A production method for 60Mn wheel steel forgings for rail transit

Abstract

The invention discloses a production method of a 60Mn wheel steel forging for rail transit, comprising the steps of forging, normalizing, rough turning, quenching and tempering in sequence; the forging adopts 60Mn steel, and the element composition of the 60Mn steel is as follows by mass percentage: C: 0.6%-0.65%, Si: 0.2%-0.37%, Mn: 0.7%-1%, Cr: 0.13%-0.25%, Ni: ≤0.25%, Cu: ≤0.2%, and the balance is Fe and unavoidable impurities. The production method of the 60Mn wheel steel forging for rail transit is based on 60Mn carbon steel. By strictly controlling the content of elemental carbon and chromium in the forging steel, especially controlling the content of chromium to a high level, the hardness and toughness of the forging are improved; the appropriate forging ratio enables the forging to obtain good mechanical properties and prevents excessive grain growth; the heating temperature and the holding time are reasonably set during the heat treatment process to avoid coarse grains; the rough turning step sets the surface angle of the forging to a transition fillet, effectively reducing the tendency of quenching cracking; the improved quenching and tempering process prevents water quenching cracking and reduces tempering brittleness.

Description

Technical Field

[0001] The invention relates to the technical field of forging production, and in particular to a production method of 60Mn wheel steel forgings for rail transportation. Background Art

[0002] 60Mn carbon steel has high strength, hardness and good durability. It is often used in China to make large-size coil springs, leaf springs, various round flat springs, spring rings, cold-drawn steel wires and springs, and is usually not used as raw material for wheel steel forgings for rail transit.

[0003] Some foreign customers have the demand to make 60Mn carbon steel into rail transit wheel steel forgings with excellent wear resistance and toughness. Under cost constraints, 60Mn carbon steel is generally made by setting the C element content in a higher range of the material to achieve high wear resistance requirements, and a higher C element content will affect the toughness of the forgings, making it difficult for the forgings to meet the toughness requirements. In addition, 60Mn carbon steel has a tendency to crack during water quenching and has temper brittleness. The specific mechanical property requirements of 60Mn wheel steel forgings for rail transit are as follows: Yield strength Re: ≥680 Mpa, tensile strength Rm: ≥900 Mpa, elongation δ: ≥10%, section shrinkage ψ: ≥14%, hardness: 280-320HB, impact resistance AKU at 20℃: ≥10J. Summary of the invention

[0004] The object of the present invention is to provide a method for producing 60Mn wheel steel forgings for rail transit, wherein the produced forgings have excellent wear resistance and toughness.

[0005] In order to achieve the above technical effects, the technical solution of the present invention is: a method for producing a 60Mn wheel steel forging for rail transit, comprising the steps of forging, normalizing, rough turning, quenching and tempering in sequence; the forging is made of 60Mn steel, and the element composition of the 60Mn steel is as follows by mass percentage: C: 0.6%~0.65%, Si: 0.2%~0.37%, Mn: 0.7%~1%, Cr: 0.13%~0.25%, Ni: ≤0.25%, Cu: ≤0.2%, the balance is Fe and unavoidable impurities. Further, the C content is 0.61%~0.65%, and the Cr content is 0.14%~0.25%.

[0006] The preferred technical solution is that the initial forging temperature of the forging step is 1230-1270°C, and the final forging temperature of the forging step is not less than 800°C.

[0007] The preferred technical solution is that the forging step includes two drawing and two upsetting operations performed alternately in sequence, the first drawing forging ratio is 2.0-2.3, the first upsetting forging ratio is 1.65-1.85, the second drawing forging ratio is 1.4-1.6, and the second upsetting forging ratio is 2.68-2.88.

[0008] The preferred technical solution is that the normalizing step comprises: The forging is heated to 890-910° C. at a heating rate of 90-100° C. / h, then kept warm for 4.3-6.5 h / 100 mm of effective thickness, and then air-cooled.

[0009] A preferred technical solution is that the rough turning step includes setting the surface angle of the forging to a transition fillet.

[0010] The preferred technical solution is that the quenching step includes: The forging is heated to 810-830°C at a heating rate of 90-100°C / h, then kept warm for 3.2-5.4h / 100mm of effective thickness, and then cooled using a quenching agent. Further, the forging is heated to 815-825°C at a heating rate of 95-100°C / h, then kept warm for 3.3-5.4h / 100mm of effective thickness, and then cooled using a quenching agent.

[0011] The preferred technical solution is that the quenching agent is water, the temperature of the water is 20-40°C, and the temperature of the forging after the quenching is 190-210°C. Furthermore, the temperature of the water is 25-35°C, and the temperature of the forging after the water quenching is 195-205°C.

[0012] The preferred technical solution is that the interval between the quenching step and the tempering step is no more than 3 hours. Furthermore, the interval between the quenching step and the tempering step is no more than 0.5 hours.

[0013] The preferred technical solution is that the tempering step includes: The forging is heated to 530-550°C at a heating rate of 90-100°C / h, then kept warm for 8.6-10.8h / 100mm of effective thickness, and then air-cooled. The forging is heated to 535-545°C at a heating rate of 95-100°C / h, then kept warm for 8.7-10.8h / 100mm of effective thickness, and then air-cooled.

[0014] The preferred technical solution is that the air cooling is to set an airflow forced cooling device around the forging, and the cooling rate of the forging is 140-160°C / h.

[0015] The advantages and beneficial effects of the present invention are: The production method of the 60Mn wheel steel forging for rail transit is based on 60Mn carbon steel. By strictly controlling the content of elemental carbon and chromium in the forging steel, especially controlling the content of chromium to a high level, the hardness and toughness of the forging are improved; the appropriate forging ratio enables the forging to obtain good mechanical properties and prevents excessive grain growth; the heating temperature and the holding time are reasonably set during the heat treatment process to avoid coarse grains; the rough turning step sets the surface angle of the forging to a transition fillet, effectively reducing the tendency of quenching cracking; the improved quenching and tempering process prevents water quenching cracking and reduces tempering brittleness. DETAILED DESCRIPTION

[0016] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0017] The element composition of carbon steel with grade 60Mn is: C: 0.57%~0.65%, Si: 0.17%~0.37%, Mn: 0.7%~1%, Cr: ≤0.25%, Ni: ≤0.3%, Cu: ≤0.25%.

[0018] The mass percentage of an element in forging steel is limited to "≤n", which means that the content of the element in the forging steel is 0~n, excluding the minimum endpoint value "0".

[0019] Effective thickness of forgings The effective thickness of forgings is used to calculate the reheating time of each fire and the holding time of positive tempering heat treatment and quenching and tempering heat treatment. 60Mn wheel steel forgings for rail transit are ring-type workpieces, and the wall thickness is used as their effective thickness.

[0020] Upsetting forging ratio The ratio of the larger value to the smaller value of the forging length before and after upsetting is the upsetting forging ratio.

[0021] Drawing forging ratio The ratio of the larger value to the smaller value of the forging length before and after drawing is the drawing forging ratio. Example

[0022] Example 1

[0023] The actual measured values ​​of the chemical composition mass percentages of the production method of 60Mn wheel steel forgings for rail transit in Example 1 are: C: 0.617%, Si: 0.27%, Mn: 0.88%, Cr: 0.14%, Ni: 0.1%, Cu: 0.07%, and the remainder is Fe and unavoidable impurities.

[0024] The production of 60Mn wheel steel forgings for rail transit includes forging, normalizing, rough turning, quenching and tempering in sequence: S1: After the steel ingot with a diameter of 380mm and a height of 163mm was charged into the furnace, it was heated to 1250℃ and kept warm for 0.5h, and then the forging was upset with a 1T air hammer. The surface and core temperatures of the forging were both 1250℃ before upsetting. The steel ingot was first drawn to 350mm, then upset to 200mm, then drawn to 300mm, then upset to 108mm, and finally a hole was punched in the middle of the forging. After punching, the outer diameter of the forging was 475mm, the inner diameter was 130mm, and the height was 108mm. At this time, the surface temperature of the forging was measured to be 920℃, and the core temperature was 900℃.

[0025] S2: The forging is returned to the furnace and heated to 1250°C and kept at this temperature for 0.5h. Then the forging is expanded with a hole expander. After expansion, the outer diameter of the forging is 670mm, the inner diameter is 485mm, and the height is 108mm.

[0026] S3: The forgings are put into the furnace and heated to 900°C at a heating rate of 100°C / h, kept at this temperature for 5 hours, and then air-cooled.

[0027] S4: Process the surface of forgings to remove minor defects on the surface of forgings and process the surface angle of forgings into transition fillets.

[0028] S5: The forging is heated to 820°C at a heating rate of 100°C / h, kept at that temperature for 4h, and then water quenched. The water quenching temperature is controlled at 30°C. After the forging is cooled to 200°C, the forging is taken out.

[0029] S6: 0.5h after the end of S5, the forgings were put into the furnace and heated to 540℃ at a heating rate of 100℃ / h. After keeping warm for 9h, three high-power fans were used to quickly cool the forgings. It was measured that the forgings cooled to 20℃ after 3.5h.

[0030] The performance test results and qualification requirements of the 60Mn wheel steel forgings for rail transit in Example 1 are as follows: 1. Mechanical properties: Yield strength Re: 690 Mpa, tensile strength Rm: 983 Mpa, elongation δ: 19.5%, section shrinkage ψ: 54%, hardness: 295HB, impact performance AKU at 20°C: 24J / 26J / 30J.

[0031] Mechanical properties test qualification requirements: yield strength Re: ≥680 Mpa, tensile strength Rm: ≥900 Mpa, elongation δ: ≥10%, section shrinkage ψ: ≥14%, hardness: 280-320HB, impact performance AKU at 20℃: ≥10J.

[0032] 2. Ultrasonic flaw detection results: qualified.

[0033] Ultrasonic flaw detection standard: ISO5948-2018 "Ultrasonic acceptance inspection of railway rolling stock materials" Comparative Example 1 The actual measured values ​​of the chemical composition mass percentages of the production method of 60Mn wheel steel forgings for rail transit in Comparative Example 1 are: C: 0.62%, Si: 0.3%, Mn: 0.9%, Cr: 0.03%, Ni: 0.2%, Cu: 0.1%, and the remainder is Fe and unavoidable impurities.

[0034] The forging process of Comparative Example 1 is the same as that of Example 1.

[0035] The performance test results of the 60Mn wheel steel forgings for rail transit in Comparative Example 1 are as follows: 1. Mechanical properties: Yield strength Re: 590Mpa, tensile strength Rm: 893 Mpa, elongation δ: 23%, section shrinkage ψ: 60%, hardness: 265HB, impact performance AKU at 20℃: 26J / 30J / 36J.

[0036] 2. Ultrasonic flaw detection results: qualified.

[0037] The chromium content of Comparative Example 1 is lower. Compared with Example 1, its yield strength, tensile strength and hardness are reduced, while its elongation, cross-sectional shrinkage and impact performance at 20°C are improved. The reduced chromium content makes it difficult to meet all the mechanical performance requirements of the forgings.

[0038] Example 2

[0039] Based on the forging steel of Example 1, the forging process of Example 2 is the same as that of Example 1, except that S5: S5: The forging is heated to 820°C at a heating rate of 100°C / h, kept at that temperature for 4h, and then water quenched. The water quenching temperature is controlled at 0°C. After the forging is cooled to 200°C, the forging is taken out.

[0040] The performance test results of the 60Mn wheel steel forging for rail transit in Example 2 are as follows: 1. Mechanical properties: Yield strength Re: 710 Mpa, tensile strength Rm: 1000 Mpa, elongation δ: 16%, section shrinkage ψ: 41%, hardness: 319HB, impact performance AKU at 20°C: 24J / 26J / 30J.

[0041] 2. Ultrasonic flaw detection results: qualified.

[0042] The water quenching temperature of the embodiment is lowered. Compared with Example 1, the yield strength, tensile strength and hardness of the forging are increased, while the elongation, cross-sectional shrinkage and impact performance at 20°C are reduced, and the hardness is close to the upper limit of the performance requirements. Rapid cooling will increase the brittleness of the material, reduce its plastic performance, and reduce its impact absorption capacity.

[0043] Example 3

[0044] Based on the forging steel of Example 1, the forging process of Example 3 is the same as that of Example 1, except that S6: S6: 4 hours after the end of S5, the forgings were put into the furnace and heated to 540°C at a heating rate of 100°C / h. After keeping warm for 9 hours, three high-power fans were used to quickly cool the forgings. It was measured that the forgings cooled to 20°C after 3.5 hours.

[0045] The performance test results of the 60Mn wheel steel forging for rail transit in Example 3 are as follows: 1. Mechanical properties: Yield strength Re: 693 Mpa, tensile strength Rm: 976 Mpa, elongation δ: 20%, section shrinkage ψ: 51%, hardness: 300HB, impact performance AKU at 20°C: 22J / 24J / 30J.

[0046] 2. Ultrasonic testing results: Accepted with concession.

[0047] The forging of Example 3 was subjected to S6 4 ​​hours after the end of S5. Compared with Example 1, the mechanical properties were not much different, but the flaw detection results were worse. If tempering was not performed in time after quenching, the internal stress of the forging continued to increase, and the internal defects of the forging increased.

[0048] Example 4

[0049] Based on the forging steel of Example 1, the forging process of Example 4 is the same as that of Example 1, except that S6: S6: 0.5h after the end of S5, the forgings were put into the furnace and heated to 540℃ at a heating rate of 100℃ / h. After keeping warm for 9h, they were water-cooled. It was measured that the forgings cooled to 20℃ after 5min.

[0050] The performance test results of the 60Mn wheel steel forging for rail transit in Example 4 are as follows: 1. Mechanical properties: Yield strength Re: 693Mpa, tensile strength Rm: 989 Mpa, elongation δ: 19%, section shrinkage ψ: 53%, hardness: 300HB, impact performance AKU at 20℃: 23J / 27J / 31J.

[0051] 2. Ultrasonic flaw detection results: qualified.

[0052] The S5 step of Example 4 adopts water cooling. Compared with Example 1, the performance of Example 4 has not changed significantly, especially the impact performance at 20°C has basically not changed. 60Mn carbon steel generally adopts water quenching or oil quenching for rapid tempering cooling to reduce temper brittleness. This shows that under the process conditions of Example 1, the tempering cooling of 60Mn carbon steel adopts rapid air cooling with lower cost and more convenient operation to achieve performance similar to water cooling.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for producing 60Mn wheel steel forgings for rail transit, comprising the steps of forging, normalizing, rough turning, quenching and tempering in sequence; characterized in that: The forging is made of 60Mn steel, and the element composition of the 60Mn steel is as follows by mass percentage: C: 0.6%~0.65%, Si: 0.2%~0.37%, Mn: 0.7%~1%, Cr: 0.13%~0.25%, Ni: ≤0.25%, Cu: ≤0.2%, and the balance is Fe and unavoidable impurities.

2. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The initial forging temperature of the forging step is 1230-1270°C, and the final forging temperature of the forging step is not less than 800°C.

3. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The forging step includes two drawing and two upsetting operations performed alternately in sequence, the first drawing forging ratio is 2.0-2.3, the first upsetting forging ratio is 1.65-1.85, the second drawing forging ratio is 1.4-1.6, and the second upsetting forging ratio is 2.68-2.

88.

4. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The normalizing step comprises: The forging is heated to 890-910° C. at a heating rate of 90-100° C. / h, then kept warm for 4.3-6.5 h / 100 mm of effective thickness, and then air-cooled.

5. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The rough turning step includes setting the surface angle of the forging to a transition fillet.

6. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The quenching step comprises: The forging is heated to 810-830° C. at a heating rate of 90-100° C. / h, then kept warm for 3.2-5.4 h / 100 mm of effective thickness, and then cooled using a quenching agent.

7. The method for producing 60Mn wheel steel forgings for rail transit according to claim 6, characterized in that: The quenching agent is water, the temperature of the water is 20-40°C, and the temperature of the forging after quenching is 190-210°C.

8. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The interval between the quenching step and the tempering step is no more than 3 hours.

9. The method for producing 60Mn wheel steel forgings for rail transit according to claim 1, characterized in that: The tempering step comprises: The forging is heated to 530-550° C. at a heating rate of 90-100° C. / h, then kept warm for 8.6-10.8 h / 100 mm of effective thickness, and then air-cooled.

10. The method for producing 60Mn wheel steel forgings for rail transit according to claim 9, characterized in that: The air cooling is to set an airflow forced cooling device around the forging, and the cooling rate of the forging is 140-160°C / h.