CN114480984B

CN114480984B - Ti alloyed low-density high-strength steel and preparation method thereof

Info

Publication number: CN114480984B
Application number: CN202111534311.2A
Authority: CN
Inventors: 曹文全; 李龙雨; 蔡明�; 黄子昕; 王存宇; 俞峰; 徐海峰
Original assignee: Central Iron and Steel Research Institute; Huawei Technologies Co Ltd
Current assignee: Central Iron and Steel Research Institute; Huawei Technologies Co Ltd
Priority date: 2021-12-15
Filing date: 2021-12-15
Publication date: 2022-12-16
Anticipated expiration: 2041-12-15
Also published as: CN114480984A

Abstract

Ti alloyed low-density high-strength steel and a preparation method thereof, belonging to the technical field of low-density steel. The chemical mass percentage is as follows: c is more than or equal to 1% in 4.5%, mn is more than or equal to 25% in 35%, al is more than or equal to 8% in 12%, ti is more than or equal to 1% in 10%, and the balance is Fe and inevitable impurities, on the basis, mo is less than or equal to 5%, V is less than or equal to 5%, nb is less than or equal to 0.5%, and rare earth microalloy elements are added for reinforcement; the microstructure consists of an austenite matrix and a precipitated phase, and the TiC precipitated phase is utilized to play a role in refining grains in the low-density steel. Through smelting, forging and solution treatment, the effects of TiC precipitated phase regulation and grain refinement are utilized to obtain the austenite-based low-density steel with the density less than or equal to 6.6g/cm ³ The tensile strength is more than or equal to 1000MPa.

Description

Ti alloyed low-density high-strength steel and preparation method thereof

Technical Field

The invention belongs to the technical field of low-density steel, and particularly relates to Ti alloyed low-density high-strength steel and a preparation method thereof.

Background

With the improvement of light weight level requirements of people on equipment, devices and the like, low-density materials are rapidly developed, and compared with nonferrous metals such as aluminum alloy, magnesium alloy and the like, plastics and the like, low-density steel has obvious advantages in the aspects of cost, strength level, low carbonization in manufacturing and the like. The low-density steel generally achieves density reduction by adding light alloy elements such as C, al, mn and the like into the steel, the degree of density reduction is increased when the addition amount of the alloy elements is larger, and low-density steels with different tissue types can be obtained when the addition amount of the low-density elements is different.

The low-density steel with an austenite matrix is generally low in strength level, domestic patents are researched, and the density, strength, plasticity and the like of the material cannot meet the requirements of the project. Such as: the Chinese patent publication numbers are: CN104711494A "Low Density high plasticity NiAl reinforced ultra high Strength Steel and method of preparation" adding 0.5-1.5% C,10-30% Mn,5-12% Al and 5-15% Ni element of FeMnAlC alloy to achieve a density of 6.5-7.2g/cm ³ The tensile strength of the NiAl phase reinforcement is 1350MPa, and the elongation is more than 10%. The Chinese patent publication numbers are: CN106011653A high strength, high toughness and low density steel and its manufacturing method add 0.1-0.6% of C,4.5-7.5% of Al, mn + Cr + Mo + Ni + Cu and less than 10%, obtaining low density and high plasticity steel with density less than 7.5g/cm3 and elongation not less than 18%. The Chinese patent publication numbers are: CN104928569A discloses a 800MPa grade low density steel having a ferrite + austenite dual phase structure in the content of 0.25-0.5% C,0.25-4.0% Mn,3.0-7.0% Al, the density of the steel being up to less than 7.5g/cm3, the tensile strength>800MPa, elongation percentage>25 percent. The Chinese patent publication numbers are: CN103820735A an ultra-high strength C-Al-Mn-Si series low density steel and a preparation method thereof invents a low density steel with a density of less than or equal to 7.4g/cm3 and a tensile strength of more than or equal to 800MPa, invents an alloy system with a content of 0.28-1.15% C, a content of 6.9-27.6% Mn, a content of Si0.01-2.0%, a content of 3-12% Al as a main component,obtaining the low-density steel with the tensile strength of more than or equal to 800 MPa. CN110066969A discloses a high corrosion resistant high Al content low density steel for ocean platform medium plate and its preparation method, which is composed of 0.01-0.035C, 4.01-6.00% Al,0.01-0.2% Mn,1-3% Ni,0.01-0.3% Si,0.008-0.02% Nb,0.1-0.8% Mo, 0-0.05% Ce. Compared with Corten-A, the corrosion resistance of the alloy in the ocean atmosphere environment is improved by more than 50%, and the density is reduced by more than 6%.

In conclusion, the low-density steel is usually added with Al with the mass fraction less than or equal to 7.5 percent under the Fe-Mn-Al-C alloy system, the density can be reduced by about 7.5 percent, and meanwhile, the use of the Ti element in the iron-based low-density steel as a main alloy element is not found. In iron-based steel materials, ti is generally used as a microalloying element, and the element content is generally less than 0.1% (mass percentage) by forming a precipitation phase to achieve the effects of grain refinement and precipitation strengthening, rather than utilizing the effect of density reduction. The density of Ti element is 4.54g/cm ³ The exploration of the effect of Ti as a main alloy element in low-density steel on density reduction is of great significance to the development of low-density steel.

Disclosure of Invention

The invention aims to provide Ti alloyed low-density high-strength steel and a preparation method thereof, and solves the problems that the existing austenitic low-density steel is low in strength and is high in density reduction difficulty under the condition of keeping a certain mechanical property. Ti element is used as a main alloying element rather than microalloying; through smelting, forging and solution treatment, the matrix structure of the steel is austenite by utilizing the control of TiC precipitated phase and the effect of grain refinement, the tensile strength is more than or equal to 1000MPa, and the density is less than or equal to 6.6g/cm ³ 。

The Ti alloyed high-strength low-density steel comprises the following chemical components in percentage by mass: c is more than or equal to 1% at 4.5%, mn is more than or equal to 25% at 35%, al is more than or equal to 8% at 12%, ti is more than or equal to 1% at 10%, and the balance is Fe and inevitable impurities, and microalloy elements such as Mo is less than or equal to 5%, V is less than or equal to 5%, nb is less than or equal to 0.5%, and rare earth can be added for reinforcement.

Ti is used as a main alloy element for alloying the low-density steel, and a large amount of TiC precipitated phases are formed by utilizing Ti and C, so that the addition amount of light elements is ensured; the microstructure consists of an austenite matrix and a precipitated phase, and the TiC precipitated phase is utilized to play a role in refining grains in the low-density steel.

The design principle of the chemical elements in the Ti alloyed high-strength low-density steel is as follows:

carbon: c is used as an austenite stabilizing element to promote the formation of a single-phase austenite structure, and the C element which is dissolved in the steel in a solid way plays a role in strengthening the solid solution of gaps and obviously reducing the density of the steel. The addition amount of the element C is 1.0-4.5%.

Manganese: the addition of Mn expands an austenite phase region, is beneficial to obtaining a large amount of metastable austenite at room temperature, improves the stacking fault energy of the alloy, reduces the Ms temperature, inhibits martensite phase transformation, generates dense twin crystals in the deformation process, and obviously improves the elongation of the low-density steel. Mn can exist in a solid solution state, can enter a cementite to replace a part of Fe atoms, can also form sulfide, easily forms a segregation zone structure when the Mn content is too high, and reduces the welding performance, thereby being not beneficial to improving the comprehensive performance of the low-density steel. The Mn element weakly lowers the density of the steel. In order to obtain the austenite matrix, the content of Mn element is more than or equal to 25 percent.

Aluminum: al not only reduces the density of the alloy, but also improves the stacking fault energy, inhibits the transformation from austenite to transitional martensite, is beneficial to the formation of deformation twin crystals, is easy to react with Fe/Mn to generate intermetallic compounds, forms B2 brittle phase which cannot be sheared, causes dislocation plug product at the phase interface, and improves the work hardening rate. The high manganese steel contains certain aluminum, so that the heat deformation resistance of the steel can be obviously improved, the dynamic recrystallization can be delayed, and austenite grains can be refined after the dynamic recrystallization. The Al element can obviously reduce the density of the steel, but the adding amount is too large, so that the brittleness of the material is increased. The content of Al element is 8-12%.

Titanium: the density of the Ti element is 4.54g/cm ³ The addition of a large amount of Ti element can obviously reduce the density of steel, the Ti element is easy to form TiC precipitation with C element, and the Ti element is used as the characteristic of low density and easy to form TiC precipitation phase in the invention, and is added at the same timeThe C and Ti realize the low density of the steel, and the content of Ti element in the invention is more than or equal to 1 percent

In addition, micro alloy elements such as Mo, V, nb, rare earth and the like can be added into the steel for strengthening, and impurity elements mainly comprising O, N, P and S are inevitably present, wherein P is less than or equal to 0.010 percent, and S is less than or equal to 0.005 percent.

The microstructure of the Ti alloyed high-strength low-density steel is an austenite matrix, wherein a TiC precipitated phase and a k phase are distributed.

In order to achieve the aim, the invention discloses a preparation method of Ti alloyed high-strength low-density steel, which sequentially comprises the following steps:

(1) Smelting; adopting a vacuum induction furnace or an electric furnace + LF + VD;

(2) Casting; adopting die casting; the casting blank heating comprises two modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling, the finish forging temperature or the finish rolling temperature is 800-1000 ℃, the solution treatment directly reaches the use state after rolling/forging, or the off-line treatment is carried out after slow cooling.

(3) Rolling or forging; the casting blank heating comprises two seed separation modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling, the finish forging temperature or the finish rolling temperature is 800-1000 ℃, the solution treatment directly reaches the use state after rolling/forging, or the off-line treatment is carried out after slow cooling.

(4) Solid solution (+ aging): according to the product performance, the forged blank or the steel plate/bar is subjected to solution treatment at 900-1150 ℃ and aging treatment at 400-750 ℃.

Compared with the prior art, the method has the advantages that the scientific component design and the process flow are adopted to obtain the low-density ultrahigh-strength steel, and the difference from the previously disclosed technical means in the field is as follows:

1. according to the invention, a large amount of Ti element is added into the low-density austenite FeMnAlC steel, and more low-density elements C and Ti can be added compared with the original austenite steel, so that the density of the steel is obviously reduced;

2. the microstructure has austenite matrix, a great amount of TiN is used as a strengthening phase, and the material has tensile property of more than 1000MPa.

Drawings

FIG. 1 is a metallographic picture of a steel C containing Ti in the example.

FIG. 2 is a metallographic picture of comparative steel E.

FIG. 3 is a photograph of EBSD of the example Ti-containing steel C.

FIG. 4 is a photograph of an EBSD of comparative steel E.

FIG. 5 tensile diagram of example Ti-containing steel C.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. 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.

Examples

The inventive steels (A, B, C, D) and the comparative steel (E) were melted in a vacuum induction furnace according to the chemical composition shown in Table 1, and vacuum cast into steel ingots, which were forged into round bars 15mm in diameter after heat preservation at 1150 ℃ for 2 hours, final forging temperature was 850 ℃, and ash-cooled to room temperature after forging. The tensile properties of the samples were evaluated in accordance with GB/T228, and the results are shown in Table 2.

TABLE 1 chemical composition of inventive steels

The microstructure of TiC precipitated particles with a certain proportion distributed on austenite as a matrix is obtained after the test steel is subjected to solution treatment, the metallographic picture of the microstructure of a C steel 1150 ℃ solution treatment sample is shown in figure 1, and due to the existence of TiC precipitated phases, the heating process is effectively preventedGrain growth, with a grain size significantly lower than that of similar low density steels (comparative steel E, FIG. 2); an EBSD photo of a sample of C steel subjected to 1150 ℃ solution treatment is shown in figure 3, 15-degree large-angle grain boundaries are defined, black lines are analyzed to be austenite grain boundaries, a blocky structure is TiC precipitated particles, and a matrix is austenite. FIG. 4 is an EBSD photograph of comparative steel E containing no Ti, with a significantly coarse grain size. The tensile curve of the C steel sample subjected to the solution treatment at 1150 ℃ is shown in FIG. 3, and it can be seen that the density is 6.42g/cm ³ The tensile strength is more than or equal to 1000MPa, and the elongation after fracture of the steel can reach more than 20 percent.

TABLE 2 Heat treatment Process and mechanical Properties of the inventive steels

Claims

1. A Ti alloyed low-density high-strength steel is characterized by comprising the following components in percentage by mass: c is more than or equal to 2 percent in 4.5 percent, mn is more than or equal to 25 percent in 35 percent, al is more than or equal to 11 percent in 12 percent, ti is more than or equal to 1 percent in 3 percent, and Fe and inevitable impurities are added for reinforcement, wherein Mo is less than or equal to 5 percent, V is less than or equal to 5 percent, nb is less than or equal to 0.5 percent, and rare earth micro-alloy elements are added for reinforcement; the microstructure consists of an austenite matrix and a precipitated phase, and the TiC precipitated phase is utilized to play a role in refining grains in the low-density steel;

the preparation method of the Ti alloyed low-density high-strength steel comprises the following process steps and technical parameters:

(1) Smelting; remelting in a vacuum induction furnace or an electric furnace + LF + VD/RH or on the basis of the smelting;

(2) Casting; adopting die casting; the casting blank heating comprises two seed separation modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling;

(3) Rolling or forging; the casting blank heating comprises two modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling, the finish forging temperature or the finish rolling temperature is 800-1000 ℃, the solution treatment directly reaches the use state after rolling/forging, or the off-line treatment is carried out after slow cooling;

(4) Solid solution and aging: according to the product performance, the forging stock or the steel plate/bar is subjected to solution treatment at 1150 ℃ and aging treatment at 400-750 ℃.

2. A method for preparing Ti alloyed low density high strength steel as claimed in claim 1, characterized in that the technological steps and controlled technical parameters are as follows:

(2) Casting; die casting is adopted; the casting blank heating comprises two modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling;

(3) Rolling or forging; the casting blank heating comprises two seed separation modes of hot charging and hot conveying or cold discharging and reheating, the heating temperature is 1100-1200 ℃, and the furnace holding time is 2-20 hours; the deformation mode of the billet comprises forging or rolling, the finish forging temperature or the finish rolling temperature is 800-1000 ℃, the solution treatment directly reaches the use state after rolling/forging, or the offline treatment is carried out after slow cooling;