Patent Application
20240318273
The present application belongs to the technical field of metal materials, and specifically relates to a high-toughness ultrahigh-strength steel and a manufacturing method thereof.
Key components in the automobile industry work in a harsh environment, and thus materials for the key components need to have an ultrahigh strength and excellent toughness. Currently, 35CrMnSiA steel with a tensile strength of 1,650 MPa to 1,950 MPa is most commonly used for the key components in the aerospace field. 35CrMnSiA is an ancient variety with a high strength and a low price developed in the 1950s. However, 35CrMnSiA has low toughness, an impact energy required to be merely higher than or equal to 31 J in the current national standard, and a measured impact energy mostly of 35 J to 50 J. The hardenability of 35CrMnSiA is seriously insufficient, and a critical hardening size is merely @ 40 mm, such that the application of 35CrMnSiA is limited by a component specification.
In view of the above analysis, the present application is intended to provide a high-toughness ultrahigh-strength steel. The present application can solve at least one of the following technical problems: (1) The existing low-alloy ultrahigh-strength steel has poor toughness. (2) The existing low-alloy ultrahigh-strength steel has poor hardenability.
The objective of the present application is mainly achieved by the following technical solutions.
In a first aspect, the present application provides a high-toughness ultrahigh-strength steel, including the following elements in mass percentages: C: 0.27% to 0.35%; Si: 1.10% to 1.70%; Mn: 0.70% to 1.10%; Cr: 1.00% to 1.40%; Ni: 0.10% to 0.50%; Mo: 0.05% to 0.50%; W: 0.05% to 0.10%; Nb: 0.01% to 0.04%; and iron and unavoidable impurities: the balance.
Optionally, the high-toughness ultrahigh-strength steel further includes: V: 0% to 0.150%.
Optionally, the high-toughness ultrahigh-strength steel includes the following elements in mass percentages: C: 0.28% to 0.34%; Si: 1.20% to 1.60%; Mn: 0.80% to 1.10%; Cr: 1.20% to 1.35%; Ni: 0.15% to 0.30%; Mo: 0.05% to 0.30%; W: 0.05% to 0.10%; Nb: 0.015% to 0.038%; and iron and unavoidable impurities: the balance.
Optionally, the high-toughness ultrahigh-strength steel further includes: V: 0.03% to 0.1%.
Optionally, a microstructure of the high-toughness ultrahigh-strength steel is lath martensite+film-like residual austenite+finely-diffused composite ε-carbide+nano-scale NbC.
In a second aspect, the present application provides a manufacturing method of a high-toughness ultrahigh-strength steel, where the manufacturing method is used to manufacture the high-toughness ultrahigh-strength steel described in the first aspect, and includes the following steps:
Optionally, in the S3, the forging includes forming through three-upsetting and three-drawing with a forging deformation ratio of larger than or equal to 6.
Optionally, in the S4, the hot annealing is conducted at 650° C. to 680° C. for more than or equal to 12 h.
Optionally, in the S5, the normalizing is conducted at 920° C. to 970° C.
Optionally, in the S5, the oil-quenching is conducted at 870° C. to 930° C. and the tempering is conducted at 220° C. to 260° C.
Compared with the prior art, the present application can allow at least one of the following beneficial effects:
Other features and advantages of the present application will be described in the following specification, and some of these will become apparent from the specification or be understood by implementing the present application. The objectives and other advantages of the present application may be implemented and obtained by the specification.
The accompanying drawings are provided merely to illustrate specific embodiments, rather than to limit the present application.
Preferred embodiments of the present application are specifically described below, and these embodiments are provided merely to explain the principles of the present application rather than to limit the scope of the present application.
The present application provides a high-toughness ultrahigh-strength steel, including the following elements in mass percentages: C: 0.27% to 0.35%; Si: 1.10% to 1.70%; Mn: 0.70% to 1.10%; Cr: 1.00% to 1.40%; Ni: 0.10% to 0.50%; Mo: 0.05% to 0.50%; W: 0.05% to 0.10%; Nb: 0.01% to 0.04%; and iron and unavoidable impurities: the balance.
Specifically, the high-toughness ultrahigh-strength steel further includes: V: 0% to 0.150%, such as V: 0.03% to 0.150%.
The elements in the steel of the present application each are described in detail below, and a content of each element refers to a mass percentage of the element in the steel.
In order to further improve the toughness of the steel, the high-toughness ultrahigh-strength steel of the present application may include the following elements in mass percentages: C: 0.28% to 0.34%; Si: 1.20% to 1.60%; Mn: 0.80% to 1.10%; Cr: 1.20% to 1.35%; Ni: 0.15% to 0.30%; Mo: 0.05% to 0.30%; W: 0.05% to 0.10%; Nb: 0.015% to 0.038%; V: less than or equal to 0.10%; and iron and unavoidable impurities: the balance.
Specifically, a microstructure of the high-toughness ultrahigh-strength steel is lath martensite+no more than 3% of film-like residual austenite+finely-diffused composite ε-carbide+nano-scale NbC, where solid solutions in the martensite matrix include Cr, Ni, W, and Mo; solid solutions in the composite ε-carbide include W and Mo; the solid solutions of W and Mo in the martensite matrix can improve binding forces at grain boundaries; the solid solutions of W and Mo in the composite ε-carbide lead to the generation of a composite alloy carbide with high tempering stability; and a small amount of a NbC carbide in the microstructure can play a role of grain refinement.
In the high-toughness ultrahigh-strength steel of the present application, Ni, Mo, W, and Nb are added at small amounts for alloying. The element Ni is an austenite-stabilizing element, and can produce a film-like austenite among martensite laths to enhance the toughness of the matrix. The elements Mo and W can play roles of solid-solution strengthening and alloy carbide strengthening, and enhance the hardenability of the steel. A small amount of the element Nb can produce nano-scale NbC, and the nano-scale NbC can exist at a relatively-high temperature to play a role of grain refinement, thereby further improving the toughness. Contents of C, Si, Mn, Cr, Ni, Mo, W, and Nb can be accurately controlled to ensure that the microstructure of the steel is lath martensite+film-like austenite+finely-diffused composite ε-carbide+nano-scale NbC, thereby improving the strength and toughness of the steel. For example, the steel of the present application can have a tensile strength of 1,739 MPa or more (such as 1,739 MPa to 1,842 MPa), a yield strength of 1,405 MPa or more (such as 1,405 MPa to 1,485 MPa), an elongation of 11.0% or more (such as 11.0% to 13.5%), an RA of 46% or more (such as 46% to 56%), an impact energy of 52 J or more (such as 52 J to 78 J), and a fracture toughness of 98 MPa m1/2 or more (such as 98 MPa·m1/2 to 130 MPa·m1/2).
A manufacturing method of the high-toughness ultrahigh-strength steel in the present application includes the following steps:
Specifically, in the S2, an excessively high temperature for the temperature equalization will cause coarse grains, and an excessively low temperature for the temperature equalization will cause an insufficient forging window; and an excessively long time for the temperature equalization will cause the excessive growth of grains and the waste of resources, and an excessively short time for the temperature equalization will cause failed thorough heating of a core and uneven temperatures. Therefore, the temperature for the temperature equalization is controlled at 1,170° C. to 1,220° C., and the time for the temperature equalization is calculated according to 15 min to 20 min (preferably 15 min) per 25 mm of a cross-sectional diameter.
Specifically, in the S3, the forging includes forming through three-upsetting and three-drawing, where a sufficient forging ratio is required to ensure thorough forging of a core and full fragmentation of a cast structure, and thus a forging deformation ratio needs to be larger than or equal to 6.
Specifically, in the S4, an excessively high or excessively low temperature for the hot annealing will extend a time required to reach an equilibrium state. Therefore, the hot annealing is conducted at 650° C. to 680° C. for more than or equal to 12 h.
Specifically, in the S5, the normalizing is conducted at 920° C. to 970° C. for 1 h to 4 h, and adopts air cooling. Specifically, during an implementation, the time is related to a diameter of the forged piece, and can be determined according to a specific process.
Specifically, in the S5, the quenching is conducted at 870° C. to 930° C. for 1 h to 4 h, and adopts oil cooling. Specifically, during an implementation, the time is related to a diameter of the forged piece, and can be determined according to a specific process.
Specifically, in the S5, the tempering is conducted at 220° C. to 260° C. for 2 h to 8 h, and adopts air cooling. Specifically, during an implementation, the time is related to a diameter of the forged piece, and can be determined according to a specific process.
Specifically, in the S5, a structure obtained after the quenching includes a lath martensite matrix and a trace amount of a film-like residual austenite. Because a high Si content can effectively improve the anti-tempering softening ability, a finely-diffused composite ¿-carbide is precipitated after tempering, which can avoid the precipitation of a cementite and make a high-strength martensite matrix fully restored to acquire an excellent strength and toughness combination.
Specifically, quasi-static mechanical properties of the high-toughness ultrahigh-strength steel prepared by the above method are as follows: tensile strength: 1,739 MPa or more (such as 1,739 MPa to 1,842 MPa), yield strength: 1,405 MPa or more (such as 1,405 MPa to 1,485 MPa), elongation: 11.0% or more (such as 11.0% to 13.5%), RA: 46% or more (such as 46% to 56%), impact energy: 52 J or more (such as 52 J to 78 J), and fracture toughness: 98 MPa·m1/2 or more (such as 98 MPa·m1/2 to 130 MPa·m1/2).
The advantages of accurate control of the composition and process parameters of the steel in the present application are illustrated below through specific examples and comparative example.
A 50 kg vacuum induction furnace was used to smelt test steel samples 1 # to 5 #, and corresponding chemical compositions were shown in Table 1. A steel ingot was subjected to temperature equalization in a heating furnace at 1,200° C. for 15 min per 25 mm of a cross-sectional diameter; then forging was conducted with an initial forging temperature of 1,200° C. and a finish forging temperature of 850° C. to obtain a 40×40 mm square rod, where the forging included forming through three-upsetting and three-drawing with a forging deformation ratio of larger than or equal to 6; and the square rod was subjected to hot annealing at 660° C. and then to heat treatments according to heat treatment systems shown in Table 2.
Table 3 shows microstructures of test steel samples 1 # to 5 # in the examples, and Table 4 shows quasi-static mechanical properties of test steel samples 1 # to 5 # in the examples. It can be seen that, after Ni, Mo, and W are added at small amounts and Nb (and/or V) is added at a trace amount for alloying in Examples 1 # to 5 #, a metallographic structure of a steel is lath martensite+no more than 3% (area percentage) of film-like residual austenite+a small amount of NbC/VC+ε-carbide (
Specifically, the steel of the present application has excellent hardenability with a critical hardening diameter of 80 mm to 100 mm.
The above are merely preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily conceive modifications or replacements within the technical scope of the present application, and these modifications or replacements shall fall within the protection scope of the present application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202111425641.8 | Nov 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/109923 | 8/3/2022 | WO |
