standard of the China railway industry.

The technical scheme adopted by the invention for solving the technical problems is as follows: the method for eliminating the overburning defect of the moving flash welding head of the hypereutectoid steel rail of 75kg/m comprises the following steps of:

a. a welding procedure: controlling the total heat input quantity of welding in the moving flash welding process to be 11.0-13.5MJ, the time of an early pulse heating stage to be 65-70s, the accelerated burning displacement of a later stage to be 10.0-12.0mm, and the actual upset forging quantity of welding to be 11.0-13.0 mm;

b. postweld heat treatment: after the post-welding joint is air-cooled to less than 400 ℃, the joint is heated to the tread temperature of 900-.

And in the step a, controlling the total heat input quantity of the welding in the mobile flash welding process to be 12.0-13.5 MJ.

In the step a, the actual upsetting amount of the welding is controlled to be 12.0-13.0 mm.

In the step b, the heating mode is intermediate frequency heating or flame full-section heating.

The full-section heating by flame is to heat the joint rail head, the rail web and the rail bottom simultaneously, and the temperature difference is less than 50 ℃.

In the step b, the air cooling is to spray air to the tread area of the joint by adopting the air pressure of 0.20-0.25 MPa.

Further, the air cooling adopts the air pressure of 0.20-0.22 MPa.

The tread is a contact portion between the wheel and the rail.

The invention has the beneficial effects that: the method for eliminating the overburning defect of the moving flash welding head of the 75kg/m hypereutectoid steel rail can avoid the overburning defect while ensuring that oxides in a welding line are completely extruded by controlling the heat input amount to be 11.0-13.5 MJ; controlling the later accelerated burning displacement to be 10.0-12.0mm so as to ensure the temperature situation physical distribution of the joint; the welding seam oxide can be completely extruded by controlling the actual upsetting amount of welding, and the drop hammer performance of the cold joint cannot be reduced. According to the invention, through controlling welding heat input in an early-stage pulsation stage, displacement control in a later-stage burning stage and control of upsetting amount, the defects of point-shaped or strip-shaped overburning holes at the rail bottom of the mobile flash welding head of the hypereutectoid steel rail can be eliminated; meanwhile, the invention controls the post-welding heat treatment process to refine steel rail crystal grains, improves the toughness and plasticity and the tread hardness, and ensures that the hypereutectoid steel rail flash welding head meets the technical requirement that continuous 15 joints pass drop hammer inspection according to the TB/T1632.2-2014 industrial standard.

The steel rail treated by the method has the weight of 1000kg according to the TB/T1632.2-2014 standard, the joint drop weight test is carried out according to the height of a 6.4m hammer head, and 15 continuous joints can meet the continuous technical requirement of 1 hammer. The method for eliminating the spot or strip-shaped overburning hole defects at the rail bottom of the hypereutectoid steel rail moving flash welding head has the advantages of simple and easy welding parameter setting and welding operation process, stable drop hammer detection result and strong practicability.

Drawings

FIG. 1 is a recorded curve of 75kg/m hypereutectoid steel rail moving flash welding of example 3 of the present invention.

Detailed Description

The technical solution of the present invention can be specifically implemented as follows.

The method for eliminating the overburning defect of the moving flash welding head of the hypereutectoid steel rail of 75kg/m comprises the following steps of:

a. a welding procedure: controlling the total heat input quantity of welding in the moving flash welding process to be 11.0-13.5MJ, the time of an early pulse heating stage to be 65-70s, the accelerated burning displacement of a later stage to be 10.0-12.0mm, and the actual upset forging quantity of welding to be 11.0-13.0 mm;

b. postweld heat treatment: after the post-welding joint is air-cooled to less than 400 ℃, the joint is heated to the tread temperature of 900-.

The welding heat input is the definite integral of time, current, voltage and other parameters. In the step a, the time of the early pulse heating stage is controlled to be 65-70s because the heat input of other stages of welding is small, mainly represented by the heat input of the pulse heating stage, and the time directly influences the heat input under the current and voltage setting condition.

And the excessive heat input amount can cause over-burning defects, and the insufficient heat input amount can cause incomplete extrusion of oxides in the welding seam, thereby influencing the drop weight performance of the joint, therefore, in the step a, the total heat input amount of the welding in the moving flash welding process is preferably controlled to be 12.0-13.5 MJ.

Because the burning displacement is mainly controlled in the 5-8 welding stage, other voltage and current have little influence, and only the stable flash burning can be ensured; and the control of the accelerated burning displacement can ensure the reasonable distribution of the temperature field of the joint, so in the step a, the later accelerated burning displacement is controlled to be 10.0-12.0 mm.

Controlling the amount of upset ensures that the weld bead oxide is completely extruded without reducing drop weight performance with the formation of a cold joint, and therefore it is preferable to control the actual amount of upset of the weld to be 12.0-13.0mm in step a above.

In the step b, the heating mode is intermediate frequency heating or flame full-section heating; the full-section heating of the flame is that the joint railhead, the rail web and the rail bottom are heated simultaneously, and the temperature difference is less than 50 ℃. The heating is carried out until the temperature of the whole section of the steel rail reaches A_Cm(758 ℃) above the total austenitizing temperature, and provides for the next step of increasing the ductility and hardness of the tread by accelerated air cooling. Because the heating speed of the medium-frequency or flame normalizing is higher than that of the heating speed under the equilibrium state of the common heat treatment condition, the heating speed is required to be A_CmOn the basis of improving the full austenitization at 140-160 ℃; meanwhile, the heating temperature is too high, which can cause the coarsening of the crystal grains, so after the tread heating temperature is controlled to 900-920 ℃, the heating is stopped as an infrared control signal of the heat treatment unit, and the tread air cooling program is switched.

Since the air pressure is high or low and affects the hardness of the tread (the contact part of the wheel and the steel rail) and the width of the softening zone, the higher the air pressure is, the higher the hardness of the joint is, and the narrower the softening zone is, it is preferable to blow air to the tread area of the joint by using the air pressure of 0.20-0.25 MPa. Generally, the final cooling temperature is used as a stop signal of the air cooling ending, the higher the air cooling pressure is, the higher the temperature rise of the joint after the air cooling ending is, and the lower the hardness of the joint is caused, so the air pressure needs to be controlled in a proper range, and the air pressure is more preferably 0.20-0.22 MPa.

The technical solution and effects of the present invention will be further described below by way of practical examples.

Examples

The invention provides 4 groups of examples for processing a 75kg/m hypereutectoid steel rail mobile flash welding head by adopting the method, wherein the carbon content of the hypereutectoid steel rail is 0.85-1.10%.

Example 1

When a steel rail is used for welding a long rail by using a movable flash welding machine, the time of a pulse heating stage at the early stage is controlled to be 65s, the accelerated burning displacement at the later stage is 10.0mm, the heat input of a joint is strictly controlled within the range of 11.0MJ, and the actual upsetting quantity of welding is kept at 11.0 mm.

When the welded joint is cooled to below 400 ℃, heating the joint by adopting a medium-frequency heating method until the tread temperature reaches 900 ℃ peak temperature, immediately spraying air to the tread area of the joint by adopting 0.20MPa of air pressure, and stopping air cooling after the tread temperature of the joint is cooled to 460 ℃ to naturally cool the joint to room temperature.

The joint drop weight test is carried out on the treated steel rail, the weight of the steel rail is 1000kg according to the TB/T1632.2-2014 standard, the height of a hammer head is 6.4m, and the steel rail of the embodiment 1 can continuously meet the technical requirement of 1 hammer for 15 joints.

Example 2

When the welding type detection is carried out, the time of a pulse heating stage at the early stage is controlled to be 68s, the accelerated burning displacement at the later stage is controlled to be 10.5mm, the heat input of a joint is strictly controlled to be within the range of 12.5MJ, and the actual upsetting amount of welding is kept to be 11.0 mm.

When the welded joint is cooled to below 400 ℃, heating the joint by adopting a flame full-section heating method until the tread temperature reaches 910 ℃ peak temperature, immediately spraying air to the tread area of the joint by adopting 0.22MPa of air pressure, and stopping air cooling after the tread temperature of the joint is cooled to 460 ℃ to naturally cool the joint to room temperature.

The joint drop weight test is carried out on the treated steel rail, the weight of the steel rail is 1000kg according to the TB/T1632.2-2014 standard, the height of the hammer head is 6.4m, and the steel rail of the embodiment 2 can continuously meet the technical requirement of 1 hammer for 15 joints.

Example 3

When the welding type detection is carried out, the time of the pulse heating stage at the 2-4 stages at the early stage is controlled to be 70s, the accelerated burning displacement at the 5-8 stages at the later stage is set to be 12.0mm, the total heat input of the joint is strictly controlled within the range of 13.5MJ, and the actual upsetting amount of the welding is kept at 13.0 mm.

FIG. 1 is a recorded curve of the 75kg/m hypereutectoid steel rail mobile flash welding of the embodiment 3 of the present invention, which can be known as follows: wherein the voltage of phase 2 is set to 360V, the time is 25s, the current 1 is set to 300A, the current 2 is set to 350A, the current 3 is set to 350A, and the current 4 is set to 600A; stage 3 voltage set 340V, time 25s, current 1 set 200A, current 2 set 350A, current 3 set 370A, current 4 set 580A; phase 4 voltage setting 355V, time 20s, current 1 setting 200A, current 2 setting 370A, current 3 setting 370A, current 4 setting 450A; the voltage of the accelerated burning stage of the stages 5 to 8 is set to 370V, 370V and 380V, and the displacement is set to 2.2 mm.

When the welded joint is cooled to below 400 ℃, heating the joint by adopting a medium-frequency heating method until the tread temperature reaches the peak temperature of 920 ℃, immediately spraying air to the tread area of the joint by adopting air pressure of 0.25MPa, and stopping air cooling after the tread temperature of the joint is cooled to 460 ℃ to naturally cool the joint to room temperature.

The joint drop weight test is carried out on the treated steel rail, the weight of the steel rail is 1000kg according to the TB/T1632.2-2014 standard, the height of the hammer head is 6.4m, and 15 joints of the steel rail in the embodiment 3 can continuously meet the technical requirement of 1 hammer.

Example 4

When a steel rail mobile flash welding machine is used for welding a long rail, the time of a 2-4 stage pulse heating stage at the early stage is controlled to be 65s, the accelerated burning displacement at a 5-8 stage at the later stage is set to be 12.0mm, the total heat input of a joint is strictly controlled to be within a range of 13.5MJ, and the actual upset forging amount during welding is kept to be 13.0 mm.

Wherein the voltage of phase 2 is set to 360V, the time is 25s, the current 1 is set to 320A, the current 2 is set to 370A, the current 3 is set to 360A, and the current 4 is set to 610A; phase 3 voltage set 340V, time 25s, current 1 set 220A, current 2 set 370A, current 3 set 380A, current 4 set 590A; phase 4 voltage setting 355V, time 20s, current 1 setting 220A, current 2 setting 390A, current 3 setting 380A, current 4 setting 460A; the voltage of the accelerated burning stage of the stages 5 to 8 is set to 370V, 370V and 380V, and the displacement is set to 2.2 mm.

When the welded joint is cooled to below 400 ℃, the flame full-section heating joint is adopted until the tread temperature reaches the peak temperature of 920 ℃, air is sprayed to the tread area of the joint immediately by adopting the air pressure of 0.25MPa, and when the tread temperature of the joint is cooled to 460 ℃, the air cooling is stopped, and the joint is naturally cooled to the room temperature.

The joint drop weight test is carried out on the treated steel rail, the weight of the steel rail is 1000kg according to the TB/T1632.2-2014 standard, the height of the hammer head is 6.4m, and the steel rail of the embodiment 4 can continuously meet the technical requirement of 1 hammer for 15 joints.