WO2012022184A1

WO2012022184A1 - Hot-dip galvanized high strength steel with high strain hardening index and method producing same

Info

Publication number: WO2012022184A1
Application number: PCT/CN2011/075236
Authority: WO
Inventors: 王立辉; 陈宇
Original assignee: 武汉钢铁(集团)公司
Priority date: 2010-08-14
Filing date: 2011-06-03
Publication date: 2012-02-23
Also published as: CN101899619B; CN101899619A

Abstract

A hot-dip galvanized high strength steel consists of (wt.%): C：0.11-0.20，Al：0.51-1.22，Mn：1.50-2.00，Si：0.07-0.30，Cr：1.0-2.0，P≤0.015，S≤0.015, and the balance of iron and unavoidable impurities. A method for producing the same comprises the following steps: smelting and continuous casting into billet; heating the continuous cast billet and preserving heat; rough rolling; final rolling; winding up; cold rolling; and hot-dip galvanizing, i.e. heating the cold rolled steel plate, preserving heat, rapid cooling to the temperature of 480-510℃, dip galvanizing for 5-9 seconds, and then cooling to room temperature. The hot-dip galvanized high strength steel has the characteristics of good galvanizability, high tensile property and good welding performance, corrosion resistance and formability.

Description

Hot-dip galvanized high-strength steel with high strain hardening index and production method thereof

Technical field

The invention relates to a galvanized steel, in particular to a hot-dip galvanized high-strength steel, specifically, a strain hardening index, that is, an n value exceeding 0.230, a yield strength of 400-450 MPa, and a tensile strength of not less than 600 MPa. A hot-dip galvanized steel sheet having an elongation of not less than 28% and a production method thereof.

Background technique

High-strength, high-plastic hot-dip galvanized steel sheet can be used to manufacture automotive structural parts, improve vehicle safety, and at the same time increase corrosion resistance, reduce steel sheet thickness by more than 20%, reduce total vehicle weight, reduce material consumption, and reduce fuel consumption. Consumption and exhaust emissions, and vigorous development of high-strength steel is an important method for car lightweighting.

In recent years, the forming performance requirements of high-strength steel sheets with tensile strength exceeding 600 MPa are getting higher and higher. TRIP steel induces martensite nucleation under the plastic deformation of residual austenite in the steel sheet by phase transformation induced plasticity effect. Phase transformation strengthening and plastic growth, improving the strength and toughness of the steel sheet, the steel has high yield strength and tensile strength, strong ductility and high stamping forming ability. As a structural component of an automobile, it can reduce the weight of the automobile, enhance the impact resistance of the automobile, and has good formability, rigidity, collision energy absorbing ability, and weldability. A typical CMnSi-based TRIP steel contains 0.1 to 0.2% C, 1% to 2% Mn, and 1% to 2% Si, and is subjected to hot rolling deformation heat treatment or cold rolling + heat treatment. The structure of TRIP steel consists of 50% to 60% ferrite, 25% to 40% bainite or a small amount of martensite and 5% to 15% retained austenite. However, the surface of the TRIP steel is liable to form an oxide of Si, causing serious surface defects, so the wettability is poor, and there is a bottleneck of poor galvanizing adhesion property, and it is difficult to achieve the corrosion resistance of the hot-dip galvanized steel sheet.

The chemical composition of the substrate is known from the patent document No. 200810119818, entitled "A TRIP steel sheet for high-strength cold-rolled hot-dip galvanizing and its preparation method". %) is C: 0.1 to 0.4, Si ≤ 0.06, Mn: 0.5 to 2.5, Al: 0.5 to 2.0, P ≤ 0.03, S ≤ 0.02, Nb: 0.01 to 0.10, Ti: 0.01 to 0.10, Cu: 0.1 to 1.0 Ni: 0.1~0.6, the balance is Fe. The steel plate introduced in this document is made of Nb and Ti microalloyed, and other strengthening elements such as Cu and Ni are added. The deficiency of its existence: 0.54% of Cu element is added in the embodiment. Due to the high Cu content, the hot brittleness of the galvanized steel sheet substrate is easily caused, which has an adverse effect on plasticity, in order to improve the plasticity caused by the addition of Cu. Deterioration, while adding 0.31% Ni, only this content of Ni will increase the cost per ton of steel plate by more than 600 yuan, and in its embodiment, up to 0.24% of C and other elements added, which is not good for the welding of steel plates. . From the properties in the examples, the elongation of the materials was very low, and both did not exceed 27.0%.

technical problem

The purpose of the invention is to overcome the shortcomings such as the drawing property and the poor galvanizing performance, and provide a zinc layer of the galvanized steel sheet with good adhesion by changing the chemical composition and the production process, and the strain hardening index is not low. A hot-dip galvanized steel sheet having a yield strength of 400 to 450 MPa, a tensile strength of not less than 600 MPa, and an elongation of not less than 28% at 0.23 and a production method thereof.

Technical solution

Technical measures to achieve the above objectives:

High-strain hardening index of hot-dip galvanized high-strength steel, the composition and weight percentage of the substrate are: C: 0.11~0.20, Al: 0.51~1.22, Mn: 1.50~2.00, Si: 0.07~0.30, Cr: 1.0~2.0 , P ≤ 0.015, S ≤ 0.015, the balance is Fe and unavoidable impurities.

The method further comprises: adding one or more of weight percentages: Nb: 0.10 to 0.20, Mo: 0.01 to 0.05, and V: 0.01 to 0.05.

A method for producing a high strain hardening index of hot-dip galvanized high-strength steel, the steps of which:

1) Smelting under the condition of a vacuum degree of 67~134Pa, the smelting temperature is controlled to be 1590~1630 °C, and continuously cast into a billet;

2) heating the continuous casting billet to 1200~1270 °C, and maintaining at this temperature for 160~200 minutes;

3) rough rolling, controlling the rough rolling temperature to be 1080~1120 ° C;

4) Perform final rolling, control the finishing temperature to 860~900 °C, and control the thickness of the plate to 3~3.5 mm;

5) performing coiling and controlling the coiling temperature to be 580~620 °C;

6) Perform cold rolling, control the total reduction rate of 66~73%, and control the thickness of the plate to 0.8~1.2 mm;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 780 ~ 798 ° C;

b. Keep the temperature at 780~798 °C for 50~80 seconds;

c, rapid cooling, cooling the steel plate to 480 ~ 510 ° C at a cooling rate of 30 ~ 50 ° C / sec;

d, galvanizing, immersion plating for 5 to 9 seconds at a temperature of 465 to 490 ° C;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 5 to 17 ° C / sec.

It is characterized in that: the zinc liquid contains aluminum in a weight percentage of 0.20 to 0.24.

The role and mechanism of each element in steel are as follows.

C: C is an austenite stability element, and its price is low. At the same time, C is also a gap strengthening element, and the strengthening effect is very obvious. The higher the C content, the better the strengthening effect. However, the C content is too high, which is not conducive to ensuring the welding performance of the material. In addition to increasing the strength, C plays a crucial role in the improvement of plasticity in the present invention. At high temperature, C can be dissolved in the retained austenite to improve the stability of the retained austenite. By controlling the cooling, a moderately stable retained austenite is obtained at room temperature. Residual austenite undergoes a structural transformation under external force and transforms into martensite, which can increase the strength of the material. Therefore, the upper limit of the C content is controlled to 0.20% or less, and the lower limit is controlled to be 0.11% or more.

Al: At present, conventional high-strength steel mostly increases the quantity and stability of retained austenite by adding Si element, and inhibits the formation of cementite. However, Si element easily forms a dense oxide layer Mn ₂ SiO ₄ on the surface of the steel sheet, thus affecting The galvanizing properties of the material, so the present invention uses Al instead of most of the Si. Al, like Si, has fine grain and stabilized retained austenite to inhibit the formation of cementite. Al is a non-carbide forming element that promotes the diffusion of carbon atoms from ferrite into austenite. Thereby increasing the amount and stability of retained austenite. Al is prone to block the nozzle during continuous casting in industrial production. Therefore, the upper limit of Al element in steel is controlled to be less than 1.22%.

In the present invention, Si:Si further refines grains and stabilizes retained austenite, and compensates for the lack of retained austenite and insufficient stability due to insufficient Al content. Meanwhile, Si element also strengthens the steel substrate. effect. However, since the Si element easily forms a dense oxide layer Mn ₂ SiO ₄ on the surface of the steel sheet, thereby affecting the galvanizing performance of the material, it is limited to 0.07 to 0.30%.

Mn: Mn element is a conventional strengthening and toughening element. As an austenite forming element, “not only can expand the austenite region, lower the finishing temperature, delay the transformation of austenite, but also refine grains and stabilize at the same time. The role of retained austenite. However, the content of Mn is too high, on the one hand, the cost is increased, on the other hand, the hardenability of the steel is increased, and the hardened layer of the welded structure causes the crack weld and the crack sensitivity of the heat-affected zone to be increased. The upper limit of the Mn content is controlled to 2.0% or less, and the lower limit is controlled to 1.50% or more.

Cr: Cr is a ferrite forming element, and Cr element can significantly increase the strength of steel, and compensates for the adverse effect of the strength reduction caused by Al instead of Si in the present invention, and at the same time, Cr element can improve the oxidation resistance and resistance of steel. Corrosive. The Cr content is too low, the strength of the steel sheet is insufficient, and the steel sheet costs are too high, which also affects the overall performance of the steel sheet, so the Cr is controlled within the range of 1.0 to 2.0%.

S:S is disadvantageous to the plastic toughness of the material of the present invention, and the corrosion resistance is lowered, so the lower the better.

P:P is detrimental to the plasticity, weldability and formability of the material of the present invention, so the lower the better.

Nb and Ti are strong carbonitride forming elements, which are favorable for precipitation strengthening, and can prevent high temperature austenite from growing excessively, but the Nb content is too high, which tends to cause carbonitride segregation, and the processability thereof is deteriorated. , increased material costs.

Mo: Mo refines the grain of steel and maintains sufficient strength and creep resistance at high temperatures.

V:V can suppress the formation of pearlite or cementite when it is rapidly cooled from the annealing temperature. At the same time, V can improve strength and toughness, and can also improve hydrogen corrosion resistance.

Beneficial effect

The invention solves the problem that the traditional high Si content high strength steel has difficulty in galvanizing, has good platability, high drawing property, good welding performance, high corrosion resistance and good forming performance, and reflects It has a good market application prospect and significant social and economic benefits. Compared with conventional galvanized sheets, the use of the material of the invention has the following advantages:

(1) The invention contains more than 7% of retained austenite. During the forming process, the retained austenite is transformed into martensite by absorbing external energy, so that the material not only exhibits good elongation and drawability. At the same time, the strength of the material is further improved, and the size of the part after deformation is kept stable due to the release of the bending deformation stress.

(2) The invention material contains stable retained austenite. During the welding process, the retained austenite can absorb the crack tip stress and alleviate the crack formation and expansion. Therefore, no cracks and cracks occur during the welding of the parts, and the welding is good. performance.

(3) The invention material is excellent in ensuring the basic mechanical properties, and is excellent in the galvanizing property by the reasonable chemical composition and galvanizing process of the invention, not only has high strength and high drawability, but also has resistance. Corrosive, it is the ideal structural steel plate for high-end cars.

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate were: C: 0.15, Al: 1.00, Mn: 1.76, Si: 0.15, Cr: 1.50, P: 0.012, S : 0.010, Nb: 0.10, the balance is Fe and unavoidable impurities.

1) smelting under the condition of a vacuum of 105 Pa, the smelting temperature is controlled to be 1620~1630 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1260~1270 ° C, and maintaining at this temperature for 178 minutes;

3) rough rolling, control the rough rolling temperature is 1110 ~ 1120 ° C;

4) Perform final rolling, control its finishing temperature to 890~900 °C, and control the thickness of the plate to 3.5 mm;

5) performing coiling and controlling the coiling temperature to be 610~620 °C;

6) cold rolling, control the total reduction rate of 66%, the thickness of the plate is controlled at 1.2 mm;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 792 ~ 798 ° C, heating time is 220 seconds;

b, holding at a temperature of 792 ~ 798 ° C for 80 seconds;

c, rapid cooling, cooling the steel plate to 500 ~ 510 ° C at a cooling rate of 40 ~ 45 ° C / sec;

d, galvanizing, immersion plating at a temperature of 480 ~ 490 ° C for 9 seconds, the weight percentage of aluminum in the zinc solution is 0.20;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 17 ° C / sec.

Embodiments of the invention

Example 2: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate were: C: 0.15, Al: 1.10, Mn: 1.75, Si: 0.21, Cr: 1.26, P: 0.015, S : 0.009, the balance is Fe and unavoidable impurities.

1) Smelting is carried out under the condition of a vacuum degree of 67 Pa, and the smelting temperature is controlled to be 1600 to 1610 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1220~1235 ° C, and holding at this temperature for 170 minutes;

3) rough rolling, control the rough rolling temperature is 1090 ~ 1105 ° C;

4) Perform final rolling, control the finishing temperature to 880~890 °C, and control the thickness of the plate to 3.2 mm;

5) performing coiling and controlling the coiling temperature to be 590~595 °C;

6) Perform cold rolling, control the total reduction rate to be 69%, and control the thickness of the plate to 1.0 mm;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 785 ~ 795 ° C, the heating time is 210 seconds;

b, holding at a temperature of 785 ~ 795 ° C for 60 seconds;

c, rapid cooling, cooling the steel plate to 485 ~ 495 ° C at a cooling rate of 35 ~ 40 ° C / sec;

d, galvanizing, soaking for 6 seconds at a temperature of 465 to 475 ° C of zinc liquid, the weight percentage of aluminum in the zinc liquid is 0.24;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 10 ° C / sec.

Embodiments of the invention

Example 3: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate were: C: 0.11, Al: 1.22, Mn: 1.55, Si: 0.07, Cr: 1.0, P: 0.013, S : 0.008, the balance is Fe and unavoidable impurities.

1) Smelting is carried out under the condition of a vacuum degree of 80 Pa, and the smelting temperature is controlled to be 1590 to 1595 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1200~1210 ° C, and maintaining at this temperature for 160 minutes;

3) rough rolling, controlling the rough rolling temperature to be 1080~1096 ° C;

4) Perform final rolling, control its finishing temperature to 860~875 °C, and control the thickness of the plate to 3 mm;

5) performing coiling and controlling the coiling temperature to be 580~595 °C;

6) cold rolling, control the total reduction rate of 73%, the thickness of the plate is controlled at 0.8 mm;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 780 ~ 785 ° C, heating time is 200 seconds;

b, holding at a temperature of 780 ~ 785 ° C for 50 seconds;

c, rapid cooling, cooling the steel plate to 480 ~ 490 ° C at a cooling rate of 30 ~ 35 ° C / sec;

d, galvanizing, immersion plating for 5 seconds at a temperature of 465 to 475 ° C, the weight percentage of aluminum in the zinc solution is 0.22;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 5 ° C / sec.

Embodiments of the invention

Example 4: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate are: C: 0.20, Al: 0.50, Mn: 2.0, Si: 0. 30, Cr: 1.20, P: 0.009, S: 0.008, Mo: 0.01, the balance being Fe and unavoidable impurities.

1) Smelting is carried out under the condition of a vacuum degree of 134 Pa, and the smelting temperature is controlled to be 1600 to 1610 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1200~1215 °C, and keeping it at this temperature for 200 minutes;

3) rough rolling, control the rough rolling temperature is 1090 ~ 1100 ° C;

4) Perform final rolling, control the finishing temperature to 875~885 °C, and control the thickness of the plate to 3.2 mm;

5) performing coiling and controlling the coiling temperature to be 585~595 °C;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 785 ~ 790 ° C, heating time is 220 seconds;

b, holding at a temperature of 785 ~ 790 ° C for 70 seconds;

c, rapid cooling, cooling the steel plate to 485 ~ 495 ° C at a cooling rate of 45 ~ 50 ° C / sec;

d, galvanizing, immersion plating for 9 seconds at a temperature of 465 to 475 ° C, the weight percentage of aluminum in the zinc solution is 0.22;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 15 ° C / sec.

Embodiments of the invention

Example 5: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate were: C: 0.16, Al: 0.94, Mn: 1.52, Si: 0.22, Cr: 2.0, P: 0.011, S : 0.010, Mo: 0.05, V: 0.01, the balance being Fe and unavoidable impurities.

1) Smelting is carried out under the condition of a vacuum degree of 80 Pa, and the smelting temperature is controlled to be 1620 to 1630 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1230~1245 ° C, and maintaining at this temperature for 160 minutes;

3) rough rolling, control the rough rolling temperature is 1110 ~ 1120 ° C;

4) Perform final rolling, control the finishing temperature to 885~895 °C, and control the thickness of the plate to 3.2 mm;

5) performing coiling and controlling the coiling temperature to be 595~605 °C;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 792 ~ 798 ° C, heating time is 200 seconds;

b, holding at a temperature of 792 ~ 798 ° C for 50 seconds;

c, rapid cooling, cooling the steel plate to 485 ~ 495 ° C at a cooling rate of 45 ~ 49 ° C / sec;

d, galvanizing, immersion plating for 8 seconds at a temperature of 465 to 475 ° C, the weight percentage of aluminum in the zinc solution is 0.22;

e. Perform re-cooling, and cool the steel sheet to room temperature at a cooling rate of 12 ° C / sec.

Embodiments of the invention

Example 6: Hot-dip galvanized high-strength steel with high strain hardening index, the composition and weight percentage of the substrate were: C: 0.15, Al: 1.05, Mn: 1.55, Si: 0.18, Cr: 1.10, P: 0.008, S : 0.006, Mo: 0.01, V: 0.05, Nb: 0.20, the balance being Fe and unavoidable impurities.

1) Smelting under the condition of a vacuum of 85 Pa, the smelting temperature is controlled to be 1620~1628 ° C, and continuously cast into a billet;

2) heating the continuous casting billet to 1235~1245 ° C, and keeping it at this temperature for 200 minutes;

3) performing rough rolling and controlling the rough rolling temperature to be 1105~1115 °C;

4) Perform final rolling, control the finishing temperature to 880~890 °C, and control the thickness of the plate to 3.0 mm;

5) performing coiling and controlling the coiling temperature to be 600~610 °C;

6) cold rolling, control the total reduction rate of 67%, the thickness of the plate is controlled at 1.0 mm;

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 780 ~ 790 ° C, the heating time is 210 seconds;

b, holding at a temperature of 780 ~ 790 ° C for 60 seconds;

c, rapid cooling, cooling the steel plate to 485 ~ 495 ° C at a cooling rate of 40 ~ 45 ° C / sec;

d, galvanizing, immersion plating for 7 seconds at a temperature of 465 to 475 ° C, the weight percentage of aluminum in the zinc solution is 0.22;

Industrial applicability

The above examples were tested, and the performance test results are shown in Table 1.

Table 1:

It can be seen from Table 1 that the mechanical properties of the product of the present invention are superior to those of the conventional CMnSi-based TRIP steel, and the adhesion property of the zinc layer is excellent, and can fully meet the requirements for the production of automobile structural parts.

Claims

1. High-strain hardening index of hot-dip galvanized high-strength steel, the composition and weight percentage of the substrate are: C: 0.11~0.20, Al: 0.51~1.22, Mn: 1.50~2.00, Si: 0.07~0.30, Cr: 1.0 ~2.0, P ≤ 0.015, S ≤ 0.015, the balance is Fe and unavoidable impurities.

2. The high-strain hardening index hot-dip galvanized high-strength steel according to claim 1, wherein the weight percentage is: Nb: 0.10 to 0.20, Mo: 0.01 to 0.05, and V: 0.01 to 0.05. One or several.

3. A method of producing a high strain hardening index hot dip galvanized high strength steel according to claim 1, the steps of:

7) Perform hot dip galvanizing:

a, the cold rolled steel plate is heated to 780 ~ 798 ° C;

b. Keep the temperature at 780~798 °C for 50~80 seconds;

4. The method of producing high-strain hardening index hot-dip galvanized high-strength steel according to claim 3, wherein the zinc liquid has a weight percentage of aluminum of 0.20 to 0.24.