High-carbon stainless steel and heat treatment method thereof

Abstract

The invention relates to heat treatment of steel, in particular to high-carbon stainless steel and a heat treatment method thereof.The heat treatment method comprises the steps that low-temperature preheating, medium-temperature transition, quenching heating, rapid cooling quenching, subzero treatment, tempering treatment and aging treatment are sequentially conducted on a high-carbon stainless steel workpiece; the heating temperature of the low-temperature preheating is lower than the heating temperature of the medium-temperature transition, and the heating temperature of the medium-temperature transition is lower than the heating temperature of the quenching heating; the low-temperature preheating, the medium-temperature transition, the quenching heating and the rapid cooling quenching are carried out in a vacuum state. The heat treatment method is adopted for heat treatment of the high-carbon stainless steel workpiece, and the use performance of the workpiece can be improved.

Description

Technical Field

[0001] The invention relates to heat treatment of steel, in particular to high-carbon stainless steel and a heat treatment method thereof. Background Art

[0002] In the shipbuilding industry, ocean-going vessels place stringent demands on the durability and reliability of components. At the same time, the international community continues to raise standards for energy conservation and emission reduction in the shipping industry. Needle valves, core precision components in a ship's fuel injection system, have a direct impact on fuel atomization and combustion efficiency, and thus on the ship's power output and energy consumption. Needle valves are typically manufactured from high-carbon martensitic stainless steel. However, fully realizing the material's properties depends on precise heat treatment processes. In this context, developing appropriate heat treatment methods for high-carbon martensitic stainless steel is crucial. This will not only significantly improve the performance and service life of needle valves, but will also lay a solid technical foundation for optimizing the performance of key ship components and promoting the green and efficient development of the shipping industry. Summary of the Invention

[0003] The purpose of the present invention is to provide a heat treatment method for stainless steel, which can improve the performance of a workpiece.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention discloses a heat treatment method for high carbon stainless steel, comprising: The high carbon stainless steel workpiece is subjected to low temperature preheating, medium temperature transition, quenching heating, rapid cooling quenching, cryogenic treatment, tempering treatment and aging treatment in sequence; The heating temperature of the low-temperature preheating is lower than the heating temperature of the medium-temperature transition, and the heating temperature of the medium-temperature transition is lower than the heating temperature of the quenching heating; The low-temperature preheating, medium-temperature transition, quenching heating and rapid cooling quenching are carried out in a vacuum state.

[0005] Furthermore, the heating temperature of the low-temperature preheating is 600±10°C, and the holding time is 30-60 minutes.

[0006] Furthermore, the heating temperature of the medium temperature transition is 800±5°C, and the holding time is 60-80 minutes.

[0007] Furthermore, the heating temperature of the quenching heating is 1030±10°C, and the holding time is 30~60min.

[0008] Furthermore, the cooling rate of the rapid cooling quenching is 30-50°C / min, and the workpiece is taken out of the furnace when it cools to 60°C or below.

[0009] Furthermore, the cryogenic treatment specifically includes: transferring the workpiece after rapid cooling and quenching treatment into a cryogenic treatment machine with a temperature of ≤-180°C for cryogenic treatment within a first preset time, and the cryogenic treatment time is 120~180min.

[0010] Furthermore, the tempering treatment specifically includes: performing a tempering treatment on the workpiece after the deep freezing treatment within a second preset time, the tempering temperature is 540±5°C, and the holding time is 120~150min.

[0011] Furthermore, the aging treatment temperature is 130±10° C., and the holding time is 15-16 hours.

[0012] Furthermore, the high carbon stainless steel workpiece is cast 108Cr17 stainless steel.

[0013] In a second aspect, the present invention discloses stainless steel, which is produced by the above-mentioned heat treatment method for stainless steel.

[0014] The present invention has the following unexpected beneficial effects: 1. The heat treatment method for high-carbon stainless steel described in the present invention, through the arrangement of low-temperature preheating and medium-temperature transition stages, makes the temperature distribution inside the material more uniform during the gradual heating process of the workpiece, effectively reducing the thermal stress caused by rapid temperature changes. This gradual heating method greatly reduces the possibility of deformation and cracking of the material in subsequent quenching and other processing links, thereby improving the product yield. Quenching heating can fully dissolve the carbides inside the workpiece, creating good conditions for subsequent cooling and transformation into martensite structure. The rapid cooling and quenching process quickly transforms the high-temperature austenite structure into martensite structure. Combined with quenching heating, a fine and uniform martensite structure can be obtained, significantly improving the hardness and strength of the material, and enhancing the wear resistance and fatigue resistance of the material. Deep cryogenic treatment can promote the further transformation of retained austenite into martensite, reduce the content of retained austenite, reduce the risk of dimensional change caused by the instability of retained austenite, and effectively improve the dimensional stability of the material. This is crucial for the manufacture of precision parts such as needle valves that require extremely high dimensional accuracy. Tempering and aging treatments can eliminate the internal stress generated during the quenching process, reduce the brittleness of the material, and at the same time decompose and recrystallize the martensite structure, precipitating fine and dispersed carbides, thereby improving the toughness, plasticity and comprehensive mechanical properties of the material. This allows the high-carbon martensitic stainless steel product to have high strength while also having good toughness, thus avoiding brittle fracture of the material.

[0015] 2. The low-temperature preheating, medium-temperature transition, quenching heating and rapid cooling quenching processes of the heat treatment method of high-carbon stainless steel described in the present invention are carried out under a vacuum state, which effectively avoids chemical reactions between the material and oxygen, water vapor, etc. in the air, prevents the occurrence of problems such as surface oxidation and decarburization, ensures the purity and surface quality of the material, is beneficial to improving the corrosion resistance of the material, and at the same time reduces the processing steps due to surface defects in the subsequent processing process, improves production efficiency and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation or prior art description. Obviously, the drawings described below are only some embodiments of the present invention.

[0017] Figure 1 A schematic flow chart of an embodiment of a heat treatment method for high carbon stainless steel according to an embodiment of the present invention is shown.

[0018] Figure 2 A schematic flow chart of another embodiment of the heat treatment method for high carbon stainless steel according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0020] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. The illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0021] In one embodiment, the present invention discloses a heat treatment method for high carbon stainless steel. Figure 1 As shown, the method includes: The high carbon stainless steel workpiece is subjected to low temperature preheating, medium temperature transition, quenching heating, rapid cooling quenching, cryogenic treatment, tempering treatment and aging treatment in sequence; The heating temperature of the low-temperature preheating is lower than the heating temperature of the medium-temperature transition, and the heating temperature of the medium-temperature transition is lower than the heating temperature of the quenching heating; The low-temperature preheating, medium-temperature transition, quenching heating and rapid cooling quenching are carried out in a vacuum state.

[0022] By implementing low-temperature preheating and a medium-temperature transition phase, the workpiece's internal temperature distribution becomes more uniform during the gradual heating process, effectively reducing thermal stress caused by rapid temperature changes. This gradual heating method significantly reduces the possibility of material deformation and cracking during subsequent quenching and other processing steps, thereby improving product yield.

[0023] Quenching heating fully dissolves the carbides within the workpiece, creating favorable conditions for subsequent cooling and transformation into martensite. Rapid cooling quenching rapidly transforms high-temperature austenite into martensite. Combined with quenching heating, a fine, uniform martensite structure can be obtained, significantly improving the material's hardness and strength, and enhancing its wear resistance and fatigue resistance.

[0024] Cryogenic treatment can further transform retained austenite into martensite, reducing the retained austenite content and the risk of dimensional change due to unstable retained austenite, effectively improving the material's dimensional stability. This is crucial for manufacturing precision parts such as needle valves, which require extremely high dimensional accuracy.

[0025] Tempering and aging treatments can eliminate the internal stress generated during the quenching process, reduce the brittleness of the material, and at the same time decompose and recrystallize the martensite structure, precipitating fine and dispersed carbides, thereby improving the toughness, plasticity and comprehensive mechanical properties of the material. This allows the high-carbon martensitic stainless steel product to have high strength while also having good toughness, thus avoiding brittle fracture of the material.

[0026] The low-temperature preheating, medium-temperature transition, quenching heating and rapid cooling quenching processes of the heat treatment method for high-carbon stainless steel described in the present invention are carried out in a vacuum state, which effectively prevents oxidation and decarburization of the workpiece surface and ensures the material performance. Specifically, preventing surface oxidation: There is almost no oxygen in a vacuum environment, which can completely prevent the oxidation reaction between the material surface and oxygen at high temperature (such as the generation of oxides such as Fe2O3), and prevent the formation of oxide scale on the surface. This is especially important for precision parts (such as needle valves), which can avoid problems such as increased surface roughness and decreased dimensional accuracy caused by oxidation. Inhibiting decarburization: The carbon element in high-carbon stainless steel easily reacts with oxygen and water vapor in the air at high temperatures to generate CO or CO2, resulting in a decrease in the surface carbon content, that is, decarburization, which further weakens the hardness and wear resistance of the material. The vacuum environment can effectively block the loss of carbon elements, ensure the uniformity of carbon concentration on the surface of the material, and maintain its mechanical properties.

[0027] A vacuum environment contains very few gas molecules, and heat conduction is primarily by radiation. Compared to air or a protective atmosphere, materials are heated more evenly in a vacuum furnace, avoiding concentrated thermal stresses caused by localized temperature differences and reducing the risk of deformation and cracking. Furthermore, furnace temperature fluctuations are minimal in a vacuum environment, allowing the temperature control system to more accurately control the temperature curve during low-temperature preheating, intermediate-temperature transition, and quenching heating stages, ensuring repeatability and stability of the heat treatment process. This is particularly suitable for temperature-sensitive materials such as high-carbon stainless steel.

[0028] In addition, when quenching and cooling in a vacuum environment, such as using vacuum oil cooling or air cooling, the heat exchange efficiency between the cooling medium (oil, inert gas) and the material surface is higher and is not affected by air resistance or oxide layer, which can achieve a more uniform and faster cooling rate, promote the consistency of martensitic transformation, and improve the material hardness and structural uniformity.

[0029] At the same time, since there is no oxidation, decarburization and other defects on the surface of the material after vacuum heat treatment, there is no need for additional descaling treatment such as pickling and sandblasting, which ensures that it can directly enter the subsequent deep cold treatment within a limited time, shortening the process flow and reducing production costs.

[0030] As a preferred embodiment of the present invention, see Figure 2 As shown, the heating temperature of the low-temperature preheating is 600±10°C, and the holding time is 30~60min.

[0031] 600±10℃ is in the early stage of austenitization of high carbon stainless steel, which is lower than its Ac1 phase transition point. At this time, the material only undergoes lattice expansion without phase change. This temperature can not only enable the atoms inside the material to obtain sufficient kinetic energy to diffuse heat, but also avoid the sudden change in volume caused by phase change. Among them, Ac1 is the "starting temperature of pearlite to austenite transformation during heating", usually around 700~750℃. High-carbon stainless steel has a low thermal conductivity, and rapid heating can easily lead to large temperature differences between the inside and outside. Low-temperature preheating around 600°C allows the material to be heated slowly at a rate of ≤10°C / min. This insulation keeps the cross-sectional temperature difference ≤50°C, significantly reducing thermal stress. This is particularly suitable for precision parts with large aspect ratios and significant cross-sectional variations, such as needle valves, and can keep deformation within 0.05mm.

[0032] High-carbon stainless steel (such as 108Cr17) ​​contains a large amount of carbides. When held at 600°C, the fine carbides begin to decompose into free carbon and alloying elements, forming a solid solution precursor. This lays the foundation for further homogenization of the carbides during the subsequent intermediate-temperature transition stage, thereby refining the carbide particle size in the final martensitic structure and improving the material's wear resistance.

[0033] Temperature precision of ±10°C and a flexible holding time range of 30 to 60 minutes accommodate parts of varying sizes, such as needle valves with diameters ranging from 5 to 20 mm. For example, a 30-minute holding time for a 10 mm diameter needle valve will meet temperature uniformity requirements, while a 20 mm diameter part can be extended to 60 minutes. This prevents overheating (grain coarsening) in small parts or underheating in large parts due to a "one-size-fits-all" process.

[0034] As a preferred embodiment of the present invention, see Figure 2 As shown, the heating temperature of the medium temperature transition is 800±5°C, and the holding time is 60~80min.

[0035] This preferred embodiment can accurately control the phase transformation process and prepare for quenching. 800±5℃ is in the partial austenitization temperature zone of high-carbon stainless steel. At this temperature, the ferrite matrix begins to transform into austenite, and at the same time, the undissolved carbides continue to decompose to form a three-phase coexistence structure of "austenite + residual carbides + alloy element solid solution". Keeping warm for 60~80min can control the austenite transformation amount within the preset range, further refine the size of the residual carbides after preheating, and make the residual carbides evenly distributed near the austenite grain boundaries. This "semi-austenitization" state can not only avoid the coarsening of grains caused by complete austenitization, but also provide a good foundation for the complete dissolution of carbides during subsequent quenching heating, so that the grain size of the final martensitic structure reaches above level 10.

[0036] Moreover, this preferred embodiment can also coordinate the previous and subsequent processes to optimize the overall heat treatment efficiency. The temperature range spanning from 600±10℃ to 800±5℃ is moderate, and a heating rate of 15~20℃ / min can be adopted, which not only avoids thermal stress caused by excessive temperature jumps, but also shortens the transition time. After the medium-temperature transition, the internal temperature uniformity of the material is further improved, and the degree of austenitization is controllable, which can shorten the holding time of the subsequent quenching heating (1030±10℃) from 90min in the traditional process to 30~60min, reducing the risk of grain coarsening while reducing high-temperature energy consumption.

[0037] As a preferred embodiment of the present invention, see Figure 2 As shown, the heating temperature of the quenching heating is 1030±10°C and the holding time is 30~60min.

[0038] 1030±10°C is within the fully austenitizing temperature range of high-carbon stainless steel, above its Ac3 phase transition point. For example, the Ac3 phase transition point of 108Cr17 is approximately 860°C. At this temperature, the remaining carbides in the material can fully dissolve into the austenite. This process evenly distributes carbon and alloying elements within the austenite lattice, forming a high-carbon, high-alloy austenite structure, laying the foundation for subsequent cooling and transformation into high-performance martensite.

[0039] A holding time of 30 to 60 minutes ensures complete dissolution of carbides within parts of varying sizes. For example, for needle valve parts ≤15mm thick, a 30-minute holding period can achieve a carbide dissolution rate of over 98%. For thicker parts, extending the holding time to 60 minutes ensures full dissolution of the core carbides, avoiding uneven hardness or soft spots after quenching due to localized undissolved carbides.

[0040] As a preferred embodiment of the present invention, see Figure 2 As shown, the cooling rate of the rapid cooling quenching is 30~50℃ / min, and the workpiece is taken out of the furnace when it cools to 60℃ or below.

[0041] The rapid cooling of this preferred embodiment ensures sufficient martensitic transformation. High-carbon stainless steel (such as 108Cr17) ​​requires rapid cooling to suppress the formation of non-martensitic structures such as pearlite and bainite. When the cooling rate reaches a critical value, the high-temperature austenite can quickly transform into fine martensitic structure, thereby significantly improving the hardness and wear resistance of the material. In addition, high-speed cooling can also cause the austenite grains to undergo phase transformation before they have time to grow, thereby obtaining fine martensitic laths or twin structures. This fine grain strengthening effect not only increases the strength of the material, but also improves the toughness, allowing the material to maintain good impact resistance at high hardness. In addition, rapid and uniform cooling can reduce the internal thermal stress differences in the material, avoiding deformation and cracking caused by uneven cooling. Combined with the vacuum quenching environment, the heat exchange efficiency between the cooling medium and the workpiece surface is higher, which can achieve more precise cooling control, so that the dimensional deviation of precision parts such as needle valves can be controlled within ±0.01mm.

[0042] By limiting the workpiece's removal from the furnace to 60°C or below, we ensure that internal thermal stresses in the material have been significantly released. This allows for the avoidance of secondary deformation caused by excessively high temperatures. Furthermore, workpiece temperatures below 60°C facilitate rapid transition to cryogenic treatment, reducing waiting time and improving production efficiency. Furthermore, lower temperatures prevent rapid cooling damage caused by large temperature differences during cryogenic treatment, ensuring sufficient transformation of retained austenite and further optimizing material properties.

[0043] This preferred implementation also synergizes with other processes. The initial low-temperature preheating and intermediate-temperature transition provide a uniform microstructure for rapid cooling, reducing the risk of cracking. Quenching fully dissolves carbides, while rapid cooling "freezes" them within the martensite. A subsequent cryogenic treatment after exiting the furnace at 60°C promotes the transformation of retained austenite, followed by stress relief through tempering, ultimately achieving a balance of hardness, toughness, and corrosion resistance.

[0044] As a preferred embodiment of the present invention, see Figure 2As shown, the cryogenic treatment specifically includes: transferring the workpiece after rapid cooling and quenching treatment into a cryogenic treatment machine with a temperature of ≤-180°C for cryogenic treatment within a first preset time, and the cryogenic treatment time is 120~180min.

[0045] This preferred embodiment can promote the full transformation of retained austenite, improve hardness and wear resistance, and quickly transfer the workpiece to a deep-cold environment with a temperature of ≤-180°C after rapid cooling and quenching. Liquid nitrogen is usually used for refrigeration, and the temperature can reach -196°C. The free energy difference between austenite and martensite is used to drive the transformation of retained austenite to martensite.

[0046] The first preset time is set to ensure that the workpiece is quickly transferred to the cryogenic equipment after quenching. This prevents the "aging stabilization" of retained austenite during room temperature stagnation, where carbon atoms aggregate at dislocations, increasing the resistance to phase transformation. This maximizes the driving force for phase transformation and ensures a more complete martensitic transformation. For example, the first preset time is 30 minutes.

[0047] During cryogenic treatment, the solubility of carbon atoms in the supersaturated martensite decreases dramatically with decreasing temperature, prompting the dispersion and precipitation of fine, nanoscale ε-carbides. These precipitated nanocarbides act as secondary strengthening particles, significantly improving the material's wear resistance. This is particularly true for precision parts like needle valves, which are subject to fuel erosion, extending their fatigue life.

[0048] During cryogenic treatment, the material undergoes a volume shrinkage of about 0.5% to 0.8% due to thermal expansion and contraction, which releases the residual macroscopic thermal stress during the quenching process. At the same time, the microstructural stress (such as the shear stress generated by the martensitic phase transformation) is relaxed through dislocation slip and twinning.

[0049] Furthermore, rapid deep cooling after quenching "locks in" the alloying elements dissolved during quenching and heating, preventing the precipitation of coarse carbides when left at room temperature. Furthermore, the ultrafine martensite structure and dispersed carbides formed during cryogenic treatment provide a better foundation for subsequent tempering, resulting in an even better match between the strength and toughness of the tempered material. Tempering after cryogenic treatment eliminates the microstresses generated during the cryogenic process and promotes tempering decomposition of the martensite, forming a stable structure of tempered martensite and fine carbides.

[0050] As a preferred embodiment of the present invention, see Figure 2 As shown, the tempering treatment specifically includes: performing a tempering treatment on the workpiece after deep freezing treatment within a second preset time, the tempering temperature is 540±5°C, and the holding time is 120~150min.

[0051] 540±5°C is the peak temperature range for secondary hardening of high-carbon stainless steel. At this temperature, supersaturated martensite decomposes, precipitating fine, dispersed alloy carbides. This "tempered martensite + dispersed carbides" structure allows the material to maintain high hardness while improving impact toughness, resolving the "hard but brittle" problem of high-carbon steel.

[0052] The 120-150 minutes of heat preservation allows the carbides to be fully precipitated and evenly distributed, avoiding insufficient precipitation due to insufficient heat preservation or coarsening of carbides due to too long heat preservation.

[0053] During the tempering process, alloying elements such as Cr and Mo are enriched in carbides, the alloying elements dissolved in the matrix are reduced, the degree of lattice distortion is reduced, and the toughness of the material is improved; at the same time, the precipitated alloy carbides produce a strong second-phase strengthening effect, so that the hardness of the material increases instead of decreases after tempering. This "secondary hardening" characteristic is crucial for wear-resistant parts.

[0054] After cryogenic treatment, tempering is quickly performed. For example, the second preset time is 30 minutes. This can prevent the microcracks generated by cryogenic treatment from expanding when staying at room temperature. At the same time, hot tempering can more efficiently release the stress generated during the cryogenic process.

[0055] As a preferred embodiment of the present invention, see Figure 2 As shown, the temperature of the aging treatment is 130±10°C and the holding time is 15~16h.

[0056] 130±10°C is within the low-temperature aging temperature range for high-carbon stainless steel. At this temperature, alloying elements and carbon atoms in the supersaturated martensite matrix diffuse to form nanoscale precipitates. These precipitates are evenly distributed along dislocation lines and grain boundaries, inhibiting dislocation slip and grain growth through a "pinning effect," ensuring the material maintains dimensional stability and consistent performance over long-term service.

[0057] The long-term heat preservation of 15~16 hours ensures the sufficient nucleation and growth of the precipitated phase, and the strengthening effect is significant.

[0058] During the aging process, the retained austenite undergoes micro-decomposition due to temperature induction, forming extremely fine carbide particles. At the same time, the carbon and alloy elements in the austenite diffuse into the precipitated phase, which improves its stability and avoids dimensional fluctuations caused by austenite phase transformation during service.

[0059] As a preferred embodiment of the present invention, the high carbon stainless steel workpiece is cast 108Cr17 stainless steel.

[0060] Calculated by mass fraction, the as-cast 108Cr17 stainless steel includes 1.00% to 1.10% of C, 16.00% to 18.00% of Cr, ≤1.00% of Mn, ≤1.00% of Si, and the balance is Fe and unavoidable impurities.

[0061] As-cast 108Cr17 stainless steel exhibits typical dendritic segregation and microporosity. The multi-stage heat treatment process of the present invention, comprising low-temperature preheating, intermediate-temperature transition, and quenching, specifically promotes initial atomic diffusion and reduces component segregation. The intermediate-temperature transition undergoes partial austenitization, weakening dendrite boundaries and paving the way for subsequent homogenization. High-temperature diffusion during quenching evens out the Cr and C elements, and combined with the micro-pressure in a vacuum environment, improves material density.

[0062] The thermal conductivity of as-cast 108Cr17 (approximately 15 W / m·K) is lower than that of forged material, making rapid heating susceptible to cracking due to internal and external temperature differences. This invention utilizes a step-wise heating process with low-temperature preheating and intermediate-temperature transitions, controlling the heating rate to 5-10°C / min to maintain a cross-sectional temperature difference of ≤30°C, thus reducing the cracking rate during heat treatment of the as-cast workpiece. To address the uneven composition of the as-cast structure, the holding time during the quenching heating phase is extended to 30-60 minutes to ensure full dissolution of the core carbides.

[0063] In one embodiment, the present invention discloses stainless steel, which is produced by the above-mentioned stainless steel heat treatment method.

[0064] The following analysis and explanation are combined with specific examples.

[0065] Example 1: A heat treatment method for high carbon stainless steel, comprising the following steps: S1, after rough machining of φ21 108Cr17 round steel, gas quenching is carried out in a vacuum gas quenching furnace. Specifically, after the furnace is in a vacuum state, the temperature is heated to 600℃ and kept warm for 60 minutes, namely the low-temperature preheating stage; the temperature is again heated to 800℃ and kept warm for 70 minutes, namely the medium-temperature transition stage; finally, the temperature is raised to the quenching heating temperature of 1030℃ and kept warm for 50 minutes, namely the quenching heating stage; then rapid cooling quenching is carried out, and the workpiece is quenched by rapidly cooling the workpiece with nitrogen at a pressure of 4 bar. The cooling rate is controlled at 30℃ / min, and the workpiece is cooled to below 60℃ and then taken out of the furnace.

[0066] S2: After being taken out of the furnace, transfer it to the ultra-low temperature cold treatment machine within 30 minutes and perform deep freezing treatment at ≤-180℃ for 120 minutes.

[0067] S3: Temper once within 30 minutes after deep cryogenic treatment at 540°C for 120 minutes. After tempering and holding, air cool to room temperature.

[0068] S4, aging treatment, aging temperature is 130℃, and holding time is 16h.

[0069] The hardness was tested by Rockwell hardness tester, the retained austenite content was tested by XRD, and the grain size and tempering structure were tested by metallographic microscope.

[0070] The hardness of the 108Cr17 needle valve after sample treatment can reach about 52.5~54HRC, the retained austenite content is 4.21%, the overheating structure is level 2, and the core grain size is level 11.

[0071] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A heat treatment method for high carbon stainless steel, characterized in that: include: The high carbon stainless steel workpiece is subjected to low temperature preheating, medium temperature transition, quenching heating, rapid cooling quenching, cryogenic treatment, tempering treatment and aging treatment in sequence; The heating temperature of the low-temperature preheating is lower than the heating temperature of the medium-temperature transition, and the heating temperature of the medium-temperature transition is lower than the heating temperature of the quenching heating; The low-temperature preheating, medium-temperature transition, quenching heating and rapid cooling quenching are carried out in a vacuum state.

2. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The heating temperature of the low-temperature preheating is 600±10°C, and the holding time is 30-60 minutes.

3. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The heating temperature of the medium temperature transition is 800±5°C, and the holding time is 60-80 minutes.

4. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The heating temperature of the quenching heating is 1030±10° C., and the holding time is 30-60 minutes.

5. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The cooling rate of the rapid cooling quenching is 30-50°C / min, and the workpiece is taken out of the furnace when it cools to 60°C or below.

6. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The cryogenic treatment specifically includes: transferring the workpiece after rapid cooling and quenching treatment into a cryogenic treatment machine with a temperature of ≤-180°C for cryogenic treatment within a first preset time, and the cryogenic treatment time is 120~180 minutes.

7. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The tempering treatment specifically includes: performing a tempering treatment on the workpiece after the deep freezing treatment within a second preset time, the tempering temperature is 540±5° C., and the holding time is 120-150 minutes.

8. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The temperature of the aging treatment is 130±10° C., and the holding time is 15-16 hours.

9. The heat treatment method of high carbon stainless steel according to claim 1, characterized in that: The material of the high carbon stainless steel workpiece is 108Cr17 stainless steel.

10. A high carbon stainless steel, characterized in that: The stainless steel is prepared by the heat treatment method of high carbon stainless steel according to any one of claims 1 to 9.

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