Non-quenched and tempered 2200MPa-grade low-cost ultrahigh-toughness steel and preparation method thereof

Abstract

The invention relates to the technical field of alloys, and discloses non-quenched and tempered 2200MPa-grade low-cost ultrahigh-toughness steel and a preparation method thereof. The non-quenched and tempered 2200MPa-grade low-cost ultrahigh-toughness steel is prepared from the following chemical components in percentage by mass: 0.4 percent to 0.6 percent of C, 1.0 percent to 3.0 percent of Si, 0.5 percent to 3 percent of Mn, 0.05 percent to 0.2 percent of V, 1.9 percent to 4.0 percent of Ni, 0.03 percent to 0.05 percent of Nb, 0.2 percent to 0.4 percent of Mo and 0.7 percent to 3 percent of Cr. The original austenite of the ultrahigh-toughness steel is equiaxial, and the grain equivalent circle size ranges from 10 micrometers to 36 micrometers. The microstructure of the ultrahigh-toughness steel comprises martensite, and the average grain size of the martensite is 0.5-0.8 [mu] m. The non-quenched and tempered 2200MPa-grade low-cost ultrahigh-toughness steel disclosed by the invention has the advantages of high toughness, high strength and low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloys, and particularly relates to a non-quenched and tempered 2200MPa-grade low-cost super-high toughness steel and a preparation method thereof. BACKGROUND

[0002] At present, the super-high strength steel with a tensile strength of 2200MPa (2.2GPa) is a core and key material for realizing structural lightweight and service safety. For example, it can be used for structural parts or equipment such as protective armored vehicles, battery package shells, and civilian automobile bump beams, so as to improve the performance of the structural parts or equipment.

[0003] In a low-alloy system, although the cost is relatively low, the technical route mainly aims at pursuing super-high strength. For example, the mainstream commercial 300M steel has a strength of about 1920MPa after hot stamping forming, which is far lower than the strength requirement of 2.2GPa. Moreover, the room temperature V-notch impact is less than 30J / cm 2 , and the toughness is limited.

[0004] In a high-alloy system, a large amount of expensive cobalt (Co), tungsten (W) and other elements are added to improve the strength, but the cost is relatively high. For example, the maraging steel can reach a strength of more than 2000MPa by adding a large amount of expensive cobalt (Co), tungsten (W) and other elements, but the cost is high. Moreover, the room temperature V-notch impact of the maraging steel is less than 35J / cm 2 , and the toughness is insufficient.

[0005] In addition, the maraging steel introduces a low volume fraction (10% to 30%) of metastable austenite in the ultra-fine grain lath martensite by annealing at the critical zone temperature, so as to obtain a martensite-austenite dual-phase structure, so as to improve the toughness of the maraging steel. However, due to the excessive austenite content or the large grain size, the strength of the maraging steel is reduced, and it is difficult to reach a tensile strength of 2200MPa.

[0006] Therefore, the 2200MPa-grade super-high strength steel in the related art is difficult to realize high toughness, high strength and low cost. SUMMARY

[0007] The present application aims to at least solve one of the technical problems in the related art.

[0008] Therefore, a first aspect of the present application provides a non-quenched and tempered 2200MPa-grade low-cost super-high toughness steel.

[0009] A second aspect of the present application provides a preparation method of the non-quenched and tempered 2200MPa-grade low-cost super-high toughness steel.

[0010] Therefore, according to a first aspect of the present application, a non-quenched 2200 MPa grade low-cost super-high toughness steel is provided. The chemical composition of the non-quenched 2200 MPa grade low-cost super-high toughness steel includes, in terms of mass percentage, C: 0.4% to 0.6%, Si: 1.0% to 3.0%, Mn: 0.5% to 3%, V: 0.05% to 0.2%, Ni: 1.9% to 4.0%, Nb: 0.03% to 0.05%, Mo: 0.2% to 0.4%, Cr: 0.7% to 3%, and the balance of Fe and inevitable impurities. The original austenite of the non-quenched 2200 MPa grade low-cost super-high toughness steel is equiaxed, and the grain equivalent circle size of the original austenite is 10 μm to 36 μm. The microstructure of the non-quenched 2200 MPa grade low-cost super-high toughness steel includes martensite, and the average grain size of the martensite is 0.5 μm to 0.8 μm. In the process of transformation of the original austenite into the martensite, the martensite occurs intracrystalline nucleation in the grain of the original austenite.

[0011] In a possible implementation, the ratio of the length and the width of the grain of the martensite is 1.1 to 4.6.

[0012] In a possible implementation, the microstructure of the non-quenched 2200 MPa grade low-cost super-high toughness steel further includes austenite, the austenite is in the form of film, and the grain equivalent circle size of the austenite is 0.1 μm to 10 μm. In the non-quenched 2200 MPa grade low-cost super-high toughness steel, the volume fraction of the austenite is 10% to 20%, and the volume fraction of the martensite is 80% to 90%.

[0013] In a possible implementation, the tensile strength of the non-quenched 2200 MPa grade low-cost super-high toughness steel is greater than 2200 MPa, the V-notch impact toughness at room temperature is greater than 50 J / cm 2 , and the V-notch impact toughness at -60 ℃ is greater than 40 J / cm 2 .

[0014] According to a second aspect of the present application, a preparation method of a non-quenched 2200 MPa grade low-cost super-high toughness steel is provided. The method includes the following steps: preparing a cast metal according to the chemical composition and the proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel as described above; performing complete austenitization treatment on the cast metal to obtain an austenitized metal; performing multi-stage and multi-pass rotary forging on the austenitized metal to obtain a forged metal; and performing tempering and partitioning treatment on the forged metal to obtain the non-quenched 2200 MPa grade low-cost super-high toughness steel.

[0015] In a possible implementation, the step of preparing the as-cast metal according to the chemical composition and proportion of the non-quenched 2200MPa-grade low-cost ultrahigh toughness steel as described above comprises: preparing raw materials according to the chemical composition and proportion of the non-quenched 2200MPa-grade low-cost ultrahigh toughness steel as described above; smelting the raw materials to form a casting blank or an ingot to obtain the as-cast metal.

[0016] In a possible implementation, the temperature of the complete austenitizing treatment is 1050 DEG C to 1200 DEG C, and the holding time is 2h to 5h.

[0017] In a possible implementation, the step of performing multi-stage multi-pass rotary forging on the austenitized metal to obtain the forged metal comprises: performing first-stage multi-pass rotary forging on the austenitized metal, wherein the total reduction is greater than 40%, and the final forging temperature is greater than 900 DEG C; waiting for the temperature of the metal obtained after the first-stage multi-pass rotary forging, and the temperature of the waiting is 900 DEG C; performing second-stage multi-pass rotary forging on the metal obtained after the waiting, wherein the total reduction is greater than 50%, and the final forging temperature is greater than 800 DEG C; cooling the metal obtained after the second-stage multi-pass rotary forging to room temperature to obtain the forged metal.

[0018] In a possible implementation, in the step of performing multi-stage multi-pass rotary forging on the austenitized metal, the total reduction is greater than 90%; and the microstructure of the forged metal comprises austenite, and the volume fraction of the austenite is 10% to 20%. The microstructure of the forged metal further comprises martensite, and the volume fraction of the martensite is 80% to 90%.

[0019] In a possible implementation, the step of performing tempering and partitioning treatment on the forged metal to obtain the non-quenched 2200MPa-grade low-cost ultrahigh toughness steel comprises: performing tempering and partitioning treatment on the forged metal at a temperature of 150 DEG C to 350 DEG C for 40min to 180min, and cooling to room temperature to obtain the non-quenched 2200MPa-grade low-cost ultrahigh toughness steel.

[0020] The non-quenched 2200MPa-grade low-cost ultrahigh toughness steel and the preparation method thereof provided in the application can at least achieve the following technical effects:

[0021] In the present application, the chemical composition of the non-quenched 2200 MPa low-cost ultra-high toughness steel includes C: 0.4%~0.6%, Si: 1.0%~3.0%, Mn: 0.5%~3%, V: 0.05%~0.2%, Ni: 1.9%~4.0%, Nb: 0.03%~0.05%, Mo: 0.2%~0.4%, Cr: 0.7%~3%, and the rest is Fe and inevitable impurities, which belongs to a low alloy system and has low alloy cost, thereby realizing cost reduction. The original austenite of the non-quenched 2200 MPa low-cost ultra-high toughness steel is equiaxed, and the equivalent circle size of the original austenite grain is 10 um to 36 um, that is, the non-quenched 2200 MPa low-cost ultra-high toughness steel has coarse original austenite and a large number of dislocations, which can provide multiple nucleation sites. In the process of transforming the original austenite into martensite, intragranular nucleation of martensite occurs in the coarse original austenite grain, and the average grain size of the martensite grain is 0.5 um to 0.8 um, that is, finer martensite structure is obtained, and the martensite grain size is small and the orientation difference is large, so that cracks are difficult to form, the toughness and strength are improved, so that the non-quenched 2200 MPa low-cost ultra-high toughness steel has high toughness and high strength. Through the synergistic effect of various chemical components and proportions, the non-quenched 2200 MPa low-cost ultra-high toughness steel has high toughness, high strength and low cost.

[0022] The foregoing general description and the following description are only exemplary and explanatory, and are not intended to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] One or more embodiments are exemplarily illustrated by corresponding drawings, which are not intended to limit the embodiments, elements with the same reference numerals in the drawings are shown as similar elements, the drawings do not constitute a proportional limit, and wherein:

[0024] Figure 1 The flow chart of the preparation method of the non-quenched 2200 MPa low-cost ultra-high toughness steel provided by the embodiments of the present disclosure is shown in the figure;

[0025] Figure 2 The XRD energy spectrum diagram of the non-quenched 2200 MPa low-cost ultra-high toughness steel provided by Embodiment 1 is shown in the figure;

[0026] Figure 3 The original austenite reconstruction diagram of the non-quenched 2200 MPa low-cost ultra-high toughness steel provided by Embodiment 1 is shown in the figure;

[0027] Figure 4 The electron backscattering diffraction (EBSD) phase diagram of the non-quenched 2200 MPa low-cost ultra-high toughness steel provided by Embodiment 1 is shown in the figure;

[0028] Figure 5 A histogram of the frequency distribution of the martensite grain size of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel provided for Example 1;

[0029] Figure 6 A tensile engineering stress-strain curve diagram of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel provided for Example 1. DETAILED DESCRIPTION

[0030] In order to enable a more detailed understanding of the features and technical content of the embodiments of the present disclosure, the implementation of the embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings, which are for reference only and do not limit the embodiments of the present disclosure. In the following technical description, in order to facilitate explanation, a plurality of details are provided to provide a sufficient understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be simplified to facilitate the drawings.

[0031] It should be noted that the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0032] According to a first aspect of the embodiments of the present application, a non-quenched 2200 MPa grade low-cost ultra-high toughness steel is provided. The chemical composition of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel includes, in terms of mass percentage: C: 0.4% to 0.6%, Si: 1.0% to 3.0%, Mn: 0.5% to 3%, V: 0.05% to 0.2%, Ni: 1.9% to 4.0%, Nb: 0.03% to 0.05%, Mo: 0.2% to 0.4%, Cr: 0.7% to 3%, and the balance of Fe and inevitable impurities. The original austenite of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is equiaxed, and the grain equivalent circle size of the original austenite is 10 μm to 36 μm. The microstructure of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel includes martensite, and the average grain size of the martensite is 0.5 μm to 0.8 μm. In the process of transforming the original austenite into martensite, intracrystalline nucleation of the martensite occurs in the grains of the original austenite.

[0033] In the embodiments, the chemical composition of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel includes C: 0.4% to 0.6%, Si: 1.0% to 3.0%, Mn: 0.5% to 3%, V: 0.05% to 0.2%, Ni: 1.9% to 4.0%, Nb: 0.03% to 0.05%, Mo: 0.2% to 0.4%, Cr: 0.7% to 3%, and the balance of Fe and inevitable impurities, which belongs to a low alloy system, has low alloy cost, and realizes cost reduction.

[0034] In the embodiment, the original austenite of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is equiaxed, and the grain equivalent circle size of the original austenite is 10 μm to 36 μm, that is, the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has coarse original austenite and a large number of dislocations, and the coarse original austenite and the large number of dislocations can provide multiple nucleation sites. In the process of transforming the original austenite into martensite, the martensite occurs intracrystalline nucleation in the grains of the coarse original austenite, and the average grain size of the martensite is 0.5 μm to 0.8 μm, that is, a finer martensite structure is obtained, and the grain size of the martensite is small and the orientation difference is large, so that cracks are difficult to form, the toughness and strength are improved, and the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has high toughness and high strength. In the description of the embodiment of the present disclosure, the average grain size refers to the average value of the equivalent circle size of the grains, which will not be described hereinafter.

[0035] In the embodiment, through the synergistic effect of various chemical components and proportions, the grain equivalent circle size of the original austenite of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is 10 μm to 36 μm, and the average grain size of the martensite is 0.5 μm to 0.8 μm, so that in the process of transforming the original austenite into martensite, the martensite occurs intracrystalline nucleation in the grains of the original austenite, and the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has high toughness, high strength and low cost.

[0036] In some embodiments, the ratio of the length and width of the grain of the martensite is 1.1 to 4.6.

[0037] In the embodiment, the ratio of the length and width of the grain of the martensite in the microstructure of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is 1.1 to 4.6, that is, the martensite has a smaller ratio of length and width, has more slip systems, and further improves the toughness of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel.

[0038] In the embodiment, through the equiaxed original austenite and the grain equivalent circle size of the original austenite being 10 μm to 36 μm, the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has coarse original austenite and a large number of dislocations, and the coarse original austenite and the large number of dislocations can serve as numerous nucleation sites. In the process of transforming the original austenite into martensite, the martensite occurs intracrystalline nucleation in the grains of the coarse original austenite, a finer martensite structure is obtained, and the grain size of the martensite is small and the orientation difference is large, so that cracks are difficult to form, the toughness and strength are improved. In combination with the ratio of the length and width of the grain of the martensite being 1.1 to 4.6, more slip systems are provided, the toughness is further improved, and the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has high toughness, high strength and low cost.

[0039] In some embodiments, the microstructure of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel further includes austenite, the austenite is in the form of thin film, the grain equivalent circle size of the austenite is 0.1 μm to 10 μm. In the non-quenched 2200 MPa grade low-cost ultra-high toughness steel, the volume fraction of the austenite is 10% to 20%, and the volume fraction of the martensite is 80% to 90%.

[0040] In the present embodiment, the microstructure of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel at room temperature includes martensite and austenite. By the austenite being in the form of thin film, the grain equivalent circle size of the austenite being 0.1 μm to 10 μm, and the volume fraction of the austenite being 10% to 20% and the volume fraction of the martensite being 80% to 90%, the refined microstructure is achieved, the deformation is coordinated, and the strength and toughness of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel are further improved.

[0041] In some embodiments, the tensile strength of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is greater than 2200 MPa, the V-notch impact toughness at room temperature is greater than 50 J / cm 2 , and the V-notch impact toughness at -60℃ is greater than 40 J / cm 2 .

[0042] In the present embodiment, the tensile strength of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel is greater than 2200 MPa to achieve high strength. The V-notch impact toughness of the non-quenched 2200 MPa grade low-cost ultra-high toughness steel at room temperature is greater than 50 J / cm 2 , and the V-notch impact toughness at -60℃ is greater than 40 J / cm 2 to achieve high toughness. That is, the non-quenched 2200 MPa grade low-cost ultra-high toughness steel has high toughness, high strength and low cost.

[0043] In the description of the present embodiment, the temperature of room temperature includes 25℃.

[0044] In a possible implementation, provided is a non-quenched 2200 MPa grade low-cost super-high toughness steel. The chemical composition of the non-quenched 2200 MPa grade low-cost super-high toughness steel includes, in percentage by mass, C: 0.4% to 0.6%, Si: 1.0% to 3.0%, Mn: 0.5% to 3%, V: 0.05% to 0.2%, Ni: 1.9% to 4.0%, Nb: 0.03% to 0.05%, Mo: 0.2% to 0.4%, Cr: 0.7% to 3%, P≤0.015%, S≤0.008%, N≤0.004%, and the balance of Fe and inevitable impurities. The original austenite of the non-quenched 2200 MPa grade low-cost super-high toughness steel is equiaxed, and the grain equivalent circle size of the original austenite is 10 μm to 36 μm. The microstructure of the non-quenched 2200 MPa grade low-cost super-high toughness steel includes martensite, and the average grain size of the martensite is 0.5 μm to 0.8 μm. In the process of transformation of the original austenite into the martensite, intracrystalline nucleation of the martensite occurs in the grains of the original austenite.

[0045] In the embodiment, through the synergistic effect of the respective chemical components and proportions, the non-quenched 2200 MPa grade low-cost super-high toughness steel has high toughness, high strength, and low cost.

[0046] In combination Figure 1 As shown in the second aspect, the application provides a preparation method of the non-quenched 2200 MPa grade low-cost super-high toughness steel, including the following steps:

[0047] In S101, a cast state metal is prepared according to the chemical composition and proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel.

[0048] In the embodiment, the cast state metal is prepared according to the chemical composition and proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel as described above, and the alloy cost is low, so as to reduce the overall cost and provide a raw blank for subsequent processing. The chemical composition and proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel are referred to the foregoing embodiments of the application, and will not be described herein again.

[0049] In some embodiments, the step of preparing the cast state metal according to the chemical composition and proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel includes: preparing raw materials according to the chemical composition and proportion of the non-quenched 2200 MPa grade low-cost super-high toughness steel as described above. The raw materials are smelted and cast to form a casting blank or an ingot, so as to obtain the cast state metal.

[0050] In this embodiment, by preparing raw materials, the non-quenched 2200MPa grade low-cost ultra-high toughness steel is made into a low alloy system to reduce the cost. By smelting the raw materials and casting to form a casting blank or ingot, a cast metal is obtained to provide an original blank for subsequent processing.

[0051] S102, the cast metal is fully austenitized to obtain an austenitized metal.

[0052] In this embodiment, by fully austenitizing the cast metal, it is helpful to eliminate casting defects and adjust the grain size to provide a substrate for subsequent multi-stage multi-pass rotary forging.

[0053] In some embodiments, the temperature of the full austenitizing treatment is 1050-1200℃, and the holding time is 2-5h.

[0054] In this embodiment, the temperature of the full austenitizing treatment is 1050-1200℃, and the holding time is 2-5h, which adjusts the grain size and refines the grains to provide a uniform substrate for subsequent multi-stage multi-pass rotary forging.

[0055] In one possible implementation, the temperature of the full austenitizing treatment is 1050℃, 1100℃, 1150℃ or 1200℃.

[0056] In one possible implementation, the holding time during the full austenitizing treatment is 2h, 3h, 4h or 5h.

[0057] S103, the austenitized metal is subjected to multi-stage multi-pass rotary forging to obtain a forged metal.

[0058] In this embodiment, by multi-stage multi-pass rotary forging of the austenitized metal, fine-grain strengthening and dislocation strengthening are achieved to improve the strength and provide a good organizational form for subsequent tempering partitioning treatment.

[0059] In this embodiment, the shape of the forged metal is not limited. For example, the shape of the forged metal is rod-shaped, and the radial cross-section is circular or square.

[0060] In some embodiments, in the step of multi-stage multi-pass rotary forging of the austenitized metal, the total reduction is greater than 90%. The microstructure of the forged metal includes austenite, and the volume fraction of the austenite is 10-20%. The microstructure of the forged metal also includes martensite, and the volume fraction of the martensite is 80-90%.

[0061] In the embodiment, the total reduction of the multi-stage multi-pass rotary forging of the austenitized metal is greater than 90%, so that the as-forged metal has coarse primary austenite and a large number of dislocations, to provide more nucleation sites for the subsequent intragranular nucleation of the martensite in the coarse primary austenite.

[0062] In the embodiment, the microstructure of the as-forged metal includes austenite and martensite, the volume fraction of the austenite is 10% to 20%, and the volume fraction of the martensite is 80% to 90%, so as to realize the microstructure of the non-quenched and tempered 2200MPa-grade low-cost ultrahigh toughness steel including austenite and martensite, the volume fraction of the austenite is 10% to 20%, and the volume fraction of the martensite is 80% to 90%, which is helpful to realize that the non-quenched and tempered 2200MPa-grade low-cost ultrahigh toughness steel has high toughness, high strength and low cost.

[0063] In some embodiments, the step of multi-stage multi-pass rotary forging of the austenitized metal to obtain the as-forged metal includes: first-stage multi-pass rotary forging of the austenitized metal, wherein the total reduction is greater than 40% and the final forging temperature is greater than 900℃. The metal obtained after the first-stage multi-pass rotary forging is subjected to temperature holding, and the temperature holding temperature is 900℃. The metal obtained after the temperature holding is subjected to second-stage multi-pass rotary forging, wherein the total reduction is greater than 50% and the final forging temperature is greater than 800℃. The metal obtained after the second-stage multi-pass rotary forging is cooled to room temperature to obtain the as-forged metal.

[0064] By first-stage multi-pass rotary forging of the austenitized metal, wherein the total reduction is greater than 40% and the final forging temperature is greater than 900℃, the organization is preliminarily broken, dislocations are introduced, and deformation energy is accumulated, to provide an energy basis for the subsequent second-stage multi-pass rotary forging.

[0065] By temperature holding of the metal obtained after the first-stage multi-pass rotary forging, and the temperature holding temperature is 900℃, the homogenization temperature and the organization are realized, internal stress is released, and the continuity of the deformation process and the consistency of the organization in the subsequent second-stage multi-pass rotary forging are improved.

[0066] By second-stage multi-pass rotary forging of the metal obtained after the temperature holding, wherein the total reduction is greater than 50% and the final forging temperature is greater than 800℃, a higher density of dislocations is introduced, to greatly improve the strength through fine-grain strengthening and dislocation strengthening.

[0067] By cooling the metal obtained after the second-stage multi-pass rotary forging to room temperature to obtain the as-forged metal, the target organization is realized.

[0068] Through the synergistic effect of the above steps, the as-forged metal has coarse primary austenite and a large number of dislocations to provide more nucleation sites for intragranular nucleation of the subsequent martensite in the coarse primary austenite grain. In particular, through the synergistic cooperation of the Mn content of 0.5% to 3%, the temperature of the temperature holding of 900℃, and the total reduction of the as-austenitized metal subjected to the multi-stage multi-pass rotary forging of greater than 90%, the primary austenite is equiaxed, and a large number of dislocations are introduced as nucleation points to provide more nucleation sites.

[0069] Of course, the multi-stage multi-pass rotary forging of the as-austenitized metal is not limited to the first stage multi-pass rotary forging and the second stage multi-pass rotary forging, but can also include a third stage multi-pass rotary forging. The specific process parameters can be set according to actual processing needs.

[0070] S104, the as-forged metal is subjected to tempering and partitioning treatment to obtain a non-quenched and tempered 2200MPa grade low-cost super-high toughness steel.

[0071] In this embodiment, the as-forged metal is directly subjected to tempering and partitioning treatment to simplify the process, improve the strength and toughness, and obtain a non-quenched and tempered 2200MPa grade low-cost super-high toughness steel.

[0072] In some embodiments, the step of subjecting the as-forged metal to tempering and partitioning treatment to obtain a non-quenched and tempered 2200MPa grade low-cost super-high toughness steel includes: subjecting the as-forged metal to tempering and partitioning treatment at a temperature of 150℃ to 350℃ for 40min to 180min, and cooling to room temperature to obtain a non-quenched and tempered 2200MPa grade low-cost super-high toughness steel.

[0073] In this embodiment, during the heat treatment process, the as-forged metal is directly subjected to tempering and partitioning treatment at a temperature of 150℃ to 350℃ for 40min to 180min, without the need for quenching and tempering treatment, thereby simplifying the process and reducing the cost.

[0074] In the related art, the preparation of the maraging steel requires a long aging process, resulting in high energy consumption and a sharp increase in cost. Compared with the preparation of the maraging steel, the as-forged metal of this embodiment is directly subjected to tempering and partitioning treatment, the preparation method is simple and low in cost, and the non-quenched and tempered 2200MPa grade low-cost super-high toughness steel has high toughness, high strength and low cost.

[0075] Next, taking two as-forged metal samples with the same material, shape and size as examples, the technical effects of this embodiment are described. The two as-forged metal samples are a first sample and a second sample.

[0076] The original austenite of the ultra-high strength steel obtained by first performing a quenching and tempering treatment on the first sample is equiaxed, the equivalent circle size of the original austenite is 7 μm to 15 μm, and the average grain size of the martensite formed by the original austenite is 1.1 μm to 1.4 μm, so that the toughness of the ultra-high strength steel is relatively low.

[0077] The original austenite of the non-tempered 2200 MPa grade low-cost ultra-high toughness steel obtained by directly performing a quenching and tempering treatment on the second sample without quenching and tempering treatment is equiaxed, the equivalent circle size of the original austenite is 10 μm to 36 μm, and the original austenite is coarse and has a large number of dislocations. By directly performing a quenching and tempering treatment on the second sample, the process of transforming the original austenite into martensite, intracrystalline nucleation of the martensite occurs in the grains of the coarse original austenite, so that the average grain size of the martensite is 0.5 μm to 0.8 μm, a finer martensite structure than the first sample is obtained, cracks are difficult to form, and the ratio of the length to the width of the grains of the martensite is 1.1 to 4.6, so that more slip systems are provided, and the toughness is further improved. In summary, the toughness and strength of the non-tempered 2200 MPa grade low-cost ultra-high toughness steel are effectively improved.

[0078] Embodiment 1

[0079] A non-tempered 2200 MPa grade low-cost ultra-high toughness steel, the chemical composition of which comprises, by mass percentage: C 0.49%, Si 1.71%, Mn 1%, V 0.07%, Ni 1.92%, Nb 0.04%, Mo 0.37%, Cr 0.8%, P≤0.015%, S≤0.008%, N≤0.004%, and the balance being Fe and unavoidable impurities.

[0080] A preparation method of a non-tempered 2200 MPa grade low-cost ultra-high toughness steel, comprising the following steps:

[0081] Raw materials are prepared according to the chemical composition and proportion of the non-tempered 2200 MPa grade low-cost ultra-high toughness steel of Embodiment 1. The raw materials are smelted and cast to form a cast blank or an ingot, to obtain a cast metal.

[0082] The cast metal is subjected to complete austenitization treatment, and the cast metal is heated to 1200℃, so that the temperature of the complete austenitization treatment is 1200℃, and the temperature is maintained for 3 h, to obtain an austenitized metal. The austenitized metal is in the shape of a square bar, and the radial cross-sectional size of the square bar is 80 mm×80 mm.

[0083] The austenitized metal is subjected to a first stage multi-pass rotary forging with a total reduction of 75% and a final forging temperature greater than 900°C. A square bar with a radial cross-sectional dimension of 80mm x 80mm is forged into a square bar with a radial cross-sectional dimension of 40mm x 40mm.

[0084] The metal obtained after the first stage multi-pass rotary forging (square bar with a radial cross-sectional dimension of 40mm x 40mm) is subjected to a tempering at a temperature of 900°C.

[0085] The metal obtained after the tempering is subjected to a second stage multi-pass rotary forging with a total reduction of 61% and a final forging temperature greater than 800°C. A square bar with a radial cross-sectional dimension of 40mm x 40mm is forged into a square bar with a radial cross-sectional dimension of 25mm x 25mm.

[0086] The metal obtained after the second stage multi-pass rotary forging is cooled in air to room temperature to obtain a wrought metal. The microstructure of the wrought metal includes austenite and martensite, with a volume fraction of austenite of 20% and a volume fraction of martensite of 80%.

[0087] The original austenite is equiaxed and a large number of dislocations are introduced as nucleation sites by a content of Mn of 1% (less than 3%), a tempering temperature of 900°C and a total reduction of more than 90% in the multi-stage multi-pass rotary forging (from a square bar with a radial cross-sectional dimension of 80mm x 80mm to a square bar with a radial cross-sectional dimension of 25mm x 25mm).

[0088] The wrought metal is subjected to a tempering and partitioning treatment at a temperature of 350°C for 40min and cooled in air to room temperature to obtain a non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel. The tempering process makes the distribution of martensite grains more uniform and the toughness better.

[0089] Combining Figure 2 as shown in FIG. 1, Figure 2 for illustrating the X-ray diffraction (XRD) spectrum of the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel. Figure 2 The abscissa in FIG. 1 is the diffraction angle (2θ) in degrees (degree). Figure 2 The ordinate in FIG. 1 is the diffraction intensity (Intensity). According to the XRD spectrum, it can be obtained that 50°, 75° and 90° are the diffraction angles of austenite, 65° and 82° are the diffraction angles of martensite, and the dislocation density can be obtained by using the half-peak width of the diffraction peaks of austenite and martensite, and thus the dislocation density of the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel is 5.5 x 1013m-2. 15Therefore, more nucleation sites can be provided, the martensite grain size is small and the orientation distribution is multi, and the ratio of the length and the width of the martensite grain is small, so that it is difficult to form a crack in the toughness detection impact test, so as to improve the toughness of the material, and the high dislocation and small size of the martensite improve the strength of the material.

[0090] In combination with Figure 3 It is shown that F is used to illustrate the equiaxed primary austenite of the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel, Figure 3 It can be used to illustrate the grain size and distribution of the primary austenite. The primary austenite is equiaxed, and the equivalent circle size of the primary austenite grain is 10.1μm to 35μm. For example, the equivalent circle size of one primary austenite grain is about 15.2μm, and the equivalent circle size of another primary austenite grain is about 32.6μm.

[0091] In combination with Figure 4 It is shown that the red structure illustrates the thin film-shaped austenite, Figure 4 It can be used to illustrate the grain size and distribution of the austenite. At room temperature, the microstructure of the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel includes martensite and austenite, and the austenite is in the form of thin film. The equivalent circle size of the austenite grain is 0.1μm to 10μm.

[0092] In example 1, the average grain size of the martensite is 0.66μm, the ratio of the length and the width of the martensite grain is 1.2 to 4.5, and the martensite grain is in the form of near-elliptical. The average grain size of the martensite and the ratio of the length and the width of the martensite grain are not limited in the obtaining manner. For example, the average grain size of the martensite and the ratio of the length and the width of the martensite grain can be obtained based on the martensite grain size and frequency distribution histogram. Figure 5

[0093] In combination with Figure 6 It is shown that the tensile test is performed on the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel, the tensile engineering stress-strain curve is obtained, and the tensile strength of the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel is 2200MPa.

[0094] The impact test is performed on the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel, and the V-notch (V-shaped impact notch) impact toughness at room temperature of 25℃ is 52J / cm 2 , and the V-notch (V-shaped impact notch) impact toughness at a temperature of -60℃ is 42J / cm 2 .

[0095] Therefore, the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel obtained in example 1 has high toughness, high strength and low cost.

[0096] Example 2​

[0097] A non-quenched 2200MPa grade low-cost super high toughness steel, the chemical composition of which comprises, in percentage by mass: C 0.48%, Si 1.71%, Mn 3%, V 0.06%, Ni 3.9%, Nb 0.05%, Mo 0.2%, Cr 2.8%, P≤0.015%, S≤0.008%, N≤0.004%, and the balance being Fe and inevitable impurities.

[0098] A preparation method of a non-quenched 2200MPa grade low-cost super high toughness steel, comprising the following steps:

[0099] Raw materials are prepared according to the chemical composition and percentage of the non-quenched 2200MPa grade low-cost super high toughness steel of Example 2. The raw materials are smelted and cast to form a casting blank or an ingot, so as to obtain a cast metal.

[0100] The cast metal is subjected to complete austenitization treatment, the cast metal is heated to 1200℃, the temperature of the complete austenitization treatment is 1200℃, and the temperature is kept for 3h, so as to obtain an austenitized metal. The shape of the austenitized metal is a square bar, and the radial cross-sectional size of the square bar is 80mm×80mm.

[0101] The austenitized metal is subjected to first-stage multi-pass rotary forging, wherein the total reduction is 75%, and the final forging temperature is greater than 900℃. The square bar with a radial cross-sectional size of 80mm×80mm is forged into a square bar with a radial cross-sectional size of 40mm×40mm.

[0102] The metal obtained after the first-stage multi-pass rotary forging (the square bar with a radial cross-sectional size of 40mm×40mm) is subjected to temperature holding, and the temperature holding temperature is 900℃.

[0103] The metal obtained after the temperature holding is subjected to second-stage multi-pass rotary forging, wherein the total reduction is 61%, and the final forging temperature is greater than 800℃. The square bar with a radial cross-sectional size of 40mm×40mm is forged into a square bar with a radial cross-sectional size of 25mm×25mm.

[0104] The metal obtained after the second-stage multi-pass rotary forging is cooled to room temperature in air, so as to obtain a forged metal.

[0105] The forged metal is subjected to tempering and partitioning treatment at a temperature of 200℃ for 180min, and is cooled to room temperature in air, so as to obtain a non-quenched 2200MPa grade low-cost super high toughness steel.

[0106] The non-quenched 2200MPa grade low-cost super high toughness steel is subjected to a tensile test, and the tensile strength of the non-quenched 2200MPa grade low-cost super high toughness steel is 2290MPa.

[0107] The impact test is performed on the non-quenched 2200 MPa grade low-cost super high toughness steel, and the V-notch impact toughness at room temperature of 25 DEG C is 58.87 J / cm 2 , and the V-notch impact toughness at -60 DEG C temperature is 43 J / cm 2 .

[0108] Therefore, the non-quenched 2200 MPa grade low-cost super high toughness steel with high toughness, high strength and low cost is obtained in Example 2.

[0109] Example 3

[0110] A non-quenched 2200 MPa grade low-cost super high toughness steel, the chemical composition of which comprises, in percentage by mass: C 0.58%, Si 2.71%, Mn 2.3%, V 0.16%, Ni 2.9%, Nb 0.05%, Mo 0.2%, Cr 2.8%, P≤0.015%, S≤0.008%, N≤0.004%, and the rest is Fe and inevitable impurities.

[0111] A preparation method of a non-quenched 2200 MPa grade low-cost super high toughness steel, comprising the following steps:

[0112] According to the chemical composition and percentage of the non-quenched 2200 MPa grade low-cost super high toughness steel of Example 3, raw materials are prepared. The raw materials are smelted and cast to form a casting blank or an ingot, to obtain a cast metal.

[0113] The cast metal is subjected to complete austenitizing treatment, and the cast metal is heated to 1200 DEG C, so that the temperature of the complete austenitizing treatment is 1200 DEG C, and the temperature is kept for 3h, to obtain an austenitized metal. The shape of the austenitized metal is a square bar, and the radial cross-sectional size of the square bar is 80mm x 80mm.

[0114] The austenitized metal is subjected to first-stage multi-pass rotary forging, wherein the total reduction is 75%, and the final forging temperature is greater than 900 DEG C. The square bar with a radial cross-sectional size of 80mm x 80mm is forged into a square bar with a radial cross-sectional size of 40mm x 40mm.

[0115] The metal obtained after the first-stage multi-pass rotary forging (the square bar with a radial cross-sectional size of 40mm x 40mm) is subjected to temperature holding, and the temperature holding temperature is 900 DEG C.

[0116] The metal obtained after the temperature holding is subjected to second-stage multi-pass rotary forging, wherein the total reduction is 61%, and the final forging temperature is greater than 800 DEG C. The square bar with a radial cross-sectional size of 40mm x 40mm is forged into a square bar with a radial cross-sectional size of 25mm x 25mm.

[0117] The metal obtained after the second stage multi-pass rotary forging is cooled to room temperature in air to obtain a forged metal.

[0118] The forged metal is subjected to a tempering and partitioning treatment at a temperature of 150°C for 120 min and cooled to room temperature in air to obtain a non-quenched and tempered 2200 MPa grade low cost ultra-high toughness steel.

[0119] The non-quenched and tempered 2200 MPa grade low cost ultra-high toughness steel is subjected to a tensile test to obtain a tensile strength of 2228 MPa for the non-quenched and tempered 2200 MPa grade low cost ultra-high toughness steel.

[0120] The non-quenched and tempered 2200 MPa grade low cost ultra-high toughness steel is subjected to an impact test to obtain a V-notch impact toughness of 66.25 J / cm 2 at room temperature of 25°C and a V-notch impact toughness of 47 J / cm 2 at a temperature of -60°C.

[0121] Thus, the non-quenched and tempered 2200 MPa grade low cost ultra-high toughness steel of Example 3 has high toughness, high strength and low cost.

[0122] The above merely provides the preferred embodiments of the present application, but does not intend to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above merely provides the preferred embodiments of the present application, but it should be pointed out that, for the ordinary skilled in the art, some improvements and variations can be made without departing from the technical principles of the present application, and these improvements and variations should also be considered as the protection scope of the present application.

Claims

1. A non-quenched 2200 MPa grade low cost ultra-high toughness steel, characterized in that, The non-quenched 2200MPa-grade low-cost super-high toughness steel includes, in terms of mass percentage: C: 0.4%-0.6%, Si: 1.0%-3.0%, Mn: 0.5%-3%, V: 0.05%-0.2%, Ni: 1.9%-4.0%, Nb: 0.03%-0.05%, Mo: 0.2%-0.4%, Cr: 0.7%-3%, and the rest is Fe and inevitable impurities; The original austenite of the non-quenched 2200MPa-grade low-cost super-high toughness steel is equiaxed, and the grain equivalent circle size of the original austenite is 10-36μm; the microstructure of the non-quenched 2200MPa-grade low-cost super-high toughness steel includes martensite, and the average grain size of the martensite is 0.5-0.8μm; In the process of transformation of the original austenite into the martensite, the martensite intracrystalline nucleation occurs in the grain of the original austenite.

2. The non-quenched 2200MPa-grade low-cost super-high toughness steel according to claim 1, wherein the ratio of the length to the width of the grain of the martensite is 1.1-4.

6.

3. The non-quenched 2200MPa-grade low-cost super-high toughness steel according to claim 1, wherein the microstructure of the non-quenched 2200MPa-grade low-cost super-high toughness steel further includes austenite, the austenite is in the form of film, and the grain equivalent circle size of the austenite is 0.1-10μm; In the non-quenched 2200MPa-grade low-cost super-high toughness steel, the volume fraction of the austenite is 10%-20%, and the volume fraction of the martensite is 80%-90%.

4. The non-quenched 2200MPa-grade low-cost super-high toughness steel according to claim 1, comprising the following steps: preparing a cast state metal according to the chemical composition and proportion of the non-quenched 2200MPa-grade low-cost super-high toughness steel as claimed in claim 1; completely austenitizing the cast state metal to obtain an austenitized metal; The non-quenched 2200MPa grade low-cost super-high toughness steel has a tensile strength greater than 2200MPa, a V-notch impact toughness at room temperature greater than 50J / cm 2 , and a V-notch impact toughness at -60℃ temperature greater than 40J / cm 2 .

5. A method of producing a non-quenched 2200 MPa grade low cost ultra-high toughness steel, characterized in that, multi-stage and multi-pass rotary forging the austenitized metal to obtain a forged state metal; tempering and partitioning the forged state metal to obtain the non-quenched 2200MPa-grade low-cost super-high toughness steel. The step of preparing a cast state metal according to the chemical composition and proportion of the non-quenched 2200MPa-grade low-cost super-high toughness steel as claimed in claim 1 comprises: preparing raw materials according to the chemical composition and proportion of the non-quenched 2200MPa-grade low-cost super-high toughness steel as claimed in claim 1; smelting the raw materials and casting to form a casting blank or ingot to obtain the cast state metal.

6. The production method according to claim 5, wherein 7. The preparation method according to claim 5, wherein the temperature of the completely austenitizing treatment is 1050-1200℃, and the holding time is 2-5h. The step of multi-stage and multi-pass rotary forging the austenitized metal to obtain a forged state metal comprises: first-stage multi-pass rotary forging the austenitized metal, wherein the total reduction is greater than 40%, and the final forging temperature is greater than 900℃; ​ ​ 8. The preparation method according to claim 5, characterized in that, ​ ​ The metal obtained after the first stage multi-pass rotary forging is kept warm, and the temperature of the keeping warm is 900℃; The metal obtained after the keeping warm is subjected to second stage multi-pass rotary forging, wherein the total reduction is greater than 50%, and the final forging temperature is greater than 800℃; The metal obtained after the second stage multi-pass rotary forging is cooled to room temperature to obtain a wrought metal.

9. The preparation method of claim 5, wherein, In the step of subjecting the austenitized metal to multi-stage multi-pass rotary forging, the total reduction is greater than 90%; The microstructure of the wrought metal comprises austenite, and the volume fraction of the austenite is 10% to 20%.

10. The method of claim 5, wherein, The step of subjecting the wrought metal to tempering and distribution treatment to obtain the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel comprises: The wrought metal is subjected to tempering and distribution treatment at a temperature of 150℃ to 350℃ for 40min to 180min, and then cooled to room temperature to obtain the non-quenched and tempered 2200MPa grade low-cost ultra-high toughness steel.

Images