A method of refining carbides in a high carbon alloy steel

Abstract

This invention relates to the field of ferrous metal material preparation, specifically a method for refining carbides in high-carbon alloy steel. This method is applicable to refining coarse carbides within high-carbon alloy steel and controlling their distribution. The method employs a cyclical process of "thermomechanical deformation-isothermal diffusion" to increase the dissolution amount and rate of large-sized carbides, allowing them to fully dissolve into the matrix. Subsequent heat treatment then precipitates dispersed, fine carbide particles, significantly improving the homogeneity and fatigue performance of the high-carbon alloy steel.

Description

Technical Field

[0001] This invention relates to the field of ferrous metal material preparation, specifically a method for refining carbides in high-carbon alloy steel, applicable to the refinement of coarse carbides and the control of carbide distribution within high-carbon alloy steel. Background Technology

[0002] Controlling coarse carbides in high-carbon alloy steel is a challenging technical problem. Due to the high carbon and alloying element content in high-carbon alloy steel, coarse primary carbides such as MC and M2C often form during solidification. These primary carbides are large in size, and even after forging and heat treatment, their distribution remains severely uneven, with individual carbides larger than 10 μm still present. This ultimately leads to the heterogeneity of the microstructure and properties of high-carbon alloy steel. Large carbides act as fatigue crack initiation sites, severely impairing the service performance of bearings. Therefore, refining the primary carbides in high-carbon alloy steel to obtain bearing materials with fine, uniform, and dispersed carbide distribution is urgently needed.

[0003] To refine the size of primary carbides in bearing steel, traditional techniques involve forcing carbides to fragment through large forging ratios or rolling depths. However, these methods have limited carbide refinement effects and cannot improve carbide segregation. Therefore, the industry urgently needs more effective carbide refinement technologies. Summary of the Invention

[0004] The purpose of this invention is to provide a method for refining carbides in high-carbon alloy steel, forcing primary carbides to fully dissolve and then precipitate again, thereby achieving refined and dispersed carbide distribution. This invention is not only applicable to high-carbon bearing steels, such as GCr15 and M50, but also to various high-carbon alloy tool steels, gear steels, die steels, spring steels, and high-speed steels that easily produce coarse carbides, such as H13, T1, and W6Mo5Cr4V2.

[0005] The technical solution of this invention is:

[0006] A method for refining carbides in high-carbon alloy steel includes the following steps:

[0007] (a) Process the ingot raw material into bars, turn the end face, and round the corners;

[0008] (b) The bar stock is placed in a high-temperature furnace and heated to the diffusion temperature and held at that temperature for a period of time for diffusion.

[0009] (c) Cool the bar stock that has undergone heat preservation and diffusion to the initial forging temperature or initial rolling temperature, and hold it at that temperature for a period of time;

[0010] (d) Remove the bar stock from the high-temperature furnace for forging or rolling;

[0011] (e) Repeat steps (b) to (d) once or more;

[0012] (f) Stress-relief annealing or spheroidizing annealing is performed on the forged or rolled bar stock.

[0013] In the method for refining carbides in high-carbon alloy steel, in step (a), the ingot raw material is high-carbon alloy steel such as GCr15, M50, H13 or T1, including bearing steel, tool steel, mold steel or spring steel, etc.

[0014] In the method for refining carbides in high-carbon alloy steel, step (b) involves a diffusion temperature of 900℃ to 1280℃ and a holding diffusion time of 1h to 48h.

[0015] In the method for refining carbides in high-carbon alloy steel, step (c) involves an initial forging temperature of 800℃ to 1200℃ and a holding time of 0.5h to 12h.

[0016] In the method for refining carbides in high-carbon alloy steel, in step (d), the total forging ratio of forging is not less than 1.5, the number of upsetting and drawing is unlimited, and the rolling deformation is not less than 10%.

[0017] In the method for refining carbides in high-carbon alloy steel, step (e) involves repeating steps (b) to (d) once or more.

[0018] In the method for refining carbides in high-carbon alloy steel, step (f) involves stress-relief annealing, where the forged or rolled bar is directly placed into a de-energized heating furnace and cooled to room temperature with the furnace, or buried in a sand pit or ash pit for slow cooling to room temperature; and spheroidizing annealing, where the forged or rolled bar is cooled to below 600°C, placed in a heating furnace at 600°C to 700°C and held for 0.5 to 6 hours, then heated at a heating rate of <200°C / h to 750°C to 950°C and held for 2 to 8 hours, then cooled at a cooling rate of <80°C / h to 650 to 850°C and held for 2 to 8 hours, followed by furnace cooling to room temperature.

[0019] The technical principle of this invention is as follows:

[0020] This invention employs a cyclical process of "thermomechanical deformation-isothermal diffusion" to repeatedly break down and dissolve primary carbides within high-carbon alloy steel. This process ultimately allows the primary carbides to fully dissolve within the matrix, enabling subsequent conventional quenching and tempering to precipitate fine, dispersed carbides. Traditional single high-temperature diffusion treatment is ineffective at dissolving primary carbides because the carbides are large and difficult to dissolve completely. Furthermore, after a period of diffusion, the concentration of alloying elements such as carbon, molybdenum, and vanadium in the matrix surrounding the carbides increases, increasing the resistance to carbide dissolution.

[0021] The core idea of ​​this invention is to repeatedly break down carbides through mechanical deformation during the "thermomechanical deformation-isothermal diffusion" cyclic treatment process, causing the surrounding matrix to flow and redistribute. This significantly reduces the resistance to further dissolution of carbides and shortens the diffusion path of alloying elements, thereby increasing the dissolution amount and rate of large-sized carbides. Repeating this process several times achieves complete re-dissolution of the carbides. After the large-sized carbides have been fully re-dissolved, subsequent conventional heat treatment processes (such as annealing, quenching, and tempering) can achieve uniform and dispersed precipitation of fine carbides.

[0022] The present invention has the following advantages and beneficial effects:

[0023] 1. This invention fully refines carbides, avoiding stress concentration or crack initiation caused by large-sized carbides, and significantly improves the homogeneity and fatigue performance of high-carbon alloy steels (such as bearing steel, tool steel, die steel, etc.).

[0024] 2. The present invention adopts a process of "thermomechanical deformation-isothermal diffusion" cycle treatment, which can avoid defects such as micropores or grain boundary overheating caused by single long-term high-temperature diffusion, significantly shorten the heat preservation diffusion time, and improve efficiency.

[0025] 3. The present invention adopts the process of "thermomechanical deformation-isothermal diffusion" cycle treatment, which can improve the degree of carbide segregation, and large-sized carbides can be fully dissolved into the matrix. Fine carbide particles can be precipitated during subsequent quenching and tempering, so as to achieve uniform dispersion of fine carbides.

[0026] 4. The present invention adopts the process of "thermomechanical deformation-isothermal diffusion" cycle treatment, which can directly utilize the existing high-temperature furnace and forging equipment in the factory without the need for additional equipment purchase or modification, and the technology is easy to promote. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of carbide distribution in M50 steel after treatment using the traditional process of "high-temperature diffusion + high forging ratio forging".

[0028] Figure 2 This is a schematic diagram of carbide distribution in M50 steel after the "thermomechanical deformation-isothermal diffusion" cyclic treatment described in this invention. Detailed Implementation

[0029] In its specific implementation, the method for refining carbides in high-carbon alloy steel according to the present invention comprises the following steps:

[0030] (a) Process the ingot raw material into bars of a certain size, machine the end face, and round the corners;

[0031] (b) The bar stock is placed in a high-temperature furnace and heated to the diffusion temperature and held at that temperature for a period of time for diffusion.

[0032] (c) Cool the bar stock that has undergone heat preservation and diffusion to the initial forging temperature (or initial rolling temperature) and hold it for a period of time;

[0033] (d) Remove the bar stock from the high-temperature furnace for forging (or rolling);

[0034] (e) Repeat steps (b) to (d) once or more;

[0035] (f) The forged bars are subjected to stress-relief annealing or spheroidizing annealing. Any annealing process known in the industry can be used, with no particular restrictions.

[0036] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] Example 1

[0038] The original sample was an M50 steel ingot that had undergone vacuum induction melting and vacuum arc remelting. The processing procedure was as follows:

[0039] 1) Process the steel ingot into φ200mm×300mm bars, remove the oxide scale, machine the end face, and round the corners.

[0040] 2) Place the bar in a high-temperature furnace and heat it to a diffusion temperature of 1180℃, and keep it at that temperature for 8 hours.

[0041] 3) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1130℃ and hold it for 0.5 hours.

[0042] 4) Take the bar out of the high-temperature furnace and start forging. The specific process is three upsetting and three drawing, with a total strain of 2.

[0043] 5) Place the forged bar in a high-temperature furnace and heat it to a diffusion temperature of 1180℃, and hold it for 4 hours for diffusion.

[0044] 6) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1130℃ and hold it for 0.5 hours.

[0045] 7) Take the bar out of the high-temperature furnace and start forging. The specific process is three upsetting and three drawing, with a total strain of 2.

[0046] 8) Place the forged bar in a high-temperature furnace and heat it to a diffusion temperature of 1180℃, and hold it for 5 hours.

[0047] 9) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1130℃ and hold it for 0.5 hours.

[0048] 10) Take the bar out of the high-temperature furnace and start forging. The specific process is two upsetting and two drawing, with a total strain of 3.

[0049] 11) Cool the bar that has been forged three times to 600°C, put it into a 600°C heating furnace and hold it for 0.5 hours, then heat it to 840°C for 2 hours and hold it for 3 hours, then cool it down to 730°C for 3 hours and hold it for 4 hours, and then furnace cool it to room temperature.

[0050] In this embodiment, the carbides in the M50 steel ingot are fully refined, and their performance indicators are as follows: network carbides are better than grade 2, banded carbides are better than grade 2, liquid carbides are better than grade 2, the average length of a single carbide is <5μm, and the maximum size of a single carbide is <10μm.

[0051] like Figure 1 As shown in the schematic diagram of carbide distribution in M50 steel after traditional forging, the carbide banding segregation is at level 2, and the chain-like liquid carbide segregation also reaches level 2, with the largest single carbide size reaching 13 μm. These coarse carbides can cause stress concentration or form fatigue crack initiation sites, reducing the service life of the material.

[0052] like Figure 2 As shown in the schematic diagram of carbide distribution in M50 steel after the "thermomechanical deformation-isothermal diffusion" cyclic treatment described in this invention, the carbides are diffusely distributed, with no carbide banding segregation, no chain-like or strip-like liquid carbide segregation, and the carbides are significantly refined, with the maximum size of a single carbide being only 4 μm. Experimental verification shows that this material exhibits a significant improvement in rolling contact fatigue life and fracture toughness.

[0053] Example 2

[0054] The original sample was an H13 steel ingot that had undergone vacuum induction melting and vacuum arc remelting. The processing procedure was as follows:

[0055] 1) Process the steel ingot into φ200mm×400mm bars, remove the oxide scale, machine the end face, and round the corners.

[0056] 2) Place the bar in a high-temperature furnace and heat it to a diffusion temperature of 1200℃, and keep it at that temperature for 8 hours.

[0057] 3) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1120℃ and hold it for 0.5 hours.

[0058] 4) Take the bar out of the high-temperature furnace and start forging. The specific process is three upsetting and three drawing, with a total strain of 2.

[0059] 5) Place the forged bar in a high-temperature furnace and heat it to a diffusion temperature of 1200℃, and hold it for 6 hours for diffusion.

[0060] 6) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1120℃ and hold it for 0.5 hours.

[0061] 7) Take the bar out of the high-temperature furnace and start forging. The specific process is three upsetting and three drawing, with a total strain of 2.

[0062] 8) Place the forged bar in a high-temperature furnace and heat it to a diffusion temperature of 1200℃, and hold it for 8 hours.

[0063] 9) Adjust the temperature of the high-temperature furnace to the initial forging temperature of 1120℃, and hold it for 0.5 hours;

[0064] 10) Take the bar out of the high-temperature furnace and start forging. The specific process is two upsetting and two drawing, with a total strain of 2.

[0065] 11) Place the bar that has been forged three times into a sand pit and slowly cool it to room temperature.

[0066] In this embodiment, the H13 steel ingot has been thoroughly refined to produce carbides with the following performance indicators: no banded segregation of carbides, no network carbides, uniformly dispersed carbides, and the maximum size of a single carbide is <5μm.

[0067] The results of the above embodiments show that the "thermomechanical deformation-isothermal diffusion" cyclic treatment of the present invention fully breaks down and dissolves large-sized carbides in high-carbon alloy steel, and the subsequent heat treatment process causes the carbides to precipitate again, achieving a uniform and dispersed distribution of fine carbides. This significantly refines the size of the carbides and effectively improves carbide segregation, which is beneficial to improving the comprehensive mechanical properties of high-carbon alloy steel.

[0068] This invention includes, but is not limited to, the above embodiments. Various high-carbon alloy steels with large-size carbide problems can use this invention to refine the carbides. Any means and processes that use thermomechanical deformation and isothermal diffusion combined cyclic treatment to improve carbide distribution are within the scope of protection of this patent.

Claims

1. A method for refining carbides in high-carbon alloy steel, characterized in that, Includes the following steps: (a) Process the ingot raw material into bars, turn the end face, and round the corners; (b) The bar is placed in a high-temperature furnace and heated to the diffusion temperature and kept at that temperature for a period of time. The diffusion temperature is 900℃~1280℃ and the diffusion time is 1 h~48 h. (c) Cool the bar stock that has undergone heat preservation and diffusion to the initial forging temperature or the initial rolling temperature, and hold it at the temperature for a period of time. The initial forging temperature or the initial rolling temperature is 800℃~1200℃, and the holding time is 0.5 h~12 h. (d) Remove the bar stock from the high-temperature furnace for forging or rolling; (e) Repeat steps (b) to (d) more than twice. Through the "thermomechanical deformation-isothermal diffusion" cycle treatment, the primary carbides inside the high carbon alloy steel are repeatedly broken up and dissolved, and finally the primary carbides are fully dissolved in the matrix. During the "thermomechanical deformation-isothermal diffusion" cycle treatment, the carbides are repeatedly broken up by mechanical deformation and the matrix around the carbides is flowed and redistributed, thereby greatly reducing the resistance to the continued dissolution of carbides and shortening the diffusion path of alloying elements, and increasing the dissolution amount and dissolution rate of large-size carbides. (f) Stress-relief annealing or spheroidizing annealing is performed on the forged or rolled bars; wherein: the stress-relief annealing process is to directly load the forged or rolled bars into a de-energized heating furnace and cool them to room temperature with the furnace, or to bury them in a sand pit or ash pit and slowly cool them to room temperature; the spheroidizing annealing process is to cool the forged or rolled bars to below 600°C, load them into a heating furnace at 600°C~700°C and hold them at that temperature for 0.5h~6h, then heat them to 750°C~950°C at a heating rate of <200°C / h and hold them at that temperature for 2h~8h, then cool them to 650~850°C at a cooling rate of <80°C / h and hold them at that temperature for 2h~8h, and then furnace cool them to room temperature; The carbides in the steel exhibit no banded segregation or network-like carbides; they are uniformly dispersed and distributed, with the maximum size of a single carbide being <5 μm.

2. The method for refining carbides in high-carbon alloy steel according to claim 1, characterized in that, In step (a), the raw material for casting is high-carbon alloy steel, which includes bearing steel, gear steel, tool steel, mold steel or spring steel.

3. The method for refining carbides in high-carbon alloy steel according to claim 1 or 2, characterized in that, In step (a), the alloy grade of the ingot raw material is GCr15, M50, H13 or T1.

4. The method for refining carbides in high-carbon alloy steel according to claim 1, characterized in that, In step (d), the total forging ratio is not less than 1.5, and the number of upsetting and drawing is unlimited; the rolling deformation is not less than 10%.

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