An austenitic stainless steel and a method of treating the same

Abstract

This invention provides a method for processing austenitic stainless steel, relating to the preparation and application technology of austenitic stainless steel, including the following steps: preheating the austenitic stainless steel ingot to decompose some of the primary phases in the austenitic stainless steel ingot into M... 23 C6 carbides, with the remaining primary phases exhibiting a discontinuous distribution; the preheated austenitic stainless steel ingot is homogenized to ensure that M... 23 C6 carbides are dissolved back into the matrix; the homogenized austenitic stainless steel ingot is then subjected to hot deformation treatment. This invention, through preheating, decomposes the coarse primary phase into M... 23 C6 carbide; through homogenization treatment, dendrite segregation is eliminated on the one hand, and M is made more uniform on the other hand. 23 C6 carbides dissolve back into the matrix, thereby refining the primary phase; this avoids the difference in dynamic recrystallization driving force caused by dendrite segregation and coarse primary phase, ensuring complete dynamic recrystallization after hot deformation treatment, thus avoiding the formation of a dual grain structure with a mixture of coarse and fine grains.

Description

Technical Field

[0001] This invention belongs to the technical field of preparation and application of austenitic stainless steel, specifically relating to an austenitic stainless steel and its processing method. Background Technology

[0002] Austenitic stainless steel possesses excellent comprehensive properties, including mechanical properties, medium- and high-temperature stability, hot workability, weldability, and corrosion resistance, making it an important structural material in military, chemical, thermal power, and nuclear power industries. Compared to conventional austenitic stainless steel, Nb / Ti composite-stabilized nitrogen-containing austenitic stainless steel exhibits superior high-temperature strength, corrosion resistance, creep rupture performance, and fatigue life. Representative examples include NF709, a superheater material for supercritical boilers, and Alloy709, a candidate material for fourth-generation integrated long-life sodium-cooled fast reactor structures. Firstly, nitrogen, as an effective solid solution strengthening element, significantly improves the strength of stainless steel and extends the incubation time for carbide nucleation, mitigating the tendency for intergranular carbide precipitation and thus enhancing corrosion resistance. Secondly, Nb / Ti stabilization can form highly stable MX-type carbides, effectively reducing the precipitation tendency of M23C6-type carbides, thereby delaying the precipitation of M23C6-type carbides. 23 The formation of brittle intermetallic phases such as sigma, G and Laves phases induced by C6-type carbides can improve the creep rupture performance and fatigue life of stainless steel at high temperatures.

[0003] For Nb / Ti composite-stabilized N-containing austenitic stainless steel, dendritic segregation of elements such as Nb and Ti inevitably occurs during solidification, forming coarse primary Nb(C,N), Ti(C,N), and (Nb,Ti)(C,N) phases. The distribution of the Nb / Ti primary phases is uneven, mainly concentrated between dendrites or at the boundaries between dendrite trunks. During subsequent hot working, on the one hand, dendritic segregation and the unevenly distributed coarse primary phases lead to differences in the dynamic recrystallization driving force between dendrites and between dendrite trunks; on the other hand, due to the high alloying degree of the Nb / Ti composite-stabilized N-containing austenitic stainless steel, secondary (Nb,Ti)(C,N) easily precipitates during hot deformation, resulting in uneven recrystallization of the N-containing austenitic stainless steel. That is, some areas undergo dynamic recrystallization while others do not, resulting in a dual grain structure of coarse and fine grains in the N-containing austenitic stainless steel. Duplex microstructure (grain inhomogeneity) significantly reduces high-temperature fatigue performance and creep resistance, greatly shortening the service life of stainless steel. Summary of the Invention

[0004] Therefore, the present invention provides an austenitic stainless steel and a processing method thereof to solve the problem of dual grain structure in austenitic stainless steel in the prior art.

[0005] To address the above problems, the present invention provides a method for processing austenitic stainless steel, comprising the following steps:

[0006] Step 1) Preheat the austenitic stainless steel ingot to decompose some of the primary phases in the austenitic stainless steel ingot into M. 23 C6 carbides are used to make the remaining primary phases appear in a discontinuous distribution.

[0007] Step 2) Homogenize the preheated austenitic stainless steel ingot to make M 23 C6 carbides dissolve back into the matrix;

[0008] Step 3) Perform hot deformation treatment on the homogenized austenitic stainless steel ingot to cause dynamic recrystallization of the homogenized austenitic stainless steel ingot.

[0009] Further, in step 1): the austenitic stainless steel ingot is a nitrogen-containing austenitic stainless steel ingot; preferably, the austenitic stainless steel ingot is a nitrogen-containing austenitic stainless steel ingot stabilized by Nb / Ti composite; more preferably, the chemical composition of the austenitic stainless steel ingot, by weight percentage, is: C≤0.10%, Mn≤1.50%, Si≤1.00%, Cr: 19.5~23.0%, Ni: 23.0~26.0%, Mo: 1.0~4.0%, N: 0.10~0.25%, Nb: 0.10~0.40%, Ti: 0.10~0.50%, P≤0.030%, S≤0.030%, with Fe and unavoidable residual elements as the balance; and / or

[0010] The primary phase in the austenitic stainless steel ingot includes at least one of Nb(C,N), Ti(C,N), and (Nb,Ti)(C,N).

[0011] Furthermore, in step 1), the preheating treatment includes placing an austenitic stainless steel ingot in a heating furnace, then heating it to 850–950°C and holding it at that temperature for 3–6 hours.

[0012] Preferably, the temperature is heated to 880–920°C.

[0013] Furthermore, in step 2), the homogenization process includes heating the preheated austenitic stainless steel ingot to 1180–1250°C and holding it at that temperature; preferably, heating it to 1200–1220°C.

[0014] Furthermore, the heat preservation time t≥30h+m×k; where m is the thickness of the austenitic stainless steel ingot in mm; k=10~15min / mm.

[0015] Furthermore, in step 3), the temperature of the heat deformation treatment is 1200–1220°C.

[0016] Furthermore, in step 3), the hot deformation treatment employs a multi-pass hot deformation treatment; wherein the total deformation amount of the multi-pass hot deformation treatment is ≥40%; and the deformation amount of each pass is 15-25%.

[0017] Preferably, the total deformation amount of the multi-pass heat deformation treatment is ≥60%;

[0018] Preferably, the deformation amount in the final pass is 15-20%.

[0019] Furthermore, in step 3), after the hot deformation treatment step, the process further includes: cooling the hot-deformed stainless steel ingot.

[0020] Preferably, the cooling process uses water cooling.

[0021] On the other hand, the present invention provides an austenitic stainless steel in which no dual grain structure of coarse and fine grains is observed; no secondary precipitates or primary phases with a size >10 μm are observed in the austenitic stainless steel.

[0022] Furthermore, the austenitic stainless steel is obtained by any of the above-described processing methods.

[0023] The austenitic stainless steel and its processing method provided by this invention have the following beneficial effects:

[0024] 1. On one hand, the present invention provides a method for processing austenitic stainless steel, comprising: sequentially subjecting an austenitic stainless steel ingot to preheating treatment, homogenization treatment, and hot deformation treatment; based on the above method, the present invention, through preheating treatment, decomposes the coarse primary phase in the austenitic stainless steel ingot into M... 23 C6 carbides are used to make the remaining primary phases discontinuously distributed; homogenization treatment is used to eliminate dendrite segregation on the one hand, and to make M 23 C6 carbides dissolve back into the matrix, thereby refining the primary phase; through hot deformation treatment, the homogenized austenitic stainless steel ingot undergoes dynamic recrystallization; after dendritic segregation is eliminated and the primary phase is refined, the difference in driving force for dynamic recrystallization can be avoided, ensuring that complete dynamic recrystallization is achieved after hot deformation treatment, thereby avoiding the occurrence of a dual grain structure of coarse and fine grains in stainless steel, that is, obtaining a more uniform dynamic recrystallized grain.

[0025] 2. Furthermore, this invention sets the heat deformation treatment temperature to 1200–1220°C to avoid the precipitation of secondary phases (Nb,Ti)(C,N) during the heat deformation process, thereby hindering dynamic recrystallization. Additionally, this invention limits the deformation amount of the final heat deformation treatment to 15–20% to avoid insufficient deformation to break up the precipitated phases in the stainless steel and achieve complete dynamic recrystallization. Larger deformation amounts, on the other hand, tend to promote the formation of secondary precipitates, thus affecting the dynamic recrystallization process, increasing the internal stress of the stainless steel, and leading to a decrease in the subsequent service performance of the material. Therefore, this invention limits the deformation amount of the final heat deformation treatment, which is beneficial for achieving complete dynamic recrystallization while ensuring improved subsequent material performance.

[0026] 3. On the other hand, the present invention provides an austenitic stainless steel obtained by the above-described processing method; no dual grain structure of coarse and fine grains is observed in the microstructure of the austenitic stainless steel, and no secondary precipitates or primary phases with a size >10μm are observed; therefore, the austenitic stainless steel of the present invention has high high-temperature fatigue performance and creep performance. Attached Figure Description

[0027] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0028] Figure 1 Metallographic image of the austenitic stainless steel ingot in Example 1;

[0029] Figure 2 Metallographic image of the austenitic stainless steel ingot after preheating treatment in Example 1;

[0030] Figure 3 Metallographic images of austenitic stainless steel ingots after homogenization treatment in Example 1; where: (a) is the OM image at low magnification, and (b) is the OM image at high magnification;

[0031] Figure 4 Metallographic images of the dynamic recrystallization of austenitic stainless steel obtained in Example 1; where: (a) is an OM image at low magnification, and (b) is a SEM image at high magnification;

[0032] Figure 5 Metallographic image of the austenitic stainless steel ingot in Example 2;

[0033] Figure 6 Metallographic image of the austenitic stainless steel ingot after preheating treatment in Example 2;

[0034] Figure 7 Metallographic images of austenitic stainless steel ingots after homogenization treatment in Example 2; where: (a) is the OM image at low magnification, and (b) is the OM image at high magnification;

[0035] Figure 8 Metallographic images of the dynamic recrystallization of austenitic stainless steel obtained in Example 2; where: (a) is an OM image at low magnification, and (b) is a SEM image at high magnification;

[0036] Figure 9 Metallographic image of the dynamic recrystallization of the austenitic stainless steel obtained in Comparative Example 1.

[0037] Figure 10 Metallographic images of the dynamic recrystallization of austenitic stainless steel obtained in Comparative Example 2; where: (a) is the OM image at low magnification, and (b) is the SEM image at high magnification;

[0038] Figure 11 Metallographic images of the dynamic recrystallization of austenitic stainless steel obtained in Comparative Example 3; where: (a) is the OM image at low magnification, and (b) is the SEM image at high magnification.

[0039] Figure 12 Metallographic image of the dynamic recrystallization of the austenitic stainless steel obtained in Comparative Example 4.

[0040] Figure 13 In the middle: (a) is the metallographic image of the austenitic stainless steel ingot after homogenization treatment in Comparative Example 5; (b) is the metallographic image of the dynamic recrystallization of the austenitic stainless steel obtained in Example 5. Detailed Implementation

[0041] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0042] For Nb / Ti composite-stabilized N-containing austenitic stainless steel, dendritic segregation of elements such as Nb / Ti is more likely to occur, as well as the formation of coarse primary phases Nb(C,N), Ti(C,N), and (Nb,Ti)(C,N); therefore, this invention provides a method for treating austenitic stainless steel, comprising the following steps:

[0043] Step 1) The austenitic stainless steel ingot is preheated in a heating furnace to decompose some of the primary phases in the austenitic stainless steel ingot into M. 23C6 carbides are used to make the remaining primary phases appear in a discontinuous distribution; wherein, the furnace charging temperature is <700℃ to avoid the ingot cracking due to excessive furnace charging temperature; after charging, the temperature is heated to 850-950℃ and held for 3-6 hours; preferably, the temperature is heated to 880-920℃.

[0044] The austenitic stainless steel ingot (before treatment) is an Nb / Ti composite stabilized N-containing austenitic stainless steel ingot; preferably, the chemical composition of the austenitic stainless steel ingot, by weight percentage, is: C≤0.10%, Mn≤1.50%, Si≤1.00%, Cr: 19.5~23.0%, Ni: 23.0~26.0%, Mo: 1.0~4.0%, N: 0.10~0.25%, Nb: 0.10~0.40%, Ti: 0.10~0.50%, P≤0.030%, S≤0.030%, with Fe and unavoidable residual elements as the balance;

[0045] Step 2) Homogenize the preheated austenitic stainless steel ingot to make M 23 C6 carbides are dissolved back into the matrix; wherein, the homogenization treatment involves heating the preheated austenitic stainless steel ingot to 1180-1250°C and holding it at that temperature; preferably, heating it to 1200-1220°C.

[0046] The heat treatment time t ≥ 30h + m × k; where m is the thickness of the austenitic stainless steel ingot in mm; k = 10~15min / mm; limiting the heat treatment time according to the thickness of the ingot ensures complete elimination of dendrite segregation in the ingot and minimizes the decomposition of the primary phase M in step 1). 23 C6 carbides are dissolved back;

[0047] Step 3) Perform multiple hot deformation treatments on the homogenized austenitic stainless steel ingot to allow dynamic recrystallization of the homogenized austenitic stainless steel ingot; then perform rapid water cooling after hot deformation treatment.

[0048] The hot deformation treatment can be carried out by rolling, forging, etc.; the temperature of the hot deformation treatment is 1200-1220℃; the total deformation of the hot deformation treatment is ≥40%; the deformation of each pass is 15-25%; the deformation of the last pass is 15-20%; preferably, the total deformation of the hot deformation treatment is ≥60%.

[0049] Among these methods, the preheated ingot can be directly heated to the homogenization treatment temperature, or the preheated ingot can be cooled and then heated to that temperature; the homogenized ingot can be directly subjected to hot deformation.

[0050] Based on the above method, the present invention uses preheating treatment to decompose some of the coarse primary phases in the austenitic stainless steel ingot into M... 23 C6 carbides; through homogenization treatment, dendritic segregation caused by high Cr / Mo is eliminated on the one hand, and M is made more readily available. 23 C6 carbides dissolve back into the matrix, thereby refining the primary phase (e.g., the continuous primary phase partially decomposes and becomes discontinuously distributed, thus becoming finer); the homogenized austenitic stainless steel ingot undergoes dynamic recrystallization through hot deformation treatment; dendritic segregation is eliminated, and the primary phase is refined, which avoids differences in the driving force for dynamic recrystallization, ensuring complete dynamic recrystallization after hot deformation treatment, thus avoiding the formation of a mixed coarse and fine grain structure in the stainless steel, i.e., obtaining a more uniform dynamic recrystallized grain.

[0051] The primary phases in the austenitic stainless steel ingot include Nb(C,N), Ti(C,N), and (Nb,Ti)(C,N); M 23 C6 carbides include Nb 23 C6, Ti 23 At least one of C6; wherein Nb(C,N) refers to the carbides formed by Nb, C, and N in stainless steel; Ti(C,N) refers to the carbides formed by Ti, C, and N in stainless steel; and (Nb,Ti)(C,N) is a composite carbide formed by Nb(C,N) and Ti(C,N).

[0052] In some embodiments, the temperature of the hot deformation treatment is set to 1200–1220°C. If the temperature is too low, secondary phases (Nb,Ti)(C,N) are easily precipitated, which is not conducive to dynamic recrystallization. If the temperature is too high, high-temperature oxidation and high-temperature ferrite are easily generated. In addition, the deformation amount of the last hot deformation treatment is limited to 15–20% to avoid insufficient deformation to break up the precipitated phases in the stainless steel and to achieve complete dynamic recrystallization. However, a large deformation amount can easily promote the formation of secondary precipitates, thereby affecting the dynamic recrystallization process, increasing the internal stress of the stainless steel and leading to a decrease in the service performance of subsequent materials. Rapid water cooling can prevent the formation of (Nb,Ti)(C,N) secondary phases in the ingot during the cooling process after hot deformation treatment, thereby avoiding the influence of secondary phases on dynamic recrystallization.

[0053] On the other hand, the present invention provides an austenitic stainless steel in which no dual grain structure of coarse and fine grains is observed; and no secondary precipitates or primary phases with a size >10μm are observed in the microstructure of the austenitic stainless steel; the austenitic stainless steel is obtained by any of the above-mentioned treatment methods.

[0054] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0055] In the examples and comparative examples, the materials were prepared according to the chemical composition of austenitic stainless steel, then smelted using refining equipment, and finally cast and cooled to obtain austenitic stainless steel ingots before treatment. The refining equipment ensures that the chemical composition of the molten steel meets the composition control requirements. After cooling, ingots with dimensions of φ120×150mm were obtained. 3 Perform the corresponding processing.

[0056] Example 1

[0057] This embodiment provides a method for processing austenitic stainless steel, including the following steps:

[0058] Step 1) The austenitic stainless steel ingot is loaded into a heating furnace for preheating treatment; the loading temperature is 600℃, and then heated to 900℃ and held for 4 hours.

[0059] The chemical composition of the austenitic stainless steel ingot (before treatment) by weight percentage is shown in Table 1; Step 2) The preheated austenitic stainless steel ingot is heated to 1200℃ and held for 40h to achieve homogenization treatment.

[0060] Step 3) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1200℃; then water-cooled to obtain the treated austenitic stainless steel.

[0061] The total deformation amount of the hot deformation treatment is 60%; the deformation amount per pass is 20%.

[0062] In this embodiment, the metallographic structure of the (pre-processed) austenitic stainless steel ingot is as follows: Figure 1 As shown, the matrix structure of the ingot before treatment consists of coarse dendrites, with coarse (size >10μm) primary Nb(C,N) phases formed between the dendrites. These primary phases exhibit continuous, skeletal, and short rod-like structures. The microstructure of the austenitic stainless steel ingot after preheating treatment is as follows: Figure 2 As shown, it can be seen that the coarse primary phase Nb(C,N) in the interdendritic region decomposes, while fine secondary precipitates form in the interdendritic region; the microstructure of the homogenized austenitic stainless steel ingot is as follows: Figure 3 As shown, dendrite segregation has been eliminated (see...). Figure 3 a) The primary Nb(C,N) morphology is spherical or fine needle-like, i.e., it is significantly refined (see Figure 3 b); The metallographic structure of the austenitic stainless steel after treatment in this embodiment is as follows: Figure 4 As shown, complete dynamic recrystallization occurred after the heat deformation treatment, resulting in relatively uniform grain size and the absence of a dual grain structure consisting of coarse and fine grains (see...). Figure 4a) and the internal structure of the dynamically recrystallized grains of the matrix is ​​clean, with no secondary precipitates or primary phases with a size >10 μm (see [link]). Figure 4 b).

[0063] Example 2

[0064] This embodiment provides a method for processing austenitic stainless steel, including the following steps:

[0065] Step 1) The austenitic stainless steel ingot is loaded into a heating furnace for preheating treatment; the loading temperature is 600℃, and then heated to 920℃ and held for 4 hours.

[0066] The chemical composition of the austenitic stainless steel ingot (before treatment) by weight percentage is shown in Table 1; Step 2) The preheated austenitic stainless steel ingot is heated to 1220℃ and held for 40h to achieve homogenization treatment.

[0067] Step 3) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1220℃; then water-cooled to obtain the treated austenitic stainless steel.

[0068] The total deformation amount of the hot deformation treatment is 60%; the deformation amount per pass is 20%.

[0069] In this embodiment, the metallographic structure of the (pre-processed) austenitic stainless steel ingot is as follows: Figure 5 As shown, the matrix structure of the ingot before treatment consists of coarse dendrites, with coarse primary phases Nb(C,N) forming between the dendrites. These primary phases exhibit continuous, skeletal, and short rod-like structures. The microstructure of the austenitic stainless steel ingot after preheating treatment is as follows: Figure 6 As shown, it can be seen that the coarse primary phase Nb(C,N) between the dendrites decomposes, while fine secondary precipitates form between the dendrites; the microstructure of the homogenized austenitic stainless steel ingot is as follows: Figure 7 As shown, dendrite segregation has been eliminated (see...). Figure 7 a) The primary Nb(C,N) morphology is spherical or fine needle-like, i.e., it is significantly refined (see Figure 7 b); The metallographic structure of the austenitic stainless steel after treatment in this embodiment is as follows: Figure 8 As shown, complete dynamic recrystallization occurred after the heat deformation treatment, resulting in relatively uniform grain size and the absence of a dual grain structure consisting of coarse and fine grains (see...). Figure 8 a) and the internal structure of the dynamically recrystallized grains of the matrix is ​​clean, with no secondary precipitates present (see...). Figure 8 b).

[0070] Table 1. Chemical composition (wt.%) of austenitic stainless steel ingots in Examples 1 and 2

[0071]

[0072] Comparative Example 1

[0073] This comparative example provides a method for treating austenitic stainless steel, including the following steps:

[0074] The austenitic stainless steel ingot was subjected to three hot deformation treatments at 1200℃; then water-cooled to obtain the treated austenitic stainless steel.

[0075] In this case, the chemical composition of the austenitic stainless steel ingot (before treatment) was the same as in Example 1, by weight percentage; the total deformation amount of the hot deformation treatment was 60%; and the deformation amount per pass was 20%.

[0076] The metallographic structure of the austenitic stainless steel after the comparative treatment is as follows: Figure 9 As shown, dendritic structures still exist in some areas, indicating incomplete dynamic recrystallization. The dendritic structure affects dynamic recrystallization, and incomplete dynamic recrystallization occurs at the interdendritic sites, resulting in uneven recrystallized grain sizes. Simultaneously, a large number of secondary precipitates are formed at the interdendritic sites where dynamic recrystallization has not occurred. In this comparative example, due to the lack of preheating and homogenization treatments, the coarse (Nb,Ti)(C,N) primary phases and solidification segregation were not eliminated, significantly affecting the recrystallization driving force. Dynamic recrystallization has been completed in some areas, while it has not occurred in others, resulting in uneven recrystallized grain sizes.

[0077] Comparative Example 2

[0078] This comparative example provides a method for treating austenitic stainless steel, including the following steps:

[0079] Step 1) The austenitic stainless steel ingot is loaded into a heating furnace for preheating treatment; the loading temperature is 600℃, and then heated to 900℃ and held for 4 hours.

[0080] The chemical composition of the austenitic stainless steel ingot (before treatment) is the same as in Example 1, by weight percentage.

[0081] Step 2) Heat the preheated austenitic stainless steel ingot to 1200℃ and hold for 40 hours to achieve homogenization.

[0082] Step 3) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1100℃; then water-cooled to obtain the treated austenitic stainless steel.

[0083] The total deformation amount of the hot deformation treatment is 60%; the deformation amount per pass is 20%.

[0084] The metallographic structure of the austenitic stainless steel after the comparative treatment is as follows: Figure 10 As shown, it can be seen that the recrystallized grains are of varying sizes (see...). Figure 10 a) A large amount of secondary precipitates were precipitated in some areas (see a) Figure 10 (b) This is because the heat distortion treatment temperature in this comparative example is below 1200℃, which easily promotes the precipitation of the secondary phase. The secondary phase will hinder the thermal diffusion movement, resulting in a slowdown in the rate of dynamic recrystallization, which inhibits the dynamic recrystallization process and prevents the formation of complete dynamic recrystallization.

[0085] Comparative Example 3

[0086] This comparative example provides a method for treating austenitic stainless steel, including the following steps:

[0087] Step 1) The austenitic stainless steel ingot is loaded into a heating furnace for preheating treatment; the loading temperature is 600℃, and then heated to 900℃ and held for 4 hours.

[0088] The chemical composition of the austenitic stainless steel ingot (before treatment) is the same as in Example 1, by weight percentage.

[0089] Step 2) Heat the preheated austenitic stainless steel ingot to 1200℃ and hold for 40 hours to achieve homogenization.

[0090] Step 3) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1200℃; then water-cooled to obtain the treated austenitic stainless steel.

[0091] The total deformation amount of the hot deformation treatment is 60%; the deformation amount of the last pass is 25%.

[0092] The metallographic structure of the austenitic stainless steel after the comparative treatment is as follows: Figure 11 As shown, it can be seen that the recrystallized grains are of varying sizes (see...). Figure 11 a) A large amount of secondary precipitates were precipitated in some areas (see a) Figure 11 b). This is because the deformation amount of the last hot deformation in this comparative example is 25%. The large deformation amount leads to the formation of a large number of secondary precipitates during the dynamic recrystallization process. On the one hand, the secondary precipitates have a pinning effect on the grain boundaries, inhibiting grain growth. On the other hand, they reduce the driving force of dynamic recrystallization, which is not conducive to the nucleation and growth of dynamic recrystallization, thus inhibiting the dynamic recrystallization process and ultimately causing grain inhomogeneity.

[0093] Comparative Example 4

[0094] This comparative example provides a method for treating austenitic stainless steel, including the following steps:

[0095] Step 1) The austenitic stainless steel ingot is loaded into a heating furnace for preheating treatment; the loading temperature is 600℃, and then heated to 900℃ and held for 4 hours.

[0096] The chemical composition of the austenitic stainless steel ingot (before treatment) is the same as in Example 1, by weight percentage.

[0097] Step 2) Heat the preheated austenitic stainless steel ingot to 1200℃ and hold for 40 hours to achieve homogenization.

[0098] Step 3) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1200℃; then water-cooled to obtain the treated austenitic stainless steel.

[0099] The total deformation amount of the hot deformation treatment is 60%; the deformation amount of the last pass is 10%.

[0100] The metallographic structure of the austenitic stainless steel after the comparative treatment is as follows: Figure 12 As shown, the recrystallized grain size is uneven. This is because the deformation amount of the last hot deformation in this comparative example is 10%. The small deformation amount reduces the efficiency of dynamic softening of austenitic stainless steel, thus inhibiting the dynamic recrystallization process and preventing complete dynamic recrystallization.

[0101] Comparative Example 5

[0102] This comparative example provides a method for treating austenitic stainless steel, including the following steps:

[0103] Step 1) Heat the austenitic stainless steel ingot to 1200°C and hold for 40 hours to achieve homogenization treatment; wherein, by weight percentage, the chemical composition of the austenitic stainless steel ingot (before treatment) is the same as in Example 1;

[0104] Step 2) The homogenized austenitic stainless steel ingot is subjected to three hot deformation treatments at 1200℃; then water-cooled to obtain the treated austenitic stainless steel.

[0105] The total deformation amount of the hot deformation treatment is 60%; the deformation amount of each pass is 20%.

[0106] The metallographic structure of the austenitic stainless steel after the comparative treatment is as follows: Figure 13 As shown, the primary phase Nb(C,N) in the homogenized austenitic ingot undergoes slow dissolution and still exhibits a continuous skeletal morphology (see...). Figure 13a) The grain size of the treated austenitic stainless steel is uneven. This is because the comparative example was not preheated, and the presence of a large number of coarse Nb,Ti(C,N) primary phases affected the recrystallization driving force, resulting in some areas not undergoing dynamic recrystallization and causing uneven recrystallization.

[0107] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method of treating an austenitic stainless steel, characterized by, Includes the following steps: Step 1) Preheat the austenitic stainless steel ingot to decompose some of the primary phases in the austenitic stainless steel ingot into M. 23 C6 carbides are used to make the remaining primary phases appear in a discontinuous distribution. The austenitic stainless steel ingot is an Nb / Ti composite stabilized N-containing austenitic stainless steel ingot; the chemical composition of the austenitic stainless steel ingot by weight percentage is: C≤0.10%, Mn≤1.50%, Si≤1.00%, Cr: 19.5~23.0%, Ni: 23.0~26.0%, Mo: 1.0~4.0%, N: 0.10~0.25%, Nb: 0.10~0.40%, Ti: 0.10~0.50%, P≤0.030%, S≤0.030%, with Fe and unavoidable residual elements as the balance; The preheating treatment includes: placing the austenitic stainless steel ingot in a heating furnace, then heating it to 850~950℃ and holding it at that temperature for 3~6 hours; Step 2) subjecting the preheated austenitic stainless steel ingot to homogenization treatment to make M 23 C6 carbides re-dissolve into the matrix; The homogenization process includes heating the preheated austenitic stainless steel ingot to 1180~1250℃ and then holding it at that temperature. Step 3) Perform hot deformation treatment on the homogenized austenitic stainless steel ingot to cause dynamic recrystallization of the homogenized austenitic stainless steel ingot. The temperature of the heat deformation treatment is 1200~1220℃; the heat deformation treatment adopts a multi-pass heat deformation treatment; the total deformation of the multi-pass heat deformation treatment is ≥40%; the deformation of each pass is 15~25%; and the deformation of the last pass is 15~20%.

2. The method of treating an austenitic stainless steel according to claim 1, characterized in that, In step 1), the primary phase in the austenitic stainless steel ingot includes at least one of Nb(C,N), Ti(C,N), and (Nb,Ti)(C,N).

3. The method for processing austenitic stainless steel according to claim 1, characterized in that, In step 1), the preheating process involves heating to 880-920°C.

4. The method of treating an austenitic stainless steel according to claim 1, characterized in that, In step 2): the homogenization process is heated to 1200~1220℃.

5. The method of treating an austenitic stainless steel according to claim 4, characterized in that, The heat preservation time t≥30h+m×k; where m is the thickness of the austenitic stainless steel ingot in mm; k=10~15min / mm.

6. The method of treating an austenitic stainless steel according to claim 1, characterized in that, In step 3), the total deformation of the multi-pass heat deformation treatment is ≥60%.

7. The method of treating an austenitic stainless steel according to claim 1, characterized in that, In step 3): after the hot deformation treatment step, the method further includes: cooling the hot-deformed austenitic stainless steel ingot.

8. The method of treating an austenitic stainless steel according to claim 7, characterized in that, The cooling process uses water cooling.

9. An austenitic stainless steel, characterized in that, The austenitic stainless steel is obtained by the processing method according to any one of claims 1 to 8; no dual grain structure of coarse and fine grains is observed in the austenitic stainless steel; no secondary precipitates or primary phases with a size >10 μm are observed in the austenitic stainless steel.

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