CN114107821A - High-toughness ultrahigh-strength steel and manufacturing method thereof - Google Patents
High-toughness ultrahigh-strength steel and manufacturing method thereof Download PDFInfo
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Abstract
The invention discloses high-toughness ultrahigh-strength steel and a manufacturing method thereof, belongs to the technical field of metal materials, and aims to solve the problems of poor toughness and poor hardenability of the conventional low-alloy ultrahigh-strength steel. The high-toughness ultrahigh-strength steel comprises the following elements in percentage by mass: 0.27 to 0.35 percent of C, 1.10 to 1.70 percent of Si, 0.70 to 1.10 percent of Mn, 1.00 to 1.40 percent of Cr, 0.10 to 0.50 percent of Ni, 0.05 to 0.50 percent of Mo, 0.05 to 0.10 percent of W, 0.01 to 0.04 percent of Nb, and the balance of iron and inevitable impurities. The steel has good obdurability and hardenability.
Description
Technical Field
The invention belongs to the technical field of metal materials, and particularly relates to high-toughness ultrahigh-strength steel and a manufacturing method thereof.
Background
The service environment of key parts in the aerospace field is severe, the materials are required to have ultrahigh strength and good toughness, and at present, 35CrMnSiA steel is most commonly used, and the tensile strength range is 1650-. The 35CrMnSiA is an ancient variety developed in the 50 th of the last century, has high strength and low price, but has lower toughness, the requirement of the impact energy in the current national standard is only more than or equal to 31J, and the actually measured impact energy is mostly in the range of 35-50J; and the hardenability is seriously insufficient, the critical hardenability dimension is only phi 40mm, and the application is limited as the specification of the part is increased.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a high-toughness ultrahigh-strength steel capable of solving at least one of the following technical problems: (1) the toughness of the existing low-alloy ultrahigh-strength steel is poor; (2) the existing low-alloy ultrahigh-strength steel has poor hardenability.
The purpose of the invention is mainly realized by the following technical scheme:
in one aspect, the invention provides high-toughness ultrahigh-strength steel, which comprises the following elements in percentage by mass: 0.27 to 0.35 percent of C, 1.10 to 1.70 percent of Si, 0.70 to 1.10 percent of Mn, 1.00 to 1.40 percent of Cr, 0.10 to 0.50 percent of Ni, 0.05 to 0.50 percent of Mo, 0.05 to 0.10 percent of W, 0.01 to 0.04 percent of Nb, and the balance of iron and inevitable impurities.
Optionally, the high-toughness ultrahigh-strength steel further comprises 0-0.150% of V.
Optionally, the high-toughness ultrahigh-strength steel comprises the following elements in percentage by mass: 0.28 to 0.34 percent of C, 1.20 to 1.60 percent of Si, 0.80 to 1.10 percent of Mn, 1.20 to 1.35 percent of Cr, 0.15 to 0.30 percent of Ni, 0.05 to 0.30 percent of Mo, 0.05 to 0.10 percent of W, 0.015 to 0.038 percent of Nb, and the balance of iron and inevitable impurities.
Optionally, the high-toughness ultrahigh-strength steel further comprises 0.03-0.1% of V.
Optionally, the microstructure of the high-toughness ultrahigh-strength steel is lath martensite, thin-film retained austenite, fine-dispersed composite epsilon-carbide and nano-grade NbC.
The invention also provides a manufacturing method of the high-toughness ultrahigh-strength steel, which is used for manufacturing the high-toughness ultrahigh-strength steel, and the manufacturing method of the high-toughness ultrahigh-strength steel comprises the following steps:
step S1, smelting to obtain a steel ingot;
step S2, placing the steel ingot into a heating furnace for temperature equalization;
step S3, forging after temperature equalization;
step S4, annealing the red steel after forging to obtain a forged piece;
and step S5, sequentially carrying out normalizing, oil quenching and tempering on the forged piece to obtain the high-toughness ultrahigh-strength steel.
Optionally, in step S3, the forging process includes forming by triple upsetting and triple drawing, and the forging deformation ratio is greater than or equal to 6.
Optionally, in step S4, the annealing temperature is 650 to 680 ℃, and the annealing time is not less than 12 hours.
Optionally, in step S5, the normalizing and heat preserving temperature is 920-970 ℃.
Optionally, in step S5, the quenching temperature is 870-930 ℃, and the tempering temperature is 220-260 ℃.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
a) in the invention, a small amount of Ni, Mo, W and Nb are added for alloying, and Ni element is austenite stabilizing element and can form film austenite among martensite laths to enhance the toughness of a matrix; mo and W can play a role in solid solution strengthening and alloy carbide strengthening, and the hardenability of the steel is enhanced; a small amount of Nb element can form nano NbC which can exist at a higher temperature, thus playing a role in refining grains and further improving the toughness.
b) According to the invention, the contents of elements such as C, Si, Mn, Cr, Ni, Mo, W and Nb are accurately controlled, and the microstructure of the steel is ensured to be lath martensite, film austenite not more than 3%, fine dispersed composite epsilon-carbide and nano NbC by a control process, so that the toughness of the steel is improved. For example, tensile strength is 1739MPa or more (e.g., 1739-1842 MPa), yield strength is 1405MPa or more (e.g., 1405-1485 MPa), elongation is 11.0% or more (e.g., 11.0-13.5%), face shrinkage is 46% or more (e.g., 46-56%), impact energy is 52J or more (e.g., 52-78J), fracture toughness is 98MPa, and m is1/2The above (e.g., 98-130 MPa & ltm & gt)1/2)。
c) In the manufacturing method, the microstructure obtained by quenching is a lath martensite matrix and trace film-shaped residual austenite, because the high Si content effectively improves the anti-tempering softening capability, fine and dispersed composite epsilon-carbide is separated out after tempering, the separation of cementite is avoided, and the high-strength martensite matrix can be fully recovered to obtain good toughness and toughness matching.
d) The high-toughness ultrahigh-strength steel has better toughness and hardenability, and the alloy and manufacturing cost is not obviously increased.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.
FIG. 1 is a metallographic structure of a sample No. 2 in example of the present invention;
FIG. 2 is a transmission electron micrograph of a sample No. 2 in example 2 of the present invention.
Detailed Description
The following detailed description of the preferred embodiments of the invention, which are given for the purpose of illustrating the principles of the invention and are not to be taken in a limiting sense.
The invention provides high-toughness ultrahigh-strength steel, which comprises the following elements in percentage by mass: 0.27 to 0.35 percent of C, 1.10 to 1.70 percent of Si, 0.70 to 1.10 percent of Mn, 1.00 to 1.40 percent of Cr, 0.10 to 0.50 percent of Ni, 0.05 to 0.50 percent of Mo, 0.05 to 0.10 percent of W, 0.01 to 0.04 percent of Nb, and the balance of iron and inevitable impurities.
Specifically, the elements of the ultrahigh-strength steel can be added with 0-0.150% of V, such as 0.03-0.150% of V.
The elements of the present invention are explained in detail below, and the contents refer to the mass percentages of the respective elements in the steel.
C: c is a strengthening element, mainly carbon atoms are subjected to solid solution strengthening after martensite transformation and metastable carbide precipitation strengthening through low-temperature tempering, the strength cannot reach the required level when the carbon content is too low, and the toughness is damaged when the carbon content is too high, so that the designed carbon content is between 0.27 and 0.35 percent.
Si: as one of the main alloy elements of the steel of the present invention, Si added is dissolved in a martensite matrix, the strength of the steel is improved by solid solution strengthening, and the tempering resistance of the steel is improved so that the tempering temperature (low temperature tempering) of the steel of the present invention is far from the temperature range of tempered martensite brittleness, but excessive Si reduces the solubility of elements such as Mo in a steel matrix, and alloy carbides remain during quenching heating, and the toughness of the steel is damaged, so that the Si content of the present invention is controlled to be 1.10 to 1.70%.
Cr: as one of the main alloy elements of the steel of the present invention, the hardenability of the steel can be improved, the strength of the steel can be improved by solid solution strengthening, and the tempering resistance of the steel can be improved by Cr, but too high Cr content reduces the thermal conductivity of the steel, and simultaneously, the martensite transformation temperature (Ms) is reduced and the proportion of twin crystal martensite is increased, so that the Cr content of the present invention is controlled to be 1.00-1.40%.
Ni: as an austenite forming element, the small amount of the austenite forming element can improve the toughness of a steel matrix and the hardenability; however, too high Ni increases the cost, lowers the martensitic transformation temperature (Ms), and increases the proportion of twin martensite. Therefore, the Ni content of the invention is controlled between 0.10 percent and 0.50 percent.
Mo: the steel of the present invention has the effects of improving strength by solid solution strengthening or formation of alloy carbide by adding a small amount of Mo, improving hardenability, purifying grain boundaries, and suppressing temper embrittlement, but excessively high Mo causes alloy carbide to remain during quenching heating, and deteriorates the toughness of the steel. Therefore, the Mo content of the invention is controlled between 0.05 percent and 0.50 percent.
W: according to the invention, trace W element is added into the steel, so that the hardenability is improved, and the strength of the steel can be improved by solid solution in a matrix or formation of alloy carbide; w and Mo are easy to be subjected to segregation in grain boundaries, so that the grain boundary binding force can be improved, and the toughness is enhanced. But W will form M6C carbide, the re-solution temperature of which is high, obviously increases the solid solution temperature when the W content is increased, and increases the solid solution temperature by about 50-80 ℃ every time when the W content is increased by 0.5 percent, thereby generating coarse grains to reduce the ductility and toughness; and the addition of W also obviously improves the hot working difficulty and is easy to cause cracking. Therefore, the W content of the invention is controlled within the range of 0.05-0.10%.
Nb is microalloying element, a proper amount of nano-grade NbC carbide is remained during quenching and heating so as to prevent austenite grains from growing large, and the martensite scale of the quenched lath is refined; however, too high Nb content will form large Nb (C/N) inclusions, which reduce the toughness of the steel. Therefore, Nb is controlled to be 0.01 to 0.04 percent.
V is microalloying element to form MC type carbide with stability lower than NbC, low precipitation temperature and small size. Proper amount of nano-scale VC carbide is remained during quenching and heating to prevent austenite grains from growing and refine the martensite scale of the quenched lath. Too much V content does not enhance the effect of grain refinement, so V: less than or equal to 0.15 percent, such as 0.03 to 0.1 percent.
In order to further improve the toughness of the steel, the mass percentages of the elements in the high-toughness ultrahigh-strength steel of the invention can comprise: 0.28 to 0.34 percent of C, 1.20 to 1.60 percent of Si, 0.80 to 1.10 percent of Mn, 1.20 to 1.35 percent of Cr, 0.15 to 0.30 percent of Ni, 0.05 to 0.30 percent of Mo, 0.05 to 0.10 percent of W, 0.015 to 0.038 percent of Nb, less than or equal to 0.10 percent of V, and the balance of iron and inevitable impurities.
Specifically, the microstructure of the high-toughness ultrahigh-strength steel is lath martensite, film-shaped retained austenite not more than 3%, finely dispersed composite epsilon-carbide and nano-grade NbC, wherein Cr, Ni, W and Mo are dissolved in a martensite matrix, and W, Mo is dissolved in the composite epsilon-carbide; w, Mo is dissolved in a martensite matrix to improve the bonding force of the grain boundary, W, Mo is dissolved in composite epsilon-carbide to form composite alloy carbide with higher tempering stability, and a small amount of NbC carbide is contained in the structure to play a role in refining grains.
In addition, the high-toughness ultrahigh-strength steel is alloyed by adding a small amount of Ni, Mo, W and Nb, wherein the Ni element is an austenite stabilizing element and can form film-shaped austenite among martensite laths to enhance the toughness of a matrix; mo and W can play a role in solid solution strengthening and alloy carbide strengthening, and the hardenability of the steel is enhanced; a small amount of Nb element can form nano NbC which can exist at a higher temperature, so that the function of refining grains is achieved, and the toughness is further improved; and the contents of elements such as C, Si, Mn, Cr, Ni, Mo, W and Nb are accurately controlled, so that the microstructure of the steel is guaranteed to be lath martensite, thin-film austenite, fine dispersed composite epsilon-carbide and nano NbC, and the toughness of the steel is further improved. For example, the tensile strength is 1739MPa or more (e.g., 1739 to 1842MPa), the yield strength is 1405MPa or more (e.g., 1405 to 1485MPa), the elongation is 11.0% or more (e.g., 11.0% to 13.5%), and the area shrinkage is 46% or more(e.g., 46% -56%), impact work of 52J or more (e.g., 52-78J), fracture toughness of 98 MPa-1/2The above (e.g., 98-130 MPa & ltm & gt)1/2)。
The method for manufacturing the high-toughness ultrahigh-strength steel comprises the following steps:
step S1, smelting by adopting the process of an electric furnace or a non-vacuum induction furnace, external refining and electroslag remelting to obtain a steel ingot;
s2, placing the steel ingot into a heating furnace for temperature equalization, wherein the temperature equalization is maintained at 1170-1220 ℃, and the temperature maintaining time is calculated according to the temperature maintaining time of 15-20 min (preferably 15min) for each 25mm of section diameter;
step S3, forging after temperature equalization; the initial forging temperature is more than or equal to 1150 ℃, and the final forging temperature is more than or equal to 850 ℃;
step S4, annealing the red steel after forging to obtain a forged piece;
step S5, final heat treatment: and (3) normalizing, oil quenching and tempering the forging piece in sequence to obtain the high-toughness ultrahigh-strength steel.
Specifically, in the step S2, too high temperature equalization causes coarse grains, too low temperature equalization causes insufficient forging window, too long temperature equalization time causes excessive growth of crystal grains and resource waste, too short temperature equalization causes heat failure in the core and uneven temperature, therefore, the holding temperature of the temperature equalization is controlled to 1170-1220 ℃, and the holding time is calculated according to the holding time of 15-20 min (preferably, 15min) per 25mm of section diameter.
Specifically, in step S3, the forging process includes three upsetting and three drawing to form, and the sufficient forging ratio ensures that the core is completely forged and the as-cast structure is sufficiently crushed, so that the forging deformation ratio is not less than 6.
Specifically, in the step S4, too high or too low of the annealing heat preservation temperature will prolong the time to reach the equilibrium state, so the annealing heat preservation temperature is controlled to be 650-680 ℃, and the annealing heat preservation time is not less than 12 h.
Specifically, in the step S5, normalizing, heat-preserving at 920-970 ℃ for 1-4 h, and air-cooling. Specifically, during implementation, the heat preservation time is related to the diameter of the forging, and can be determined according to a specific process.
Specifically, in the step S5, the quenching temperature is 870-930 ℃, the heat preservation time is 1-4 hours, and the oil cooling is carried out. Specifically, during implementation, the heat preservation time is related to the diameter of the forging, and can be determined according to a specific process.
Specifically, in the step S5, the tempering temperature is 220-260 ℃, the heat preservation time is 2-8 hours, and air cooling is carried out. Specifically, during implementation, the heat preservation time is related to the diameter of the forging, and can be determined according to a specific process.
Specifically, in step S5, the structure obtained by quenching is lath martensite matrix and trace film-like retained austenite, and due to the higher Si content, the tempering softening resistance is effectively improved, fine and dispersed composite epsilon-carbides are precipitated after tempering, thereby avoiding the precipitation of cementite, and the high-strength martensite matrix can be fully recovered to obtain good toughness and toughness matching.
Specifically, the quasi-static mechanical properties of the high-toughness ultrahigh-strength steel prepared by the method are as follows: tensile strength of 1739MPa or more (e.g. 1739-1842 MPa), yield strength of 1405MPa or more (e.g. 1405-1485 MPa), elongation of 11.0% or more (e.g. 11.0-13.5%), face shrinkage of 46% or more (e.g. 46-56%), impact energy of 52J or more (e.g. 52-78J), fracture toughness of 98MPa and m1/2The above (e.g., 98-130 MPa & ltm & gt)1/2)。
The advantages of the steel according to the invention with regard to the precise control of the composition and process parameters will be shown in the following in the specific examples and comparative examples.
Examples
A vacuum induction furnace of 50kg was used to produce test steels Nos. 1-5, the chemical compositions of which are shown in Table 1. Placing the steel ingot into a heating furnace for temperature equalization, wherein the heat preservation temperature is 1200 ℃, and the heat preservation time is calculated according to the heat preservation time of every 25mm of the section diameter for 15 min; carrying out forging after temperature equalization; forging the steel ingot into a square bar of 40 multiplied by 40mm, wherein the forging initial forging temperature is 1200 ℃, the finish forging temperature is 850 ℃, the forging process comprises three upsetting and three drawing, and the forging deformation ratio is more than or equal to 6; annealing at 660 ℃ after forging; then, heat treatment was carried out by using the heat treatment schedule shown in Table 2.
Table 1 chemical composition (wt.%) of the examples of the present invention
| Numbering | C | Si | Mn | Cr | Ni | Mo | W | Nb | V |
| 1# | 0.30 | 1.20 | 0.90 | 1.21 | 0.29 | 0.05 | 0.09 | 0.022 | - |
| 2# | 0.28 | 1.35 | 1.04 | 1.25 | 0.30 | 0.10 | 0.10 | 0.015 | - |
| 3# | 0.32 | 1.51 | 0.93 | 1.35 | 0.15 | 0.26 | 0.08 | 0.038 | - |
| 4# | 0.34 | 1.43 | 0.85 | 1.30 | 0.21 | 0.30 | 0.06 | 0.027 | 0.08 |
| 5# | 0.32 | 1.60 | 0.80 | 1.20 | 0.26 | 0.24 | 0.05 | 0.030 | 0.10 |
| Comparative example | 0.33 | 1.29 | 0.97 | 1.28 | - | - | - | - | - |
TABLE 2 Heat treatment Process parameters
| Numbering | Normalizing | Quenching | Tempering |
| 1# | Air cooling at 940 deg.C for 1 hr | 890 ℃ for 1h, oil cooling | Air cooling at 240 deg.C for 2 hr |
| 2# | Air cooling at 950 deg.C for 1h | At 880 ℃ for 1h, cooling with oil | Cooling at 230 deg.C for 2 hr, and air cooling |
| 3# | Cooling at 930 deg.C for 1 hr | At 880 ℃ for 1h, cooling with oil | Air cooling at 235 deg.C for 2 hr |
| 4# | 955 ℃ for 1h, and is air-cooled | Cooling at 920 ℃ for 1h in oil | Air cooling at 250 deg.C for 2 hr |
| 5# | Air cooling at 960 deg.C for 1h | Cooling at 930 deg.C for 1 hr | Air cooling at 260 deg.C for 2 hr |
| Comparative example | At 950 ℃ for 1h, oil cooling | 890 ℃ for 1h, oil cooling | Cooling at 230 deg.C for 2 hr, and air cooling |
TABLE 3 microstructure of heat-treated examples of the invention
| Numbering | Microstructure of |
| 1# | Lath martensite + about 1% thinFilm-like retained austenite + small amount of NbC + epsilon-carbide |
| 2# | Lath martensite + about 1% film-like retained austenite + a small amount of NbC + epsilon-carbide |
| 3# | Lath martensite + about 1% film-like retained austenite + a small amount of NbC + epsilon-carbide |
| 4# | Lath martensite + about 1% film-like retained austenite + a small amount of NbC/VC + epsilon-carbide |
| 5# | Lath martensite + about 1% film-like retained austenite + a small amount of NbC/VC + epsilon-carbide |
| Comparative example | Lath martensite + epsilon-carbide |
TABLE 4 quasi-static mechanical Properties
Table 3 shows the microstructure of the test steels of examples 1 to 5# and Table 4 shows the quasi-static mechanical properties of the steels of examples 1 to 5# respectively. It can be seen that in examples 1# to 5# alloyed by adding small amounts of Ni, Mo, W elements and trace amounts of Nb (and or V), the metallographic structure of the steel was lath martensite + thin-film retained austenite of not more than 3% (area%) plus a small amount of NbC/VC + ε -carbides (FIGS. 1-2). W, Mo solid solution in martensite matrix to produce solid solution strengthening, enhance hardenability and promote grain boundary binding force, W, Mo solid solution in epsilon-carbide to form composite alloy carbide with high tempering stability(ii) a Ni is dissolved in a matrix in a solid mode to improve the toughness of martensite laths and form a small amount of film-shaped residual austenite among the laths; nb and V form nano carbide and play a role in refining grains during quenching. Compared with the comparative example (the existing 35CrMnSiA), the impact toughness of the example is obviously improved (41J is improved to more than 52J), and the fracture toughness is improved by more than 58 percent (62 MPa.m)1/2Is increased to 98 MPa.m1/2The above); in this example, if the strength level is properly lowered to 1700MPa (as shown in example 2), the impact toughness can be further greatly improved to 78J, and the fracture toughness can be doubled (130 MPa. m)1/2)。
Specifically, the steel has good hardenability, and the critical hardenability diameter can reach 80-100 mm.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. The high-toughness ultrahigh-strength steel is characterized by comprising the following elements in percentage by mass: 0.27 to 0.35 percent of C, 1.10 to 1.70 percent of Si, 0.70 to 1.10 percent of Mn, 1.00 to 1.40 percent of Cr, 0.10 to 0.50 percent of Ni, 0.05 to 0.50 percent of Mo, 0.05 to 0.10 percent of W, 0.01 to 0.04 percent of Nb, and the balance of iron and inevitable impurities.
2. The high toughness ultra high strength steel according to claim 1, further comprising V0-0.150%.
3. The high toughness ultra high strength steel according to claim 1, wherein the mass percentages of the elements of said high toughness ultra high strength steel comprise: 0.28 to 0.34 percent of C, 1.20 to 1.60 percent of Si, 0.80 to 1.10 percent of Mn, 1.20 to 1.35 percent of Cr, 0.15 to 0.30 percent of Ni, 0.05 to 0.30 percent of Mo, 0.05 to 0.10 percent of W, 0.015 to 0.038 percent of Nb, and the balance of iron and inevitable impurities.
4. The high toughness ultra high strength steel according to claim 2, further comprising V0.03% to 0.1%.
5. A high toughness ultra high strength steel according to claims 1 to 4, wherein the microstructure of said high toughness ultra high strength steel is lath martensite + thin film-like retained austenite + finely dispersed complex ε -carbide + nanoscale NbC.
6. A method for producing a high toughness ultra high strength steel, characterized by comprising the steps of:
step S1, smelting to obtain a steel ingot;
step S2, placing the steel ingot into a heating furnace for temperature equalization;
step S3, forging after temperature equalization;
step S4, annealing the red steel after forging to obtain a forged piece;
and step S5, sequentially carrying out normalizing, oil quenching and tempering on the forged piece to obtain the high-toughness ultrahigh-strength steel.
7. The manufacturing method according to claim 6,
in the step S3, the forging process includes three-heading and three-drawing for forming, and the forging deformation ratio is more than or equal to 6.
8. The manufacturing method according to claim 6,
in the step S4, the annealing heat preservation temperature is 650-680 ℃, and the annealing heat preservation time is more than or equal to 12 h.
9. The manufacturing method according to claim 6,
in the step S5, the normalizing and heat preserving temperature is 920-970 ℃.
10. The production method according to any one of claims 6 to 9, wherein in step S5, the quenching temperature is 870 to 930 ℃ and the tempering temperature is 220 to 260 ℃.
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| WO2023093119A1 (en) * | 2021-11-26 | 2023-06-01 | 钢铁研究总院有限公司 | High-toughness ultrahigh-strength steel and manufacturing method therefor |
| CN114774630B (en) * | 2022-04-21 | 2024-05-03 | 河南中原特钢装备制造有限公司 | Low-cost low-alloy ultrahigh-strength steel and manufacturing method thereof |
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