Secondary aging heat treatment method of maraging stainless steel

Abstract

The invention discloses a secondary aging heat treatment method for maraging stainless steel, and belongs to the technical field of stainless steel production. The secondary aging heat treatment method for the maraging stainless steel comprises the following steps that S130 maraging stainless steel is heated to the temperature 5-55 DEG C higher than the austenite transformation temperature for solution treatment, then cooling is conducted, and an intermediate A is obtained; heating the intermediate A to 35-125 DEG C below the dissolution temperature of a precipitated phase, carrying out first aging treatment, and then cooling to obtain an intermediate B; and the intermediate B is heated to 125-175 DEG C below the dissolved temperature of the precipitated phase for secondary aging treatment, then cooling is conducted, and the modified S130 martensitic stainless steel is obtained. The invention aims to solve the problem of toughness and plasticity loss caused by a solid solution and aging process of the traditional S130 maraging stainless steel through modification in the aspect of a heat treatment process, and meanwhile, the yield strength and the tensile strength are improved as much as possible.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel production, in particular to a secondary aging heat treatment method of a martensite aging stainless steel. BACKGROUND

[0002] S130 martensite aging stainless steel, as a typical Fe-Ni-Cr-Mo high alloy steel, has shown significant application potential in the field of ultra-low temperature engineering. S130 steel has the characteristics of high strength, good toughness, weldability and excellent corrosion resistance. Compared with traditional austenitic or ferritic stainless steel, this steel has ultra-high strength and excellent toughness, and shows unique strength and toughness matching advantages.

[0003] From the perspective of alloy design, the addition of Ni element in S130 steel not only stabilizes the reverse austenite, but also improves the matrix strength through solid solution strengthening; Cr element forms a dense Cr2O3 passivation film on the surface, which gives the material excellent corrosion resistance; Mo element refines the grain and promotes the precipitation of MX type carbide, realizing the dual effect of grain boundary strengthening and second phase strengthening. This multi-element synergistic strengthening mechanism effectively overcomes the bottleneck problem of mutual restriction between strength and toughness of traditional martensitic stainless steel, and optimizes the mechanical properties of the material.

[0004] In terms of hot working process, "solid solution + aging" treatment is one of the typical process routes for this type of steel. Through high temperature solid solution treatment, uniform lath martensite structure can be obtained, and then aging treatment is carried out to promote the precipitation of Ni3Mo, Fe2Mo and other intermetallic compounds, realizing significant precipitation strengthening effect. However, this process has obvious contradiction between strength and toughness. This heat treatment method can effectively improve the strength of martensite aging stainless steel, but will lose some toughness.

[0005] With the development of extreme working condition equipment fields such as spacecraft propulsion system and superconducting magnet container, more stringent requirements are put forward for the comprehensive mechanical properties of materials in low temperature area. Therefore, the development of new heat treatment process plays a very important role in the research and application of low temperature martensite aging stainless steel. How to continue to improve the toughness and plasticity of S130 steel while ensuring the strength has become an effective research direction in the performance development of S130 martensite aging stainless steel. SUMMARY

[0006] The purpose of the present application is to provide a secondary aging heat treatment method of a martensite aging stainless steel to solve the above problems in the background art. The present application aims to solve the problem of toughness and plasticity loss caused by the traditional "solid solution + aging" process of S130 martensite aging stainless steel through modification of the heat treatment process, while improving the yield strength and tensile strength as much as possible.

[0007] To achieve the above object, the present application provides the following technical solutions.

[0008] One of the technical solutions of the present application: a secondary aging heat treatment method of a martensitic aging stainless steel, characterized in that it comprises the following steps:

[0009] (1) heating S130 martensitic aging stainless steel to 5-55℃ (700-850℃) above the austenite transformation temperature for solid solution treatment, so that it is completely austenitized, and then cooled to obtain intermediate A;

[0010] (2) heating the intermediate A to 35-125℃ (450-540℃) below the precipitated phase dissolution temperature for the first aging treatment, so that the precipitated phase is fully precipitated, and then cooled to obtain intermediate B;

[0011] (3) heating the intermediate B to 125-175℃ (400-450℃) below the precipitated phase dissolution temperature for the second aging treatment, the temperature of the second aging treatment needs to be much lower than the precipitated phase dissolution temperature to inhibit the coarsening and transformation process of the precipitated phase and promote the formation of reversed austenite, and then cooled to obtain modified S130 martensitic stainless steel.

[0012] Preferably, the martensitic aging stainless steel is S130 martensitic aging stainless steel.

[0013] More preferably, the alloy composition of the S130 martensitic aging stainless steel, by mass percentage, is: C≤0.03%, Si 0.20-0.30%, Mn 0.18-0.22%, Co 6.50-6.80%, Cr 11.50-11.80%, Ni 7.00-9.00%, Mo 2.95-3.05%, Al 0.05-0.15%, and the balance is Fe.

[0014] The S130 martensitic aging stainless steel used in the present application is optimized in element ratio compared with the existing standard component system, so as to improve the comprehensive mechanical properties under secondary aging treatment, especially to improve the toughness while maintaining the strength.

[0015] Further, the carbon (C) content is preferably controlled at 0.01-0.03wt%, which can inhibit excessive precipitation of carbides while avoiding insufficient strength caused by too low carbon content.

[0016] Further, the Ni content is preferably 8.0±0.5wt%, which can stabilize austenite, promote the formation of reversed austenite, and help to improve toughness; at the same time, it participates in the formation of precipitated strengthening phases such as Ni3Ti.

[0017] Further, the Co content is preferably controlled at 6.60-6.80wt%, Co as a γ stabilizing element, by weakening the stacking fault energy, is beneficial to dislocation activity and the formation of inverse austenite, significantly improving plasticity; at the same time, it can improve the morphology of precipitates and enhance the aging strengthening ability.

[0018] Further, the Al addition amount is preferably 0.08-0.12wt%, mainly for refining grains and regulating precipitation behavior (such as forming fine NiAl B2 structure precipitates), and is beneficial to improving oxidation resistance.

[0019] The Mo content is preferably 2.95-3.05wt%, Mo promotes the precipitation of fine Laves phase or η-Ni3(Ti, Mo) and makes it coarsen, which helps to improve strength and high temperature stability.

[0020] The Cr content is moderately reduced to 11.50-11.80wt%, avoiding excessive Cr to form δ ferrite or adverse precipitation behavior, while maintaining good corrosion resistance.

[0021] Mn and Si are both deoxidizing elements, and their content ranges are accurately controlled at 0.18-0.22wt% and 0.20-0.30wt% respectively, to ensure metallurgical purity and suppress inclusions.

[0022] Preferably, the heating rate of step (1) is 10-15℃ / min; the solid solution treatment time is 60 minutes.

[0023] Preferably, the heating rate of step (2) is 10-15℃ / min; the first aging treatment time is 4 hours.

[0024] Preferably, the heating rate of step (3) is 10-15℃ / min; the second aging treatment time is 4 hours.

[0025] Preferably, the cooling method of step (1) is water cooling; the cooling method of step (2) is air cooling; the cooling method of step (3) is air cooling.

[0026] More preferably, the secondary aging heat treatment method comprises the following steps:

[0027] The martensitic age-hardening stainless steel is heated to 790-810℃ at a heating rate of 10-15℃ / min and held for 60 minutes, then water cooled to 20-25℃, then heated to 480-520℃ at a heating rate of 10-15℃ / min and held for 4 hours, air cooled to 20-25℃, then heated to 400℃ at a heating rate of 10-15℃ / min and held for 4 hours, air cooled to 20-25℃, to obtain a modified martensitic stainless steel.

[0028] When the temperature of the first aging treatment is outside the range of 480-520℃, the morphology of the precipitated phase changes, which deteriorates the material performance.

[0029] The second technical solution of the present application provides a modified martensitic stainless steel prepared by the secondary aging heat treatment method.

[0030] The third technical solution of the present application provides an application of the modified martensitic stainless steel in the field of ultra-low temperature engineering.

[0031] The beneficial technical effects of the present application are as follows:

[0032] The present application aims to solve the problem of loss of toughness and plasticity caused by the traditional "solution + aging" process of S130 martensitic aging stainless steel through modification of the heat treatment process, while improving the yield strength and tensile strength as much as possible.

[0033] The use of the secondary aging heat treatment process of the present application to treat martensitic aging stainless steel can significantly improve the final mechanical properties of the steel, and can meet the comprehensive performance requirements of the material in the low temperature region. The secondary aging heat treatment method used in the present application is different from the aging process of traditional martensitic aging stainless steel. Compared with the conventional "solution + aging" process in the art, the tensile strength and yield strength of the product prepared by the heat treatment method defined in the present application are significantly improved, and the impact energy is also significantly improved. Under the condition of the first aging temperature of 500℃, the yield strength is increased by 10% compared with the traditional process, and the impact energy is also increased.

[0034] The present application improves the product performance of S130 martensitic aging stainless steel by changing the temperature of the two aging treatments. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0036] Figure 1 It is a flow chart of the double aging treatment process of the present application.

[0037] Figure 2 It is a STEM image of the product of Example 1.

[0038] Figure 3 It is a STEM image of the product of Examples 2-5 of the present application. Among them, (a) is Example 2, (b) is Example 3, (c) is Example 4, and (d) is Example 5.

[0039] Figure 4 Stress-strain curves at low temperature for the product of Example 1-4 of the present application. DETAILED DESCRIPTION

[0040] The detailed description set forth below describes various illustrative embodiments of the application and is not intended to represent the only embodiments in which the present application can be practiced. The detailed description is intended only to provide a more complete description of the aspects, features, and advantages of the present application.

[0041] Additionally, for numerical ranges that are expressed in lower and upper limits, each intervening value of the range is also expressly contemplated. For values which are less than one or greater than one (e.g., 1 to 5), or 1 to 4.999999), this is also contemplated. For ranges using both Ranges and intervening values there between, any business combination of the range is also specifically contemplated.

[0042] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. It is to be noted that the present application is not limited to the methods and materials described, but includes any methods and materials similar or equivalent to those described herein.

[0043] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having" or the like are open-ended terms that are intended to permit but not limit the inclusion of elements or the like not expressly listed.

[0044] The alloy composition of S130 maraging stainless steel used in the following examples of the present application is shown in Table 1, the austenite transformation temperature of which is 695℃, and the precipitated phase dissolution temperature is 575℃.

[0045] Table 1 Chemical composition of S130 maraging stainless steel

[0046] Component Content (wt. %) C 0.01 Si 0.25 Mn 0.20 Co 6.70 Cr 10.75 Ni 8.00 Mo 3.00 Al 0.1 Fe Balance

[0047] The microstructure characterization was performed by TEM (JEM-2100f, JEOL, Japan), and the test results are shown in Table 2. Figures 2-3

[0048] In the present application, "room temperature" refers to 20-25℃ unless otherwise specified.

[0049] The raw materials used in the following examples of the present application are all commercially available products.

[0050] Figure 1 ​A flow chart of the double aging process of the present application.

[0051] Example 1 (conventional "solution + aging" heat treatment process)

[0052] A secondary aging heat treatment method of a martensitic aging stainless steel, comprising the following steps:

[0053] The S130 martensitic aging stainless steel is heated to 800℃ at a heating rate of 10℃ / min and held for 1h, water cooled to room temperature, then heated to 500℃ at a heating rate of 10℃ / min and held for 4h, air cooled to room temperature, to obtain a modified martensitic stainless steel.

[0054] The steel material with the composition shown in Table 1 is austenitized at 800℃ for 1h, then water quenched to room temperature (20-25℃), and then aged at 500℃ for 4h and cooled to room temperature.

[0055] The yield strength of the sample prepared by the process is 1416MPa, and the impact energy is 59J.

[0056] TEM images of Example 1 are taken as a comparison sample, and the test results are shown in Figure 2 .

[0057] Figure 2 STEM images of the product of Example 1.

[0058] It can be seen from Figure 2 that the distribution of nano precipitates in the microstructure of the product of Example 1 is relatively uniform, which can pin dislocations and provide basic strengthening; at the same time, the presence of reversed austenite is observed, which helps to improve toughness; however, the strengthening effect of the precipitates has not yet reached the optimum.

[0059] Example 2 (lower temperature of the first aging treatment)

[0060] A secondary aging heat treatment method of a martensitic aging stainless steel, comprising the following steps:

[0061] The S130 martensitic aging stainless steel is heated to 800℃ at a heating rate of 10℃ / min and held for 1h, water cooled to room temperature, then heated to 420℃ at a heating rate of 10℃ / min and held for 4h, air cooled to room temperature, then heated to 400℃ at a heating rate of 10℃ / min and held for 4h, air cooled to room temperature, to obtain a modified martensitic stainless steel.

[0062] Figure 3 STEM images of the products of Examples 2-5 of the present application. Among them, (a) is Example 2, (b) is Example 3, (c) is Example 4, and (d) is Example 5.

[0063] The yield strength of the sample prepared by the treatment process is 1299 MPa, and the impact energy is 71 J. From Figure 3 (a) of the present application can be seen that, due to the low temperature of the first aging treatment, the nano-precipitates are not fully precipitated, resulting in small size and uneven distribution of the nano-precipitates; and the reverse austenite is not formed in the final product, which results in a strength even significantly lower than that of Example 1.

[0064] Example 3

[0065] A secondary aging heat treatment method for a maraging stainless steel is provided, comprising the following steps:

[0066] The S130 maraging stainless steel is heated to 800℃ at a heating rate of 10℃ / min and held for 1h, then water-cooled to room temperature, then heated to 500℃ at a heating rate of 10℃ / min and held for 4h, air-cooled to room temperature, then heated to 400℃ at a heating rate of 10℃ / min and held for 4h, air-cooled to room temperature, to obtain a modified S130 maraging stainless steel.

[0067] Compared with Example 1 using the conventional "solution + aging" process, the yield strength of the sample treated by this process is increased by about 10%, and the impact energy is increased from 59J to 64J. From Figure 3 (b) of the present application can be seen that the microstructure shows uniformly dispersed nano-precipitates, and the strengthening effect is optimal; meanwhile, the reverse austenite exists to optimize the toughness. The combined effect of precipitate strengthening and reverse austenite toughening makes the product of Example 3 obtain the best comprehensive performance.

[0068] Example 4

[0069] A secondary aging heat treatment method for a S130 maraging stainless steel is provided, comprising the following steps:

[0070] The S130 maraging stainless steel is heated to 800℃ at a heating rate of 10℃ / min and held for 1h, then water-cooled to room temperature, then heated to 540℃ at a heating rate of 10℃ / min and held for 4h, air-cooled to room temperature, then heated to 400℃ at a heating rate of 10℃ / min and held for 4h, air-cooled to room temperature, to obtain a modified maraging stainless steel.

[0071] The yield strength of the sample prepared by the treatment process is 1487 MPa, and the impact energy is 62 J. From Figure 3 (c) of the present application can be seen that a large amount of reverse austenite is formed in the microstructure, but the precipitates are significantly coarsened; the coarsening of the precipitates will provide crack propagation sources during deformation, thereby reducing the performance of the material.

[0072] Example 5

[0073] A secondary aging heat treatment method of a martensitic aging stainless steel, the steps are as follows:

[0074] The S130 martensitic aging stainless steel is heated to 800℃ at a heating rate of 10℃ / min and kept for 1h, water cooled to room temperature, then heated to 500℃ at a heating rate of 10℃ / min and kept for 4h, air cooled to room temperature, then heated to 480℃ at a heating rate of 10℃ / min and kept for 4h, air cooled to room temperature, to obtain a modified martensitic stainless steel.

[0075] The yield strength of the sample prepared by the treatment process is 1346MPa, and the impact absorption energy is 60J. It can be seen from Figure 3 (d) that the microstructure morphology is not much different from single aging due to the too high secondary aging temperature. Therefore, the secondary aging temperature needs to be controlled.

[0076] Effect verification

[0077] 1. In order to verify the tensile strength, elongation, impact absorption energy and yield strength of the product obtained by the present application, the steel materials in each example were tested as follows. The specific test method is:

[0078] (1) Tensile test: tested according to GB / T 228.1-2010 Metal Materials Tensile Test Part 1: Room Temperature Test Method;

[0079] (2) Impact test: tested according to GB / T 229-2007 Metal Materials Charpy Pendulum Impact Test Method. The test results are shown in Table 2.

[0080] Table 2 Mechanical properties of steel materials after treatment of examples 1-4

[0081]

[0082] 2. The working performance of the steel materials in each example at low temperature was tested. The specific test method is: the tensile property test is carried out on a tensile testing machine (METS Industrial Systems (China) Co., Ltd., model CMT5105) at low temperature (-196℃), with Epsilon contact extensometer, SDYDGD high and low temperature environmental chamber and special low temperature test container. The sample is fully immersed in liquid nitrogen to ensure uniform temperature, and the tensile rate is 0.01mm / min. The test results are shown in Figure 4

[0083] Figure 4 The stress-strain curve of the product of examples 1-4 of the present application at low temperature.

[0084] ​According to the process parameter adjustment according to the content of the application, the performance improvement of the S130 type low martensite aging stainless steel can be realized. The above described embodiments are only used to describe the preferred modes of the application, and do not limit the scope of the application. Without departing from the design spirit of the application, various modifications and improvements of the technical solutions of the application made by those skilled in the art shall fall within the protection scope determined by the claims of the application.

Claims

1. A secondary aging heat treatment method for maraging stainless steel, characterized in that: The following steps are involved: (1) heating S130 maraging stainless steel to 5-55°C above the austenite transformation temperature for solution treatment, and then cooling to obtain intermediate A; (2) heating the intermediate A to 35-125° C. below the dissolution temperature of the precipitated phase for a first aging treatment, and then cooling to obtain the intermediate B; (3) The intermediate B is heated to 125-175° C. below the dissolution temperature of the precipitated phase for a second aging treatment, and then cooled to obtain modified S130 martensitic stainless steel.

2. The secondary aging heat treatment method according to claim 1, characterized in that: Calculated by mass percentage, the alloy composition of the S130 maraging stainless steel is: C≤0.03%, Si 0.20-0.30%, Mn 0.18-0.22%, Co6.50-6.80%, Cr 11.50-11.80%, Ni 7.00-9.00%, Mo 2.95-3.05%, Al 0.05-0.15%, and the balance is Fe.

3. The secondary aging heat treatment method according to claim 1, characterized in that: The heating rate of step (1) is 10-15°C / min; the solution treatment time is 60 minutes.

4. The secondary aging heat treatment method according to claim 1, characterized in that: The heating rate of step (2) is 10-15°C / min; the time of the first aging treatment is 4 hours.

5. The secondary aging heat treatment method according to claim 1, characterized in that: The heating rate of step (3) is 10-15°C / min; the time of the second aging treatment is 4 hours.

6. The secondary aging heat treatment method according to claim 1, characterized in that: The cooling method described in step (1) is water cooling; the cooling method described in step (2) is air cooling; the cooling method described in step (3) is air cooling.

7. The secondary aging heat treatment method according to claim 2, characterized in that: The steps of the secondary aging heat treatment method are as follows: The martensitic aging stainless steel is heated to 790-810°C at a heating rate of 10-15°C / min and kept warm for 60 minutes, then water-cooled to 20-25°C, then heated to 480-520°C at a heating rate of 10-15°C / min again and kept warm for 4 hours, then air-cooled to 20-25°C, then heated to 400°C at a heating rate of 10-15°C / min and kept warm for 4 hours, then air-cooled to 20-25°C to obtain a modified martensitic stainless steel.

8. A modified martensitic stainless steel prepared according to the secondary aging heat treatment method according to any one of claims 1 to 7.

9. Use of the modified martensitic stainless steel according to claim 8 in the field of ultra-low temperature engineering.

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