CN113774291A - Ultra-low carbon high-performance maraging stainless steel and preparation method thereof - Google Patents
Ultra-low carbon high-performance maraging stainless steel and preparation method thereof Download PDFInfo
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Abstract
Disclosure of the inventionAn ultra-low carbon high performance maraging stainless steel and a preparation method thereof, the stainless steel comprises the following components: the alloy material comprises, by mass, 2.0-4.0% of Co, 7.0-9.0% of Ni, 11.0-15.0% of Cr, 0.3-2.0% of Ti, 3.0-6.0% of Mo, 0.08-1.0% of Mn, 0.08-0.3% of Si, less than or equal to 0.01% of C, less than or equal to 0.003% of P, less than or equal to 0.003% of S, and the balance of Fe. The method comprises the following steps: (1) alloy element proportioning (2) carrying out vacuum smelting on an electrode in a vacuum induction smelting furnace; (3) vacuum consumable remelting; (4) carrying out high-temperature flame equalizing treatment; (5) forging or hot rolling cogging; (6) and (6) heat treatment. The elongation of the stainless steel reaches 15.8 percent, and the tensile strength reaches 2160 MPa; and the pitting potential Epit can reach 0.20VSCE。
Description
Technical Field
The invention relates to ultra-low carbon high-performance maraging stainless steel and a preparation method thereof, belonging to the field of martensitic stainless steel.
Background
The martensite precipitation strengthened stainless steel is a new steel bell developed in the 60's of the 20 th century. The corrosion-resistant steel has the strength of the maraging strengthening steel and the corrosion resistance of the stainless steel. Due to excellent comprehensive mechanical properties, the material is often used in the fields of critical high-end equipment such as aviation, aerospace, navigation and the like.
The main reason why the martensite precipitation strengthening stainless steel can realize the ultrahigh strength is that the martensite phase transformation strengthening and the aged precipitation strengthening are superposed; the main reason for the corrosion resistance is that the addition of Cr and Mo forms a passive film on the surface, thereby providing the corrosion resistance. Table 1 shows the composition and properties of commercially available high-strength stainless steels. It can be seen that the current high-strength stainless steel has the following problems: firstly, the ductility and toughness are poorer when the strength is higher; secondly, when the mechanical property is excellent, the corrosion resistance is poor; it is difficult to unify the strength, ductility and toughness and corrosion resistance to obtain excellent comprehensive performance. Therefore, how to improve the obdurability of the stainless steel on the premise of ensuring the corrosion resistance of the stainless steel so as to meet higher requirements of engineering application on the comprehensive performance of the stainless steel is a research hotspot and difficulty in the field of stainless steel, and therefore, the research on novel ultrahigh-strength maraging stainless steel with independent intellectual property rights is urgent.
Table 1 commercial high strength stainless steel compositions and properties thereof currently on the market
The high content of Co ensures that the mechanical property of the high-strength stainless steel is excellent. When the content of Co is low or 0, the comprehensive mechanical property performance is low. The Co is added into the high-strength stainless steel to form a double-edged sword, the Co can reduce the solubility of Ti and Mo in the martensite matrix, and a precipitate phase containing Mo or Ti is formed, so that the strength is improved. Meanwhile, Co can also hinder the recovery of dislocation, reduce the size of a precipitated phase and stabilize a martensite matrix, can generate higher secondary hardening, and is a guarantee for better mechanical properties such as strength and the like. Therefore, to obtain excellent mechanical properties, a large amount of Co element is inevitably added. However, the spinodal decomposition of Cr is promoted by the addition of Co to the martensitic stainless steel, and the higher the content of Co, the greater the spinodal decomposition degree of Cr, which lowers the pitting corrosion resistance of the substrate. Therefore, an appropriate amount of Co is added. The innovation of the invention is that nano-sized lath martensite with high dislocation density is obtained through the alloy components, the double vacuum melting process and the thermal mechanical treatment process, and the nano-phase precipitation kinetics, the inverse transformed austenite nucleation and growth kinetics are improved, so that the cooperative control strengthening and the inverse transformed austenite toughening of the nano-phase precipitation and the martensite matrix are realized, and the improvement of the mechanical property is realized. Meanwhile, on one hand, carbon strengthening is replaced by nano-phase strengthening, so that the carbon content is greatly reduced, and on the other hand, the pitting corrosion resistance equivalent of the alloy is improved through component optimization. The extremely low carbon content and high pitting corrosion resistance equivalent design ensures excellent corrosion resistance of the stainless steel of the present invention. Therefore, compared with the existing stainless steel, the mechanical property and the corrosion resistance of the stainless steel are improved.
The patent application of the invention with the publication number of CN 106906429A discloses an ultrahigh-strength martensitic stainless steel and a preparation method thereof, wherein the stainless steel comprises (by mass percent) 0.10-0.25% of C, 11.0-17.0% of Cr, 0.5-2.0% of Mn, 1.1-3.0% of Si, 0.1-4.0% of Ni, 0.1-0.3% of Cu, less than or equal to 0.02% of P, less than or equal to 0.02% of S, and the balance of iron and inevitable impurity elements; the yield strength is 1300MPa, the tensile strength is 1600MPa, and the plasticity is 16%. The invention patent application with publication number CN103695796A discloses a high-strength high-toughness stainless steel and a manufacturing method thereof, wherein the stainless steel comprises 0.13-0.19% of C, less than or equal to 0.6% of Si, 0.6-1.0% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 15.0-16.0% of Cr, 3.0-4.0% of Ni, 1.4-1.9% of Mo, 1.0-2.0% of Cu, 0.7-1.2% of W, 0.0-0.6% of V, 0.05-0.12% of N, and the balance of Fe and inevitable impurities; the yield strength is 690-1388 MPa, the tensile strength is 1200-1670 MPa, and the plasticity is more than 10%. The invention patent application with publication number CN 103614649A discloses a high-strength high-toughness high-plasticity martensitic stainless steel and a preparation method thereof, wherein the stainless steel comprises (by mass percent) 0.15-0.40% of C, 0-0.12% of N, 0.2-2.5% of Si, 0.4-3% of Mn, less than or equal to 0.02% of P, less than or equal to 0.02% of S, 13.0-17.0% of Cr, 0-5.0% of Ni, 0-2.0% of Mo, 0-0.3% of V, 0-0.2% of Nb, 0-0.05% of Ti, 0-0.08% of Al, and the balance of Fe and inevitable impurities; the yield strength is 650-1250 MPa, the tensile strength is 1300-1800 MPa, and the plasticity is 16-25%. Although the three technical schemes have the performance of high-strength stainless steel, the high carbon seriously deteriorates the corrosion resistance due to the high carbon content, the existing size, form and distribution of carbide in a matrix are difficult to control, and the mechanical property is seriously deteriorated when the size is large and appears on a grain boundary.
The invention patent application with publication number CN 110358983A discloses a precipitation hardening martensitic stainless steel and a preparation method thereof, wherein the stainless steel comprises the following specific chemical components (by mass percent), 0.14-0.20% of C, 13.0-16.0% of Cr, 0.5-2.0% of Ni, 12.0-15.0% of Co, 4.5-5.5% of Mo, 0.4-0.6% of V, less than or equal to 0.1% of Si, less than or equal to 0.5% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, less than or equal to 0.10% of N, and the balance of Fe; the tensile strength is 1840-1870 MPa, the yield strength is 780-820 MPa, and the elongation is 12.5-14.0%. Although the precipitation hardening martensitic stainless steel is obtained by the technical scheme, the raw material cost is high due to the high addition of Co; the content of Co is increased, so that the scroll of Cr can be decomposed, a Cr-poor area and a Cr-rich area are further generated, and the corrosion resistance of the Cr-poor area and the Cr-rich area is reduced; the carbon content is also high, the corrosion resistance is seriously deteriorated by high carbon, the existing size, form and distribution of carbide in a matrix are difficult to control, and the mechanical property is seriously deteriorated when the size is large and appears on a grain boundary; the production process needs two times of aging and two times of deep cooling treatment, the process is complex, and the strength is still far lower than that of the invention under the condition that the carbon content is obviously higher than that of the invention.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems of complex preparation process, low corrosion resistance and mechanical property and the like of the existing ultrahigh-strength stainless steel, the invention provides the maraging stainless steel with ultralow carbon and high performance and a preparation method thereof.
The technical scheme is as follows: the invention relates to an ultra-low carbon high performance maraging stainless steel and a preparation method thereof, wherein the stainless steel comprises the following components: the alloy material comprises, by mass, 2.0-4.0% of Co, 7.0-9.0% of Ni, 11.0-15.0% of Cr, 0.3-2.0% of Ti, 3.0-6.0% of Mo, 0.08-1.0% of Mn, 0.08-0.3% of Si, less than or equal to 0.01% of C, less than or equal to 0.003% of P, less than or equal to 0.003% of S, and the balance of Fe.
The invention principle and the component design of the ultra-low carbon high-performance maraging stainless steel are as follows:
the invention principle is as follows: the stainless steel of the invention is not reinforced by carbon, the carbon is controlled at a very low level, and the toughness and the corrosion resistance of the stainless steel can be simultaneously improved. But the greatest problem with ultra-low carbon is low strength. The nano lath structures with different dislocation densities in the martensite matrix are controlled through the composition design and the creative thermal mechanical treatment scheme, the quenching and cooling of ice water can lead the martensite laths to be fine and the dislocation density to be increased, the fine martensite laths can provide nucleation sites for precipitation phase and membranous metastable reverse transformed austenite, meanwhile, the higher dislocation density increases element distribution channels for the reverse transformed austenite, the reverse transformed austenite generated by the method is easier to generate TRIP (transformation Induced plasticity) effect when being loaded, and the plasticity and the strength are obviously improved by utilizing the unique nano phase strengthening and TRIP effect. The precipitated phase of the invention is formed by adjusting the contents of Ni, Ti, Mo and Si to form Mo-rich R' phase and Ni3The strength of the (Ti, Mo) nano-phase is improved by cooperative strengthening, the two nano-strengthening phases are mainly represented by a cooperative precipitation relation, Ni-Ti-Mo-Si clusters which are fine in size and distributed in a dispersion manner are formed in the martensite lath or on dislocation at the early stage of aging, and the aging time is prolongedThe prolonged Mo and Si are gradually removed from the cluster, and the nano-sized Ni is formed first3The (Ti, Mo) strengthening phase, after a period of heat preservation, Mo and Si are completely removed from Ni3The surface of Ti forms a Mo-rich R' phase to wrap it, Ni3The growth of Ti is inhibited, the fine dispersion of precipitated phase is ensured, and the newly formed Mo-rich R' phase and Ni3Together, Ti provides the matrix with higher strength. The fine dispersed precipitated phases can be used as dislocation sources in the plastic deformation process, so that the dislocation is continuously added in the deformation process, and the plasticity is further increased. Simultaneously, Ni of DO24 structure is dispersed and distributed3The reverse transformed austenite with a film-shaped structure and dispersed distribution can be formed by the climb of edge dislocation and the diffusion of Fe atoms by taking coherent strain energy of a matrix interface as driving force of Ti, the energy required by reverse austenite nuclei is greatly reduced by high dislocation density and fine martensite laths, and a diffusion channel is provided for the growth of the reverse austenite by high dislocation density. The invention has the important innovation that the content of the expensive alloying element Co is greatly reduced, and the cost can be obviously reduced while the corrosion resistance is improved. Although the low Co content design reduces the forming capability of the Ni-Ti cluster, the precipitation of the Mo-rich R' phase and the metastable state film-like reverse austenite is realized through creative components and process optimization design, so that the strength and the ductility and toughness are remarkably improved. According to the invention, on the basis of innovation in the aspects of a strengthening mechanism, corresponding components, thermal mechanical treatment design, thermal treatment and the like, the mechanical property and the corrosion resistance are effectively improved on the basis of simple and controllable process and cost reduction.
The basis of component design is as follows: co is one of important elements to be considered in the invention, can improve Ms point and ensure that the matrix is martensite, but 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, form precipitates containing Mo or Ti, and further improve the strength. Co also hinders the recovery of dislocations, reduces the size of the precipitate phase and the matrix, and can produce a higher secondary hardening. However, addition of Co to martensitic stainless steel promotes spinodal decomposition of Cr, and the higher the content of Co, the greater the spinodal decomposition degree of Cr, which lowers the pitting corrosion resistance of the substrate. Meanwhile, the Co element is expensive, the content of Co is high, and the cost of the raw materials of the ultrahigh-strength stainless steel is high. Comprehensively considering that the mass percentage of Co is controlled to be 2.0-6.0%.
Ni is an important element for forming intermetallic compounds, and is formed by forming B2-Ni (Ti, Mn) and eta-Ni in the early stage3(Ti, Mo) for strengthening matrix, eta-Ni3(Ti, Mo) is also the core of the Mo-R' rich phase nucleation; in addition, Ni can strengthen the matrix and provide certain ductility and toughness for the stainless steel; ni also improves the hardenability of martensite. Meanwhile, Ni is also a main element for forming reverse austenite, but too high content of Ni promotes the formation of residual austenite in the matrix, thereby affecting the strength of the stainless steel. Comprehensively considering that the mass percentage of Ni is controlled to be 7.0-9.0%.
Mo is an important precipitation strengthening element. Mo is formed as Mo-R' rich phase and Ni3One of the main elements of (Ti, Mo). The Mo-R' rich phase is formed after long-time aging and is wrapped by Ni3Ti forms a core-shell structure with fine dispersion distribution, and the strength can be effectively improved. Mo is also an effective corrosion-resistant element, and the corrosion resistance of the material can be obviously improved by adding Mo. Meanwhile, Mo is also a forming element of ferrite, and the excessive content of Mo increases the precipitation tendency of delta ferrite, so that the content of Mo is increased, and the performance of the material is deteriorated. The mass percentage of Mo is comprehensively considered to be controlled to be 3.0-6.0%.
Cr is an important element in stainless steel. In order to ensure the corrosion resistance of the stainless steel, the mass percentage of the stainless steel is generally more than 10 percent. However, Cr is a ferrite-forming element, and the content thereof is too high, so that the content of delta ferrite in the matrix is increased, and the toughness and corrosion resistance of the material are affected. Therefore, the mass percentage of Cr is controlled to be 11.0-15.0%.
Si is one of important elements of the novel stainless steel, Si is one of main forming elements of the Mo-R 'rich phase, and the addition of Si can effectively promote the formation of the Mo-R' rich phase; si can also effectively inhibit the precipitation and growth of carbides in the martensite matrix in the tempering process, thereby preventing the occurrence of a Cr-poor area to reduce the corrosion resistance; however, too high a content of Si may seriously deteriorate the plasticity of the material. Comprehensively considering, the mass percentage of Si is controlled to be 0.08-0.30%.
Ti is a main strengthening phase forming element, which can form Ni-Ti clusters at the initial stage in preparation for the subsequent precipitation of a strengthening phase. When the content of Ti is too large, the tendency of precipitation of the precipitated phase at the boundary of the martensite lath becomes large, and when the content of the precipitated phase at the boundary of the martensite lath is too large, the precipitated phase is liable to develop into a crack source and propagate along the interface of the martensite lath, thereby initiating a quasi-cleavage crack. Comprehensively considering, the mass percentage of Ti should be controlled to be 1.0-2.0%.
Mn is mainly participated in the precipitation of nano-phase to form Ni (Mn, Ti, Mo) intermetallic compounds, thereby replacing Ti and Mo elements in a small amount and reducing the cost. Mn is a main element affecting reverse austenite. However, too high Mn content causes serious segregation of the steel slab, large thermal stress and structural stress, and deterioration of weldability. Comprehensively considering, the mass percentage of Mn should be controlled to be 0.08-1.0%.
C exists in the matrix as an impurity element in the stainless steel, and when the content of C is too high, MX or M is formed23C6Form carbides (M ═ Cr, Ti) which seriously retard the formation of reverse austenite, offset the gain of high dislocation density by cold rolling, and seriously deteriorate the toughness and corrosion resistance of steel when the size is too large, so that the C content is strictly controlled to 0.01% or less; p and S are impurity elements, and the performance of the stainless steel is seriously damaged by increasing the content of P and S, so the content is strictly controlled.
The invention relates to an ultra-low carbon high performance maraging stainless steel and a preparation method thereof, comprising the following steps:
(1) proportioning alloy elements;
(2) carrying out vacuum smelting on the electrode by using a vacuum induction smelting furnace;
(3) vacuum consumable remelting;
(4) carrying out high-temperature flame equalizing treatment;
(5) forging or hot rolling cogging;
(6) and (6) heat treatment.
After the alloy is smelted, cooling and forming to room temperature, cutting off a riser, removing the skin, and then entering a thermal mechanical treatment process. The structure with uniform and fine size can be obtained by hot rolling and cogging and then heat treatment, so that the steel has higher strength, toughness and corrosion resistance.
In the step (1), the alloy elements are proportioned, according to the mass percentage of each element in the stainless steel, metal chromium, metal nickel, metal manganese, metal molybdenum, metal cobalt, metal titanium and iron silicon are selected, and the balance is pure iron and inevitable impurities.
In the step (2), the vacuum induction smelting furnace is adopted for vacuum smelting of the electrode, high vacuum smelting is adopted in the whole process, and the vacuum degree is below 0.1 Pa; adding pure iron, metallic nickel, metallic molybdenum and metallic cobalt into the furnace, adding metallic chromium and metallic titanium into the furnace from a high-level bin, and adding industrial silicon and metallic manganese into the furnace from an alloy bin. Adding materials along with the furnace, melting down, adding high-level bin metal, completely melting, performing deoxidation alloying, and finally adding alloy bin metal. In the smelting period, 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 in front of the furnace to analyze smelting components, and then adjusting the components according to the target designed by the claim 1; and after the target components are adjusted, pouring at the temperature of 1530-1550 ℃, and carrying out ordinary heat preservation on a riser.
In the step (3), the vacuum consumable remelting is carried out at a melting speed of 100-260 Kg/h, and the vacuum degree is kept at 10 in the remelting process-2Pa and below.
In the step (4), the high-temperature homogenizing treatment is carried out, heating is carried out in air, vacuum or protective atmosphere, the heating mode is furnace heating, the heating rate is 100-180 ℃/h, heat preservation is carried out for 4-8 h at 600-900 ℃, then the temperature is raised to 1100-1300 ℃, heat preservation is carried out for 20-50 h, and furnace cooling, air cooling or oil cooling is carried out until the room temperature is reached.
In the step (5), the forging or rolling may be performed by casting or rolling into a square ingot or a round ingot; the technological conditions of forging or hot rolling cogging are as follows: heating the casting blank to 1100-1300 ℃, preserving heat for 10-24 h, and then discharging for rolling; the forging or hot rolling starting temperature is more than or equal to 1100 ℃, the finish forging or rolling temperature is more than or equal to 950 ℃, the total hot rolling load of the plate is not less than 50%, the forging ratio of a forging billet is not less than 6, and after the forging or rolling deformation, the plate is cooled in air or water to the room temperature.
In the step (6), the heat treatment process includes: twice high-temperature quenching treatment, deep cooling treatment and bipolar aging treatment. .
Further, in the step (6), the two high-temperature quenching processes are as follows: the temperature of the first high-temperature quenching is kept at 900-1100 ℃, the temperature keeping time is 10-60 min later, and then the quenching and cooling are carried out in an ice-water mixture at 0 ℃; and performing heat preservation at 1050-1200 ℃ for the second high-temperature quenching, wherein the heat preservation time is 60-120 min, and then quenching and cooling in an ice-water mixture at 0 ℃.
Further, in the step (6), the cryogenic treatment process comprises the following steps: and (4) performing liquid nitrogen cryogenic treatment for 4-10 hours, and recovering to room temperature after cryogenic treatment.
Further, in step (6), the bipolar aging treatment: the temperature of the first time aging treatment is 450-600 ℃, the aging time is 0.5-500h, the air cooling or quenching is carried out to the room temperature, the temperature of the second time aging treatment is 650-900 ℃, and the air cooling or quenching is carried out for 1-60min to the room temperature.
Has the advantages that: compared with the prior art, the invention has the advantages that:
(1) compared with other high-strength stainless steel, the high-strength stainless steel has the advantages that the content of noble metal is low, and the cost of raw materials is low;
(2) the stainless steel of the present invention contains very little or no carbon;
(3) the preparation method of the ultra-low carbon high performance maraging stainless steel is simple, the high strength stainless steel can be obtained through different heat treatment processes, the process controllability is strong, and the industrial production is easy to realize. Finally, the stainless steel with good corrosion resistance and excellent mechanical property is obtained, the elongation of the martensitic stainless steel reaches 15.8%, and the tensile strength reaches 2160 MPa; and the pitting potential Epit can reach 0.20VSCE。
Drawings
FIG. 1 metallographic morphology after aging of example 1;
FIG. 2 engineering stress-strain curve of example 2;
figure 3 XRD curves after high temperature quenching and aging treatment of example 3.
Detailed Description
The ultra-low carbon high performance maraging stainless steel and the method for manufacturing the same according to the present invention will be further explained and illustrated with reference to the accompanying drawings and the specific examples, which, however, should not be construed to unduly limit the technical solutions of the present invention.
Example 1
Selecting pure iron, chromium metal, nickel metal, manganese metal, molybdenum metal, cobalt metal, titanium metal and iron silicon as raw materials, wherein the stainless steel comprises the following components in percentage by mass: co 3.0, Cr 11.0, Mn 0.08, Mo 6.0, Ni 9.0, Si 0.08, Ti 1.5, and the balance Fe.
And preparing a billet by adopting vacuum melting in the whole process.
And (3) carrying out high-temperature flame equalizing treatment, heating in air in a mode of heating along with a furnace, keeping the temperature at 600 ℃ for 4h at a heating rate of 100 ℃/h, then heating to 1100 ℃ and keeping the temperature for 20h, and cooling to room temperature along with the furnace.
The technological conditions of hot rolling and cogging are as follows: heating the casting blank to 1100 ℃, preserving heat for 10 hours, and then discharging and rolling; the starting temperature of hot rolling is 1100 +/-20 ℃, the finishing temperature is more than or equal to 950 ℃, the total hot rolling amount of the plate is 50%, and the plate is cooled to room temperature by water.
Quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the first high-temperature quenching treatment is 950 ℃ and the heat preservation time is 10min, and quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the second high-temperature quenching treatment is 1200 ℃ and the heat preservation time is 60 min; after the two high-temperature quenching treatments, performing liquid nitrogen cryogenic treatment for 6 hours, and recovering to room temperature after the cryogenic treatment; and (3) after cryogenic treatment, performing bipolar aging treatment, wherein the first aging temperature is 480 ℃, the aging time is 10h, air cooling is performed at room temperature, the second aging temperature is 650 ℃, the heat preservation time is 5min, and the air cooling is performed to the room temperature.
Mechanical Properties of example 1As shown in Table 1, the average hardness was 508.1HV, the yield strength was 1750MPa, the tensile strength was 2080MPa, the elongation was 15.8%, and the pitting potential was 0.17VSCE. FIG. 1 is the metallographic morphology after aging of example 1, which is a typical martensitic hierarchical structure.
Example 2
Selecting pure iron, chromium metal, nickel metal, manganese metal, molybdenum metal, cobalt metal, titanium metal and iron silicon as raw materials, wherein the stainless steel comprises the following components in percentage by mass: co 2.0, Cr 13.0, Mn 0.8, Mo 4.0, Ni 7.0, Si 0.3, Ti 2.0, and the balance Fe.
And preparing a billet by adopting vacuum melting in the whole process.
And (3) carrying out high-temperature flame equalizing treatment, heating in air in a mode of heating along with a furnace, keeping the temperature at 900 ℃ for 7h at the heating rate of 180 ℃/h, then heating to 1250 ℃, keeping the temperature for 50h, and cooling to room temperature along with the furnace.
The technological conditions of hot rolling and cogging are as follows: heating the casting blank to 1200 ℃, preserving heat for 20 hours, and then discharging and rolling; the starting temperature of hot rolling is 1150 +/-20 ℃, the finishing temperature is more than or equal to 950 ℃, the total hot rolling amount of the plate is 60 percent, and the plate is cooled to room temperature by water.
Quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the first high-temperature quenching treatment is 900 ℃ and the heat preservation time is 20min, and quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the second high-temperature quenching treatment is 1100 ℃ and the heat preservation time is 120 min; after the two high-temperature quenching treatments, performing liquid nitrogen cryogenic treatment for 10 hours, and recovering to room temperature after the cryogenic treatment; after the cryogenic treatment, bipolar aging treatment is carried out, wherein the first aging temperature is 600 ℃, the aging time is 5h, the room temperature is cooled in air, the second aging temperature is 650 ℃, the heat preservation time is 5min, and the room temperature is cooled in air.
The mechanical properties of example 2 are shown in Table 1, the average hardness is 510.6HV, the yield strength is 1860MPa, the tensile strength is 2160MPa, the elongation is 14.1%, and the pitting potential is 0.20VSCE. FIG. 2 is an engineering stress-strain curve of example 2.
Example 3
Selecting pure iron, chromium metal, nickel metal, manganese metal, molybdenum metal, cobalt metal, titanium metal and iron silicon as raw materials, wherein the stainless steel comprises the following components in percentage by mass: co 4.0, Cr 12.0, Mn 0.5, Mo 6.0, Ni 8.0, Si 0.2, Ti 1.0, and the balance Fe.
And preparing a billet by adopting vacuum melting in the whole process.
And (3) carrying out high-temperature flame equalizing treatment, heating in air in a mode of furnace heating, keeping the temperature at 750 ℃ for 5h at the heating rate of 180 ℃/h, then heating to 1200 ℃ and keeping the temperature for 30h, and cooling to room temperature in a furnace.
The technological conditions of hot rolling and cogging are as follows: heating the casting blank to 1200 ℃, preserving heat for 20 hours, and then discharging and rolling; the starting temperature of hot rolling is 1150 +/-20 ℃, the finishing temperature is more than or equal to 950 ℃, the total hot rolling amount of the plate is 70 percent, and the plate is cooled to room temperature by water.
Quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the first high-temperature quenching treatment is 900 ℃ and the heat preservation time is 10min, and quenching and cooling the plate in the 0 ℃ ice-water mixture after the temperature of the second high-temperature quenching treatment is 1050 ℃ and the heat preservation time is 120 min; after the two high-temperature quenching treatments, performing liquid nitrogen cryogenic treatment for 4 hours, and recovering to room temperature after the cryogenic treatment; after the cryogenic treatment, bipolar aging treatment is carried out, wherein the first aging temperature is 450 ℃, the aging time is 20h, the room temperature is cooled in air, the second aging temperature is 650 ℃, the heat preservation time is 10min, and the room temperature is cooled in air.
The mechanical properties of example 3 are shown in Table 1, the average hardness is 511.7HV, the yield strength is 1810MPa, the tensile strength is 2090MPa, the elongation is 11.7%, and the pitting potential is 0.12VSCE. FIG. 3 is an XRD pattern after the high temperature quenching and the aging treatment in example 3, and it can be seen that reverse austenite is precipitated after the aging treatment.
The test methods for the corrosion resistance, hardness and tensile mechanical properties of the ultra-low carbon high performance maraging stainless steel in the above examples are as follows.
(1) Hardness: the hardness test was carried out using an HVS-50 Vickers hardness tester with a load of 1Kg, and 5 points were hit and averaged, as shown in Table 1.
(2) Tensile mechanical properties: an electronic universal tester is adopted for carrying out a tensile test, a rectangular sample with the nominal section size of 2-3 multiplied by 4 multiplied by 20.6mm is taken, and the average values of the tensile strength, the yield strength and the elongation of 3 samples treated in the same way are listed in table 1.
(3) Corrosion resistance
The molded product is processed into a specification of 10mm x 2mm, and is exposed by 1cm after being packaged by epoxy resin2And (4) performing a test, polishing the surface to 2000# with sand paper, scrubbing with alcohol to remove oil stains, cleaning with deionized water, and drying for later use. The experimental solution was 0.1MNa2SO4+ xnacal (PH 3) experimental temperature 25 ℃. Electrochemical testing was performed using the CHI660E electrochemical workstation. A common three-electrode system is adopted for carrying out electrochemical experiments, the experiment of ultrahigh-strength stainless steel is taken as a working electrode, a Pt sheet is taken as an auxiliary electrode, and a Saturated Calomel Electrode (SCE) is taken as a reference electrode. Prior to the electrochemical experiments, the pattern was first applied with-1.2VSECThe applied potential of (2) is polarized for 5min at constant potential so as to remove the oxide film formed on the surface of the sample in the air. The system was stable for 30min and recording was started. The potentiodynamic polarization test has a scanning rate of 0.5mV/S and a scanning potential area of-0.3V (vs. open circuit potential E)OC) 1.5V (vs. reference electrode potential E)R) The test was stopped after the current change was stable. The average value was obtained after 3 measurements and is shown in Table 1.
TABLE 1 compositions and hardness, tensile properties and pitting points of the examples
Note: the contents of C, P, S and the like in the examples in Table 1 correspond to the elemental composition of stainless steel
In summary, the following steps: the invention discloses an ultra-low carbon high performance maraging stainless steel and a preparation method thereof, wherein the stainless steel comprises the following components: the alloy material comprises, by mass, 2.0-4.0% of Co, 7.0-9.0% of Ni, 11.0-15.0% of Cr, 0.3-2.0% of Ti, 3.0-6.0% of Mo, 0.08-1.0% of Mn, 0.08-0.3% of Si, less than or equal to 0.01% of C, less than or equal to 0.003% of P, less than or equal to 0.003% of S, and the balance of Fe. The preparation method of the ultra-low carbon high-performance maraging stainless steel comprises the following steps: (1) alloy element proportioning (2) carrying out vacuum smelting on an electrode in a vacuum induction smelting furnace; (3) vacuum consumable remelting; (4)carrying out high-temperature flame equalizing treatment; (5) forging or hot rolling cogging; (6) and (6) heat treatment. The stainless steel of the invention adjusts and controls the size, volume fraction and dispersion of precipitated phase and reverse transformed austenite by optimizing alloy elements, double vacuum melting and corresponding thermal mechanical treatment process, thereby obtaining the stainless steel with excellent performance. The elongation of the stainless steel reaches 15.8 percent, and the tensile strength reaches 2160 MPa; and the pitting potential Epit can reach 0.20VSCE. The ultra-low carbon high performance maraging stainless steel can be used for key bearing structures such as aircraft engine hanging bolts, marine platform crane hook pins and the like.
Claims (10)
1. An ultra-low carbon high performance maraging stainless steel, characterized in that the composition of the stainless steel is as follows: according to mass percent, Co is 2.0-4.0%, Ni is 7.0-9.0%, Cr is 11.0-15.0%, Ti is 0.3-2.0%, Mo is 3.0-6.0%, Mn is 0.08-1.0%, Si is 0.08-0.3%, C is less than or equal to 0.01%, 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 comprises the following steps: (1) proportioning alloy elements; (2) carrying out vacuum smelting on the electrode by using a vacuum induction smelting furnace; (3) vacuum consumable remelting; (4) carrying out high-temperature flame equalizing treatment; (5) forging or hot rolling cogging; (6) and (6) heat treatment.
2. A method of manufacturing an ultra low carbon high performance maraging stainless steel according to claim 1, comprising the steps of:
(1) proportioning alloy elements;
(2) carrying out vacuum smelting on the electrode by using a vacuum induction smelting furnace;
(3) vacuum consumable remelting;
(4) carrying out high-temperature flame equalizing treatment;
(5) forging or hot rolling cogging;
(6) and (6) heat treatment.
3. The method for preparing the ultra-low carbon high performance maraging stainless steel according to claim 2, wherein in the step (1), the alloy element is selected from chromium metal, nickel metal, manganese metal, molybdenum metal, cobalt metal, titanium metal, iron silicon metal, and the balance of pure iron and unavoidable impurities according to the mass percent of each element in the stainless steel.
4. The method for preparing the ultra-low carbon high performance maraging stainless steel according to claim 2, wherein in the step (2), the electrode is smelted in vacuum by using a vacuum induction smelting furnace, high vacuum smelting is adopted in the whole process, and the vacuum degree is below 0.1 Pa; adding pure iron, metallic nickel, metallic molybdenum and metallic cobalt into a furnace, adding metallic chromium and metallic titanium into a high-level stock bin, adding industrial silicon and metallic manganese into an alloy stock bin, adding the high-level stock bin metal into the furnace after the industrial silicon and the metallic manganese are melted down, performing deoxidation alloying after the industrial silicon and the metallic manganese are completely melted, and finally adding the alloy stock bin metal into the furnace; in the smelting period, 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 in front of the furnace, analyzing smelting components, and then adjusting the components; after the target components are adjusted, pouring is carried out at the temperature of 1530-1550 ℃, and ordinary heat preservation is adopted for a riser.
5. The method for preparing the ultra-low carbon high performance maraging stainless steel according to claim 2, wherein in the step (3), the vacuum consumable remelting is carried out at a melting speed of 100-260 Kg/h, and the vacuum degree is kept at 10 during the remelting process-2Pa and below.
6. The preparation method of the ultra-low carbon high performance maraging stainless steel according to claim 2, wherein in the step (4), the high temperature homogenizing treatment is performed, heating is performed in air, vacuum or protective atmosphere, the heating mode is furnace heating, the heating rate is 100-180 ℃/h, the heat preservation is performed for 4-8 h at 600-900 ℃, then the temperature is increased to 1100-1300 ℃ and the heat preservation is performed for 20-50 h, and furnace cooling, air cooling or oil cooling is performed to the room temperature.
7. The method of preparing an ultra-low carbon high performance maraging stainless steel according to claim 2, wherein in the step (5), the forging or rolling may be cast or rolled into a square or round ingot in size; the technological conditions of forging or hot rolling cogging are as follows: heating the casting blank to 1100-1300 ℃, preserving heat for 10-24 h, and then discharging for rolling; the forging or hot rolling starting temperature is more than or equal to 1100 ℃, the finish forging or rolling temperature is more than or equal to 950 ℃, the total hot rolling load of the plate is not less than 50%, the forging ratio of a forging billet is not less than 6, and after the forging or rolling deformation, the plate is cooled in air or water to the room temperature.
8. The method of manufacturing an ultra low carbon high performance maraging stainless steel according to claim 2, wherein in step (6), the heat treatment process comprises: performing high-temperature quenching treatment twice, cryogenic treatment and bipolar aging treatment;
the temperature of the first time aging treatment is 450-600 ℃, the aging time is 0.5-500h, the temperature of the second time aging treatment is 650-900 ℃, and the temperature of the second time aging treatment is 1-60 min.
9. The preparation method of the ultra-low carbon high performance maraging stainless steel as claimed in claim 8, wherein the first high temperature quenching temperature is maintained at 900-1100 ℃, and the temperature is maintained for 10-60 min and then quenched and cooled in an ice-water mixture at 0 ℃; and performing heat preservation at 1050-1200 ℃ for the second high-temperature quenching, wherein the heat preservation time is 60-120 min, and then quenching and cooling in an ice-water mixture at 0 ℃.
10. The method for preparing the ultra-low carbon high performance maraging stainless steel according to claim 8, wherein liquid nitrogen is used for cryogenic treatment for 4-10 hours, and the temperature is returned to room temperature after cryogenic treatment.
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