CN111455146A - Strengthening and toughening treatment method for low-alloy martensitic steel and martensitic steel - Google Patents
Strengthening and toughening treatment method for low-alloy martensitic steel and martensitic steel Download PDFInfo
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Abstract
The invention discloses a strengthening and toughening treatment method of low-alloy martensitic steel and martensitic steel, comprising the following steps: (S1) preprocessing: obtaining a uniform single-phase austenite structure; (S2) high-temperature forging: the forging ratio is 50-80%, the finish forging temperature is 50-100 ℃ higher than the austenite transformation temperature, and the structure mainly comprising martensite is obtained after cooling to room temperature; (S3) warm forging: keeping the temperature at 30-70 ℃ higher than the austenite transformation temperature, cooling in air, starting forging when the temperature is reduced to 30-100 ℃ lower than the eutectoid transformation temperature, wherein the forging ratio is 70-90%, the finish forging temperature is 150-250 ℃ lower than the eutectoid transformation temperature, the total forging time is less than 2min, and then quenching and cooling to room temperature to obtain a uniform and fine lath martensite-based structure; (S4) low-temperature tempering. The method of the invention can obviously refine the original austenite grains by combining high-temperature forging and medium-temperature forging, and obviously improve the plasticity and the toughness while improving the strength of the martensitic steel.
Description
Technical Field
The invention relates to a treatment method of low-alloy martensitic steel, in particular to a strengthening and toughening treatment method of low-alloy martensitic steel and martensitic steel.
Background
The low-alloy martensitic steel has low production cost, simple process and good welding performance, and is widely applied to the fields of large-size components such as automobile industry, machinery, mines and the like. With the development trend of environmental protection, energy conservation and emission reduction and light weight of automobiles, higher requirements are put forward on the strength, plasticity and toughness of steel. Generally, the higher the strength of the steel, the lower the plasticity and toughness. The general technical problem in the production and service process of martensite steel is insufficient plasticity and toughness.
For high strength martensitic steels, the improvement of toughness is particularly important while improving strength. The toughness of the martensitic steel can be improved to a certain extent by alloying the steel and adding a large amount of alloy elements. However, high alloy steel has more complex process requirements, high production cost and poorer weldability.
Theoretically, the strength and toughness of the steel material can be improved simultaneously by refining the grains, and the purpose of fine grain strengthening is achieved. By implementing processes such as large plastic deformation (SPD), High Pressure Torsion (HPT), equal channel Extrusion (ECAP) and the like on the martensitic steel, a remarkable grain refinement effect can be generated, and even the grains of the steel can reach the nanometer level. For example, nanometer bainite steel developed at Cambridge university, UK has strength as high as 2.5GPa and good plasticity.
However, in actual production, since the work hardening effect is significant, the deformation resistance is extremely large, the requirement for equipment is high, and the cost is high. Therefore, the above process is generally only suitable for preparing parts of small and micro size, and cannot be widely used.
In production practice, the forging process is applied to grain refinement, is relatively mature and is more widely applied. However, forging presents major problems: (1) during forging at room temperature, the high-strength steel also generates a remarkable work hardening phenomenon, and the processing is difficult to implement; (2) during high-temperature forging, the grains are recovered and recrystallized, and even the grains grow up, so that the grain refining effect is not obvious.
Disclosure of Invention
The invention aims to provide a strengthening and toughening treatment method of low-alloy martensitic steel and the martensitic steel, which solve the problem of poor forging effect in the prior art, can obviously refine original austenite grains, and can obviously improve plasticity and toughness while improving the strength of the martensitic steel.
In order to achieve the aim, the invention provides a strengthening and toughening treatment method of low-alloy martensitic steel, which aims at the low-alloy martensitic steel comprising the following components in percentage by mass: 0.25-0.45% of C, 1-2.5% of Cr, 0.5-1.5% of Mn, 1-2% of Si, 0.3-0.5% of Mo, 0-0.3% of Ni, 0-0.3% of V, 0-0.3% of B, and the balance of Fe; the method comprises the following steps:
(S1) preprocessing: heating the low-alloy martensitic steel to 1150-1250 ℃ in an inert atmosphere protection furnace, and preserving heat to obtain a uniform single-phase austenitic structure;
(S2) high-temperature forging: high-temperature forging is carried out on the low-alloy martensitic steel obtained in the step (S1), the forging ratio is 50-80%, the finish forging temperature is 50-100 ℃ higher than the austenite transformation temperature, and the low-alloy martensitic steel is immersed into quenching oil at the temperature of 60 +/-10 ℃ after finish forging and cooled to room temperature to avoid deformation and cracking of parts and obtain a structure mainly comprising martensite;
(S3) warm forging: keeping the temperature of the low-alloy martensitic steel obtained in the step (S2) at a temperature higher than the austenite transformation temperature by 30-70 ℃, cooling in air after the temperature is kept, and starting forging when the temperature is reduced to a temperature 30-100 ℃ lower than the eutectoid transformation temperature, wherein the forging ratio is 70-90%, the finish forging temperature is 150-250 ℃ lower than the eutectoid transformation temperature, and the total forging time is within 2 min; after finish forging, immersing the blank into quenching oil at the temperature of 60 +/-10 ℃ for cooling to room temperature so as to avoid deformation and cracking of parts and obtain a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) carrying out low-temperature tempering treatment on the low-alloy martensitic steel subjected to the step (S3) at the temperature of 200-220 ℃, and air-cooling to room temperature after the heat preservation is finished to obtain the low-alloy martensitic steel subjected to strengthening and toughening treatment.
Preferably, the low-alloy martensitic steel comprises the following components in percentage by mass: 0.27-0.4% of C, 1.2-2.2% of Cr, 0.8-1.5% of Mn, 1.2-1.5% of Si, 0.5% of Mo, 0-0.3% of Ni and the balance of Fe.
Preferably, in the step (S2), the finish forging temperature is 70 to 100 ℃ higher than the austenite transformation temperature; in the step (S3), the forging start temperature is 35 to 70 ℃ lower than the eutectoid transformation temperature, and the finish forging temperature is 190 to 220 ℃ lower than the eutectoid transformation temperature.
Preferably, the austenite transformation temperature of the low-alloy martensitic steel is 810-830 ℃, and the eutectoid transformation temperature is 745-750 ℃.
Preferably, in the step (S2), the finish forging temperature is 900-920 ℃; in the step (S3), the heat preservation temperature is 850-870 ℃, the forging starting temperature is 680-710 ℃, and the finish forging temperature is 530-560 ℃.
Preferably, in the step (S1), the heat preservation time is 30-60 min; in the step (S3), the heat preservation time is 60-90 min; in the step (S4), the heat preservation time is 2-4 h. More preferably, in the step (S1), the heat preservation time is 30-45 min; in the step (S4), the heat preservation time is 2-3 h.
Preferably, in the step (S2), the forging ratio is 70 to 80%; in the step (S3), the forging ratio is 80-90%.
Preferably, in the step (S3), the low alloy martensitic steel subjected to the step (S2) is heat-preserved at 35 to 50 ℃ above the austenite transformation temperature.
Preferably, in steps (S2) and (S3), the finish forging is followed by immersion in a 60 ℃ quenching oil to cool to room temperature.
Another object of the invention is to provide a low-alloy martensitic steel treated by said method.
Preferably, the low-alloy martensitic steel obtained by the treatment method has the tensile strength of 1950-2160 MPa, the yield strength of 1765-1995 MPa and the elongation rate of about 9-14%.
The strengthening and toughening treatment method of the low-alloy martensitic steel and the martensitic steel solve the problem of poor forging effect in the prior art, and have the following advantages:
(1) the strengthening and toughening treatment method can improve the stability and hardenability of the super-cooled austenite in the forging process and ensure good strength and toughness matching aiming at the martensitic steel with specific components; according to the method, original austenite grains can be obviously refined through a combined process of high-temperature forging and medium-temperature forging, a uniform and fine lath martensite structure is finally obtained, the purpose of grain refinement is achieved, and the plasticity and the toughness are obviously improved while the strength of the martensite steel is improved;
(2) in the toughening treatment method, hot forging is carried out at the temperature of A3 (austenite transformation temperature) in a high-temperature forging stage to obtain a compact, uniform and fine original austenite structure, so as to prepare the structure for a subsequent process; in the medium-temperature forging stage, under the temperature A1 (eutectoid transformation temperature), large forging ratio is implemented to further refine austenite grains, and fine lamellar lath martensite is obtained after quenching;
(3) according to the strengthening and toughening treatment method, during medium-temperature forging, the forging temperature is selected to be 30-100 ℃ below A1, so that the deformed grains after forging can generate a recovery effect to a certain extent, the work hardening is reduced, the large forging ratio is convenient to implement, the austenite grains are obviously refined, and meanwhile, the temperature range does not generate an obvious recrystallization phenomenon; the finish forging temperature is controlled to be 150-250 ℃ below A1, the internal stress of forging processing can be eliminated while crystal grains are refined, and the phenomenon that the finish forging temperature is too low to generate work hardening is avoided;
(4) the strengthening and toughening treatment method disclosed by the invention has the following remarkable effects that when the medium-temperature forging is carried out, the large forging ratio of 70-90% is implemented at the medium temperature: (a) super-cooled austenite grains can be obviously refined, and preparation is made for obtaining fine lath martensite through quenching; (b) the distortion of a super-cooled austenite lattice can be intensified, the dislocation density is increased, the nucleation of martensite during quenching is facilitated, the martensite lath can be further refined, and the toughness is improved; (c) the formed high-density dislocation is also beneficial to the dispersion and precipitation of carbides in austenite, and the toughness of the martensitic steel is further improved; (d) the formed high-density dislocation hinders the crack propagation, and the strength, the toughness and the plasticity can be obviously improved;
(5) according to the strengthening and toughening treatment method, during medium-temperature forging, the medium-temperature forging is finished within 2 minutes, the supercooled austenite is prevented from precipitating high-temperature phases (such as needle-shaped, lamellar, massive ferrite, pearlite and other structures) in the forging process, and the strength and toughness of the martensitic steel are reduced;
(6) the strengthening and toughening treatment method has the advantages of simple preparation, low production cost, obvious strengthening and toughening effect and the like, can finally obtain fine and uniform lath martensite structures, and obtains good plasticity and toughness while keeping high strength of the low-alloy martensite steel.
Drawings
FIG. 1 shows the microstructure of a low-alloy martensitic steel after strengthening and toughening treatment in example 1 of the present invention.
FIG. 2 shows the tensile fracture morphology of the low alloy martensitic steel after the strengthening and toughening treatment in example 1 of the present invention.
FIG. 3 shows the microstructure of a low alloy martensitic steel of comparative example 1 of the present invention after the toughening treatment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The strengthening and toughening treatment method of the low-alloy martensitic steel comprises the following steps of smelting a steel ingot with the weight percent of about 15Kg, wherein the steel ingot comprises the following components in percentage by mass: 0.27% C, 1.2% Cr, 1.1% Mn, 1.3% Si, 0.5% Mo, and the balance Fe, the alloy having an A3 temperature (austenite transformation temperature) of about 830 ℃ and an A1 temperature (eutectoid transformation temperature) of about 750 ℃, the strengthening and toughening process comprising:
(S1) preprocessing: heating the steel ingot with the components in an inert atmosphere (such as nitrogen) protection furnace to 1150 ℃, and preserving heat for 30min for high-temperature homogenization treatment to obtain a uniform single-phase austenite structure;
(S2) high-temperature forging: taking the steel ingot out of the atmosphere protection furnace, immediately forging at high temperature, wherein the forging ratio is about 70%, the finish forging temperature is 70 ℃ higher than the temperature of A3, specifically 900 ℃, immediately immersing the steel ingot into quenching oil at about 60 ℃ after finish forging, and cooling to room temperature to obtain a structure mainly comprising martensite;
(S3) warm forging: and (S2) keeping the temperature of the steel ingot in the step (S2) at 35 ℃ higher than A3, specifically 865 ℃, and keeping the temperature for 60 min. And then air cooling is carried out, and forging is started when the temperature is reduced to 60 ℃ lower than the temperature of A1, specifically 690 ℃, the forging ratio is 80%, the finish forging temperature is 190 ℃ lower than the temperature of A1, specifically 560 ℃, and the total forging time is controlled within 2 min. After finish forging, immediately immersing the blank into quenching oil at about 60 ℃ to cool the blank to room temperature, and obtaining a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) low-temperature tempering treatment is carried out on the steel ingot obtained in the step (S3), the tempering temperature is 220 ℃, heat preservation is carried out for 2 hours, and then air cooling is carried out to the room temperature, so that the low-alloy martensitic steel subjected to strengthening and toughening treatment is obtained.
As shown in FIG. 1, the microstructure of the low alloy martensitic steel after the strengthening and toughening treatment in example 1 of the present invention was observed by a Scanning Electron Microscope (SEM), and it was found that the steel had a fine and uniform lath martensite as a main component (average width less than 1 μm) and contained a small amount of finely dispersed carbides.
As shown in fig. 2, the tensile fracture morphology of the low alloy martensitic steel after the strengthening and toughening treatment in example 1 of the present invention is a typical ductile dimple fracture.
The low alloy martensitic steel after the strengthening and toughening treatment in the example 1 is subjected to a mechanical property test, and the tensile strength sigma isb1970 + -20 MPa, yield strength sigmas1750 +/-15 MPa, and the elongation rate is approximately equal to 14%.
Example 2
A strengthening and toughening treatment process for low-alloy martensitic steel comprises the following components in percentage by mass: 0.4% C, 2.0% Cr, 1.5% Mn, 1.5% Si, 0.5% Mo, and the balance Fe, the alloy having an A3 temperature of about 810 ℃ and an A1 temperature of about 745 ℃, the strengthening and toughening process comprising:
(S1) preprocessing: heating the steel ingot with the components to 1200 ℃ in an inert atmosphere protection furnace, and preserving heat for 45min for high-temperature homogenization treatment to obtain a uniform single-phase austenite structure;
(S2) high-temperature forging: taking the steel ingot out of the atmosphere protection furnace, immediately carrying out high-temperature forging, wherein the forging ratio is about 80%, the finish forging temperature is 50 ℃ higher than the temperature of A3, specifically 860 ℃, immediately immersing the steel ingot into quenching oil at about 60 ℃ after finish forging, and cooling to room temperature to obtain a structure mainly comprising martensite;
(S3) warm forging: and (S2) keeping the temperature of the steel ingot in the step (S2) at 40 ℃ higher than A3, specifically at 850 ℃ for 90 min. And then air cooling is carried out, the forging is started when the temperature is reduced to 35 ℃ lower than the temperature of A1, specifically 710 ℃, the forging ratio is about 90 percent, the finish forging temperature is 195 ℃ lower than the temperature of A1, specifically 550 ℃, and the total forging time is controlled within 2 min. After finish forging, immediately immersing the blank into quenching oil at about 60 ℃ to cool the blank to room temperature, and obtaining a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) low-temperature tempering treatment is carried out on the steel ingot obtained in the step (S3), the tempering temperature is 200 ℃, heat preservation is carried out for 2 hours, and then air cooling is carried out to the room temperature, so that the low-alloy martensitic steel subjected to strengthening and toughening treatment is obtained.
The structure of the low-alloy martensitic steel obtained in example 2 is mainly composed of fine and uniform lath martensite, and contains a small amount of finely dispersed carbides. The low alloy martensitic steel after the strengthening and toughening treatment in the example 2 is subjected to a mechanical property test, and a tensile strength sigma is measuredb2140. + -. 20MPa, yield strength σs1980 + -15 MPa, elongation ≈ 9%.
Example 3
The strengthening and toughening treatment process of the low-alloy martensitic steel comprises the following steps of smelting a steel ingot with the weight percentage of about 12Kg, wherein the steel ingot comprises the following components: 0.3% C, 2.2% Cr, 0.8% Mn, 1.2% Si, 0.5% Mo, 0.3% Ni, and the balance Fe, the alloy having an A3 temperature of about 820 ℃ and an A1 temperature of about 750 ℃, the strengthening and toughening process comprising:
(S1) preprocessing: heating the steel ingot with the components to 1250 ℃ in an inert atmosphere protection furnace, and preserving heat for 30min for high-temperature homogenization treatment to obtain a uniform single-phase austenite structure;
(S2) high-temperature forging: and taking the steel ingot out of the atmosphere protection furnace, and immediately forging at high temperature, wherein the forging ratio is about 70%, and the finish forging temperature is 100 ℃ higher than the A3 temperature, specifically 920 ℃. Immediately immersing the blank after finish forging into quenching oil at about 60 ℃ to cool the blank to room temperature to obtain a structure mainly comprising martensite;
(S3) warm forging: and (S2) keeping the temperature of the steel ingot in the step (S2) at 50 ℃ higher than A3, specifically 870 ℃ for 60 min. And then air cooling is carried out, and forging is started when the temperature is reduced to 70 ℃ lower than the temperature of A1, specifically 680 ℃, the forging ratio is about 80%, the finish forging temperature is 250 ℃ lower than the temperature of A1, specifically 530 ℃, and the total forging time is controlled within 2 min. After finish forging, immediately immersing the blank into quenching oil at about 60 ℃ to cool the blank to room temperature, and obtaining a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) low-temperature tempering treatment is carried out on the steel ingot obtained in the step (S3), the tempering temperature is 210 ℃, heat preservation is carried out for 3 hours, and then air cooling is carried out to the room temperature, so that the low-alloy martensitic steel subjected to strengthening and toughening treatment is obtained.
The structure of the low-alloy martensitic steel obtained in example 3 is mainly composed of fine and uniform lath martensite, and contains a small amount of finely dispersed carbides. The low alloy martensitic steel after the strengthening and toughening treatment in example 3 was subjected to a mechanical property test, and a tensile strength σ was measuredb2060. + -. 20MPa, yield strength σs1820 ± 15MPa, elongation ≈ 12%.
Example 4
The strengthening and toughening treatment process of the low-alloy martensitic steel comprises the following steps of smelting a steel ingot with the weight percentage of about 16Kg, wherein the steel ingot comprises the following components: 0.45% C, 2.3% Cr, 1.2% Mn, 1.5% Si, 0.5% Mo, 0.3% Ni, 0.3% V, 0.2% B, and the balance Fe, the alloy having an A3 temperature of about 805 ℃ and an A1 temperature of about 750 ℃, the toughening process comprising:
(S1) preprocessing: heating the steel ingot with the components to 1150 ℃ in an inert atmosphere protection furnace, and preserving heat for 30min for high-temperature homogenization treatment to obtain a uniform single-phase austenite structure;
(S2) high-temperature forging: taking the steel ingot out of the atmosphere protection furnace, immediately forging at high temperature, wherein the forging ratio is about 50%, the finish forging temperature is 100 ℃ higher than the temperature of A3, specifically 905 ℃, immediately immersing the steel ingot into quenching oil at about 60 ℃ after finish forging, and cooling to room temperature to obtain a structure mainly comprising martensite;
(S3) warm forging: and (S2) keeping the temperature of the steel ingot in the step (S2) at 30 ℃ higher than A3, specifically 835 ℃, and keeping the temperature for 90 min. And then air cooling is carried out, the forging is started when the temperature is reduced to 30 ℃ lower than the temperature of A1, specifically 720 ℃, the forging ratio is about 70%, the finish forging temperature is 220 ℃ lower than the temperature of A1, specifically 530 ℃, and the total forging time is controlled within 2 min. After finish forging, immediately immersing the blank into quenching oil at about 60 ℃ to cool the blank to room temperature, and obtaining a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) low-temperature tempering treatment is carried out on the steel ingot obtained in the step (S3), the tempering temperature is 220 ℃, heat preservation is carried out for 2 hours, and then air cooling is carried out to the room temperature, so that the low-alloy martensitic steel subjected to strengthening and toughening treatment is obtained.
The structure of the low-alloy martensitic steel obtained in example 4 is mainly composed of fine and uniform lath martensite, and contains a small amount of finely dispersed carbides. The low alloy martensitic steel of which the strengthening and toughening treatment is performed in the example 4 is subjected to mechanical property test, and the tensile strength sigma is measuredb2250 ± 20MPa, yield strength σs1960 +/-15 MPa, and the elongation rate is approximately equal to 9%.
Comparative example 1
A steel ingot having the same composition as in example 1 was treated in the following manner: comparative example 1 the step (S3) of example 1, i.e., the medium temperature forging process was not performed, and the remaining steps were the same as example 1.
By observing with a Scanning Electron Microscope (SEM), as shown in fig. 3, which is a microstructure of the low-alloy martensitic steel of the present invention after the toughening treatment of comparative example 1, it can be seen that the size of the martensite lath of comparative example 1 is significantly larger than that of example 1, and the grain refining effect is insufficient.
Comparative example 1 was subjected to mechanical property test and tensile strength σb1680 ± 20MPa ═ yield strength σsThe tensile strength, yield strength and elongation of the material are obviously less than those of the material in the embodiment 1, and the medium-temperature forging can well improve the mechanical property of the material.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
Claims (10)
1. The method for strengthening and toughening the low-alloy martensitic steel is characterized in that the low-alloy martensitic steel comprises the following components in percentage by mass: 0.25-0.45% of C, 1-2.5% of Cr, 0.5-1.5% of Mn, 1-2% of Si, 0.3-0.5% of Mo, 0-0.3% of Ni, 0-0.3% of V, 0-0.3% of B, and the balance of Fe;
the method comprises the following steps:
(S1) preprocessing: heating the low-alloy martensitic steel to 1150-1250 ℃ in a nitrogen atmosphere protective furnace, and preserving heat to obtain a uniform single-phase austenitic structure;
(S2) high-temperature forging: high-temperature forging is carried out on the low-alloy martensitic steel obtained in the step (S1), the forging ratio is 50-80%, the finish forging temperature is 50-100 ℃ higher than the austenite transformation temperature, and the low-alloy martensitic steel is immersed in quenching oil at the temperature of 60 +/-10 ℃ after finish forging and cooled to room temperature to obtain a structure mainly comprising martensite;
(S3) warm forging: keeping the temperature of the low-alloy martensitic steel obtained in the step (S2) at a temperature higher than the austenite transformation temperature by 30-70 ℃, cooling in air after the temperature is kept, and starting forging when the temperature is reduced to a temperature 30-100 ℃ lower than the eutectoid transformation temperature, wherein the forging ratio is 70-90%, the finish forging temperature is 150-250 ℃ lower than the eutectoid transformation temperature, and the total forging time is within 2 min; after finish forging, immersing the steel plate into quenching oil at the temperature of 60 +/-10 ℃ and cooling the steel plate to room temperature to obtain a uniform fine lath martensite-based structure;
(S4) low-temperature tempering: and (S3) carrying out low-temperature tempering treatment on the low-alloy martensitic steel subjected to the step (S3) at the temperature of 200-220 ℃, and air-cooling to room temperature after the heat preservation is finished to obtain the low-alloy martensitic steel subjected to strengthening and toughening treatment.
2. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein the low-alloy martensitic steel contains the following components in percentage by mass: 0.27-0.4% of C, 1.2-2.2% of Cr, 0.8-1.5% of Mn, 1.2-1.5% of Si, 0.5% of Mo, 0-0.3% of Ni and the balance of Fe.
3. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein in the step (S2), the finish forging temperature is 70 to 100 ℃ higher than the austenite transformation temperature; in the step (S3), the forging start temperature is 35 to 70 ℃ lower than the eutectoid transformation temperature, and the finish forging temperature is 190 to 220 ℃ lower than the eutectoid transformation temperature.
4. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein the low-alloy martensitic steel has an austenite transformation temperature of 810 to 830 ℃ and a eutectoid transformation temperature of 745 to 750 ℃.
5. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 4, wherein in the step (S2), the finish forging temperature is 900 to 920 ℃; in the step (S3), the heat preservation temperature is 850-870 ℃, the forging starting temperature is 680-710 ℃, and the finish forging temperature is 530-560 ℃.
6. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein in the step (S1), the heat preservation time is 30-60 min; in the step (S3), the heat preservation time is 60-90 min; in the step (S4), the heat preservation time is 2-4 h.
7. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein in the step (S2), the forging ratio is 70 to 80%; in the step (S3), the forging ratio is 80-90%.
8. The method for strengthening and toughening a low-alloy martensitic steel as claimed in claim 1, wherein in the step (S3), the low-alloy martensitic steel obtained in the step (S2) is kept at a temperature higher than the austenite transformation temperature by 35 to 50 ℃.
9. The method for strengthening and toughening a low-alloy martensitic steel as claimed in any one of claims 1 to 8, wherein in steps (S2) and (S3), the finish forging is followed by immersion in 60 ℃ quenching oil and cooling to room temperature.
10. A low alloy martensitic steel treated by a method as claimed in any one of claims 1 to 9.
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| CN112941274A (en) * | 2021-01-28 | 2021-06-11 | 西京学院 | Method for improving high-carbon chromium steel strength and toughness and application thereof |
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