CN114921730B - Ultra-high-strength high-performance sheet maraging stainless steel and preparation method thereof - Google Patents

Abstract

The invention discloses an ultra-high-strength high-performance sheet maraging stainless steel and a preparation method thereof, wherein the stainless steel comprises the following components: the alloy comprises, by mass, co=2.0-5.0, ni=6.0-9.0, cr=11.0-17.0, ti=0.5-1.8, mo=3.0-7.0, mn=0.08-1.0, si=0.08-0.5, C is less than or equal to 0.02, P is less than or equal to 0.003, S is less than or equal to 0.003, and the balance Fe. Under the conditions that C is less than or equal to 0.02 percent and Co is not more than 5 percent, the stainless steel has tensile strength as high as 2700MPa, elongation as high as 10.5 percent and pitting potential as high as 0.24V _SCE The method comprises the steps of carrying out a first treatment on the surface of the Can be used in the fields of ocean platform, cabin materials of ships and warships, and the like.

Description

A kind of ultra-high-strength and high-performance thin-plate maraging stainless steel and its preparation method

technical field

The invention relates to a super-high-strength and high-performance thin-plate maraging stainless steel and a preparation method thereof, belonging to the field of martensitic stainless steel.

Background technique

Martensitic precipitation strengthened stainless steel is a new steel bell developed in the 1960s. It not only has the strength of maraging strengthened steel but also has the corrosion resistance of stainless steel. Due to its excellent comprehensive mechanical properties, it is often used in key high-end equipment such as aviation, aerospace, and navigation.

The main reason why martensitic precipitation-strengthened stainless steel can achieve ultra-high strength is the superposition of martensitic transformation strengthening and aging precipitation strengthening; the main reason for its corrosion resistance is that the addition of Cr and Mo forms a passivation film on the surface, making it corrosion-resistant. Table 1 shows the composition and properties of commercially available high-strength stainless steels on the market. It can be seen that the current high-strength stainless steel has the following problems: first, when the strength is high, its plasticity and toughness are poor; second, when the mechanical properties are excellent, its corrosion resistance is poor; it is difficult to unify the strength, plasticity, toughness and corrosion resistance to obtain excellent comprehensive performance. It can be seen that how to improve the strength and toughness of stainless steel on the premise of ensuring the corrosion resistance of stainless steel to meet the higher requirements for the comprehensive performance of stainless steel in engineering applications is a research hotspot and difficulty in the field of stainless steel. Therefore, it is imminent to develop a new type of ultra-high strength maraging stainless steel with independent intellectual property rights.

Table 1 Composition and properties of existing commercial high-strength stainless steels on the market

The higher content of Co makes the mechanical properties of high-strength stainless steel better. When the content of Co is low or its content is 0, its comprehensive mechanical properties are low. The addition of Co is a double-edged sword in high-strength stainless steel. The addition of Co can reduce the solubility of Ti and Mo in the martensite matrix, form a precipitate phase containing Mo or Ti, and then improve the strength. At the same time, Co can also hinder the recovery of dislocations, reduce the size of the precipitated phase and stabilize the martensite matrix, which can produce a higher secondary hardening, which is the guarantee of better mechanical properties such as strength. Therefore, to obtain excellent mechanical properties, it is inevitable to add a large amount of Co element. However, the addition of Co to martensitic stainless steel will promote the amplitude modulation decomposition of Cr. The higher the Co content, the greater the amplitude modulation decomposition of Cr, which will reduce the pitting corrosion resistance of the matrix. Therefore, Co should be added in an appropriate amount. The innovation of the present invention is to form a special structure through the combination of optimized alloy elements, double vacuum smelting and corresponding thermomechanical treatment process. This structure is composed of martensite lath and amorphous layer modified by lath boundary, wherein the martensite lath contains a variety of precipitated phases dispersedly distributed in nanometer size. A variety of nanophases are synergistically strengthened to obtain ultra-high strength; at the same time, the lath boundaries decorated by amorphous can both promote dislocation proliferation and absorb dislocations, thereby obtaining large plasticity and great work hardening ability. At the same time, the presence of reverse transformed austenite also contributes to the plasticity and toughness of the material. On the one hand, the stainless steel of the invention replaces carbon strengthening by nano phase strengthening, greatly reducing the carbon content, and on the other hand, improves the pitting corrosion resistance equivalent of the alloy through component optimization. The design of extremely low carbon content and high pitting corrosion resistance equivalent ensures the excellent corrosion resistance of the stainless steel of the invention. Therefore, compared with the existing stainless steel, the mechanical properties and corrosion resistance of the stainless steel of the present invention are all improved.

The invention patent application with the publication number CN 102031459 A discloses a high-strength and high-toughness secondary hardening stainless steel containing W. The composition of the stainless steel is (in mass percentage, %) C=0.10-0.20%, Cr=11.0-13.0%, Ni=2.0-3.5%, Mo=3.5-5.5%, Co=12-15%, W=0.8-3.0%, V=0.1-0.6 %, Nb=0.01～0.06%, Si≤0.2%, Mn≤0.2%, S≤0.01%, P≤0.01%, O≤30PPm, N≤30PPm, and the rest is Fe; its yield strength is 1300～1600MPa, tensile strength is 1920～2030MPa, and its plasticity is 10～13.5%. U.S. Patent 7160399 invented ultra-high-strength corrosion-resistant steel; the nominal composition of the Ferrium S53 alloy is: 14.0Co, 10.0Cr, 5.5Ni, 2.0Mo, 1.0W, 0.30V, 0.21C, and the rest is Fe; the room temperature ultimate tensile strength of Ferrium S53 alloy is about 1980MPa, and the room temperature 0.2% yield stress is about 1560MPa. The invention patent application with the publication number CN 110358983 A discloses a precipitation hardening martensitic stainless steel and its preparation method. The specific chemical composition of the stainless steel is (in mass percentage, %), C=0.14-0.20%, Cr=13.0-16.0%, Ni=0.5-2.0%, Co=12.0-15.0%, Mo=4.5-5.5%, V=0.4-0.6%, Si≤0 .1%, Mn≤0.5%, P≤0.01%, S≤0.01%, N≤0.10%, and the balance is Fe; its tensile strength is 1840-1870MPa, yield strength is 780-820MPa, and elongation is 12.5-14%. Although the above three technical schemes have the performance of high-strength stainless steel, the cost of raw materials is high due to the high addition of Co; the increase in Co content can decompose the banners of Cr, further producing Cr-poor areas and Cr-rich areas, reducing its corrosion resistance; its carbon content is also high, high carbon will seriously deteriorate corrosion resistance, and the size, shape and distribution of carbides in the matrix are difficult to control. The production process of S53 requires two aging treatments and two cryogenic treatments, and the process is relatively complicated.

The invention patent application with the publication number CN 107653421 A discloses a super-high-strength maraging stainless steel resistant to seawater corrosion. The specific chemical composition of the stainless steel is (expressed in mass percentage, %) C≤0.03%, Cr=13.0-14.0%, Ni=5.5-7.0%, Co=5.5-7.5%, Mo=3.0-5.0%, Ti=1.9-2.5%, Si≤0.1%, Mn≤0.1%, P≤0.01%, S≤0.01%, and the balance is Fe. Its tensile strength is 1926-2032MPa, yield strength is 1538-1759MPa, elongation is 7.5-13.0%, and pitting potential Epit≥0.15V. Although the strengthening mechanism of this invention is a precipitation strengthening mechanism, the type of precipitated phase is different from that of the patent of the present invention. Compared with the present invention, the mechanical properties and corrosion resistance of this invention are not as high as the present invention, which shows that the strengthening and toughening mechanism and corrosion resistance of the two inventions are completely different.

Contents of the invention

Purpose of the invention: In view of the problems of complex preparation process, low corrosion resistance and low mechanical properties of the existing ultra-high-strength stainless steel, the present invention provides an ultra-high-strength and high-performance thin-plate maraging stainless steel, and provides a method for preparing the maraging stainless steel.

Technical solution: The composition of an ultra-high-strength and high-performance thin-plate maraging stainless steel according to the present invention is as follows: by mass percentage, Co=2.0-5.0%, Ni=6.0-9.0%, Cr=11.0-17.0%, Ti=0.5-1.8%, Mo=3.0-7.0%, Mn=0.08-1.0%, Si=0.08-0.5%, C≤0.02%, P≤ 0.003%, S≤0.003%, the balance is Fe.

The invention principle and composition design basis of the ultra-high-strength and high-performance thin-plate maraging stainless steel are as follows:

Invention principle: The stainless steel of the present invention does not use carbon to strengthen, and the carbon is controlled at a very low level, which can improve the toughness and corrosion resistance of stainless steel at the same time. But the biggest problem brought by ultra-low carbon is low strength. A special structure is formed by optimizing alloy elements, double vacuum melting and corresponding thermomechanical treatment process. This structure is composed of martensitic lath and amorphous layer modified by lath boundary, in which the martensitic lath contains a variety of precipitated phases dispersed in nanometer size. Ice water quenching and large cold rolling deformation will make the size of martensite laths small and the dislocation density will increase. These small and high dislocation density martensite laths will provide nucleation sites for the precipitated phase body; at the same time, the high-density dislocations and defects between the lamellar structures of these nano laths concentrate a large amount of lattice strain, and a large amount of elastic strain energy is generated due to the inconsistency between atoms. In order to release the elastic strain energy between atoms, they must interact with each other. As a result, the local lattice breaks down and the atomic arrangement becomes disordered, creating nucleation regions of an amorphous structure. The attraction to atoms at the lath boundary is strong. During the aging process, the elements are distributed to the lath boundary, which further increases the disorder of the lath boundary and increases the formation ability of the amorphous on the lath boundary. During the deformation process, this composite structure contributes extremely high yield strength through the precipitation strengthening of various nano-phases. After yielding, the nano-sized amorphous phase at the interface can promote dislocation proliferation and provide plasticity and strength. In the process of thermomechanical treatment, there will be precipitation of reverse transformed austenite in the matrix. During the deformation process, these precipitates can also delay the stress concentration of the material and ensure the plasticity.

本发明的沉淀相是通过调整Ni、Ti、Mo、Si的含量形成富Mo的R'相、α`-Cr与Ni <sub>3</sub> (Ti、Mo)纳米相通过协同强化来实现强度的提升，三个纳米强化相主要表现为协同沉淀的关系，时效初期马氏体板条内部或位错上形成尺寸细小且弥散分布的Ni-Ti-Mo-Si团簇，随着时效时间的延长Mo与Si逐渐被排除团簇外，率先形成了纳米尺寸的Ni <sub>3</sub> (Ti、Mo)强化相，经一段保温后，Mo与Si被完全排除在Ni <sub>3</sub> Ti的表面形成富Mo的R'相，将其包裹住，Ni <sub>3</sub> Ti的长大受到抑制，保证析出相细小弥散，同时在马氏体板条内部还会生成纳米尺寸的α`-Cr；新形成的富Mo的R'相、Ni ₃ Ti以及α`-Cr一起为基体提供较高的强度。 Ni ₃ Ti with a dispersed DO24 structure takes the coherent strain energy at the interface with the matrix as the driving force to form nanometer-sized inversely transformed austenite through the climbing of edge dislocations and the diffusion of Fe atoms, which are evenly distributed in the matrix, prone to the TRIP effect, and can effectively relieve stress concentration.

At the same time, during the process of partitioning the highly alloyed Fe, Cr, Co, Ni, and Mo elements to the lath boundary, the composition of the lath boundary becomes a near-eutectic composition, which improves the formation ability of amorphous and makes the interface change from segregation to amorphous. In the process of uniform deformation, the amorphous phase can promote dislocation proliferation on the one hand to provide plasticity and strength, and at the same time can absorb dislocations to avoid excessive dislocation entanglement hardening and fracture, and further provide work hardening, so as to obtain ultra-high strength and large plasticity.

An important innovation of the present invention is that the content of the expensive alloy element Co is greatly reduced, and the cost can be obviously reduced while improving the corrosion resistance. Although the content of Co in the present invention is designed at a relatively low level, the formation of Ni-Ti clusters is reduced, but through the combination of optimized alloy elements, double vacuum smelting and corresponding thermomechanical treatment processes, a variety of nanophase synergistic strengthening is used to obtain ultra-high strength; at the same time, an amorphous layer is introduced into the lath boundary, and the lath boundary decorated with amorphous can not only promote dislocation proliferation but also absorb dislocations, thereby obtaining large plasticity and great work hardening ability. On the basis of innovations in strengthening mechanism, corresponding composition, thermomechanical treatment design, etc., the present invention realizes simple and controllable process and effectively improves mechanical properties and corrosion resistance.

Composition design basis: Co is one of the important elements to be considered in this invention. Co can increase the Ms point and ensure that the matrix is martensite, but it is a double-edged sword for martensite precipitation strengthening stainless steel. The addition of Co can reduce the solubility of Ti and Mo in the martensite matrix, and form Mo or Ti-containing precipitates, thereby improving the strength. Co can also hinder the recovery of dislocations, reduce the size of the precipitated phase and the matrix, and produce a higher secondary hardening. However, the addition of Co to martensitic stainless steel will promote the amplitude modulation decomposition of Cr. The higher the Co content, the greater the amplitude modulation decomposition of Cr, which will reduce the pitting corrosion resistance of the matrix. Considering the corrosion resistance, the addition of Co should also be appropriate. At the same time, the price of Co element is also relatively expensive, and the high content of Co also forces the raw material cost of ultra-high-strength stainless steel to be high. Comprehensively considering that the mass percentage of Co should be controlled at 2.0-5.0%. For example, 2.0%, 2.5%, 3.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, etc.

Ni is an important element for the formation of intermetallic compounds. In the early stage, the matrix is strengthened by forming B2-Ni (Ti, Mn) and η-Ni ₃ (Ti, Mo). η-Ni ₃ (Ti, Mo) is also the core of Mo-R'-rich phase nucleation; in addition, Ni can strengthen the matrix and provide certain plasticity and toughness for the stainless steel of the invention; Ni can also improve the hardenability of martensite. At the same time, Ni is also the main element for the formation of reversed austenite, but too high Ni content will promote the formation of retained austenite in the matrix, thus affecting the strength of the stainless steel. Comprehensively considering that the mass percentage of Ni should be controlled at 6.0-9.0%. For example, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, etc.

Mo is a very important precipitation strengthening element. Mo is one of the main elements forming the Mo-R'-rich phase as well as Ni ₃ (Ti, Mo). The Mo-R'-rich phase is formed after long-term aging, and wraps Ni ₃ Ti to form a fine and dispersed core-shell structure, which can effectively improve the strength. Mo is also an effective corrosion-resistant element, and the addition of Mo can significantly improve the corrosion resistance of materials. At the same time, Mo is also a forming element of ferrite. Excessive Mo content will increase the precipitation tendency of δ ferrite, increase its content, and deteriorate the performance of the material. Considering that the mass percentage of Mo should be controlled at 3.0-7.0%. For example, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, etc.

Cr is a very important element in stainless steel. In order to ensure the corrosion resistance of stainless steel, its mass percentage generally needs to be greater than 10%. However, Cr is a ferrite-forming element, and its content is too high, which will increase the content of δ ferrite in the matrix and affect the strength, toughness and corrosion resistance of the material. Therefore, the mass percentage of Cr should be controlled at 11.0-17.0%. For example, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, etc.

Si is one of the important elements of new stainless steel. Si is one of the main forming elements of Mo-R'-rich phase. Its addition can effectively promote the formation of Mo-R'-rich phase; Si can also effectively inhibit the precipitation and growth of carbides in the martensite matrix during tempering, thereby preventing the appearance of Cr-poor areas and reducing corrosion resistance; but excessive Si content will seriously damage the plasticity of the material. Considering comprehensively, the mass percentage of Si should be controlled at 0.08-0.50%. For example, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, etc.

Ti is the main strengthening phase forming element, and it can form Ni-Ti clusters in the early stage to prepare for the subsequent precipitation of strengthening phases. When the Ti content is too much, the tendency of precipitates to precipitate at the martensite lath boundary becomes larger. When there are too many precipitates at the martensite lath boundary, it is easy to evolve into a crack source and propagate along the martensite lath interface, causing quasi-cleavage cracking. Considering comprehensively, the mass percentage of Ti should be controlled at 0.5-1.8%. For example, 0.5%, 1.0%, 1.5%, 1.8%, etc.

Mn mainly participates in the precipitation of nano phases to form Ni (Mn, Ti, Mo) intermetallic compounds, so it can replace Ti and Mo elements in a small amount to reduce costs. Mn element is the main element affecting reversed austenite. However, too high Mn content will lead to serious segregation of billets, large thermal stress and structural stress, and decreased weldability. Considering comprehensively, the mass percentage of Mn should be controlled at 0.08-1.0%. For example, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

C exists in the matrix as an impurity element in this stainless steel. When the C content is too high, MX or M ₂₃ C ₆ -shaped carbides (M=Cr, Ti) will be formed. These carbides will seriously delay the formation of inverted austenite and offset the benefits of high dislocation density brought by cold rolling. So to strictly control its content.

The preparation method of the ultra-high-strength and high-performance thin-plate maraging stainless steel of the present invention comprises the following steps:

(1) Proportion of alloying elements;

(2) Vacuum induction melting furnace for vacuum smelting electrodes;

(3) Vacuum self-consumption remelting;

(4) high temperature uniform fire treatment;

(5) Forging or hot-rolling billets;

(6) cold rolling deformation;

(7) Heat treatment.

After the alloy is smelted, it is cooled and formed to room temperature, then the riser is cut off and the skin is peeled off, and then enters the thermomechanical treatment process. After hot-rolling, cold-rolling deformation, and heat treatment, a uniform and fine-sized structure can be obtained, which makes it have high strength, toughness and corrosion resistance.

In step (1), the ratio of the alloying elements is selected according to the mass percentage of each element in the stainless steel, including metal chromium, metal nickel, metal manganese, metal molybdenum, metal cobalt, metal titanium, iron silicon, and the rest are pure iron and unavoidable impurities. The above metals are all high-purity metals and do not contain industrial waste metals.

In the above step (2), the vacuum induction melting furnace is used to smelt the electrode in vacuum, and the whole process is smelted in a high vacuum, and the vacuum degree reaches below 0.1Pa; pure iron, metallic nickel, metallic molybdenum, and metallic cobalt are added with the furnace; metallic chromium and metallic titanium are added from high-level silos; industrial silicon and metallic manganese are added from alloy silos. After the furnace feeding materials are melted, the high-level silo metal is added. After complete melting, deoxidation alloying is carried out, and finally the alloy silo metal is added. During the smelting period, the refining temperature reaches 1550-1650°C, the refining time is not less than 60 minutes, and the stirring time is not less than 10 minutes; samples are taken before the furnace to analyze the smelting composition, and then the composition is adjusted according to the design goal of claim 1; after adjustment to the target composition, the temperature is 1530-1550°C for pouring, and the riser adopts ordinary heat preservation.

In the above step (3), the vacuum self-consumption remelting, the melting rate is 100-260Kg/h, and the vacuum degree is kept at 10 ^-2 Pa or below during the remelting process.

In the above step (4), the high-temperature homogenization treatment is heated in air, vacuum or in a protective atmosphere. The heating method is heating with the furnace, the heating rate is 100-180 °C/h, and the temperature is kept at 600-900 °C for 4-8 hours. Then the temperature is raised to 1100-1300 °C and kept for 20-50 hours, and the furnace is cooled, air-cooled or oil-cooled to room temperature.

In the above step (5), the forging or rolling can be cast or rolled into a square ingot or a round ingot; the process conditions for the forging or hot rolling billet are: the cast billet is heated to 1100-1300°C, kept for 10-24 hours and then rolled out of the furnace; the forging or hot rolling start temperature is ≥1100°C, the final forging or final rolling temperature is ≥950°C, the total drop of the plate hot rolling is not less than 50%, and the ice-water mixture is cooled to room temperature.

In the above step (6), the cold rolling deformation, the total cold rolling reduction of the plate is not less than 60%, and can be cold rolled to 1.5-5mm according to product requirements.

In the above step (7), the heat treatment process includes: aging treatment.

Further, in step (7), the aging treatment: the temperature is 450°C-600°C, the aging time is 0.5-300h, air cooling or quenching to room temperature.

Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) Compared with other high-strength stainless steels, the precious metal content of the present invention is lower, and the cost of raw materials is less; (2) The carbon content of the stainless steel of the present invention is extremely low or does not contain carbon; (3) The preparation method of the ultra-high-strength and high-performance thin-plate maraging stainless steel of the present invention is simple, and high-strength stainless steel can be obtained through different heat treatment processes. The process is highly controllable and easy to realize industrial production. Finally, a stainless steel with good corrosion resistance and excellent mechanical properties was obtained.

Description of drawings

The stress-strain curve figure after the aging of Fig. 1 embodiment 1; Among the figure, abscissa is engineering strain, and ordinate is engineering stress;

The XRD graph after the aging of Fig. 2 embodiment 1; Among the figure, the abscissa is the scanning angle, and the ordinate is the diffraction intensity;

Fig. 3 embodiment 1 aging rear transmission electron microscope high-resolution electron diffraction pattern;

The metallographic appearance figure after the aging of Fig. 4 embodiment 2;

Figure 5 is the TEM image of Example 2 after aging.

Detailed ways

The ultra-high-strength and high-performance thin-plate maraging stainless steel and its preparation method described in the present invention will be further explained and described below in conjunction with the description of the drawings and specific examples. However, the explanation and description do not constitute an improper limitation on the technical solution of the present invention.

Example 1

Select pure iron, metal chromium, metal nickel, metal manganese, metal molybdenum, metal cobalt, metal titanium, iron-silicon raw materials, stainless steel composition as follows (mass percentage): Co=2.0, Cr=12.0, Mn=0.8, Mo=7.0, Ni=6.0, Si=0.08, Ti=1.5, C≤0.02%, P≤0.003%, S≤0.003%, Fe balance. C, P, and S are inevitable impurities.

Vacuum melting is used throughout the process to prepare ingots.

High-temperature homogenization treatment, heating in air, the heating method is heating with the furnace, the heating rate is 100°C/h, holding at 700°C for 4 hours, then raising the temperature to 1100°C for 20 hours, and cooling to room temperature with the furnace.

The process conditions for hot rolling blanking are: the cast billet is heated to 1100°C, held for 10 hours and then rolled out of the furnace; the hot rolling start temperature is 1100±20°C, the final rolling temperature is ≥950°C, the total amount of hot rolling of the plate is 60%, and the ice water mixture is cooled.

The plate is cold-rolled, the total reduction of the plate is 90%, and the plate is rolled 1.5mm.

The cold-rolled sheet is subjected to aging treatment, the aging temperature is 480°C, the aging time is 20h, and air-cooled to room temperature.

The mechanical properties of Example 1 are shown in Table 2. The average hardness is 578.3HV, the yield strength is 2330MPa, the tensile strength is 2713MPa, the elongation is 10.8%, and the pitting potential is 0.24V _SCE . Fig. 1 is the stress-strain curve figure after aging of embodiment 1. Fig. 2 is a TEM image after aging in Example 1, from which it can be seen that there are dislocations with a high number density in the martensite lath. Fig. 3 is a transmission electron microscope high-resolution electron diffraction pattern after aging in Example 1; there is an amorphous diffraction ring on the interface of the martensitic lath.

Example 2

Select pure iron, metal chromium, metal nickel, metal manganese, metal molybdenum, metal cobalt, metal titanium, iron-silicon raw materials, stainless steel composition as follows (mass percentage): Co=5.0, Cr=11.0, Mn=0.5, Mo=6.0, Ni=9.0, Si=0.5, Ti=1.8, C≤0.02%, P≤0.003%, S≤0.003%, Fe balance. C, P, and S are inevitable impurities.

Vacuum melting is used throughout the process to prepare ingots.

High-temperature homogenization treatment, heating in air, the heating method is heating with the furnace, the heating rate is 150°C/h, holding at 800°C for 6 hours, then raising the temperature to 1150°C for 30 hours, and cooling to room temperature with the furnace.

The process conditions for hot forging billet opening are as follows: the billet is heated to 1250°C, held for 10 hours and then out of the furnace for forging; the hot forging start temperature is 1200±20°C, the final forging temperature is ≥950°C, the forging ratio of the forged billet is 6, and the forging is completed and the ice-water mixture is cooled.

The samples were cold rolled with a total reduction of 80%, and the sheet was rolled to 3.0 mm.

Cold-rolled sheet aging treatment, the aging temperature is 450°C, the aging time is 30h, and air-cooled to room temperature.

The mechanical properties of Example 2 are shown in Table 2. The average hardness is 568.1HV, the yield strength is 2250MPa, the tensile strength is 2690MPa, the elongation is 10.5%, and the pitting potential is 0.19V _SCE . Fig. 4 is the metallographic appearance diagram of embodiment 2 after aging. Fig. 5 is a TEM image after aging in Example 2, from which it can be seen that there are dislocations with a high number density in the martensite lath.

The test methods for the corrosion resistance, hardness and tensile mechanical properties of ultra-high-strength and high-performance thin-plate maraging stainless steel in the above examples are as follows.

(1) Hardness: HVS-50 Vickers hardness tester is used for hardness test, the load is 1Kg, and the average value is taken after punching 5 points, which is listed in Table 2.

(2) Tensile mechanical properties: An electronic universal testing machine was used to carry out the tensile test. The nominal section size of the sample was a rectangular sample with a size of 2 to 3×4×20.6mm. The average values of the tensile strength, yield strength and elongation of three samples with the same treatment were listed in Table 2.

(3) Corrosion resistance

The sample is processed into a specification of 10mmⅹ10mmⅹ2mm, encapsulated with epoxy resin and expose 1cm ² for testing, the surface is polished to 2000# with sandpaper, scrubbed with alcohol to remove oil, cleaned with deionized water, and dried for use. The experimental solution is 0.1M Na ₂ SO ₄ +xNaCl (PH=3), and the experimental temperature is room temperature 25°C. Electrochemical tests were performed using a CHI660E electrochemical workstation. The commonly used three-electrode system was used for electrochemical experiments. The ultra-high-strength stainless steel was used as the working electrode, the Pt sheet was used as the auxiliary electrode, and the saturated calomel electrode (SCE) was used as the reference electrode. Before the electrochemical experiment, an external potential of -1.2V _SEC was applied to the sample, and the constant potential was polarized for 5 minutes to remove the oxide film formed on the surface of the sample in the air. The system was stable for 30 minutes, and the recording was started. Potentiodynamic polarization test, the scan rate is 0.5mV/S, the scan potential area is -0.3V (vs. open circuit potential E _OC ) ~ 1.5V (vs. reference electrode potential E _R ), and the test is stopped after the current changes stably. Take the average value after measuring 3 times, and list it in Table 2.

Composition and hardness, tensile properties and pitting corrosion site of table 2 embodiment

Note: The contents of C, P, S and other components in each embodiment in Table 2 conform to the elemental composition of stainless steel. Among them, C≤0.02%, P≤0.003%, S≤0.003%, which are not listed in Table 2. Bal. Indicates the balance.

In summary, the present invention discloses an ultra-high-strength and high-performance thin-plate maraging stainless steel and a preparation method thereof. The composition of the stainless steel is as follows: % by mass, Co=2.0-5.0, Ni=6.0-9.0, Cr=11.0-17.0, Ti=0.5-1.8, Mo=3.0-7.0, Mn=0.08-1.0, Si=0.08-0.5, C≤0.02, P≤0 .003, S≤0.003, the balance is Fe. The stainless steel of the present invention combines optimization of alloying elements, double vacuum smelting and corresponding thermomechanical treatment processes to obtain ultra-high strength by synergistic strengthening of multiple nanophases; at the same time, an amorphous layer is introduced into the lath boundary, and the lath boundary decorated by the amorphous not only promotes dislocation proliferation but also absorbs dislocations, thereby obtaining large plasticity and huge work hardening capacity. The stainless steel of the present invention has a tensile strength of up to 2700MPa, an elongation of up to 10.5%, and a pitting potential of up to 0.24V _SCE when C≤0.02% and Co no more than 5%. It can be used in fields such as cabin materials of ocean platforms and ships.

Claims (9)

1. An ultra-high strength high performance sheet maraging stainless steel, characterized in that the stainless steel has the following composition: according to mass percentage, co=2.0-2.5%, ni=6.0-7.0%, cr=15.0-17.0%, ti=1.8%, mo=6.0-7.0%, mn=0.8-1.0%, si=0.08-0.1%, C is less than or equal to 0.02%, P is less than or equal to 0.003%, S is less than or equal to 0.003%, and the balance is Fe; the preparation method of the ultra-high-strength high-performance sheet maraging stainless steel comprises the following steps: (1) alloy element proportioning; (2) carrying out vacuum smelting electrodes by a vacuum induction smelting furnace; (3) vacuum consumable remelting; (4) high-temperature homogenizing treatment; (5) forging or hot rolling cogging; (6) cold rolling deformation; (7) heat treatment;

in the step (5), the forging or hot rolling size is square ingot or round ingot; the forging or hot rolling cogging process conditions are as follows: heating a casting blank to 1100-1300 ℃, preserving heat for 10-24 hours, and discharging and rolling; the forging or hot rolling starting temperature is more than or equal to 1100 ℃, the final forging or final rolling temperature is more than or equal to 950 ℃, the total hot rolling reduction of the plate is not more than 50%, and the ice-water mixture is cooled to room temperature.

2. A method for producing ultra high strength high performance sheet maraging stainless steel as recited in claim 1, comprising the steps of:

(1) Alloy element proportioning;

(2) Vacuum smelting electrodes in a vacuum induction smelting furnace;

(3) Remelting in vacuum;

(4) Performing high-temperature homogenizing treatment;

(5) Forging or hot rolling cogging;

(6) Cold rolling and deforming;

(7) Heat treatment;

in the step (5), the forging or hot rolling size is square ingot or round ingot; the forging or hot rolling cogging process conditions are as follows: heating a casting blank to 1100-1300 ℃, preserving heat for 10-24 hours, and discharging and rolling; the forging or hot rolling starting temperature is more than or equal to 1100 ℃, the final forging or final rolling temperature is more than or equal to 950 ℃, the total hot rolling reduction of the plate is not more than 50%, and the ice-water mixture is cooled to room temperature.

3. The ultra-high strength high performance sheet maraging stainless steel and the manufacturing method thereof as recited in claim 2, wherein in the step (1), the alloy element ratio is selected from the group consisting of chromium metal, nickel metal, manganese metal, molybdenum metal, cobalt metal, titanium metal, iron silicon, and the balance being pure iron and unavoidable impurities according to the mass percentages of the elements in the stainless steel.

4. The ultra-high strength high performance sheet maraging stainless steel and the preparation method thereof according to claim 2, wherein in the step (2), the vacuum smelting electrode is performed by a vacuum induction smelting furnace, and the whole process adopts high vacuum smelting, and the vacuum degree is below 0.1 Pa; adding pure iron, metallic nickel, metallic molybdenum and metallic cobalt along with a furnace, adding metallic chromium and metallic titanium from a high-level bin, adding industrial silicon and metallic manganese from an alloy bin, melting the materials along with the furnace, adding high-level bin metal, completely melting, deoxidizing and alloying, and finally adding alloy bin metal, wherein the melting period is when the refining temperature reaches 1550-1650 ℃, the refining time is not less than 60 minutes, and the stirring time is not less than 10 minutes; sampling and analyzing smelting components in front of a furnace, and then adjusting the components; after the temperature is regulated to the target composition, casting is carried out at the temperature of 1530-1550 ℃, and the riser is subjected to common heat preservation.

5. The ultra-high strength high performance sheet maraging stainless steel and method for producing the same as recited in claim 2, wherein in step (3), the vacuum self-consuming remelting is performed at a melting speed of 100 to 260kg/h, and the vacuum degree is maintained at 10 during the remelting ^-2 Pa and below.

6. The ultra-high strength high performance sheet maraging stainless steel and the preparation method thereof according to claim 2, wherein in the step (4), the high temperature soaking treatment is performed by heating in air, vacuum or protective atmosphere, the heating mode is heating with a furnace, the heating rate is 100-180 ℃/h, the temperature is kept at 600-900 ℃ for 4-8 h, then the temperature is kept at 1100-1300 ℃ for 20-50 h, and the temperature is cooled with the furnace, air cooled or oil cooled to room temperature.

7. The ultra-high strength high performance sheet maraging stainless steel and the manufacturing method thereof as recited in claim 2, wherein in the step (6), the cold rolling deformation, the total rolling reduction of the sheet is not less than 60%, and the sheet is cold-rolled to 1.5-5 mm according to the product requirement.

8. The ultra-high strength high performance sheet maraging stainless steel as recited in claim 2, wherein in step (7), the heat treatment process comprises: and (5) aging treatment.

9. The ultra-high strength high performance sheet maraging stainless steel and the manufacturing method thereof as recited in claim 7, wherein the aging treatment temperature is 450-600 ℃, the aging time is 0.5-300h, and the sheet maraging stainless steel is air-cooled or quenched to room temperature.