Novel high-toughness corrosion-resistant stainless steel and preparation method thereof

Abstract

The invention discloses novel high-toughness corrosion-resistant stainless steel and a preparation method thereof, and relates to the technical field of stainless steel. The novel high-toughness corrosion-resistant stainless steel is prepared from the following elements in percentage by mass: less than or equal to 0.06 percent of C, 13 to 13.9 percent of Cr, 5.6 to 6 percent of Ni, 1.5 to 2.5 percent of Mo, 2.1 to 2.4 percent of Cu, 0.4 to 1.1 percent of Si, 0.5 to 1.1 percent of Mn, 0.15 to 0.35 percent of Nb, less than or equal to 0.015 percent of P, less than or equal to 0.01 percent of S and the balance of Fe and other inevitable impurity elements. According to the novel high-toughness corrosion-resistant stainless steel and the preparation method thereof, the novel high-toughness corrosion-resistant stainless steel has high toughness, corrosion resistance and certain mechanical strength, and can meet the comprehensive performance requirements of high strength, high toughness and corrosion resistance under the coastal environment working condition.

Description

Technical Field

[0001] The present application relates to the technical field of stainless steel, and in particular to a novel high-strength, toughness, and corrosion-resistant stainless steel and a preparation method thereof. Background Art

[0002] High-strength stainless steel is widely used in equipment manufacturing fields related to the national economy and people's livelihood, such as aerospace, marine engineering, and energy. With the rapid development of society and economy, working conditions have become more and more complex and harsh, especially working conditions in the ocean, which not only need to face sediment scouring and complex load effects, but also need to face various forms of corrosion problems. Therefore, the comprehensive performance requirements for high strength, high toughness and corrosion resistance of materials are higher.

[0003] 15-5PH stainless steel is a precipitation hardening stainless steel with high strength and corrosion resistance. It mainly achieves high strength by adding elements such as Cu and Al, which is superimposed on the martensitic transformation strengthening and precipitation strengthening by aging. Its corrosion resistance is improved by adding elements such as Cr and Mo. This stainless steel has excellent strength, toughness, strong corrosion resistance, and can be used in a wide temperature range. However, in an environment containing chloride ions, its corrosion resistance is poor and cannot meet the requirements of high toughness and excellent corrosion resistance in coastal environment conditions.

[0004] Chinese patent CN115717221A proposes a high-strength, tough, and corrosion-resistant three-phase stainless steel, which is a three-phase stainless steel designed using a multiphase composite structure and a nano-precipitation phase strengthening mechanism. The strength and toughness of the material are maintained by the three phases of martensite, ferrite, and austenite, and the dispersed nano-scale intermetallic compounds formed by Cu, Ni, and Mo are used as reinforcements. The two work together to improve the tensile strength and yield strength of the stainless steel. By increasing the content of Si elements and using it in conjunction with Cr elements to improve corrosion resistance, the final product can achieve higher strength, but it cannot match the requirements of high toughness and excellent corrosion resistance.

[0005] In view of the above situation, it is urgent to study a new high-strength, toughness and corrosion-resistant stainless steel and its preparation method suitable for coastal environmental conditions, adjust the element composition, and make it easy to process so as to meet the comprehensive performance requirements of high strength, high toughness and corrosion resistance under coastal environmental conditions. Summary of the invention

[0006] The purpose of the embodiments of the present invention is to provide a new type of high-strength and toughness corrosion-resistant stainless steel and a preparation method thereof. The new type of high-strength and toughness corrosion-resistant stainless steel has high strength and toughness, corrosion resistance and a certain mechanical strength, and can meet the comprehensive performance requirements of high strength, high toughness and corrosion resistance under coastal environmental conditions.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] The embodiment of the present invention provides a novel high-strength, toughness and corrosion-resistant stainless steel, wherein the novel high-strength, toughness and corrosion-resistant stainless steel comprises the following element compositions by mass content:

[0009] C≤0.06%, Cr:13~13.9%, Ni:5.6~6%, Mo:1.5~2.5%, Cu:2.1~2.4%, Si:0.4~1.1%, Mn:0.5~1.1%, Nb:0.15~0.35%, P≤0.015%, S≤0.01%, the rest are Fe and other inevitable impurity elements.

[0010] In some embodiments, the novel high-strength, toughness and corrosion-resistant stainless steel is forged stainless steel, which is a high-performance steel with room temperature tensile strength>1100MPa, elongation>18%, room temperature impact toughness>110J, and pitting potential value>60mV.

[0011] The embodiment of the present invention also provides a method for preparing the novel high-strength, toughness and corrosion-resistant stainless steel as described above, comprising the following steps:

[0012] S1 Ingredients: Prepare the ingredients according to the following element composition ratios by mass content:

[0013] C≤0.06%, Cr:13~13.9%, Ni:5.6~6%, Mo:1.5~2.5%, Cu:2.1~2.4%, Si:0.4~1.1%, Mn:0.5~1.1%, Nb:0.15~0.35%, P≤0.015%, S≤0.01%, the rest are Fe and other unavoidable impurity elements;

[0014] S2 smelting: smelting the raw materials prepared according to the composition ratio in step S1, and casting into ingots after reaching the target composition range;

[0015] S3 forging: preheating the forging tool at a heating temperature of 1160-1220°C, forging the ingot at a forging temperature of 950-1180°C, and forming a forged ingot;

[0016] S4 heat treatment: The forging blank is subjected to solution heat treatment and aging heat treatment.

[0017] In some embodiments, the solution heat treatment comprises heating the forging blank to 950-1050°C, keeping the temperature for 2 hours, and air cooling to room temperature; the aging heat treatment comprises heating the forging blank to 500-550°C, keeping the temperature for 4 hours, and air cooling to room temperature.

[0018] In some embodiments, in step S1, during the element composition ratio process, the element burnout rate is estimated according to the equipment parameters, and the addition amount is calculated according to the element mass percentage.

[0019] The chemical composition design principle of the present invention for manufacturing the new high-strength and tough corrosion-resistant stainless steel is as follows:

[0020] Carbon (C) is an interstitial solid solution element that can significantly improve the matrix strength of steel, but too high a carbon content will reduce the toughness of the steel and precipitate chromium carbides, reducing the content of solid-solution chromium atoms in the matrix, thereby reducing the corrosion resistance of the steel. Optionally, the content of C in the invention is controlled to be below 0.06%.

[0021] Chromium (Cr) mainly improves corrosion resistance and oxidation resistance in stainless steel, and the corrosion resistance of stainless steel increases with the increase of Cr content. In the novel high-strength and tough corrosion-resistant stainless steel of the present invention, in order to meet the use requirements of coastal environments and ensure good corrosion resistance, the Cr content is not less than 13%, but too high Cr content will lead to the formation of a large amount of ferrite, affecting the overall toughness of the stainless steel. Optionally, the Cr content in the present invention is 13 to 13.9%.

[0022] Nickel (Ni) can ensure that stainless steel has good plasticity. Increasing the nickel content of steel can effectively reduce the delta ferrite content. Nickel has a certain promoting effect on the corrosion resistance and oxidation resistance of stainless steel, but too high a nickel content will reduce the strength of the material. Optionally, the content of Ni in the invention is controlled at 5.6-6%.

[0023] Molybdenum (Mo) promotes the strength, toughness and corrosion resistance of martensitic stainless steel. Molybdenum not only strengthens the steel, but also maintains the toughness of the steel, playing an important role in strengthening and toughening the stainless steel. Molybdenum can effectively inhibit the pitting corrosion tendency of chloride ions on steel and improve the ability to resist intergranular corrosion. Optionally, the content of Mo in the invention is controlled at 1.5-2.5%.

[0024] Copper (Cu) can improve the corrosion resistance of stainless steel and can more effectively resist corrosion from media such as acid, alkali, and salt. In addition, through the aging precipitation hardening process, a second phase of nanometer size, such as copper-rich phase, Ni3Mo, carbide, carbonitride, and intermetallic compound, is precipitated, which produces a precipitation strengthening effect, which can not only improve the strength of stainless steel but also maintain its sufficient toughness. Optionally, the content of Cu element in the invention is controlled at 2.1-2.4%.

[0025] Silicon (Si) is mainly used as a deoxidizer during smelting, and silicon can strengthen the matrix and improve the corrosion resistance and high-temperature oxidation resistance of steel. Since silicon promotes the precipitation and growth of harmful phases in stainless steel and reduces the hot working performance and toughness of steel, when the silicon content exceeds 1%, it is easy to cause cracks and fractures in the material. Optionally, the Si content in the invention is 0.4-1.1%.

[0026] Manganese (Mn) can reduce the hardenability of steel, but too much Mn will affect the toughness of stainless steel and reduce the corrosion resistance of stainless steel. Optionally, the Mn content in the invention is 0.5-1.1%.

[0027] Niobium (Nb) can refine the grains and has a significant solid solution strengthening effect, which can improve the welding performance and prevent intergranular corrosion. At the same time, Nb can effectively stabilize C and N elements and effectively refine the grains. Through aging precipitation hardening treatment, dispersed micro-nano NbC, copper-rich phase and M 23 C6, thereby greatly improving the yield and tensile strength of the material. However, too high a content of Nb will generate too much ferrite or other brittle phases, resulting in reduced plasticity and toughness of the stainless steel. Optionally, the content of Nb in the invention is 0.15-0.35%.

[0028] The present invention provides a novel high-strength, tough and corrosion-resistant stainless steel and a preparation method thereof. Under the raw material ratio, the tensile strength and yield strength of the stainless steel are improved to a certain extent after further adjustment by heat treatment. The stable carbide formed between the Nb element and a small amount of the C element can inhibit the carbide formed between the Cr element and the C element, thereby affecting the corrosion performance.

[0029] The present invention provides a new type of high-strength, toughness and corrosion-resistant stainless steel and a preparation method thereof. The new type of steel is developed by adjusting the element composition content on the basis of comprehensive three-phase stainless steel and precipitation hardening martensitic stainless steel. The new type of steel has high strength, high toughness and excellent corrosion resistance.

[0030] The present invention provides a novel high-strength, toughness and corrosion-resistant stainless steel and a preparation method thereof. The prepared novel high-strength, toughness and corrosion-resistant stainless steel is a high-performance steel with room temperature tensile strength>1100MPa, elongation>18%, room temperature impact toughness>110J, and pitting potential value>60mV (3.5wt.% NaCl solution).

[0031] In the preparation method of the embodiment of the present invention, aging heat treatment is also performed after the solution heat treatment. The combined effect of the two can greatly improve the tensile strength, yield strength and toughness of the forged stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present disclosure, the following briefly introduces the drawings required for use in some embodiments of the present disclosure. Obviously, the drawings described below are only drawings of some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can also be obtained based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams, and are not limitations on the actual size of the products involved in the embodiments of the present disclosure, the actual process of the method, etc.

[0033] Figure 1 1 is a SEM image of a novel high-strength, toughness, and corrosion-resistant stainless steel sample according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in some embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments provided by the present disclosure, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present disclosure.

[0035] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as an open, inclusive meaning, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "examples" or "some examples" and the like are intended to indicate that specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representations of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics described may be included in any one or more embodiments or examples in any appropriate manner.

[0036] The embodiment of the present invention provides a new type of high-strength, toughness and corrosion-resistant stainless steel, which includes the following element composition by mass content: C≤0.06%, Cr: 13-13.9%, Ni: 5.6-6%, Mo: 1.5-2.5%, Cu: 2.1-2.4%, Si: 0.4-1.1%, Mn: 0.5-1.1%, Nb: 0.15-0.35%, P≤0.015%, S≤0.01%, and the rest are Fe and other inevitable impurity elements.

[0037] A novel high-strength, toughness and corrosion-resistant stainless steel provided in an embodiment of the present invention has martensite as the matrix structure.

[0038] A new type of high-strength, toughness and corrosion-resistant stainless steel provided in an embodiment of the present invention is forged stainless steel, which is a high-performance steel with room temperature tensile strength>1100MPa, elongation>18%, room temperature impact toughness>110J, and pitting potential value>60mV (3.5wt.% NaCl solution).

[0039] The embodiment of the present invention further provides a method for preparing a novel high-strength, toughness and corrosion-resistant stainless steel, comprising steps: S1 to S4.

[0040] S1 Ingredients: Prepare the ingredients according to the following element composition ratios by mass content:

[0041] C≤0.06%, Cr:13~13.9%, Ni:5.6~6%, Mo:1.5~2.5%, Cu:2.1~2.4%, Si:0.4~1.1%, Mn:0.5~1.1%, Nb:0.15~0.35%, P≤0.015%, S≤0.01%, the rest are Fe and other inevitable impurity elements.

[0042] S2 smelting: smelting the raw materials prepared according to the composition ratio in step S1, and casting them into ingots after reaching the target composition range.

[0043] S3 forging: preheat the forging tool at a heating temperature of 1160-1220°C, forge the ingot at a forging temperature of 950-1180°C to form a forged ingot.

[0044] S4 heat treatment: The forging blank is subjected to solution heat treatment and aging heat treatment.

[0045] In some embodiments, the solution heat treatment comprises heating the forging blank to 950-1050°C, keeping the temperature for 2 hours, and cooling to room temperature; the aging heat treatment comprises heating the forging blank to 500-550°C, keeping the temperature for 4 hours, and cooling to room temperature.

[0046] In the preparation method of the embodiment of the present invention, aging heat treatment is also performed after the solution heat treatment. The combined effect of the two can greatly improve the tensile strength, yield strength and toughness of the forged stainless steel.

[0047] It can be understood that after the raw materials are prepared into forging blanks, solid solution treatment and aging heat treatment are performed, and the new type of high-strength, toughness and corrosion-resistant stainless steel formed is forged stainless steel.

[0048] The preparation method of the embodiment of the present invention forms corrosion-resistant and high-strength stainless steel by forging, which is suitable for preparing various equipment working in complex environments.

[0049]

[0050]

[0051] The parameters of the preparation method of the novel high-strength, toughness and corrosion-resistant stainless steel of the present invention are shown in Table 2.

[0052] Table 2 Preparation parameters of new high-strength and tough corrosion-resistant stainless steel

[0053]

[0054]

[0055] Among them, the preparation methods of Examples 11 to 15 are the same as those of Example 1 and will not be repeated here.

[0056] Take the stainless steel after heat treatment in Example 1, prepare a scanning electron microscope observation sample, and observe the sample by scanning electron microscope. The results of scanning electron microscope observation are as follows: Figure 1 When preparing the sample, first use multiple sandpapers to grind the sample in sequence, the mesh number of the sandpaper is between 600 and 3000 mesh, and the mesh number of the sandpaper is increased in sequence. After grinding, the sample is further polished with a polishing paste containing 0.5μm diamond particles.

[0057] The stainless steel after heat treatment in each embodiment was processed into test specimens for testing mechanical properties, and the room temperature tensile strength, elongation, room temperature impact toughness, and pitting points were tested respectively.

[0058] The mechanical properties were tested using a DDL-300 electronic universal testing machine in accordance with GB / T228.1-2021 "Room Temperature Tensile Test Method for Metallic Materials", using an R4 specimen, a standard circular section specimen with a gauge length of 50 mm and a diameter of 10 mm. The impact test was performed using a NI500C instrumented oscillographic impact tester in accordance with GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials", using a standard Charpy V-notch specimen with a size of 10×10×55 mm. The pitting point measurement was performed using a Gamryinterface1010E electrochemical workstation in accordance with GB / T17899-1999 "Stainless Steel Pitting Point Measurement Method", the test temperature was 30±1°C, and the test medium was 3.5% NaCl solution.

[0059] The properties of the new high-strength, toughness and corrosion-resistant stainless steel obtained in Examples 1-10 are shown in Table 3.

[0060] Table 3 Performance test results of new high-strength and tough corrosion-resistant stainless steel in Examples 1-10

[0061]

[0062] As can be seen from Table 3, the new high-strength and tough corrosion-resistant stainless steels obtained in Examples 1-10 of the present invention have tensile strengths of more than 1100 MPa, elongations of more than 18%, impact values ​​of more than 105 J at room temperature and -40°C, and pitting points greater than 60 mV. The new high-strength and tough corrosion-resistant stainless steels of the present invention have good strength, toughness and corrosion resistance.

[0063] Comparative test:

[0064] The present invention provides the following comparative examples to help those skilled in the art understand the intent and effects of the present invention.

[0065] For the chemical composition design of the new high-strength, toughness and corrosion-resistant stainless steel of Comparative Examples 1-4, see Table 4.

[0066] Table 4 Composition design of new high-strength and corrosion-resistant stainless steel (wt%)

[0067]

[0068] For the preparation method of the novel high-strength, toughness and corrosion-resistant stainless steel of Comparative Examples 1-4, please refer to Example 1 and will not be described in detail.

[0069] For the preparation method parameters of the new high-strength, toughness and corrosion-resistant stainless steel of Comparative Example 5-6, see Table 5.

[0070] Table 5 Preparation parameters of new high-strength and tough corrosion-resistant stainless steel

[0071]

[0072] The performance of Comparative Examples 1-6 was tested according to the testing method of Examples 1-10. After testing, the performance of the new high-strength, toughness and corrosion-resistant stainless steel obtained in Comparative Examples 1-6 is shown in Table 6.

[0073] Table 6 Comparative Examples 1-6 New High-Toughness Corrosion-Resistant Stainless Steel Performance Test Results

[0074]

[0075]

[0076] It can be seen from Table 6 that after some elements or contents of stainless steel are adjusted, some performance indicators of the corresponding steel grade have changed significantly compared with the steel grade of the present invention. Among them:

[0077] Comparative Examples 1 and 2 adjusted the contents of Cr, Ni, Mo, and Cu, and the steel grades prepared had improved elongation index compared with the corresponding embodiments, but the tensile strength, cross-sectional shrinkage, room temperature and -40°C impact values, and pitting performance were significantly deteriorated. Analysis shows that the Cr content in Comparative Examples 1 and 2 is too high, which improves the toughness of stainless steel, the Ni content is low, which affects the tensile strength of stainless steel, the Mo content is low, and the Cu content is high, which affects the corrosion resistance of stainless steel.

[0078] Comparative Examples 3 and 4 adjusted the contents of Ni, Mo, Cu, and Si, and the steel grades prepared had improved tensile strength indexes compared with the corresponding embodiments, but the cross-sectional shrinkage, room temperature and -40°C impact values, and pitting performance were significantly deteriorated. Analysis shows that the high Ni content in Comparative Examples 3 and 4 improves the tensile strength of stainless steel, the low Mo content and low Cu content affect the corrosion resistance of stainless steel, and the high Si content affects the elongation of stainless steel.

[0079] The present invention systematically adjusts the element composition content on the basis of comprehensive three-phase stainless steel and precipitation hardening martensitic stainless steel, optimizes and matches each component, develops into a new steel grade, and globally optimizes and adjusts the components such as Cr, Ni, Mo, Cu, Si or their contents. These adjustments and optimizations are coordinated and matched, so that the steel grade has high strength, high toughness, and excellent corrosion resistance.

[0080] The present invention not only optimizes the components of the system, but also makes targeted improvements to the production process. Specifically, the present invention adds a solution heat treatment process and an aging heat treatment process, so that the stainless steel can be prepared smoothly with high quality, and the tensile strength and yield strength of the steel can be improved, thus achieving good environmental and economic benefits and being more practical.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A new type of high-strength, tough and corrosion-resistant stainless steel, characterized in that: The novel high-strength, tough and corrosion-resistant stainless steel comprises the following elemental compositions by mass content: C≤0.06%, Cr:13~13.9%, Ni:5.6~6%, Mo:1.5~2.5%, Cu:2.1~2.4%, Si:0.4~1.1%, Mn:0.5~1.1%, Nb:0.15~0.35%, P≤0.015%, S≤0.01%, the rest are Fe and other inevitable impurity elements.

2. A new type of high-strength, tough and corrosion-resistant stainless steel as claimed in claim 1, characterized in that: The novel high-strength, toughness and corrosion-resistant stainless steel is forged stainless steel, which is a high-performance steel with room temperature tensile strength>1100MPa, elongation>18%, room temperature impact toughness>110J, and pitting potential value>60mV.

3. A method for preparing the novel high-strength, toughness and corrosion-resistant stainless steel as claimed in claim 1 or 2, characterized in that: The following steps are involved: S1 Ingredients: Prepare the ingredients according to the following element composition ratios by mass content: C≤0.06%, Cr:13~13.9%, Ni:5.6~6%, Mo:1.5~2.5%, Cu:2.1~2.4%, Si:0.4~1.1%, Mn:0.5~1.1%, Nb:0.15~0.35%, P≤0.015%, S≤0.01%, the rest are Fe and other unavoidable impurity elements; S2 smelting: smelting the raw materials prepared according to the composition ratio in step S1, and casting into ingots after reaching the target composition range; S3 forging: preheating the forging tool at a heating temperature of 1160-1220°C, forging the ingot at a forging temperature of 950-1180°C, and forming a forged ingot; S4 heat treatment: The forging blank is subjected to solution heat treatment and aging heat treatment.

4. A method for preparing a novel high-strength, tough and corrosion-resistant stainless steel as claimed in claim 3, characterized in that: The solution heat treatment comprises heating the forging blank to 950-1050° C., keeping the temperature for 2 hours, and air cooling the forging blank to room temperature; the aging heat treatment comprises heating the forging blank to 500-550° C., keeping the temperature for 4 hours, and air cooling the forging blank to room temperature.

5. The method for preparing a novel high-strength, tough and corrosion-resistant stainless steel as claimed in claim 3, characterized in that: In the step S1, during the element composition ratio process, the element burnout rate is estimated according to the equipment parameters, and the addition amount is calculated according to the element mass percentage.

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