阅读说明：本技术 一种消除碳钢/合金钢中沿晶界析出α相的热处理方法 (Heat treatment method for eliminating alpha phase precipitated along grain boundary in carbon steel/alloy steel ) 是由 万训智 刘澄 吕犇 李嘉诚 李擎天 郑艺 周文韬 王璇 于 2021-07-08 设计创作，主要内容包括：本发明提供一种消除碳钢/合金钢中沿晶界析出α相的热处理方法,通过分步高温奥氏体化,两级控温冷却,多次短程往复递减循环淬火,最后进行高温回火以及空冷至室温工艺,使易在晶界析出的α相数量减少甚至消失,进而使工件显微组织均匀,力学性能增强,减少工件早期失效的风险,延长服役寿命,可广泛应用于含碳量为0.5-0.7wt％的碳钢/合金钢中沿晶界析出α相的数量降低和消除。经过本发明处理的工件具有高性能、高寿命的优点,降低了生产产品的成本,具有较高的经济价值和社会价值,同时符合节能减排的要求,实用性强,适宜推广。(The invention provides a heat treatment method for eliminating alpha phase precipitated along a grain boundary in carbon steel/alloy steel, which reduces or even eliminates the quantity of the alpha phase easily precipitated at the grain boundary by the processes of step-by-step high-temperature austenitization, two-stage temperature control cooling, multiple short-range reciprocating descending circular quenching, and finally high-temperature tempering and air cooling to room temperature, thereby ensuring that the microstructure of a workpiece is uniform, the mechanical property is enhanced, the risk of early failure of the workpiece is reduced, the service life is prolonged, and the heat treatment method can be widely applied to the reduction and elimination of the quantity of the alpha phase precipitated along the grain boundary in the carbon steel/alloy steel with the carbon content of 0.5-0.7 wt%. The workpiece treated by the method has the advantages of high performance and long service life, the cost of producing products is reduced, the economic value and the social value are higher, the requirements of energy conservation and emission reduction are met, the practicability is high, and the method is suitable for popularization.)

1. A heat treatment method for eliminating alpha phase precipitated along grain boundaries in carbon steel/alloy steel is characterized by comprising the following steps:

s1, step-by-step high-temperature austenitizing:

placing a carbon steel/alloy steel workpiece into a heating furnace, heating the heating furnace to 600-680 ℃, and preserving heat for 10-15 min; then slowly heating the heating furnace to 950-1050 ℃, and preserving heat for 30-45 min;

s2, controlling cooling:

taking the workpiece processed by the step S1 out of the high-temperature furnace quickly, and performing primary controlled cooling and secondary controlled cooling;

s3, short-distance reciprocating decreasing circular quenching:

the first stage is as follows: cooling the workpiece subjected to the controlled cooling treatment of S2 in the quenching liquid for 8-10S, then lifting the workpiece out of the liquid level of the quenching liquid, placing the workpiece in air, and keeping the residence time consistent with the cooling time; repeating the operation a times;

and a second stage: cooling the workpiece treated in the first stage in quenching liquid for 1s, and taking the workpiece out of the liquid level of the quenching liquid again, wherein the retention time is consistent with the cooling time; repeating the above operation b times;

and a third stage: cooling the workpiece treated in the second stage in the quenching liquid for 1s, and taking the workpiece out of the liquid level of the quenching liquid again, wherein the retention time is consistent with the cooling time; repeating the above operation c times;

wherein a + b + c is 9-12;

s4, high-temperature tempering:

and (5) putting the workpiece processed by the S3 into a resistance furnace for heat preservation, and then air-cooling to room temperature to finish the operation.

2. The heat treatment method for eliminating the alpha phase precipitated along the grain boundary in the carbon steel/alloy steel as claimed in claim 1, wherein in S2, the cooling speed is controlled to be 200-300 ℃/min and the cooling time is 1-3S during primary controlled cooling; and in the secondary controlled cooling, the cooling speed is 400 ℃/min, and the cooling time is 3-5 s.

3. The heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel according to claim 1, characterized in that the operation of S3 is:

the first stage is as follows: cooling the workpiece subjected to the controlled cooling treatment of S2 in the quenching liquid for 8S, then lifting the workpiece out of the liquid level of the quenching liquid, placing the workpiece in air, and staying for 8S; repeating the above operation 4 times;

and a second stage: putting the workpiece treated in the first stage into quenching liquid for cooling for 7s, lifting the workpiece out of the liquid level of the quenching liquid again, and staying for 7 s; repeating the above operation for 3 times;

and a third stage: putting the workpiece treated in the second stage into the quenching liquid for cooling for 6s, lifting the workpiece out of the liquid level of the quenching liquid again, and staying for 6 s; the above operation was repeated 2 times.

4. The heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel according to claim 1, wherein in S3, the flow rate of the quenching liquid is maintained to be 0.3-0.6 m/S by stirring when the workpiece is cooled in the quenching liquid.

5. The heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel according to claim 1, wherein in S3, after each cooling, the workpiece is lifted out of the quenching liquid level height of 10 cm.

6. The heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel as claimed in claim 1, characterized in thatAnd in S3, the proportion of the quenching liquid is SiO₂:Al₂O₃:Fe₂O₃:CaO:H₂O＝4:3:2:1:50。

7. The heat treatment method for eliminating the alpha phase precipitated along the grain boundary in the carbon steel/alloy steel as claimed in claim 1, wherein in S4, the resistance furnace temperature is 560-620 ℃ and the holding time is 1-2 h.

8. The use of the heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel as claimed in any one of claims 1 to 7 for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel with carbon content of 0.5 to 0.7 wt%.

The technical field is as follows:

the invention belongs to the technical field of heat treatment processes, and particularly relates to a heat treatment method for eliminating alpha phase precipitated along a grain boundary in carbon steel/alloy steel.

Background art:

in recent years, with the development of economy and society, on the premise of meeting the sustainable development of ecological environment, people put higher demands on the mechanical properties of parts. At the present stage, how to improve the existing industrial production mode, realize energy conservation and environmental protection of an industrial chain, and improve the production efficiency and the product quality becomes an important target of various companies and enterprises. Taking the manufacturing industry as an example, the forging waste heat is utilized to carry out subsequent heat treatment on steel, 400kW & h of electric energy can be saved for each ton of steel, the production cost is saved, and the aim of carbon peak reaching and carbon neutralization is favorably realized. Although many researchers have conducted theoretical studies and process improvements, the effect is not ideal. It is known that 0.5-0.7 wt% carbon steel/alloy steel is widely used in various fields such as petroleum industry, electric power industry, metallurgical industry and mechanical industry, and is also used in precision instruments in the fields of ships, automobiles, capital construction, aerospace and the like, and shows a trend of increasing year by year. The medium carbon steel is easy to generate a reticular alpha phase in the heat treatment process, and can not meet the requirements of high strength, high hardness and high fatigue life. The presence of the reticulated alpha phase has severely hampered the production and use of this type of steel and its high quality articles.

Take 60Si2Mn spring steel as an example, it is widely used medium carbon silicon manganese spring steel, and has better elasticity, plasticity, hardness and strength. 60Si2Mn is one of the main raw materials for manufacturing disc spring steel in China, and is not only suitable for plate springs, but also suitable for spiral springs, heat-resistant springs and coiled springs in the industries of railway vehicles, automobiles and tractors. During forging, when the forging temperature is cooled to the Ar3 line, eutectoid ferrite is precipitated in austenite. However, since the forging stop temperature is high and the supercooling degree is too low, when the steel is slowly cooled at a temperature of Ac3 point or less, eutectoid ferrite is preferentially precipitated at austenite grain boundaries, and the rate of ferrite growth along the austenite grain boundaries is higher than the rate of ferrite growth in the austenite grain boundaries, thereby forming network ferrite. The net ferrite seriously partitions the synergy between pearlite and makes the strength of steel far lower than normal value, especially yield strength. Meanwhile, the plasticity of the steel is obviously reduced, so that the comprehensive performance of the 60Si2Mn spring steel is reduced, and early failure is generated. The net-shaped ferrite can obviously increase the brittleness of steel, and the cold working limit can be greatly reduced, so that the elimination of the net-shaped ferrite which is very easy to exist after forging is very important.

The invention is a novel heat treatment process, which can mostly or completely eliminate alpha phase structure separated out from 0.5-0.7 wt% carbon steel/alloy steel along grain boundary in production by unique cooling mode and special quenching process, thereby reducing the risk of early failure of workpieces, prolonging service life and having high economic value and social value.

The invention content is as follows:

the invention aims to overcome the defects of the prior art and provides a heat treatment method for eliminating alpha phase precipitation along grain boundaries in carbon steel/alloy steel.

The invention adopts the following technical scheme:

a heat treatment method for eliminating alpha phase precipitated along grain boundaries in carbon steel/alloy steel comprises the following steps:

s1, step-by-step high-temperature austenitizing: placing a carbon steel/alloy steel workpiece into a heating furnace, heating the heating furnace to 600-680 ℃, and preserving heat for 10-15 min; then slowly heating the heating furnace to 950-1050 ℃, and preserving heat for 30-45 min;

s2, controlling cooling: taking the workpiece processed by the step S1 out of the high-temperature furnace quickly, and performing primary controlled cooling and secondary controlled cooling;

s3, short-distance reciprocating decreasing circular quenching:

the first stage is as follows: cooling the workpiece subjected to the controlled cooling treatment of S2 in the quenching liquid for 8-10S, then lifting the workpiece out of the liquid level of the quenching liquid, placing the workpiece in air, and keeping the residence time consistent with the cooling time; repeating the operation a times;

and a second stage: cooling the workpiece treated in the first stage in quenching liquid for 1s, and taking the workpiece out of the liquid level of the quenching liquid again, wherein the retention time is consistent with the cooling time; repeating the above operation b times;

and a third stage: cooling the workpiece treated in the second stage in the quenching liquid for 1s, and taking the workpiece out of the liquid level of the quenching liquid again, wherein the retention time is consistent with the cooling time; repeating the above operation c times;

wherein a + b + c is 9-12;

s4, high-temperature tempering: and (5) putting the workpiece processed by the S3 into a resistance furnace for heat preservation, and then air-cooling to room temperature to finish the operation.

Further, in S2, during the primary controlled cooling, the cooling speed is controlled to be 200-300 ℃/min, and the cooling time is 1-3S; and in the secondary controlled cooling, the cooling speed is 400 ℃/min, and the cooling time is 3-5 s.

Further, the operation of S3 is:

the first stage is as follows: cooling the workpiece subjected to the controlled cooling treatment of S2 in the quenching liquid for 8S, then lifting the workpiece out of the liquid level of the quenching liquid, placing the workpiece in air, and staying for 8S; repeating the above operation 4 times;

and a second stage: putting the workpiece treated in the first stage into quenching liquid for cooling for 7s, lifting the workpiece out of the liquid level of the quenching liquid again, and staying for 7 s; repeating the above operation for 3 times;

and a third stage: putting the workpiece treated in the second stage into the quenching liquid for cooling for 6s, lifting the workpiece out of the liquid level of the quenching liquid again, and staying for 6 s; the above operation was repeated 2 times.

Further, in S3, the workpiece is cooled in the quenching liquid, and the flow rate of the quenching liquid is maintained to be 0.3-0.6 m/S by stirring.

Further, in S3, after each cooling, the workpiece was lifted out of the surface of the quenching liquid by 10 cm.

Further, in S3, the ratio of the quenching liquid is SiO₂:Al₂O₃:Fe₂O₃:CaO:H₂O＝4:3:2:1:50。

Further, in S4, the temperature of the resistance furnace is 560-620 ℃, and the heat preservation time is 1-2 h.

The invention also provides application of the heat treatment method for eliminating the alpha phase precipitated along the grain boundary in the carbon steel/alloy steel in eliminating the alpha phase precipitated along the grain boundary in the carbon steel/alloy steel with the carbon content of 0.5-0.7 wt%.

The invention has the beneficial effects that:

the invention is a novel heat treatment process, through a unique cooling mode and combining with a special quenching process, the alpha-phase structure precipitated along the grain boundary in the production of 0.5-0.7 wt% carbon steel/alloy steel can be mostly or completely eliminated, the microstructure is uniform, the mechanical property is enhanced, the risk of early failure of a workpiece is reduced, and the service life is prolonged; the carbon steel/alloy steel workpiece with the weight percent of 0.5-0.7, which is treated by the method, has the advantages of high performance and long service life, reduces the cost for producing products, has higher economic value and social value, meets the requirements of energy conservation and emission reduction, and is beneficial to realizing the aims of carbon peak reaching and carbon neutralization.

Description of the drawings:

FIG. 1 is a schematic view of a heat treatment process according to the present invention;

FIG. 2 is an optical microstructure of 55 steel after treatment in example 1 of the present invention;

FIG. 3 is an optical microstructure of 55 steel after conventional forging followed by direct isothermal normalizing heat treatment;

FIG. 4 is a graph comparing Brinell hardness of 55 steels treated according to example 1 of the present invention and directly isothermally normalized after forging.

The specific implementation mode is as follows:

in order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

The embodiment of the invention provides a heat treatment method for eliminating alpha phase precipitated along a grain boundary in carbon steel/alloy steel, which can be used as an experimental operator and comprises the following steps:

s1, step-by-step high-temperature austenitizing: heating the heating furnace to 600-680 ℃, placing a 0.5-0.7 wt% carbon steel/alloy steel sample with alpha phase precipitated along the grain boundary into the heating furnace, and preserving heat for 15 min; then slowly heating the heating furnace to 950-;

s2, controlling cooling: taking the workpiece processed by the S1 out of the high-temperature furnace quickly, and firstly carrying out primary controlled cooling, wherein the cooling speed is controlled to be 300 ℃/min, and the cooling time is 2S; then, secondary controlled cooling is carried out, the cooling speed is 400 ℃/min, and the cooling time is 4 s;

s3, short-distance reciprocating decreasing circular quenching:

the first stage is as follows: the workpiece subjected to the controlled cooling treatment of S2 is placed in quenching liquid (the weight ratio of each component of the quenching liquid is SiO)₂:Al₂O₃:Fe₂O₃:CaO:H₂Cooling for 8s in a ratio of O to 3:2:1:50), then taking the workpiece out of the liquid level of the quenching liquid by 10cm, placing the workpiece in air, and staying for 8 s; repeating the above operation 4 times;

and a second stage: putting the workpiece treated in the first stage into quenching liquid for cooling for 7s, taking the workpiece out of the liquid level of the quenching liquid for 10cm again, and staying for 7 s; repeating the above operation for 3 times;

and a third stage: putting the workpiece treated in the second stage into the quenching liquid for cooling for 6s, taking the workpiece out of the liquid level of the quenching liquid for 10cm again, and staying for 6 s; repeating the above operation for 2 times;

the short-range reciprocating decreasing circular quenching is carried out for 9 times in the step;

when the workpiece was cooled in the quenching liquid, the flow rate of the quenching liquid was kept at 0.5m/s by stirring.

S4, high-temperature tempering: and (3) putting the workpiece treated in the step (S3) into a resistance furnace at the temperature of 560-620 ℃ for heat preservation for 1-2 h, then taking out the workpiece, air-cooling to room temperature, observing the microstructure of the workpiece after the operation is finished, and measuring the hardness.

Test example 1

The microstructure of the 55 steel directly subjected to isothermal normalizing heat treatment after the treatment of example 1 of the present invention and the conventional forging was observed, and the optical microstructure was schematically shown in FIGS. 2 and 3.

FIG. 2: the optical microstructure picture of 55 steel obtained after the heat treatment of the invention.

FIG. 3: the 55 steel optical microstructure is directly subjected to isothermal normalizing heat treatment after traditional forging.

As can be seen from FIG. 2, the 55 steel treated in example 1 of the present invention can see a fine and discontinuous latticed ferrite structure, and the local latticed ferrite structure has been completely eliminated; as can be seen from fig. 3, the net-shaped ferrite is coherent and relatively coarse, and severely divides the connection between pearlite, so that the hardness is reduced, and the service life is influenced. Compared with the prior 55 steel directly subjected to isothermal normalizing after forging, the 55 steel treated by the method disclosed by the invention in the embodiment 1 obviously breaks up and eliminates the net-shaped ferrite. Compared with the common heat treatment process, the method can effectively eliminate alpha phase (such as net ferrite) precipitated along the grain boundary.

Test example 2

The 55 steel treated according to example 1 of the present invention and the 55 steel subjected to the conventional forging and direct isothermal normalizing heat treatment were subjected to hardness tests, respectively, and the graph showing the Brinell hardness is shown in FIG. 4.

As can be seen from fig. 4, the hardness of the 55 steel after the heat treatment of example 1 of the present invention was higher than that of the 55 steel after the direct isothermal normalizing treatment after forging, because the association between pearlite was strengthened and the hardness was significantly increased by about 16.3% after the network ferrite was broken.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention, it should be noted that, for those skilled in the art, several modifications and decorations without departing from the principle of the present invention should be regarded as the protection scope of the present invention.