CN102383059A - Hot rolled transformation induced plasticity (TRIP) steel and preparation method thereof - Google Patents

Abstract

The invention discloses a hot-rolled phase transformation-induced plastic steel, which belongs to special steel materials used in automobile, coal and oil exploitation. Mn: 1-2%; Cr: 0.1-1.5%; Ni: ≤1.5%; Al: ≤0.06; N: ≤0.01%, and the rest are Fe and unavoidable impurities. After being smelted into a billet, heat treatment after hot rolling: first, heat preservation at 950°C for 30-60 minutes, then air cooling to 750-800°C and heat preservation for 30-60 minutes, then quenching in a salt bath, and heat preservation at 400-500°C for 20-120 minutes , and then coiled, air-cooled to room temperature, and finally obtain a hot-rolled phase transformation induced plasticity steel with a tensile strength of 600-900MPa, an elongation of 25%-35%, and a strength-plastic product greater than 18000MPa%. The hot-rolled phase transformation induced plasticity steel provided by the invention also has good coating ability, weldability and wear resistance.

Description

A kind of hot-rolled phase transformation induced plasticity steel and preparation method thereof

technical field

The invention relates to a preparation method of a special steel material, which belongs to the application fields of automobile, coal and oil exploitation. In particular, it relates to a hot-rolled transformation-induced plasticity steel (TRIP) and a manufacturing method thereof.

Background technique

Transformation Induced Plasticity (TRIP: Transformation Induced Plasticity) steel is a new type of steel, which uses a new idea to strengthen and toughen steel, that is, to use the retained austenite in the steel to generate strain under stress Transform into martensite, so as to achieve the purpose of strengthening, and at the same time, the plasticity of the material will be greatly increased, so as to realize the optimization of strength and toughness at the same time, which is not available in other steel types. TRIP steel plate has high yield strength and tensile strength, strong ductility, and high stamping ability. Compared with traditional steel plate, the weight of parts made of TRIP steel plate is reduced by about 12%, and the weight of the vehicle is reduced by 10%, which can reduce fuel consumption. %-7%, and at the same time the emission of exhaust gas is also reduced, which reduces the pollution to the environment. At the same time, it has a strong ability to absorb energy and can resist plastic deformation during impact, which significantly improves the safety level of the car and the overall economic benefits. The application of this steel plate has aroused widespread concern and attention in the automotive industry. Since the properties of TRIP steel can be adjusted in a wide range, TRIP steel with different components can obtain different combinations of strength and toughness through different heat treatments, so as to meet the different needs of suspension systems, transmission systems, and safety structural parts. Therefore, the composition ratio and heat treatment process of TRIP steel are still the focus of research in recent years.

Contents of the invention

Aiming at the problems in the preparation process of TRIP steel, in order to make the steel plate have good coating ability, weldability and wear resistance, as well as high strength and plasticity, the invention provides a hot-rolled phase transformation induced plasticity steel The preparation method thereof, combined with a suitable heat treatment process, obtains a hot-rolled phase transformation induced plasticity steel with high yield strength and elongation.

In order to solve the above-mentioned technical problems, the hot-rolled phase-change-induced plasticity steel of the present invention, the material of the hot-rolled phase-change-induced plasticity steel consists of the following components by weight percentage:

C: 0.05-0.4%;

Si: 0.1-0.5%;

Mn: 1~2%;

Cr: 0.1～1.5%;

Ni: ≤1.5%;

Al: ≤0.06%;

N: ≤0.01%;

The rest is Fe and unavoidable impurities.

The material of the hot-rolled phase-transformation-induced plasticity steel of the present invention also contains 0.01-0.1% by weight of V.

The impurity in the material of the hot-rolled phase-transformation-induced plasticity steel of the present invention contains P ≤ 0.025% by weight and S ≤ 0.005% by weight.

The preparation method of a kind of hot-rolled phase transformation induced plasticity steel of the present invention comprises the following steps:

(1) After mixing all raw materials evenly according to the composition and content requirements, smelting in a vacuum induction furnace;

(2) After smelting into steel ingots, heat the steel ingots to 1200°C, heat them for 2 hours and forge them into billets, heat the steel billets to 1250°C for 1.5 hours, and then hot-roll them after the heat preservation is over;

(3) The process of hot rolling is: firstly carry out rough rolling, the rolling temperature is 1150 ~ 1250 ℃, the total deformation of 3 rough rolling passes is 85%; then carry out finish rolling, the total deformation of 2 passes 15%, the rolling temperature is 890-1000°C; the final rolling temperature is 800-850°C, and finally the billet is hot-rolled into a 5-10mm thick steel plate;

(4) Heat treatment of the hot-rolled steel plate: first, keep it at 950°C for 30-60 minutes, then air-cool it to 750-800°C and keep it for 30-60 minutes, then quench it in a salt bath, and keep it at 400-500°C for 20-120 minutes. Minutes, then roll the plate, air-cool to room temperature, and finally obtain a hot-rolled phase transformation induced plasticity steel with a tensile strength of 600-900Mpa, an elongation of 25%-35%, and a strength-plastic product greater than 18000MPa%.

Compared with prior art, the beneficial effect of the present invention is:

The content of carbon C in the hot-rolled phase transformation-induced plasticity steel of the present invention is between 0.05% and 0.4%. When the carbon content is too low, the TRIP effect is not easy to appear; In order to maintain better weldability of the steel plate, the carbon content is generally taken as a small value. For the alloying element silicon Si, when its content is large, stable oxides are likely to be formed on the surface of the steel plate during heat treatment, which will deteriorate the coating ability of the phase transformation-induced plastic steel, affect the surface quality of the steel plate, and reduce the performance. Therefore, the present invention controls the silicon content between 0.1% and 0.5%. At the same time, the present invention also adds 0.1 to 1.5% Cr, which can reduce the austenite transformation zone and increase the critical zone transformation temperature A _C3 , so that the bainite transformation zone moves to the low temperature zone and reduces the martensite transformation temperature (Ms), which is conducive to the acquisition of retained austenite. At the same time, the addition of Cr can also improve the wear resistance and corrosion resistance of the material.

The present invention can optionally add 0.01-0.1% of V. V is a ferrite stabilizing element, which is generally used to inhibit the phase transformation behavior in TRIP steel, and has the effect of precipitation strengthening and grain refinement.

The process of obtaining austenite phase in hot-rolled TRIP steel is relatively easy. Combining phase transformation and deformation heat treatment together, the composition and content of different phases can be obtained by controlling the temperature and time of the two-phase zone and the temperature and time of bainite holding and mechanical properties of steel plates. However, the temperature deviation has a strong influence on the phase transformation behavior and performance. Only by making the temperature uniform in the width and length of the steel plate at the same time can the uniform structure be achieved and the difference in mechanical properties of different parts of the steel plate can be reduced. Therefore, in combination with the characteristics of the alloy composition of the hot-rolled phase transformation-induced plasticity steel of the present invention, a reasonable heat treatment process is formulated at the same time, so that the finally obtained TRIP steel has high strength and high plasticity at the same time.

Description of drawings

Fig. 1 is a schematic diagram of the preparation process of hot-rolled phase transformation-induced plasticity steel of the present invention;

Fig. 2 is the scanning electron micrograph picture after heat treatment of embodiment 1 of the hot-rolled phase-transformation-induced plasticity steel of the present invention;

Fig. 3 is a scanning electron microscope photograph of Example 2 of the hot-rolled phase transformation-induced plasticity steel of the present invention after heat treatment;

Fig. 4 is a scanning electron microscope photograph of Example 3 of the hot-rolled phase transformation-induced plasticity steel of the present invention after heat treatment;

Fig. 5 is a scanning electron micrograph of Example 4 of the hot-rolled transformation-induced plasticity steel of the present invention after heat treatment.

Detailed ways

The following describes the detailed process of the present invention through the examples, and the examples are provided for the convenience of understanding, and are by no means limiting the present invention.

Fig. 1 shows the preparation process of the hot-rolled transformation-induced plasticity steel of the present invention.

The alloy composition of each embodiment of the hot-rolled phase-transformation-induced plasticity steel of the present invention is specified in Table 1; the heat treatment (hot rolling) process parameters in each embodiment of the hot-rolled phase-transition-induced plasticity steel of the present invention are specified in Table 2; Table 3 The tensile test data of each embodiment obtained according to the test method of the national standard is shown.

Embodiment one:

Example 1 The material of the hot-rolled transformation-induced plasticity steel is composed of the components specified in Table 1 below.

The process of preparing hot-rolled phase transformation induced plasticity steel is:

(1) After mixing the raw materials according to the composition and content requirements of the specified embodiment 1 in table 1, smelting in a 25kg vacuum induction furnace;

(2) Smelting the steel with the above components and contents into steel ingots, then heating the steel ingots to 1200°C, forging them into billets after holding for 2 hours, heating the billets to 1250°C for 1.5 hours, and heating them after the heat preservation is over. rolling;

(3) Rough rolling is carried out at first, the rolling temperature is 1200 ℃, the total deformation of 3 passes of rough rolling is 85%; then finish rolling is carried out, the total deformation of 2 passes of finish rolling is 15%, and the rolling temperature is 1000 ℃; the final rolling temperature is 890 ℃, and finally the billet is hot-rolled to a steel plate with a thickness of 6.45 mm; the process parameters of hot rolling are specified in Table 2.

(4) Heat treatment of the hot-rolled steel plate: first, keep it at 870°C for 30 minutes, then air-cool it to 790°C (that is, the dual-phase zone) and keep it for 30 minutes, and then quench it in a salt bath (50% KNO ₃ +50% NaNO ₃ ) treatment, heat preservation at 400°C for 90 minutes, coiling, air cooling to room temperature, and finally obtaining high-strength and high-plasticity hot-rolled phase transformation induced plasticity steel.

Table 3 shows the tensile test data of the hot-rolled transformation-induced plasticity steel in this embodiment.

Embodiment two:

Example 2 The material of the hot-rolled transformation-induced plasticity steel is composed of the components specified in Table 1 below.

Repeat Example 1 to obtain the smelting and hot-rolling forging process of preparing hot-rolled phase transformation-induced plasticity steel, but the final rolling temperature of step (3) for rolling the steel plate is 920°C, and finally the steel billet is hot-rolled to a thickness of 6.5mm The steel plate; Step (4) is different to the heat treatment of steel plate and embodiment one, specifically: first at 900 ℃ of insulation 30 minutes, then air-cooled to 760 ℃ of insulation 30 minutes, then salt bath (50%KNO ₃ +50% NaNO ₃ ) quenching treatment, heat preservation at 400°C for 90 minutes, then coiling, air cooling to room temperature, the tensile test data of the finally obtained hot-rolled phase transformation induced plasticity steel is shown in Table 3.

Embodiment three:

Example 3 The material of the hot-rolled transformation-induced plasticity steel is composed of the components specified in Table 1 below.

Repeat Example 1 to obtain the smelting and hot-rolling forging process of preparing hot-rolled phase transformation-induced plasticity steel, but in step (3), the final rolling temperature for rolling the steel plate is 950°C, and finally the steel billet is hot-rolled to a thickness of 6.38mm The steel plate; Step (4) is different to the heat treatment of steel plate and embodiment one, specifically: first at 900 ℃ of insulation 30 minutes, then air-cooled to 760 ℃ of insulation 30 minutes, then salt bath (50%KNO ₃ +50% NaNO ₃ ) quenching treatment, heat preservation at 500°C for 60 minutes, then coiling, air cooling to room temperature, the tensile test data of the finally obtained hot-rolled phase transformation induced plasticity steel is shown in Table 3.

Embodiment four:

Example 4 The material of the hot-rolled transformation-induced plasticity steel is composed of the components specified in Table 1 below.

Repeat Example 1 to obtain the smelting and hot-rolling forging process of preparing hot-rolled phase transformation-induced plasticity steel, but in step (3), the final rolling temperature for rolling the steel plate is 970 ° C, and finally the steel billet is hot-rolled to a thickness of 6.55 mm The steel plate; Step (4) is different to the heat treatment of steel plate and embodiment one, specifically: first at 950 ℃ of insulation 30 minutes, then air-cooled to 720 ℃ of insulation 30 minutes, then salt bath (50%KNO ₃ +50% NaNO ₃ ) quenching treatment, heat preservation at 500°C for 60 minutes, then coiling, air cooling to room temperature, the tensile test data of the finally obtained hot-rolled phase transformation induced plasticity steel is shown in Table 3.

Table 1 Alloy composition of hot-rolled transformation-induced plasticity steel for each example

Table 2 Hot rolling and heat treatment process parameters

The tensile test data of each embodiment of table 3

In summary, the hot-rolled hot-rolled phase-change-induced plasticity steel of the present invention is combined with a suitable heat treatment process in its preparation to make it have higher yield strength and elongation, and the finally obtained steel plate has good coating ability , weldability and wear resistance, but also has high strength and plasticity.

Although the present invention has been described above in conjunction with the drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the inspiration, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (4)

1. a hot-rolling phase change induction plasticity steel is characterized in that, the material of hot-rolling phase change induction plasticity steel is composed of the following components by weight percentage:

C：0.05～0.4％；

Si：0.1～0.5％；

Mn：1～2％；

Cr：0.1～1.5％；

Ni：≤1.5％；

Al：≤0.06％；

N：≤0.01％；

All the other are Fe and unavoidable impurities.

2. hot-rolling phase change induction plasticity steel according to claim 1 wherein, also contains weight percent and is 0.01～0.1% V.

3. hot-rolling phase change induction plasticity steel according to claim 1 and 2, wherein, impurity is that to contain weight percent be≤0.005% S for≤0.025% P and weight percent.

4. a method for preparing the hot-rolling phase change induction plasticity steel of claim 1 or 2 is characterized in that, may further comprise the steps:

(1) according to component and content requirement with all raw materials mix evenly after, in vacuum induction furnace, smelt;

(2) smelt into steel ingot after, steel ingot is heated to 1200 ℃, be incubated and forge into steel billet after 2 hours, steel billet is heated to 1250 ℃ of insulations 1.5 hours, after insulation finishes, it carry out hot rolling system;

(3) process of hot rolling system is:

At first carry out roughing, start rolling temperature is 1150～1250 ℃, 3 passage total deformations 85% of roughing;

Carry out finish rolling then, 2 passage total deformations of finish rolling are 15%;

Finishing temperature is 850 ℃～1000 ℃, is the thick steel plate of 5-10mm with hot rolling of steel billet at last;

(4) steel plate after the hot rolling is heat-treated: at first 950 ℃ of insulations 30～60 minutes, air cooling to 750～800 ℃ insulation is 30～60 minutes then, and salt bath quenching is handled then; 400-500 ℃ of insulation 20～120 minutes; Roll bending then, air cooling is to room temperature, and finally obtaining tensile strength is 600～900MPa; Unit elongation is 25%～35%, and strength and ductility product is greater than the hot-rolling phase change induction plasticity steel of 18000MPa%.

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