Stainless steel part, hot isostatic pressing method for preparing same and application thereof

Abstract

The application belongs to the technical field of powder metallurgy, and particularly discloses a stainless steel part, a hot isostatic pressing preparation method thereof and application, and the hot isostatic pressing preparation method comprises the following steps: 1) preparing stainless steel powder, performing screening treatment on the stainless steel powder, and selecting powder with a set particle size range as raw material; 2) performing plasma activation treatment on the raw material; 3) loading the treated raw material into a prefabricated package, and sequentially performing heating and degassing treatment and sealing and welding treatment on the package after loading of the powder; 4) performing segmented hot isostatic pressing forming treatment on the treated package to obtain a part blank with a package; 5) performing heat treatment on the obtained part blank; and 6) sequentially performing package removal and mechanical processing on the treated part blank to obtain the stainless steel part. The application breaks through the bottleneck that the PPB defect is difficult to control in the traditional hot isostatic pressing process, realizes the synergistic improvement of PPB defect suppression and mechanical property, and provides a stainless steel part with more reliable performance for high-end fields such as nuclear power.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of powder metallurgy, and particularly relates to a stainless steel part and a hot isostatic pressing preparation method and application thereof. BACKGROUND

[0002] Stainless steel is widely used in high-end fields such as nuclear power, aerospace, chemical industry and the like due to excellent corrosion resistance, high-temperature strength and mechanical properties. In particular, in nuclear power equipment, as a key structural material such as a reactor structural part, a nuclear-grade pipeline and a steam generator heat pipe, it is directly related to the safe and stable operation of nuclear facilities. Taking 316 series austenitic stainless steel as an example, in the nuclear reactor loop system and the nuclear waste treatment system, ultra-low carbon 316L is often used to prepare nuclear-grade pipelines, and high-carbon 316H is used for high-temperature steam generator heat pipes and the like, so as to protect the internal reaction materials and prevent the leakage of internal fission products to contaminate the outside coolant. During the entire life cycle of the nuclear power equipment assembly, these pipes are long-term placed in harsh service environments such as high temperature, high pressure, strong neutron irradiation, fluid vibration and scouring, and pressure fluctuation, and therefore high requirements are put forward for the density, uniformity of the structure and failure resistance of the material.

[0003] Among them, the hot isostatic pressing (HIP) technology, as an advanced forming process in the field of powder metallurgy, can prepare near-net-shaped and fully-densified complex components by applying equal pressure to the powder raw material in a high-temperature and high-pressure environment. Due to the uniform structure and isotropic performance, the HIP technology has shown significant advantages in the field of nuclear power. However, when the stainless steel part is prepared by using the traditional hot isostatic pressing process, the original oxides (such as Cr2O3 and SiO2) on the surface of the stainless steel powder and the grain boundary carbides (such as Cr 23 C6) are easy to form continuous network-like primary particle boundary (PPB) precipitated phase defects, which become the key bottleneck restricting the performance of the part. In practical applications, the existence of the PPB defects can significantly deteriorate the overall performance of the material, which is specifically manifested in the following two aspects: 1) in terms of mechanical properties, the PPB, as a micro-crack initiation point, preferentially expands under stress, resulting in a 15% to 20% decrease in material strength; and in the irradiation environment, the precipitation of Cr 23 C6 at the PPB can exacerbate embrittlement, causing the impact energy at -20℃ to drop from 100J to below 40J, which can easily cause brittle fracture during cyclic service, and even lead to shutdown for maintenance. 2) in terms of corrosion resistance and structural stability, Cr 23 C6 enrichment at the PPB can cause the surrounding Cr element to be depleted, forming an anode channel, which can cause grain boundary corrosion in a high-temperature and high-pressure environment; at the same time, this area becomes a preferential aggregation area for the reaction products of helium bubbles, which can cause local volume expansion, and further cause dimensional instability.

[0004] At present, the inhibition means for PPB defects in the industry mainly aims at powder pretreatment (such as high-temperature reduction annealing) and composition optimization, but the method has obvious limitations: for example, high-temperature reduction annealing treatment can partially dissolve carbides in the powder, but it is easy to cause grain coarsening, and it cannot completely eliminate the influence of primary oxides; or by adding high-activity elements such as Hf to form MC type carbides inside the powder particles to reduce the precipitation at the original particle boundary, but high-activity elements such as Hf are easy to form segregation on the powder surface or grain boundary, if not uniformly dispersed, it may exacerbate the local aggregation of carbides, forming coarse MC phase, becoming a crack source, and high-activity elements such as Hf are expensive, increasing the economic cost. Therefore, how to realize the deep purification of stainless steel powder, inhibit the formation of PPB defects, and simultaneously improve the mechanical properties and service stability of the workpiece through process innovation has become a technical problem to be solved.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, provide a stainless steel workpiece and a hot isostatic pressing preparation method and application thereof, mainly used to solve the problems of the continuous network of primary particle boundary precipitates caused by the surface primary oxides and grain boundary carbides of the powder in the preparation of the stainless steel workpiece by the existing hot isostatic pressing process, resulting in the decline of the mechanical properties of the workpiece, the deterioration of the corrosion resistance, the shortening of the service life in the irradiation environment, and overcoming the limitations of the existing powder pretreatment, composition optimization and other inhibition means, realizing the deep purification of the stainless steel powder, the inhibition of the PPB defects and the synchronous improvement of the performance and service stability of the workpiece.

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, provide a stainless steel workpiece and a hot isostatic pressing preparation method and application thereof, mainly used to solve the problems of the continuous network of primary particle boundary precipitates caused by the surface primary oxides and grain boundary carbides of the powder in the preparation of the stainless steel workpiece by the existing hot isostatic pressing process, resulting in the decline of the mechanical properties of the workpiece, the deterioration of the corrosion resistance, the shortening of the service life in the irradiation environment, and overcoming the limitations of the existing powder pretreatment, composition optimization and other inhibition means, realizing the deep purification of the stainless steel powder, the inhibition of the PPB defects and the synchronous improvement of the performance and service stability of the workpiece.

[0008] In a first aspect, the present application provides a hot isostatic pressing preparation method of a stainless steel workpiece, comprising the following steps:

[0009] Step 1, preparing a stainless steel powder, screening the stainless steel powder, and selecting the powder with a set particle size range as a raw material;

[0010] Step 2, plasma activating the raw material;

[0011] Step 3, loading the raw material treated in step 2 into a prefabricated can, and sequentially performing heating and degassing treatment and sealing and welding treatment on the can after loading the powder;

[0012] Step 4, performing segmented hot isostatic pressing forming treatment on the can treated in step 3 to obtain a workpiece blank with a can;

[0013] Step 5, heat treating the workpiece blank obtained in step 4;

[0014] Step 6, the workpiece blank treated in step 5 is subjected to cover removal and machining in sequence to obtain a stainless steel workpiece.

[0015] Further, in step 1, the stainless steel powder is prepared by plasma rotating electrode atomization, vacuum induction gas atomization or electrode induction gas atomization.

[0016] Preferably, the stainless steel powder is of one of the following specific grades: 301, 302, 303, 304, 316 or 310S.

[0017] Further, the particle size of the raw material is in the range of 15 μm to 150 μm.

[0018] Further, in step 2, the parameters of the plasma activation treatment are as follows: the power is set to 100 W to 300 W, the activation atmosphere is a mixture of argon and hydrogen, the rotation speed of the tray during activation is set to 5 r / min to 10 r / min, and the raw material is treated in the plasma for 20 s to 60 s.

[0019] Preferably, the volume fraction of argon in the mixed gas is 90% to 95%, and the volume fraction of hydrogen is 5% to 10%.

[0020] Further, in step 3, the cover is designed and manufactured according to the shape and size characteristics of the target workpiece, and the material thereof is preferably low carbon steel or stainless steel.

[0021] Further, in step 4, the segmented hot isostatic pressing forming treatment includes the following two stages:

[0022] First stage: the temperature is set to 750℃ to 850℃, the pressure is set to 100MPa to 150MPa, and the holding time is set to 60min to 120min;

[0023] Second stage: the temperature is set to 1100℃ to 1200℃, the pressure is set to 110MPa to 160MPa, and the holding time is set to 120min to 240min.

[0024] Preferably, the temperature increasing rate is set to 5℃ / min-20℃ / min when the temperature is increased from room temperature to the temperature of the first stage; and the temperature increasing rate is set to 3℃ / min-8℃ / min when the temperature is increased from the temperature of the first stage to the temperature of the second stage. The present application adopts the temperature increasing rate of "fast first and slow then", because when the temperature is increased from room temperature to the temperature of the first stage, the material has not entered the critical reaction or phase change stage, and the faster temperature increasing rate can shorten the process time while ensuring the pretreatment effect, and reduce the risk of oxidation or pollution of the material surface due to long time exposure in the lower temperature range; and when the temperature is increased from the temperature of the first stage to the temperature of the second stage, the material will undergo critical processes such as phase change, diffusion and densification, and the slower temperature increasing rate can effectively reduce the temperature gradient in the material, ensure uniform reaction, and avoid excessive accumulation of internal stress to cause structural defects (such as cracking, deformation, etc.), thereby ensuring the uniformity of the microstructure of the workpiece and the stability of the overall performance, and achieving the balance between efficiency and performance.

[0025] Further, in step 5, the heat treatment process is solid solution treatment followed by annealing treatment.

[0026] In the solid solution treatment, the temperature is set to 1050℃-1150℃, the holding time is set to 60min-120min, and the cooling mode is water quenching, oil quenching or air cooling.

[0027] In the annealing treatment, the temperature is set to 800℃-900℃, the holding time is set to 120min-240min, and the cooling mode is furnace cooling or air cooling.

[0028] In a second aspect, the present application provides a stainless steel part prepared by the above-mentioned hot isostatic pressing preparation method, the microstructure of the stainless steel part is uniform, and there is no PPB defect, and the mechanical properties meet the requirements of tensile strength > 620MPa, yield strength > 280MPa, elongation > 45%, and impact energy > 120J.

[0029] In a third aspect, the present application further provides an application based on the above-mentioned stainless steel part, the stainless steel part is applied in the field of nuclear power, and can be specifically used for preparing reactor structural parts, nuclear-grade pipelines or steam generator heat transfer pipe components.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The stainless steel part provided by the present application breaks through the technical bottleneck that the PPB defect is difficult to control in the traditional hot isostatic pressing process through the synergistic effect of "ion activation purification powder - segmented hot isostatic pressing controlled densification - composite heat treatment to optimize the performance of the part", realizes the synergistic improvement of PPB defect suppression and mechanical property. Through actual detection, the stainless steel part obtained by the present application has uniform organization, no continuous network of original particle boundary precipitated phase defects, and the mechanical property meets: tensile strength > 620 MPa, yield strength > 280 MPa, elongation > 45%, impact energy > 120 J, which provides a solution with safety and reliability for the stainless steel part serving in extreme environment. Specifically as follows:

[0032] 1) The powder is treated by plasma activation technology, the powder surface is bombarded by high-energy particles to induce physical sputtering and chemical activation, and the reducing gas reduces Cr2O3 and other surface oxides to metallic Cr and H2O, thereby directly reducing the oxide inclusions at PPB. At the same time, the powder surface forms a nano-scale concave-convex structure under high-energy ion bombardment, which increases the diffusion contact area and greatly shortens the atomic diffusion path during HIP, thereby facilitating the densification of the part. In addition, the plasma generates active free radicals, which introduce dangling bonds on the powder surface, thereby reducing the grain boundary diffusion activation energy in the subsequent HIP process.

[0033] 2) Two-stage hot isostatic pressing forming, in the low-temperature stage HIP, the inter-particle pre-sintering neck is formed between the powders to avoid stress concentration of irregular powders and subsequent non-uniform deformation between the powders under high temperature and high pressure HIP, and the residual trace amount of oxides on the surface of the activated powder further reacts with residual H2 to block the formation of PPB, and at this temperature, the premature closure of the surface pores to hinder the gas discharge can also be avoided; in the high-temperature stage HIP, Cr 23 C6 carbide is fully dissolved, the grain boundary brittle phase is completely eliminated, and under the high-temperature and high-pressure environment, the powder flows plastically and diffuses, which promotes the full densification of the part on the basis of eliminating the PPB defect.

[0034] 3) Composite heat treatment is designed for the part, i.e. high-temperature solid solution treatment + low-temperature annealing treatment, the Cr 23 C6 carbide and oxides at the PPB are completely dissolved through solid solution treatment, and at the same time, the risk of grain coarsening or abnormal growth caused by excessively high temperature is avoided. Further through annealing treatment, the thermal stress is eliminated, the risk of crack initiation under the interaction of creep and fatigue is reduced, and the re-precipitation of Cr 23 C6 at high temperature is prevented. In addition, by designing the annealing treatment, the brittle phases such as sigma phase and Laves phase can be avoided from precipitating during long-term high-temperature service, and finally good comprehensive mechanical property is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate the principles of the application and, along with the description, serve to explain the application.

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those skilled in the field, other drawings can also be obtained based on these drawings without any creative effort.

[0037] Figure 1 The flow chart of the hot isostatic pressing preparation method of the stainless steel part of the present application;

[0038] Figure 2 The scanning electron microscope photo of the powder after plasma activation treatment in the embodiment 1 of the present application;

[0039] Figure 3 The metallographic structure photo of the stainless steel part A finally prepared in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0040] The exemplary embodiments will be described in detail herein below with reference to the drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples consistent with some aspects of the present application as detailed in the appended claims.

[0041] In order to make those skilled in the art better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the drawings and embodiments.

[0042] The hot isostatic pressing preparation method of the stainless steel part provided by the present application realizes PPB defect inhibition and performance improvement through multi-link synergistic effect, and the specific principles are as follows:

[0043] First, the screened stainless steel powder is subjected to plasma activation treatment: on the one hand, the original oxides on the surface of the powder are decomposed and reduced through high-energy action, thereby reducing the oxide inclusions in the PPB defects from the source; on the other hand, the high-energy particle bombardment forms a nano-scale concave-convex structure on the surface of the powder, which can shorten the atomic diffusion path in the subsequent hot isostatic pressing process by 30% to 50%, greatly increasing the contact area between the powders and creating favorable conditions for densification.

[0044] Secondly, the densification process is regulated by adopting the segmented hot isostatic pressing forming process: the first stage (low temperature stage): the powder particles are pre-sintered to form necks, avoiding irregular powder deformation due to stress concentration under high temperature and high pressure in the subsequent stage. At the same time, the residual trace amount of oxides and residual hydrogen after powder activation further undergo reduction reaction, blocking the PPB formation; the second stage (high temperature stage): under the high temperature and high pressure environment, the grain boundary carbide (Cr 23 C6) is fully dissolved, and the grain boundary brittle phase is completely eliminated. At the same time, the powder undergoes plastic flow and diffusion under the action of pressure, and finally realizes full densification forming without PPB defects.

[0045] Finally, the performance is optimized by the composite heat treatment process of "solid solution treatment + annealing treatment": the solid solution treatment can completely dissolve the carbide and residual oxide in the PPB potential area; the annealing treatment can effectively eliminate the thermal stress, reduce the crack initiation risk under the interaction of creep-fatigue, and inhibit the re-precipitation of carbide during high temperature service, so that the workpiece finally obtains excellent strength and plasticity, toughness matching.

[0046] Example 1

[0047] The 316L stainless steel workpiece A provided in this embodiment is prepared by the process as shown in Figure 1 , and specifically includes the following steps:

[0048] Step 1: 316L stainless steel powder is prepared by adopting the plasma rotating electrode atomization method (PREP), and then screened by a vibrating screening device, and the powder with a particle size in the range of 15 μm-106 μm is selected as the raw material;

[0049] Specifically, when the 316L stainless steel powder is prepared by adopting the PREP, the chemical composition of the selected 316L stainless steel raw material is as follows: Cr: 16.65%, Ni: 10.45%, Mo: 2.42%, C: 0.005%, Mn: 0.72%, P: 0.024%, S: 0.15%, and the balance is Fe and unavoidable impurity elements.

[0050] Step 2: The raw material obtained in step 1 is subjected to plasma activation treatment;

[0051] Specifically, the parameters of the plasma activation treatment are as follows: the power is set to 100 W, the activation gas is a mixture of argon and hydrogen, the volume fraction of argon is 95%, the volume fraction of hydrogen is 5%, the tray rotation speed is set to 10 r / min during activation, and the raw material is treated in the plasma for 60 s.

[0052] Step 3: The raw material obtained in step 2 is loaded into a prefabricated package, and the powder-loaded package is subjected to heating and degassing treatment and sealing treatment in sequence;

[0053] Specifically, the sleeve is designed and manufactured according to the shape and size characteristics of the target part A, and the material thereof is selected from 20 steel.

[0054] Step 4, the sleeve obtained in step 3 is subjected to segmented hot isostatic pressing forming treatment to obtain a part blank with a sleeve;

[0055] Specifically, the segmented hot isostatic pressing forming treatment includes the following two stages:

[0056] The first stage: the temperature is set to 750℃ (the temperature rising rate from room temperature to the temperature is set to 5℃ / min), the pressure is set to 150MPa, and the pressure holding time is set to 60min;

[0057] The second stage: the temperature is set to 1100℃ (the temperature rising rate from the temperature of the first stage to the temperature is set to 3℃ / min), the pressure is set to 160MPa, and the pressure holding time is set to 120min.

[0058] Step 5, the part blank obtained in step 4 is subjected to heat treatment, and the process of the heat treatment is solid solution treatment followed by annealing treatment;

[0059] Specifically, the solid solution treatment has the following system: the temperature is set to 1150℃, the holding time is set to 60min, and the cooling mode is oil quenching;

[0060] The system of the annealing treatment is: the temperature is set to 820℃, the holding time is set to 240min, and the cooling mode is furnace cooling.

[0061] Step 6, the part blank obtained in step 5 is subjected to sleeve removal and mechanical processing to obtain the 316L stainless steel part A.

[0062] Example 2

[0063] The 316H stainless steel part B provided in this example has a preparation process as shown in Figure 1 , and specifically includes the following steps:

[0064] Step 1, a 316H stainless steel powder is prepared by a vacuum induction gas atomization method (VIGA), and then screened by a vibrating sieve separation device, and the powder with a particle size in the range of 53μm-106μm is selected as a raw material;

[0065] Specifically, when the 316H stainless steel powder is prepared by VIGA, the chemical composition of the selected 316H stainless steel raw material is as follows: Cr: 17.61%, Ni: 11.43%, Mo: 2.55%, C: 0.07%, Mn: 0.65%, P: 0.022%, S: 0.13%, and the balance is Fe and unavoidable impurity elements.

[0066] Step 2, plasma activation treatment is performed on the raw material obtained in step 1;

[0067] Specifically, the parameters of the plasma activation treatment are as follows: the power is set to 200 W, the activation gas is a mixture of argon and hydrogen, the volume fraction of argon is 93%, the volume fraction of hydrogen is 7%, the rotation speed of the tray during activation is set to 8 r / min, and the raw material is treated in the plasma for 30 s.

[0068] Step 3, the raw material obtained in step 2 is loaded into a prefabricated package, and the powder-loaded package is sequentially subjected to heating and degassing treatment and sealing treatment;

[0069] Specifically, the package is designed and manufactured according to the shape and size characteristics of the target part B, and the material is 45 steel.

[0070] Step 4, the package obtained in step 3 is subjected to segmented hot isostatic pressing forming treatment to obtain a part blank with a package;

[0071] Specifically, the segmented hot isostatic pressing forming treatment includes the following two stages:

[0072] First stage: the temperature is set to 800℃ (the heating rate from room temperature to this temperature is set to 10℃ / min), the pressure is set to 120MPa, and the holding time is set to 90min;

[0073] Second stage: the temperature is set to 1150℃ (the heating rate from the temperature of the first stage to this temperature is set to 6℃ / min), the pressure is set to 140MPa, and the holding time is set to 180min.

[0074] Step 5, the part blank obtained in step 4 is subjected to heat treatment, and the heat treatment process is solid solution treatment followed by annealing treatment;

[0075] Specifically, the solid solution treatment system is as follows: the temperature is set to 1100℃, the holding time is set to 80min, and the cooling method is water quenching;

[0076] The annealing treatment system is as follows: the temperature is set to 850℃, the holding time is set to 180min, and the cooling method is furnace cooling.

[0077] Step 6, the part blank obtained in step 5 is subjected to package removal and mechanical processing to obtain a 316H stainless steel part B.

[0078] Example 3

[0079] The 316H stainless steel part C provided in this example is prepared as shown in Figure 1 , and specifically includes the following steps:

[0080] Step 1, 316H stainless steel powder is prepared by electrode induced gas atomization (EIGA), and then screened by a vibrating screening device, and the powder with a particle size in the range of 53-150 μm is selected as the raw material;

[0081] Specifically, when the 316H stainless steel powder is prepared by EIGA, the chemical composition of the selected 316H stainless steel raw material is as follows: Cr: 16.66%, Ni: 11.36%, Mo: 2.35%, C: 0.06%, Mn: 0.75%, P: 0.02%, S: 0.11%, and the balance is Fe and unavoidable impurity elements.

[0082] Step 2, the raw material obtained in step 1 is subjected to plasma activation treatment;

[0083] Specifically, the parameters of the plasma activation treatment are as follows: the power is set to 300 W, the activation gas is a mixture of argon and hydrogen, the volume fraction of argon is 90%, the volume fraction of hydrogen is 10%, the tray rotation speed is set to 5 r / min during activation, and the raw material is treated in the plasma for 25 s.

[0084] Step 3, the raw material obtained in step 2 is loaded into a prefabricated package, and the powder-loaded package is sequentially subjected to heating and degassing treatment and sealing treatment;

[0085] Specifically, the package is designed and manufactured according to the shape and size characteristics of the target part C, and the material is selected to be 316L stainless steel.

[0086] Step 4, the package obtained in step 3 is subjected to segmented hot isostatic pressing forming treatment to obtain a part blank with a package;

[0087] Specifically, the segmented hot isostatic pressing forming treatment includes the following two stages:

[0088] First stage: the temperature is set to 850℃ (the heating rate from room temperature to this temperature is set to 20℃ / min), the pressure is set to 100MPa, and the holding time is set to 120min;

[0089] Second stage: the temperature is set to 1200℃ (the heating rate from the temperature of the first stage to this temperature is set to 8℃ / min), the pressure is set to 110MPa, and the holding time is set to 240min.

[0090] Step 5, the part blank obtained in step 4 is subjected to heat treatment, and the heat treatment process is solid solution treatment followed by annealing treatment;

[0091] Specifically, the solid solution treatment system is as follows: the temperature is set to 1050℃, the holding time is set to 120min, and the cooling method is air cooling;

[0092] The annealing process is as follows: the temperature is set at 900℃, the holding time is set at 120 minutes, and the cooling method is air cooling.

[0093] Step 6: Remove the cladding from the blank obtained in Step 5 and perform machining to obtain 316H stainless steel part C.

[0094] Example 4

[0095] The 304 stainless steel part D provided in this embodiment is prepared as follows: Figure 1 As shown, the specific steps include:

[0096] Step 1: Prepare 304 stainless steel powder using PREP, and then screen it using a vibrating sieve to select powder with a particle size in the range of 53μm to 125μm as raw material;

[0097] Specifically, when using PREP to prepare 304 stainless steel powder, the chemical composition of the selected powder raw materials is as follows: Cr: 18.38%, Ni: 8.52%, C: 0.014%, Mn: 0.71%, P: 0.02%, S: 0.04%, with the balance being Fe and unavoidable impurity elements.

[0098] Step 2: Perform plasma activation treatment on the raw materials obtained in Step 1;

[0099] Specifically, the parameters for plasma activation are as follows: power is set to 250W, activation gas is a mixture of argon and hydrogen, with argon accounting for 92% and hydrogen accounting for 8%, tray rotation speed is set to 6r / min during activation, and the raw material is treated in plasma for 40s.

[0100] Step 3: Load the raw materials obtained in Step 2 into the prefabricated package, and then perform heating and degassing treatment and sealing treatment on the package after filling it with powder.

[0101] Specifically, the casing is designed and manufactured according to the shape and size characteristics of the target part D, and its material is 20 steel.

[0102] Step 4: Perform segmented hot isostatic pressing on the sleeve obtained in Step 3 to obtain a blank of the part with the sleeve.

[0103] Specifically, the segmented hot isostatic pressing process includes the following two stages:

[0104] First stage: The temperature is set to 820℃ (the heating rate from room temperature to this temperature is set to 12℃ / min), the pressure is set to 120MPa, and the holding time is set to 100min;

[0105] The second stage is set as 1160℃ (the temperature rising rate from the temperature of the first stage to the temperature is set as 6℃ / min), the pressure is set as 130MPa, and the pressure maintaining time is set as 200min.

[0106] Step 5, the workpiece blank obtained in step 4 is subjected to heat treatment, and the heat treatment process is solid solution treatment and then annealing treatment.

[0107] Specifically, the solid solution treatment system is set as 1080℃, the holding time is set as 100min, and the cooling mode is air cooling.

[0108] The annealing treatment system is set as 880℃, the holding time is set as 180min, and the cooling mode is air cooling.

[0109] Step 6, the workpiece blank obtained in step 5 is subjected to cover removal and mechanical processing to obtain the 304 stainless steel workpiece D.

[0110] Performance test

[0111] In order to further verify the technical effect of the present application, the inventors carried out the following test analysis:

[0112] 1, Microstructure observation: the powder after the plasma activation treatment of example 1 in step 2 is observed, as shown in Figure 2 In addition, the metallographic analysis of the 316L stainless steel workpiece A finally prepared in example 1 is carried out, as shown in Figure 3

[0113] 2, Mechanical property test: according to GB / T 228 "Metallic materials tensile testing methods at room temperature" and GB / T 229 "Metallic materials Charpy pendulum impact test methods", the tensile properties and impact properties of the stainless steel workpieces prepared in examples 1-4 are tested, and the specific test results are shown in table 1.

[0114] Table 1 Mechanical property test results of the stainless steel workpieces prepared in examples 1-4

[0115]

[0116] Figure 2 ​The surface morphology characteristics of the 316L stainless steel powder after the plasma activation treatment are clearly shown, the powder surface forms uniformly distributed nano-scale protrusions and recessed structures, which is directly related to the physical sputtering effect caused by the high-energy particle bombardment in the plasma activation process, the structure makes the specific surface area of the powder increase by 2-3 times compared with before the treatment, which provides more contact paths for atomic diffusion during the subsequent hot isostatic pressing, and verifies the mechanism that the atomic diffusion path is shortened by 30%-50%. In addition, through energy spectrum analysis, the ratio of Cr and O elements on the powder surface is improved compared with before the treatment, which shows that the reducing gas H2 has reduced most of the Cr2O3 to metal Cr, reducing the oxide inclusions of PPB defects from the source, and verifying the chemical purification effect of the plasma activation.

[0117] Figure 3 The metallographic structure of the 316L stainless steel part A prepared by the application is shown, there is no continuous network PPB defect, under the observation of 100 mu m magnification, no continuous distribution of oxide or carbide precipitates is found at the grain boundary, which shows that the segmented hot isostatic pressing and the combined heat treatment cooperatively inhibit the formation of PPB; at the same time, the structure is uniform and the grain is refined, which benefits from the inhibition of grain growth after solid solution treatment by rapid oil quenching, and the internal stress of the material is effectively reduced by further annealing treatment, which lays a stable organizational foundation for obtaining excellent mechanical properties.

[0118] As shown in Table 1, the tensile strength of the parts A-D is greater than 620 MPa, among which the strength of the 316H parts B and C is further improved to more than 670 MPa due to the higher carbon content; in addition, the yield strength is greater than 280 MPa; at the same time, the elongation is kept above 45%, and the impact energy is stable above 120 J, which embodies the matching of "high strength-high plasticity". In addition, the performance fluctuation range of the parts A-D under different parameter combinations is small, which shows that the plasma activation power, hot isostatic pressing temperature and other parameters have good process fault tolerance in the set range, which meets the stability requirements of large-scale production.

[0119] The above is only a specific embodiment of the application, which enables those skilled in the art to understand or implement the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application.

[0120] It should be understood that the application is not limited to the above described and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is limited only by the claims appended hereto.

Claims

1. A method for the hot isostatic pressing of a stainless steel article, characterized in that, The method comprises the following steps: Step 1, preparing a stainless steel powder, screening the stainless steel powder, and selecting a powder with a set particle size range as a raw material; Step 2, performing plasma activation treatment on the raw material; Step 3, loading the raw material treated in step 2 into a prefabricated package, and sequentially performing heating and degassing treatment and sealing treatment on the powder-loaded package; Step 4, performing segmented hot isostatic pressing forming treatment on the package treated in step 3 to obtain a package-containing workpiece blank; Step 5, performing heat treatment on the workpiece blank obtained in step 4; Step 6, sequentially performing package removal and mechanical processing on the workpiece blank treated in step 5 to obtain a stainless steel workpiece, which is applied to the field of nuclear power; In step 2, the parameters of the plasma activation treatment are as follows: the power is set to 100 W-300 W, the activation atmosphere is a mixed gas of argon and hydrogen, the volume fraction of argon in the mixed gas is 90%-95%, the volume fraction of hydrogen is 5%-10%, the rotation speed of the tray during activation is set to 5 r / min-10 r / min, and the treatment time of the raw material in the plasma is set to 20 s-60 s; In step 4, the segmented hot isostatic pressing forming treatment comprises the following two stages: First stage: the temperature is set to 750 DEG C-850 DEG C, the pressure is set to 100 MPa-150 MPa, and the pressure holding time is set to 60 min-120 min; when the temperature is raised from room temperature to the temperature of the first stage, the heating rate is set to 5 DEG C / min-20 DEG C / min; Second stage: the temperature is set to 1100 DEG C-1200 DEG C, the pressure is set to 110 MPa-160 MPa, and the pressure holding time is set to 120 min-240 min; when the temperature is raised from the temperature of the first stage to the temperature of the second stage, the heating rate is set to 3 DEG C / min-8 DEG C / min; In step 5, the heat treatment process is solid solution treatment followed by annealing treatment; The solid solution treatment system is: the temperature is set to 1050 DEG C-1150 DEG C, the holding time is set to 60 min-120 min, and the cooling method is water quenching, oil quenching or air cooling; The annealing treatment system is: the temperature is set to 800 DEG C-900 DEG C, the holding time is set to 120 min-240 min, and the cooling method is furnace cooling or air cooling.

2. The method according to claim 1, characterized in that, In step 1, the stainless steel powder is prepared by plasma rotating electrode atomization, vacuum induction gas atomization or electrode induction gas atomization.

3. The method according to claim 1, wherein In step 1, the particle size range of the raw material is 15 μm-150 μm.

4. A stainless steel article, characterized by, The stainless steel workpiece is prepared by the hot isostatic pressing method of any one of claims 1-3, and the mechanical properties of the stainless steel workpiece meet the following requirements: tensile strength > 620 MPa, yield strength > 280 MPa, elongation > 45%, and impact energy > 120 J.

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