Vacuum carburizing treatment method for duplex stainless steel

Abstract

The invention provides a vacuum carburizing treatment method for duplex stainless steel, and relates to the technical field of material treatment.The vacuum carburizing treatment method adopts an inert gas quenching process, and the inert gas quenching process is subsection cooling, that is, in the early-stage high-temperature section, high-pressure gas quenching is adopted for rapid cooling to the martensite transformation starting temperature of the duplex stainless steel; and slowly cooling to the room temperature through low-pressure gas quenching in the later low-temperature section. By the adoption of the vacuum carburizing treatment method for the duplex stainless steel, the toughness of the duplex stainless steel product can be further improved under the condition that it is guaranteed that the carburizing hardened layer formed on the surface of the duplex stainless steel has high hardness, and the deformation of the duplex stainless steel product before and after carburizing treatment can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of material processing, and in particular to a vacuum carburizing treatment method for duplex stainless steel. Background Art

[0002] For new energy methanol vehicles, the valve body of the core component, the injector, needs to be resistant not only to pore corrosion, but also to organic acid corrosion caused by methanol fuel. Therefore, the valve body of the injector needs to be made of austenite-ferrite duplex stainless steel, but the hardness of duplex stainless steel is relatively low, so the wear resistance is relatively poor. In order to improve the wear resistance of duplex stainless steel, duplex stainless steel is often carburized in the prior art to form a carburized hardened layer on the surface of duplex stainless steel. However, although the carburized hardened layer formed on the surface of duplex stainless steel by the existing carburizing treatment method has a high hardness, the toughness of the obtained duplex stainless steel product still needs to be further improved, and the deformation of the duplex stainless steel product before and after the carburizing treatment is relatively large. Summary of the invention

[0003] The problem solved by the present invention is at least one of the following problems: how to further improve the toughness of the duplex stainless steel product while ensuring that the carburized hardened layer formed on the surface of the duplex stainless steel has a high hardness; how to reduce the deformation of the duplex stainless steel product before and after carburizing treatment.

[0004] In order to solve the above problems, the present invention provides a vacuum carburizing method for duplex stainless steel, comprising:

[0005] The duplex stainless steel to be treated is subjected to vacuum carburizing treatment, quenching treatment, cryogenic treatment and tempering treatment in sequence to obtain a duplex stainless steel having a carburized hardened layer formed on the surface;

[0006] Wherein, inert gas is used as quenching medium during quenching treatment, and the quenching treatment includes:

[0007] The duplex stainless steel subjected to vacuum carburizing is heated to a first temperature in a vacuum environment, and after being kept at the first temperature for a first time, a high-pressure gas quenching cooling treatment is performed, and when austenite begins to transform into martensite, a low-pressure gas quenching cooling treatment is performed, and finally cooled to room temperature.

[0008] Optionally, the low-pressure gas quenching cooling treatment is performed when the austenite begins to transform into martensite, and finally cooled to room temperature, comprising:

[0009] When austenite begins to transform into martensite, a first low-pressure quenching cooling treatment is performed to a second temperature. After being kept at that temperature for a second time, a second low-pressure quenching cooling treatment is performed to room temperature.

[0010] Optionally, the second temperature is 100-200° C., and the second time is 5-30 min.

[0011] Optionally, the gas pressure of the first low-pressure quenching and cooling treatment and the second low-pressure quenching and cooling treatment is 0.5-1.5 bar.

[0012] Optionally, the first temperature is 1050-1150° C., and the first time is ((1-3) h+60) min, wherein h is the thickness of the duplex stainless steel to be treated.

[0013] Optionally, the gas pressure of the high-pressure gas quenching cooling treatment is 2-5 bar.

[0014] Optionally, the quenching treatment is performed 1-3 times.

[0015] Optionally, the method for preparing the duplex stainless steel to be treated comprises: subjecting the duplex stainless steel to a solid solution treatment under a vacuum environment to obtain the duplex stainless steel to be treated.

[0016] Optionally, the vacuum carburizing treatment includes:

[0017] placing the duplex stainless steel to be treated in a vacuum carburizing furnace, heating it to a third temperature under a vacuum environment, and keeping the temperature for a third time;

[0018] Carburizing process: introducing acetylene gas into the vacuum carburizing furnace to enter the intensive carburizing stage; extracting the acetylene gas in the vacuum carburizing furnace, introducing inert gas, and entering the diffusion stage;

[0019] The carburizing process is repeated until the total carburizing time reaches a fourth time.

[0020] Optionally, the third temperature is 1050-1150° C.;

[0021] And / or, the furnace pressure in the strong permeation stage is 300-2500Pa, the time is 30-180s, and the carbon concentration on the sample surface is set to 0.8-1.6%; the furnace pressure in the diffusion stage is 100-1000Pa, the time is 600-3600s, and the carbon concentration on the sample surface is set to 0.5-1.2%;

[0022] And / or, the fourth time is 2-24h.

[0023] Compared with the prior art, the present invention adopts an inert gas quenching process. Compared with the traditional oil quenching method, the inert gas quenching process has better cooling uniformity, can effectively control the transformation temperature and cooling process, thereby greatly reducing the probability of the formation of non-martensitic structure, and is conducive to preventing the presence of non-martensitic structure from causing the hardness of the carburized hardened layer to decrease, thereby ensuring that the carburized hardened layer has a higher hardness. Moreover, compared with the oil quenching method, due to the better cooling uniformity of the inert gas quenching process, the structural stress and thermal stress generated during the quenching process are more uniform, which is conducive to reducing the deformation of the duplex stainless steel product before and after carburizing treatment. In addition, the inert gas quenching process adopted by the present invention is segmented cooling, that is, the early high-temperature section is quickly cooled to the martensitic transformation starting temperature (the temperature when austenite begins to transform into martensite) of the duplex stainless steel by high-pressure gas quenching, thereby avoiding the generation of non-martensitic structure caused by too slow cooling speed, which is beneficial to further improve the hardness of the carburized hardened layer; the late low-temperature section is slowly cooled to room temperature by low-pressure gas quenching, which can slow down the mutual collision between the newly generated needle-shaped martensite and the needle-shaped martensite generated in the early stage during the transformation of austenite into needle-shaped martensite, thereby reducing the probability of microcracks, which is beneficial to improve the toughness of the duplex stainless steel product. In summary, the vacuum carburizing treatment method for duplex stainless steel provided by the present invention can ensure that the carburized hardened layer formed on the surface of the duplex stainless steel has a higher hardness, further improve the toughness of the duplex stainless steel product, and can reduce the deformation of the duplex stainless steel product before and after carburizing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a microstructure picture of the carburized hardened layer of the duplex stainless steel product prepared in Example 1;

[0025] Figure 2 This is a microstructure picture of the carburized hardened layer of the duplex stainless steel product prepared in Comparative Example 1;

[0026] Figure 3 This is a microstructure picture of the carburized hardened layer of the duplex stainless steel product prepared in Comparative Example 2;

[0027] Figure 4 This is a microstructure picture of the carburized hardened layer of the duplex stainless steel product prepared in Comparative Example 3. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific implementation methods and are not intended to limit this application;

[0030] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" is "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, the meaning of "multiple" is two or more.

[0031] It should be noted that the duplex stainless steel in the present invention refers to austenite-ferrite duplex stainless steel. In the present invention, the temperature corresponding to when austenite in the duplex stainless steel begins to transform into martensite is the martensite transformation starting temperature of the duplex stainless steel.

[0032] An embodiment of the present invention provides a vacuum carburizing method for duplex stainless steel, comprising:

[0033] The duplex stainless steel to be treated is subjected to vacuum carburizing treatment, quenching treatment, cryogenic treatment and tempering treatment in sequence to obtain a duplex stainless steel having a carburized hardened layer formed on the surface;

[0034] Wherein, inert gas is used as quenching medium during quenching treatment, and the quenching treatment includes:

[0035] The duplex stainless steel subjected to vacuum carburizing is heated to a first temperature in a vacuum environment, and after being kept at the first temperature for a first time, a high-pressure gas quenching cooling treatment is performed, and when austenite begins to transform into martensite, a low-pressure gas quenching cooling treatment is performed, and finally cooled to room temperature.

[0036] It should be noted that, in the embodiment of the present invention, the cooling rate is controlled by controlling the gas pressure of the inert gas during the quenching process. The greater the gas pressure, the greater the cooling rate.

[0037] The embodiment of the present invention adopts an inert gas quenching process. Compared with the traditional oil quenching method, the inert gas quenching process has better cooling uniformity, can effectively control the transformation temperature and cooling process, thereby greatly reducing the probability of the formation of non-martensitic structure, which is conducive to preventing the presence of non-martensitic structure from causing the hardness of the carburized hardened layer to decrease, thereby ensuring that the carburized hardened layer has a higher hardness. Moreover, compared with the oil quenching method, due to the better cooling uniformity of the inert gas quenching process, the structural stress and thermal stress generated during the quenching process are more uniform, which is conducive to reducing the deformation of the duplex stainless steel product before and after carburizing treatment. In addition, the inert gas quenching process adopted in the embodiment of the present invention is segmented cooling, that is, the early high-temperature section is quickly cooled to the martensitic transformation starting temperature of the duplex stainless steel (the temperature when austenite begins to transform into martensite) by high-pressure gas quenching, thereby avoiding the generation of non-martensitic structure caused by too slow cooling speed, which is beneficial to further improve the hardness of the carburized hardened layer; the late low-temperature section is slowly cooled to room temperature by low-pressure gas quenching, which can slow down the mutual collision between the newly generated needle-shaped martensite and the needle-shaped martensite generated in the early stage during the transformation of austenite into needle-shaped martensite, thereby reducing the probability of microcracks, which is beneficial to improve the toughness of the duplex stainless steel product. In summary, the vacuum carburizing treatment method for duplex stainless steel provided by the embodiment of the present invention can ensure that the carburized hardened layer formed on the surface of the duplex stainless steel has a high hardness, further improve the toughness of the duplex stainless steel product, and reduce the deformation of the duplex stainless steel product before and after carburizing.

[0038] In some embodiments of the present invention, the low-pressure gas quenching cooling treatment is performed when austenite begins to transform into martensite, and finally cooled to room temperature, comprising:

[0039] When austenite begins to transform into martensite, a first low-pressure quenching cooling treatment is performed to a second temperature. After being kept at that temperature for a second time, a second low-pressure quenching cooling treatment is performed to room temperature.

[0040] In this embodiment, during the cooling process in the later low-temperature stage, the heat preservation treatment is performed at a second temperature lower than the martensitic transformation start temperature, which can reduce the structural stress and thermal stress generated during the transformation of austenite to martensite, thereby further reducing the deformation of the duplex stainless steel product before and after carburizing treatment.

[0041] In some embodiments of the present invention, the second temperature is 100-200° C., and the second time is 5-30 min.

[0042] In some embodiments of the present invention, the gas pressure of the first low-pressure quenching and cooling treatment and the second low-pressure quenching and cooling treatment is 0.5-1.5 bar.

[0043] In some embodiments of the present invention, the first temperature is 1050-1150° C., the first time is ((1-3)h+60)min, wherein h is the thickness of the duplex stainless steel to be treated, in units of mm; and the gas pressure of the high-pressure gas quenching cooling treatment is 2-5bar.

[0044] In some embodiments of the present invention, preferably, the number of quenching treatments is 1-3 times, that is, the number of quenching treatments does not exceed 3 times. The martensite formed by quenching after carburizing treatment is needle-shaped, and the formation of martensite is continuous and instantaneous as the temperature drops. Therefore, the needle-shaped martensite formed later will collide with the existing needle-shaped martensite, and it is easy to form microcracks. Such microcracks can be healed in the subsequent tempering process, but too many times of quenching will form a large number of microcracks, which are difficult to heal completely in the tempering process, so that the toughness of the duplex stainless steel product decreases and affects the service life. Therefore, the number of quenching treatments in this embodiment does not exceed 3 times, which is conducive to further improving the toughness of the obtained duplex stainless steel product.

[0045] In some embodiments of the present invention, the preparation method of the duplex stainless steel to be treated includes: subjecting the duplex stainless steel to solution treatment at a vacuum degree of 1-25Pa to obtain the duplex stainless steel to be treated; the temperature of the solution treatment is 1000-1200°C, and the time of the solution treatment is ((1-3)h+60)min. In this embodiment, the duplex stainless steel is subjected to solution treatment before vacuum carburizing, which is beneficial to eliminate the σ brittle phase of the duplex stainless steel product, thereby further improving the toughness of the duplex stainless steel product. The reason why the temperature of the solution treatment is set to 1000-1200°C is, on the one hand, to prevent the temperature of the solution treatment from being too low, which makes it difficult to fully dissolve the alloy carbide phase and the intermetallic compound phase, and on the other hand, to prevent the temperature of the solution treatment from being too high, which makes it easy to make the grains coarse and cause the toughness and corrosion resistance of the duplex stainless steel product to decrease.

[0046] In some embodiments of the present invention, the vacuum carburizing treatment comprises:

[0047] The duplex stainless steel to be treated is placed in a vacuum carburizing furnace, heated to a third temperature under a vacuum degree of 1-25 Pa, and kept warm for a third time; the third temperature is 1050-1150° C., and the third time is ((1-3) h+60) min;

[0048] Carburizing process: acetylene gas is introduced into the vacuum carburizing furnace to enter the strong carburizing stage; the acetylene gas in the vacuum carburizing furnace is extracted, and an inert gas is introduced to enter the diffusion stage; wherein the furnace pressure in the strong carburizing stage is 300-2500Pa, the time is 30-180s, and the carbon concentration on the sample surface is set to 0.8-1.6%; the furnace pressure in the diffusion stage is 100-1000Pa, the time is 600-3600s, and the carbon concentration on the sample surface is set to 0.5-1.2%;

[0049] The carburizing process is repeated until the total carburizing time reaches 2-24 hours.

[0050] It should be noted that the total carburizing time in the present invention is the cumulative time consumed in the intensive carburizing stage and the diffusion stage after the carburizing process is repeated multiple times.

[0051] In some embodiments of the present invention, the temperature of the cryogenic treatment is -196°C to -70°C, and the time is 0.5-6h. Due to the high alloying elements in duplex stainless steel, a large amount of residual austenite will be generated during the quenching process after carburizing treatment while forming quenched martensite. In this embodiment, by performing cryogenic treatment after quenching, the residual austenite is transformed into martensite, the matrix structure of the duplex stainless steel product is strengthened, and the hardness of the duplex stainless steel product is improved.

[0052] In some embodiments of the present invention, the tempering treatment temperature is 150-300°C and the time is (2-4)h+60)min. Tempering the sample after cryogenic treatment can precipitate carbides in the martensite formed by cryogenic treatment, reduce residual stress, and thus improve the impact toughness of the duplex stainless steel product. In this embodiment, the tempering treatment temperature is set to 150-300°C, which can prevent the generation of brittle phases such as σ in the duplex stainless steel product, thereby facilitating the improvement of the toughness of the duplex stainless steel product.

[0053] In some embodiments of the present invention, illustratively, the duplex stainless steel to be processed is made of 022Cr25Ni7Mo4N steel.

[0054] The present invention is further described below in conjunction with specific embodiments. It should be noted that in the following embodiments of the present invention, the duplex stainless steel samples are all cylindrical, and the diameter of the duplex stainless steel samples can be regarded as the thickness of the sample to determine the insulation time of the relevant process.

[0055] Example 1

[0056] A1. Solution treatment: Under vacuum degree of 15Pa, the duplex stainless steel sample was heated to the solution treatment temperature of 1080℃ at a heating rate of 5℃ / min, kept warm for 80min, and cooled to room temperature with high-purity argon gas to obtain the duplex stainless steel to be treated; wherein, the gas pressure of high-purity argon gas was 2.5Bar, the duplex stainless steel sample was a cylinder with a diameter of 10mm and a height of 100mm, and the material of the duplex stainless steel sample was 022Cr25Ni7Mo4 N steel, by weight percentage, the components of the duplex stainless steel sample include: C: 0.016%, Si: 0.57%, Mn: 0.86%; P: 0.012%, S: 0.016%, Ni: 7.2%, Cr: 25.2%, Mo: 3.56%, Cu: 0.32%, N: 0.27%, the balance is Fe and unavoidable impurities, and the martensitic transformation starting temperature of 022Cr25Ni7Mo4N steel of this component is 230°C.

[0057] A2. Carburizing treatment:

[0058] A21, placing the duplex stainless steel to be treated in a vacuum carburizing furnace, heating to 1050° C. at a heating rate of 5° C. / min under a vacuum degree of 15 Pa, and keeping the temperature for 80 min;

[0059] A22, introducing acetylene gas into the vacuum carburizing furnace to enter the strong carburizing stage; removing the acetylene gas in the vacuum carburizing furnace, introducing inert gas, and entering the diffusion stage; wherein the furnace pressure in the strong carburizing stage is 1200Pa, the time is 60s, and the carbon concentration on the sample surface is set to 1.2%; the furnace pressure in the diffusion stage is 200Pa, the time is 900s, and the carbon concentration on the sample surface is set to 0.8%;

[0060] A23. Repeat step A22 for 30 times in total, with a total carburizing time of 8 hours. Cool the furnace to room temperature to obtain carburized duplex stainless steel.

[0061] A3. The carburized duplex stainless steel is quenched to obtain an intermediate duplex stainless steel product; wherein the quenching comprises: heating the carburized duplex stainless steel to 1050°C under a vacuum degree of 15 Pa, keeping the temperature for 80 min, performing high-pressure gas quenching cooling treatment to 230°C (martensitic transformation starting temperature), performing a first low-pressure gas quenching cooling treatment to 180°C, keeping the temperature for 10 min, and performing a second low-pressure gas quenching cooling treatment to room temperature; wherein the quenching medium of the high-pressure gas quenching cooling treatment, the first low-pressure gas quenching cooling treatment, and the second low-pressure gas quenching cooling treatment are all high-purity argon, the gas pressure of the high-pressure gas quenching cooling treatment is 3 bar, and the gas pressure of the first low-pressure gas quenching cooling treatment and the second low-pressure gas quenching cooling treatment is 1 bar.

[0062] A4. The intermediate duplex stainless steel product is subjected to cryogenic treatment and tempering treatment to obtain a duplex stainless steel product with a carburized hardened layer formed on the surface; wherein the cryogenic treatment temperature is minus 90°C for 1 hour; and the tempering treatment temperature is 180°C for 90 minutes.

[0063] Example 2

[0064] The difference from Example 1 is that step A3 is: quenching the carburized duplex stainless steel to obtain an intermediate duplex stainless steel product; wherein the quenching treatment includes: heating the carburized duplex stainless steel to 1150°C under a vacuum degree of 15Pa, keeping it warm for 80min, performing high-pressure gas quenching cooling treatment to 230°C (martensite transformation starting temperature), performing a first low-pressure gas quenching cooling treatment to 200°C, keeping it warm for 30min, and performing a second low-pressure gas quenching cooling treatment to room temperature; wherein the quenching medium of the high-pressure gas quenching cooling treatment, the first low-pressure gas quenching cooling treatment, and the second low-pressure gas quenching cooling treatment are all high-purity argon, the gas pressure of the high-pressure gas quenching cooling treatment is 5bar, and the gas pressure of the first low-pressure gas quenching cooling treatment and the second low-pressure gas quenching cooling treatment is 1.5bar.

[0065] Example 3

[0066] The difference from Example 1 is that step A3 is: quenching the carburized duplex stainless steel to obtain an intermediate duplex stainless steel product; wherein the quenching treatment includes: heating the carburized duplex stainless steel to 1080°C under a vacuum degree of 15Pa, keeping it warm for 80min, performing high-pressure gas quenching cooling treatment to 230°C (martensite transformation starting temperature), performing a first low-pressure gas quenching cooling treatment to 100°C, keeping it warm for 5min, and performing a second low-pressure gas quenching cooling treatment to room temperature; wherein the quenching medium of the high-pressure gas quenching cooling treatment, the first low-pressure gas quenching cooling treatment, and the second low-pressure gas quenching cooling treatment are all high-purity argon, the gas pressure of the high-pressure gas quenching cooling treatment is 4bar, and the gas pressure of the first low-pressure gas quenching cooling treatment and the second low-pressure gas quenching cooling treatment is 0.5bar.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that step A3 is: quenching the carburized duplex stainless steel to obtain an intermediate duplex stainless steel product; wherein the quenching treatment includes: heating the carburized duplex stainless steel to 1050° C. under a vacuum degree of 15 Pa, keeping the temperature for 80 minutes, and oil quenching to room temperature.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that step A3 is: quenching the carburized duplex stainless steel to obtain an intermediate duplex stainless steel product; wherein the quenching treatment includes: heating the carburized duplex stainless steel to 1050° C. under a vacuum degree of 15 Pa, keeping warm for 80 minutes, and performing high-pressure gas quenching cooling treatment to room temperature, and the gas pressure of the high-pressure gas quenching cooling treatment is 3 bar.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that step A3 is: quenching the carburized duplex stainless steel to obtain an intermediate duplex stainless steel product; wherein the quenching treatment includes: heating the carburized duplex stainless steel to 1050°C under a vacuum degree of 15Pa, keeping it warm for 80min, performing a first high-pressure gas quenching cooling treatment to 230°C (martensitic transformation starting temperature), and performing a second high-pressure gas quenching cooling treatment to room temperature, the gas pressure of the first high-pressure gas quenching cooling treatment is 3bar, and the gas pressure of the second high-pressure quenching gas cooling treatment is 2bar.

[0073] Experimental example

[0074] The microstructure of the carburized hardened layer of the duplex stainless steel products prepared in Example 1 and Comparative Examples 1-3 was characterized. Figure 1-4 ,from Figure 1 It can be seen that the carburized hardened layer in Example 1 has a uniform structure and no non-martensite structure. Figure 2 It can be seen that in the carburized hardened layer of Comparative Example 1, obvious non-martensitic structure appears; Figure 3 and Figure 4 It can be seen that obvious needle-shaped martensite impact marks appear in the structure of the carburized hardened layer in Comparative Examples 2 and 3. It should be noted that Figure 1-4 The length represented by the middle ruler is 10 μm. Figure 2 The dotted ellipse is a non-martensitic structure. Figure 3 and Figure 4 The dotted ellipse in the middle shows the needle-shaped martensite impact mark.

[0075] The hardness of the carburized hardened layer of the duplex stainless steel products prepared in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1. The toughness and roundness of the duplex stainless steel products prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 1. It can be seen from Table 1 that compared with Comparative Examples 1-3, the AKv of the duplex stainless steel products prepared in Examples 1-3 is larger, indicating that the toughness of the duplex stainless steel products prepared in Examples 1-3 is larger, and the roundness of the duplex stainless steel products prepared in Examples 1-3 is smaller, indicating that the deformation of the duplex stainless steel products before and after carburizing treatment in Examples 1-3 is smaller; in addition, it can be seen from Table 1 that compared with Comparative Examples 1-3, the hardness of the carburized hardened layer of the duplex stainless steel products prepared in Examples 1-3 is higher.

[0076] Table 1

[0077] serial number Hardness (HV) AKv(J) Roundness(μm) Example 1 730 127 9 Example 2 732 126 11 Example 3 731 128 10 Comparative Example 1 691 89 42 Comparative Example 2 726 94 25 Comparative Example 3 728 107 18

[0078] It should be noted that the roundness in Table 1 is an important geometric characteristic that measures the degree to which the workpiece shape deviates from the ideal circle. It indicates the deviation of the actual workpiece surface from an ideal circle. Roundness can be used to evaluate the deformation of the workpiece. AKv is used to characterize impact toughness, which represents the energy absorbed by the material when subjected to impact load.

[0079] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A vacuum carburizing method for duplex stainless steel, characterized in that: include: The duplex stainless steel to be treated is subjected to vacuum carburizing treatment, quenching treatment, cryogenic treatment and tempering treatment in sequence to obtain a duplex stainless steel having a carburized hardened layer formed on the surface; Wherein, inert gas is used as quenching medium during quenching treatment, and the quenching treatment includes: The duplex stainless steel subjected to vacuum carburizing is heated to a first temperature in a vacuum environment, and after being kept at the first temperature for a first time, a high-pressure gas quenching cooling treatment is performed, and when austenite begins to transform into martensite, a low-pressure gas quenching cooling treatment is performed, and finally cooled to room temperature.

2. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The low-pressure gas quenching cooling treatment is performed when the austenite begins to transform into martensite, and finally cooled to room temperature, comprising: When austenite begins to transform into martensite, a first low-pressure quenching cooling treatment is performed to a second temperature. After being kept at that temperature for a second time, a second low-pressure quenching cooling treatment is performed to room temperature.

3. The vacuum carburizing method for duplex stainless steel according to claim 2, characterized in that: The second temperature is 100-200° C., and the second time is 5-30 minutes.

4. The vacuum carburizing method for duplex stainless steel according to claim 2, characterized in that: The gas pressure of the first low-pressure quenching and cooling treatment and the second low-pressure quenching and cooling treatment is 0.5-1.5 bar.

5. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The first temperature is 1050-1150° C., and the first time is ((1-3) h+60) min, wherein h is the thickness of the duplex stainless steel to be treated.

6. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The gas pressure of the high-pressure gas quenching cooling treatment is 2-5 bar.

7. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The quenching treatment is performed 1 to 3 times.

8. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The method for preparing the duplex stainless steel to be treated comprises: performing a solid solution treatment on the duplex stainless steel under a vacuum environment to obtain the duplex stainless steel to be treated.

9. The vacuum carburizing method for duplex stainless steel according to claim 1, characterized in that: The vacuum carburizing treatment comprises: placing the duplex stainless steel to be treated in a vacuum carburizing furnace, heating it to a third temperature under a vacuum environment, and keeping the temperature for a third time; Carburizing process: introducing acetylene gas into the vacuum carburizing furnace to enter the intensive carburizing stage; extracting the acetylene gas in the vacuum carburizing furnace, introducing inert gas, and entering the diffusion stage; The carburizing process is repeated until the total carburizing time reaches a fourth time.

10. The vacuum carburizing method for duplex stainless steel according to claim 9, characterized in that: The third temperature is 1050-1150° C. And / or, the furnace pressure in the strong permeation stage is 300-2500Pa, the time is 30-180s, and the carbon concentration on the sample surface is set to 0.8-1.6%; the furnace pressure in the diffusion stage is 100-1000Pa, the time is 600-3600s, and the carbon concentration on the sample surface is set to 0.5-1.2%; And / or, the fourth time is 2-24h.

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