Forging heat treatment process for medium carbon bearing steel

Abstract

The invention belongs to the technical field of rolling forming of annular forgings, and particularly provides a forging heat treatment process for medium-carbon bearing steel, which comprises the following steps: step 1, carrying out ultrasonic detection on a steel ingot, and judging the defect gathering position and range in the steel ingot according to an ultrasonic detection result; and secondly, based on the defect gathering position and range in the steel ingot, blanking, forging, ring rolling and heat treatment and machining processes are set, and forging and heat treatment of the medium-carbon bearing steel are completed.

Description

Technical Field

[0001] The invention belongs to the technical field of ring forging rolling forming and relates to a forging heat treatment process of medium carbon bearing steel. Background Art

[0002] Bearing steel, especially steel used for main bearing rings of large shield machines, must possess high fatigue strength, hardness, compressive strength, elastic limit, wear resistance, and corrosion resistance, as well as high hardenability, hardenability, a certain degree of impact toughness, and dimensional stability. Main bearing rings for tunnel boring machines are typically made of medium-carbon alloy bearing steel, such as the 42CrMo series. As the size of tunnel boring machine main bearings increases, the difficulty of controlling the quality of raw materials such as steel ingots increases. In actual production, large-diameter ring forgings often exhibit severe segregation and banded structure, making subsequent ring production susceptible to quenching cracking and excessive deformation.

[0003] The production of forgings for main bearing rings for roadheaders involves complex processes such as blanking, upsetting, punching, ring rolling, heat treatment, and machining. This process involves multiple high-temperature diffusion treatments. Traditional high-temperature diffusion processes primarily focus on high-temperature diffusion treatment of steel ingots, with subsequent high-temperature diffusion treatments primarily addressing hot working requirements. However, under the same high-temperature diffusion process, the diffusion effect varies significantly depending on the steel's state (as-cast / rolled, effective cross-section, dendrite spacing, etc.). The blanking and punching processes involved in forging production are closely linked to the control of the steel ingot raw material and the quality requirements for the forgings. Furthermore, the high precision requirements of the main bearing rings place even higher demands on residual stress control in the forgings.

[0004] The main bearing rings of large shield machines have extremely high requirements for forging homogeneity control. The current traditional forging production process cannot meet the requirements. Therefore, it is urgent to develop a customized process for high-homogeneity forging heat treatment for main bearing rings. Summary of the Invention

[0005] The present invention provides a forging heat treatment process for medium carbon bearing steel, comprising the following steps: Step 1: Perform ultrasonic testing on the steel ingot, and determine the location and range of defects inside the steel ingot based on the ultrasonic testing results; Step 2: Based on the location and range of defect accumulation inside the steel ingot, set the blanking, forging, ring rolling, heat treatment and machining processes to complete the forging and heat treatment of the medium carbon bearing steel.

[0006] Furthermore, the steel ingot is ultrasonically tested using a type A pulse reflection ultrasonic testing system.

[0007] Furthermore, the specific process of using the A-type pulse reflection ultrasonic testing system to test the steel ingot is as follows: S1.1. Using any surface of the steel ingot as the reference surface, perform ultrasonic testing on the location and range of internal defects in the steel ingot, and divide the test area of ​​the surface into several test areas; S1.2. Perform ultrasonic testing on each test area, with the distance from the probe center to the riser as the test position and the direction from the riser end to the nozzle end as the test direction, to obtain several sets of ultrasonic test waveforms; S1.3. Data processing and analysis are performed based on the obtained sets of ultrasonic detection waveforms to obtain the location and range of defect accumulation inside the steel ingot under the current surface.

[0008] Furthermore, the specific method of obtaining several detection areas is as follows: The reference test surface of the steel ingot for ultrasonic testing is divided into several 100×100 mm squares. Three test points are set along the central axis from the riser to the nozzle in each square, and the interval between two adjacent test points is 33 mm.

[0009] Furthermore, the specific process of blanking is as follows: S2.1. Expand the gap 20mm-40mm towards the center of the ingot based on the defect detection boundary line at the nozzle end of the ingot, and expand the gap 20mm-40mm towards the center of the ingot based on the defect detection boundary line at the riser end of the ingot, as the blanking boundary; S2.2. Expand the center defect detection boundary of the steel ingot by 40mm-60mm as the punching boundary; and then determine the subsequent punching diameter according to the size ratio of the core defect of the steel ingot; S2.3. Cut the material according to the cutting boundary and punching boundary to obtain the forging blank.

[0010] Furthermore, the specific process of forging is as follows: S3.1. Perform a forging heat treatment on the forging blank. Specifically, heat the forging blank to 1250±10°C using a stepwise heating method and keep it at that temperature for 0.3 min / mm-0.5 min / mm. S3.2. The heated forging blank is repeatedly subjected to roughing and drawing, and after forging to the specified size, it is punched to obtain a forged blank; the punching diameter is the larger value of the ultrasonic flaw detection result and one-fifth of the forged blank diameter. The punch type is determined by the type of ring product.

[0011] Furthermore, the specific process of ring rolling is as follows: S4.1. Perform segmented heating and heat preservation on the forging blank; initially heat to 1250±10℃, and hold for 0.35min / mm-0.55min / mm; later adjust the furnace temperature to 1220±10℃, and hold for 0.05min / mm-0.15min / mm; S4.2. The forged billet is rolled out to the specified size, and the final rolling temperature is required to be ≥850℃; S4.3. After ring rolling, the ring forging is furnace cooled to below 400℃.

[0012] Furthermore, the specific processes of heat treatment and machining are as follows; S5.1. Ring forgings are subjected to normalizing and tempering heat treatment; S5.2. Rough turning of the ring forgings after normalizing and quenching and tempering heat treatment; S5.3. After rough turning to the specified dimensions, perform stress relief annealing on the ring forgings: heat the ring forgings to 520±10℃ at a heating rate of ≤40℃ / h and hold for 2.0-2.3min / mm. Cool the ring forgings to below 200℃ and then remove from the furnace for cooling. S5.4. Finish-machine the ring forgings after stress relief annealing to the designed dimensions.

[0013] The present invention provides a forging heat treatment process for high-homogeneity medium-carbon bearing steel for main bearings of roadheaders based on 42CrMo series steel, which has the following advantages: (1) Pulse reflection ultrasonic testing was added to the traditional large ring forging process, which can determine the location of defect accumulation inside the steel ingot and avoid defect accumulation in subsequent processes.

[0014] (2) Considering that the dendrite spacing of the forging blank is small, the internal defects are few, and the segregation elements are easy to diffuse, the high-temperature diffusion scheme of the multi-fire forgings was adjusted to increase the high-temperature diffusion time of the forgings after forging; the ring rolling heating process adopted a variable temperature treatment to improve the diffusion effect while reducing the risk of excessive grain size of the material and improving the homogeneity of the material.

[0015] (3) Combine the forging punching process with the steel ingot flaw detection and subsequent ring process, and select the punching process in a differentiated manner to effectively reduce costs while ensuring quality.

[0016] (4) After the forging is quenched and tempered and rough turned, a stress relief annealing process is added before the finished product is fine turned to further reduce the residual stress of the forging and achieve a uniform distribution of the residual stress of the forging.

[0017] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: FIG1( a ) is a schematic diagram of a steel ingot being inspected for defects using a type A pulse reflection ultrasonic testing system according to an embodiment of the present invention; FIG1( b ) is a schematic diagram of detecting small-sized defects on a steel ingot using an A-type pulse reflection ultrasonic testing system according to an embodiment of the present invention; FIG1( c ) is a schematic diagram of detecting large-size defects on a steel ingot using an A-type pulse reflection ultrasonic testing system according to an embodiment of the present invention; Figure 2 Schematic diagram of the division of steel ingot detection positions in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned purposes, features and advantages of the present invention more clear and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the drawings of the present invention are all simplified and non-precisely scaled, and are only used to conveniently and clearly assist in explaining the implementation of the present invention; the "numbers" mentioned in the present invention are not limited to the specific quantities in the examples in the accompanying drawings; the directions or positional relationships indicated by "front", "middle", "back", "left", "right", "up", "down", "top", "bottom", "middle", etc. mentioned in the present invention are based on the directions or positional relationships shown in the drawings of the present invention, and do not indicate or imply that the devices or components referred to must have a specific direction, nor can they be understood as limitations on the present invention.

[0020] Example: The present invention provides a medium carbon bearing steel forging heat treatment process, comprising the following steps: Step 1: Perform ultrasonic testing on the steel ingot and preliminarily determine the location and range of defects inside the steel ingot based on the ultrasonic testing results; by determining the location and range of defects inside the steel ingot, it is convenient to determine the subsequent blanking and punching process.

[0021] Preferably, the equipment used for ultrasonic testing of the steel ingot is a type A pulse reflection ultrasonic testing system.

[0022] Preferably, the specific process of using the A-type pulse reflection ultrasonic testing system to detect the steel ingot is as follows: S1.1. Using any surface of the steel ingot as a reference surface, perform ultrasonic testing on the location and range of internal defects in the steel ingot (see Figures 1(a) to 1(c) for the testing principle), and divide the testing area of ​​the surface into several zones. S1.2. Perform ultrasonic testing on each test area, with the distance from the probe center to the riser as the test position and the direction from the riser end to the nozzle end as the test direction, to obtain several sets of ultrasonic test waveforms; S1.3. Process and analyze the data based on the obtained sets of ultrasonic detection waveforms to obtain the location and range of the defect concentration inside the steel ingot below the current surface. Preferably, the specific method of processing and analyzing the data of the ultrasonic detection waveforms is referred to the existing technology.

[0023] More preferably, the specific method of obtaining several detection areas is: See also Figure 2 As shown in FIG, the reference detection surface of the steel ingot for ultrasonic testing is divided into several 100×100 mm squares, and three detection points are set along the central axis from the riser to the nozzle in each square, with an interval of 33 mm between two adjacent detection points.

[0024] Step 2: Cutting the material; S2.1. The boundaries of the blanking process are 20 mm to 40 mm (preferably 30 mm) from the nozzle end defect detection boundary line to the center of the ingot, and 20 mm to 40 mm (preferably 30 mm) from the riser end defect detection boundary line to the center of the ingot; S2.2. Use the ingot's center defect detection boundary line + 40mm-60mm (preferably 50mm) as the punching boundary; and determine the subsequent punching diameter based on the size ratio of the ingot's center defect. S2.3. Cut the material according to the cutting boundary and punching boundary to obtain the forging blank.

[0025] This method is used to cut the material to avoid the accumulation of defects such as segregation inside the ingot.

[0026] Preferably, the boundary line of the defect detection at the nozzle end of the steel ingot is expanded 30 mm toward the center of the steel ingot, and the boundary line of the defect detection at the riser end of the steel ingot is expanded 30 mm toward the center of the steel ingot as the boundaries for blanking; The boundary of the punching is the defect detection boundary line in the center of the steel ingot + 50mm.

[0027] Step 3: Forging; S3.1. Perform a forging heat treatment on the forging blank. Specifically, heat the forging blank to 1250±10°C using a stepwise heating method and keep it at that temperature for 0.3 min / mm-0.5 min / mm. S3.2. Repeatedly rough-draw and forge the forging blank after forging and heat treatment, and then punch it after forging into the specified size to obtain a forged blank. Specifically, the punching diameter is the larger value of the ultrasonic flaw detection result and one-fifth of the forged blank diameter. The punch type is determined by the type of ring product.

[0028] By appropriately reducing the holding time during forging heating, combining the forging punching process with ingot flaw detection and subsequent ring forging process, and selecting the punching process in a differentiated manner, the forging quality can be improved and the cost can be reduced.

[0029] Step 4: Ring rolling; S4.1. Perform staged heating and heat preservation on the forging blank. Specifically, initially heat to 1250±10°C with a holding time of 0.35 min / mm-0.55 min / mm; later adjust the furnace temperature to 1220±10°C with a holding time of 0.05 min / mm-0.15 min / mm. S4.2. The forged billet is rolled out to the specified size, and the final rolling temperature is required to be ≥850℃; S4.3. After the ring rolling is completed, the forged billet is furnace cooled to below 400°C to obtain a ring forging.

[0030] By ring rolling the forging blank, the high-temperature diffusion time of the forging after forging is increased. The ring rolling heating process adopts variable temperature treatment, which improves the diffusion effect while reducing the risk of excessively large material grains and improving the homogeneity of the material.

[0031] Step 5: Heat treatment and machining; S5.1. Perform normalizing and quenching and tempering heat treatment on the ring forgings; S5.2. Rough turning of the ring forgings after normalizing and quenching and tempering heat treatment; S5.3. After rough turning to the specified size, perform stress relief annealing on the ring forgings: heat the ring forgings to 520±10℃ at a heating rate of ≤40℃ / h and hold at this temperature for 2.0-2.3min / mm. Cool the ring to below 200℃ and then remove from the furnace for cooling; S5.4. Finish-machine the ring forgings after stress relief annealing to the designed dimensions to obtain medium-carbon bearing steel ring forgings for manufacturing main bearings of tunnel boring machines.

[0032] By normalizing and tempering the ring forgings, we can obtain a tempered martensite structure with excellent performance. Properly increasing the annealing time is beneficial to eliminate the residual stress in the ring forgings and achieve a highly uniform distribution of residual stress in the ring forgings.

[0033] Experimental example: Step 1: Use a type A pulse reflection ultrasonic testing system to perform ultrasonic testing on a 30-ton die-cast steel ingot, and preliminarily determine and record the location and range of internal defect accumulation in the steel ingot based on the waveform distribution obtained by the ultrasonic testing.

[0034] Step 2, cutting; According to the ultrasonic test results, the material is cut according to the defect detection boundary line at the sprue end expanding 30mm toward the center of the ingot and the defect detection boundary line at the riser end expanding 30mm toward the center of the ingot, and the location and range of the core defect accumulation of the ingot are recorded at the same time.

[0035] Step 3: Forging; S3.1. The steel ingot is heated in a segmented manner; specifically, a three-stage heating method is used; in the first stage of heating, the charging temperature is set to ≤600℃, and the temperature is increased to 600℃ at a rate of ≤80℃ / h, and then kept at this temperature for 3h; in the second stage of heating, the temperature is increased to 850℃ at a rate of ≤80℃ / h, and then kept at this temperature for 5h; in the third stage of heating, the temperature is increased to 1250℃ at a rate of ≤120℃ / h, and the holding time is 0.4 min / mm.

[0036] S3.2. The steel ingot is taken out of the furnace and forged to the specified size. The final forging temperature is 820℃ to obtain the forging billet.

[0037] S3.3. Reheat the forging blank; specifically, heat the blank to 1250°C at a rate of ≤120°C / h and hold the blank for 0.4 min / mm.

[0038] S3.4. Then, the forging blank is subjected to three upsetting and two drawing to the specified size, and the final forging temperature is 800°C to obtain the forging blank.

[0039] S3.5. Reheat the forging blank; specifically, heat the blank to 1250°C at a rate of ≤120°C / h and hold the blank for 0.6 min / mm.

[0040] S3.6. Punch the forged blank again. The punching diameter is the defect detection boundary line of the steel ingot core + 50 mm. Use a solid punch.

[0041] S3.7 After punching, the forged blank is mounted on a rack and expanded to the specified size.

[0042] Step 4: Ring rolling; S4.1. Heat the forging blank; specifically, heat the blank to 1250°C at a rate of ≤120°C / h and hold at this temperature for 0.4 min / mm.

[0043] S4.2. Adjust the furnace temperature to 1220°C and hold for 0.10 min / mm. Roll the forged billet to the required size, with a final rolling temperature of 870°C.

[0044] S4.3. After ring rolling, the ring forging is furnace cooled to below 400℃.

[0045] Step 5: heat treatment and machining; S5.1. Perform normalizing and quenching and tempering heat treatment on the ring forgings.

[0046] S5.2. Rough turning shall be performed on the ring forgings after normalizing and quenching and tempering heat treatment.

[0047] S5.3. After rough turning to the specified size, perform stress relief annealing on the ring forgings: heat the ring forgings to 520°C at a heating rate of 40°C / h and hold at that temperature for 2.2 min / mm. Cool the ring forgings to below 200°C and then take them out of the furnace to cool.

[0048] S5.4 Finish-machine the stress-relief annealed ring forgings to the specified dimensions.

[0049] Comparative Example: Step (1), forging process; (1) Cutting; Cut the material according to the limit of the water riser end.

[0050] Cut the steel ingot according to the marking line.

[0051] (2) Forging; 2.1. Heating of the steel ingot: three-stage heating, charging temperature ≤ 600℃, heating to 600℃ at ≤ 80℃ / h, keeping warm for 4h, heating to 850℃ at ≤ 80℃ / h, keeping warm for 6h, heating to 1250℃ at ≤ 120℃ / h, keeping warm for 0.5min / mm.

[0052] 2.2. The steel ingot is taken out of the furnace and forged to the specified size. The final forging temperature is 820℃ to obtain the forging blank.

[0053] 2.3. Heat the forging blank: increase the temperature to 1250℃ at ≤120℃ / h, and keep it at this temperature for 0.5min / mm.

[0054] 2.4. Then, the forging blank is subjected to three upsetting and two drawing to the specified size, and the final forging temperature is 830°C to obtain the forging blank.

[0055] 2.5. Heat the forging blank: increase the temperature to 1250℃ at ≤120℃ / h, and keep it at this temperature for 0.35min / mm.

[0056] 2.6. Punch the forging blank with a diameter of 1 / 5 of the forging blank diameter and use a hollow punch.

[0057] 2.7. After punching, the forged blank is mounted on a rack and expanded to the specified size.

[0058] (3) Ring rolling; 3.1. Heat the forging blank: increase the temperature to 1250℃ at ≤120℃ / h, and keep it at this temperature for 0.35min / mm.

[0059] 3.2. After the forging billet is taken out of the furnace, it is rolled into a ring to the specified size, with the final rolling temperature at 820℃.

[0060] 3.3. After the ring rolling is completed, the ring forging is furnace cooled to below 400℃.

[0061] Step (2), heat treatment and machining; ①. Perform normalizing and tempering heat treatment on the ring forgings.

[0062] ②. Perform stress relief annealing on the ring forgings after normalizing and quenching and tempering heat treatment: heat the ring forgings to 520℃ at a heating rate of ≤40℃ / h and keep them warm for 2.0min / mm. Cool the furnace to below 250℃ and then take them out of the furnace for cooling.

[0063] ③. Rough turning of the ring forgings after stress relief annealing.

[0064] ④. Finish-machine the ring forgings to the specified size after rough turning.

[0065] Comparison of implementation effects The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A medium carbon bearing steel forging heat treatment process, characterized in that: The following steps are involved: Step 1: Perform ultrasonic testing on the steel ingot, and determine the location and range of defects inside the steel ingot based on the ultrasonic testing results; Step 2: Based on the location and range of defect accumulation inside the steel ingot, set the blanking, forging, ring rolling, heat treatment and machining processes to complete the forging and heat treatment of the medium carbon bearing steel.

2. The medium carbon bearing steel forging heat treatment process according to claim 1, characterized in that: The steel ingots were ultrasonically tested using a type A pulse reflection ultrasonic testing system.

3. The medium carbon bearing steel forging heat treatment process according to claim 2, characterized in that: The specific process of testing steel ingots using the A-type pulse reflection ultrasonic testing system is as follows: S1.

1. Using any surface of the steel ingot as the reference surface, perform ultrasonic testing on the location and range of internal defects in the steel ingot, and divide the test area of ​​the surface into several test areas; S1.

2. Perform ultrasonic testing on each test area, with the distance from the probe center to the riser as the test position and the direction from the riser end to the nozzle end as the test direction, to obtain several sets of ultrasonic test waveforms; S1.

3. Data processing and analysis are performed based on the obtained sets of ultrasonic detection waveforms to obtain the location and range of defect accumulation inside the steel ingot under the current surface.

4. The medium carbon bearing steel forging heat treatment process according to claim 3, characterized in that: The specific method of obtaining several detection areas is as follows: The reference test surface of the steel ingot for ultrasonic testing is divided into several 100×100 mm squares. Three test points are set along the central axis from the riser to the nozzle in each square, and the interval between two adjacent test points is 33 mm.

5. The medium carbon bearing steel forging heat treatment process according to claim 4, characterized in that: The specific process of the blanking is: S2.

1. Expand the gap 20mm-40mm towards the center of the ingot based on the defect detection boundary line at the nozzle end of the ingot, and expand the gap 20mm-40mm towards the center of the ingot based on the defect detection boundary line at the riser end of the ingot, as the blanking boundary; S2.

2. Expand the center defect detection boundary of the steel ingot by 40mm-60mm as the punching boundary; and then determine the subsequent punching diameter according to the size ratio of the core defect of the steel ingot; S2.

3. Cut the material according to the cutting boundary and punching boundary to obtain the forging blank.

6. The medium carbon bearing steel forging heat treatment process according to any one of claims 1 to 5, characterized in that: The specific process of forging is as follows: S3.

1. Perform a forging heat treatment on the forging blank. Specifically, heat the forging blank to 1250±10°C using a stepwise heating method and keep it at that temperature for 0.3 min / mm-0.5 min / mm. S3.

2. The heated forging blank is repeatedly subjected to roughing and drawing, and after forging to the specified size, it is punched to obtain a forged blank; the punching diameter is the larger value of the ultrasonic flaw detection result and one-fifth of the forged blank diameter. The punch type is determined by the type of ring product.

7. The medium carbon bearing steel forging heat treatment process according to claim 6, characterized in that: The specific process of ring rolling is as follows: S4.

1. Perform segmented heating and heat preservation on the forging blank; initially heat to 1250±10℃, and hold for 0.35 min / mm-0.55 min / mm; later adjust the furnace temperature to 1220±10℃, and hold for 0.05 min / mm-0.15 min / mm; S4.

2. The forged billet is rolled out to the specified size, and the final rolling temperature is required to be ≥850℃; S4.

3. After ring rolling, the ring forging is furnace cooled to below 400℃.

8. The medium carbon bearing steel forging heat treatment process according to claim 6, characterized in that: The specific process of heat treatment and machining is as follows; S5.

1. Ring forgings are subjected to normalizing and tempering heat treatment; S5.

2. Rough turning of the ring forgings after normalizing and quenching and tempering heat treatment; S5.

3. After rough turning to the specified dimensions, perform stress relief annealing on the ring forgings: heat the ring forgings to 520±10℃ at a heating rate of ≤40℃ / h and hold for 2.0-2.3min / mm. Cool the ring forgings to below 200℃ and then remove from the furnace for cooling. S5.

4. Finish-machine the ring forgings after stress relief annealing to the designed dimensions.

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