High-strength-grade one-steel multi-stage galvanized low-alloy high-strength steel strip and manufacturing method thereof

Abstract

The invention relates to a high-strength-grade one-steel multi-stage galvanized low-alloy high-strength steel strip and a manufacturing method thereof. A base plate of the galvanized low-alloy high-strength steel strip comprises the following chemical components in percentage by mass: 0.070 to 0.110 percent of C, 1.00 to 1.20 percent of Mn, less than or equal to 0.008 percent of S, less than or equal to 0.020 percent of P, 0.15 to 0.35 percent of Si, 0.040 to 0.055 percent of Nb, 0.020 to 0.060 percent of Als, less than or equal to 0.0050 percent of N and the balance of Fe and inevitable impurities. The manufacturing method comprises the procedures of plate blank heating, hot rolling, galvanizing and finishing, one raw material component is adopted, different plate blank heating, hot rolling and galvanizing processes are designed in a grading mode, one-steel multi-stage production is achieved, and the production cost is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating, and particularly relates to a high-strength level one-steel multi-stage galvanized low-alloy high-strength steel strip and a manufacturing method thereof. Background Art

[0002] Galvanized low-alloy high-strength steel has the characteristics of high strength, certain ductility and formability, and high corrosion resistance. At the same time, it has very high surface dimensional accuracy and good flatness, which helps to reduce the thickness of parts. It is widely used in automotive structural parts, reinforcement parts, etc., such as automotive seats, crossbeams, etc., and the market demand is relatively large.

[0003] At present, there are many types and specifications of galvanized low-alloy high-strength steels used by each automobile factory. In order to meet the performance requirements of different grade steel types, a variety of raw material grades have been designed, and different galvanizing production processes have been formulated. In actual orders, the order quantity of some steel types is small, resulting in an increase in the carry-out products during the production organization of the steel mill, affecting the production scheduling efficiency of the entire process of steelmaking, hot rolling, and galvanizing. Especially during the production of the steelmaking process, the switching of different steel types will generate a large number of unplanned products, resulting in an increase in production costs. At the same time, it will affect the internal quality stability of the continuous casting billet, and further reduce the market competitiveness of the company's products.

[0004] Therefore, in order to reduce production costs, reduce unplanned products, and improve the production scheduling efficiency of the entire process, it is urgent to realize the production of different grades of galvanized low-alloy high-strength steels using one raw material composition through reasonable design of the composition and galvanizing production process.

[0005] Chinese Patent CN 109881079 B discloses a one-steel multi-stage galvanized low-alloy high-strength steel strip and its production method. The strength level produced by this method is that the yield strength level covers 300 - 450 MPa, and the covered strength is low, which cannot meet the current usage requirements of high-strength steels. This method produces by distinguishing the coiling temperature and cooling rate of raw materials for different grade steel types and formulating corresponding annealing processes. The difference in the coiling temperature of the raw material steel types will affect the head and tail temperature hit rate during continuous production, affect the head and tail performance, and lead to a decrease in performance stability.

[0006] Chinese Patent CN 106929758 B discloses a one-steel multi-stage cold-rolled low-alloy high-strength steel strip and its production method. This method produces continuous annealing low-alloy high-strength steel products. The Nb content added by this method is relatively high, resulting in high production costs. This method does not stipulate the slab tapping temperature and furnace residence time for different strength level products, and it is easy to have the problem of large performance fluctuations. Nb-strengthened steel types are sensitive to the slab tapping temperature and slab furnace residence time. Large changes in temperature and time will lead to different Nb precipitation amounts, all of which will cause performance fluctuations and are prone to problems of unqualified performance or overly high performance. Summary of the Invention

[0007] The object of the present invention is to provide a high-strength level one-steel multi-stage galvanized low-alloy high-strength steel strip and its manufacturing method. By using the same raw material composition, optimizing the slab heating, hot rolling, and galvanizing processes according to products of different strength levels, different strength level steel grades can be developed, which can reduce the production of rejects, improve production efficiency, and ensure performance stability.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions: a high-strength level one-steel multi-stage galvanized low-alloy high-strength steel strip, the chemical composition and mass percentage content of the substrate of the galvanized low-alloy high-strength steel strip are: C: 0.070 - 0.110%, Mn: 1.00 - 1.20%, S ≤ 0.008%, P ≤ 0.020%, Si: 0.15 - 0.35%, Nb: 0.040 - 0.055%, Als: 0.020 - 0.060%, N ≤ 0.0050%, and the rest are Fe and inevitable impurities.

[0009] The steel strip specifications of the present invention are: 0.7 - 3.0 mm, the yield strength level covers 420 - 500 Mpa, the tensile strength level covers 530 - 580 Mpa, and the elongation A 80 mm ≥ 13%.

[0010] The manufacturing method of the present invention includes slab heating, hot rolling, continuous hot dip galvanizing, and skin pass rolling processes; the slab heating process: includes a first heating section, a second heating section, a third heating section, and a soaking section; for products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the high-temperature section heating time of the slab is 90 - 110 min, and the slab surface temperature at the furnace outlet is controlled at 1240 - 1260 °C; for products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the high-temperature section heating time of the slab is 110 - 130 min, and the slab surface temperature at the furnace outlet is controlled at 1260 - 1280 °C; for products with a yield strength of ≥ 500 MPa, the high-temperature section heating time of the slab is 130 - 150 min, and the slab surface temperature at the furnace outlet is controlled at 1280 - 1300 °C; the high-temperature section heating time is the heating time of the third heating section + the heating time of the soaking section.

[0011] The hot rolling process of the present invention: the finish rolling temperature is controlled at 860 - 900 °C; the coiling temperature is controlled at 570 - 610 °C.

[0012] The skin pass rolling process of the present invention: the skin pass reduction rate ≥ 50%.

[0013] The continuous hot-dip galvanizing process of the present invention includes a preheating section, a first heating section, a second heating section, a soaking section, a slow cooling section, a rapid cooling section, and the process of entering the zinc pot. For products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the temperature of the second heating section and the soaking section is controlled at 760 - 820 °C, and the speed of the steel strip in the furnace area is controlled at 60 - 110 m / min. For products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the temperature of the second heating section and the soaking section is controlled at 730 - 770 °C, and the speed of the steel strip in the furnace area is controlled at 80 - 115 m / min. For products with a yield strength of ≥ 500 MPa, the temperature of the second heating section and the soaking section is controlled at 690 - 750 °C, and the speed of the steel strip in the furnace area is controlled at 60 - 85 m / min.

[0014] The skin pass rolling process of the present invention: For products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the elongation of the skin pass mill is controlled at 0.8 - 1.6%. For products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the elongation of the skin pass mill is controlled at 1.0 - 1.3%. For products with a yield strength of ≥ 500 MPa, the elongation of the skin pass mill is controlled at 0.3 - 0.6%.

[0015] The beneficial effects of adopting the above technical solutions are as follows: 1. By adopting a raw material composition and utilizing the characteristics of Nb precipitation strengthening, the present invention designs different hot rolling and galvanizing processes to produce products with a yield strength level of 420 - 500 MPa, realizing multi-level production with one type of steel and reducing production costs. 2. Through multi-level production with one type of steel, the production scheduling efficiency of the entire process of steelmaking, hot rolling, and galvanizing can be improved, significantly reducing the carry-out of unplanned products. At the same time, the frequent switching of steel grades in the steelmaking process is reduced, ensuring the internal quality of the continuous casting billets. 3. The low-alloy high-strength steel strip products produced by the present invention have a thickness of 0.7 - 3.0 mm, a yield strength level covering 420 - 500 Mpa, a tensile strength level covering 530 - 580 Mpa, and an elongation A 80 mm ≥ 13%. Detailed implementation manners

[0016] The present invention will be further described in detail below in conjunction with specific embodiments.

[0017] Examples 1 - 12 For the high-strength multi-level galvanized low-alloy high-strength steel strip, the chemical composition and mass percentage content of the substrate are shown in Table 1, and the steel strip specifications and mechanical properties are shown in Table 2.

[0018] The manufacturing method of the high-strength multi-level galvanized low-alloy high-strength steel strip includes slab heating, hot rolling, pickling and cold rolling, galvanizing, and skin pass rolling processes. The specific control methods are as follows: 1) Slab heating: It includes a first heating section, a second heating section, a third heating section, and a soaking section; for products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the high-temperature section heating time of the slab is 90 - 110 min, and the slab surface temperature when leaving the furnace is controlled at 1240 - 1260 °C; for products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the high-temperature section heating time of the slab is 110 - 130 min, and the slab surface temperature when leaving the furnace is controlled at 1260 - 1280 °C; for products with a yield strength of ≥500 MPa, the high-temperature section heating time of the slab is 130 - 150 min, and the slab surface temperature when leaving the furnace is controlled at 1280 - 1300 °C; the high-temperature section heating time is the sum of the heating time of the third heating section and the soaking section. The process parameters of the slab heating process for each example are shown in Table 3.

[0019] 2) Hot rolling process: The finish rolling temperature is controlled at 860 - 900 °C; the coiling temperature is controlled at 570 - 610 °C. The process parameters of the hot rolling process for each example are shown in Table 3.

[0020] 3) Acid rolling process: The reduction rate of acid rolling is ≥50%. The process parameters of the acid rolling process for each example are shown in Table 4.

[0021] 4) Continuous hot-dip galvanizing process: It includes a preheating section, a first heating section, a second heating section, a soaking section, a slow cooling section, a rapid cooling section, and the process of entering the zinc pot; for products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the temperature of the second heating section and the soaking is controlled at 760 - 820 °C, and the speed of the steel strip in the furnace area is controlled at 60 - 110 m / min; for products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the temperature of the second heating section and the soaking is controlled at 730 - 770 °C, and the speed of the steel strip in the furnace area is controlled at 80 - 115 m / min; for products with a yield strength of ≥500 MPa, the temperature of the second heating section and the soaking is controlled at 690 - 750 °C, and the speed of the steel strip in the furnace area is controlled at 60 - 85 m / min. The process parameters of the continuous hot-dip galvanizing process for each example are shown in Table 4.

[0022] 5) Skin pass process: For products with a yield strength of 420 MPa ≤ yield strength < 460 MPa, the elongation of the skin pass mill is controlled at 0.8 - 1.6%; for products with a yield strength of 460 MPa ≤ yield strength < 500 MPa, the elongation of the skin pass mill is controlled at 1.0 - 1.3%; for products with a yield strength of ≥500 MPa, the elongation of the skin pass mill is controlled at 0.3 - 0.6%. The process parameters of the skin pass process for each example are shown in Table 4.

[0023] Table 1. Chemical composition weight percentage (%) of the zinc-based coating substrate for each example

[0024] Table 2. Specifications and mechanical properties of the steel strips obtained in each example

[0025] Table 3. Process parameters of slab heating and hot rolling processes in each embodiment

[0026] Table 4. Process parameters of pickling and cold rolling, continuous hot dip galvanizing, and skin pass processes in each embodiment

[0027] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. High-strength grade one steel multi-grade galvanized low-alloy high-strength steel strip, characterized in that: The chemical composition and mass percentage of the substrate of the galvanized low-alloy high-strength steel strip are: C: 0.070-0.110%, Mn: 1.00-1.20%, S≤0.008%, P≤0.020%, Si: 0.15-0.35%, Nb: 0.040-0.055%, Als: 0.020-0.060%, N≤0.0050%, and the rest are Fe and unavoidable impurities.

2. The high-strength grade one steel multi-grade galvanized low-alloy high-strength steel strip according to claim 1, characterized in that: The steel strip specifications: 0.7-3.0 mm, yield strength level covers 420-500 MPa, tensile strength level covers 530-580 MPa, elongation A 80 mm≥13%.

3. The method for manufacturing a high-strength grade one steel multi-grade galvanized low-alloy high-strength steel strip according to claim 1 or 2, characterized in that: The manufacturing method comprises the steps of slab heating, hot rolling, acid rolling, continuous hot-dip galvanizing and skin-passing; the slab heating step comprises a first heating section, a second heating section, a third heating section and a soaking section; for products with a yield strength of 420MPa≤<460MPa, the heating time of the slab in the high-temperature section is 90-110min, and the surface temperature of the slab out of the furnace is controlled at 1240-1260°C; for products with a yield strength of 460MPa≤<500MPa, the heating time of the slab in the high-temperature section is 110-130min, and the surface temperature of the slab out of the furnace is controlled at 1260-1280°C; for products with a yield strength of ≥500MPa, the heating time of the slab in the high-temperature section is 130-150min, and the surface temperature of the slab out of the furnace is controlled at 1280-1300°C; the heating time of the high-temperature section is the heating time of the three heating sections + the heating time of the soaking section.

4. The method for manufacturing a high-strength grade one-steel multi-grade galvanized low-alloy high-strength steel strip according to claim 3, characterized in that: In the hot rolling process, the final rolling temperature is controlled at 860-900°C; and the coiling temperature is controlled at 570-610°C.

5. The method for manufacturing a high-strength grade one steel multi-grade galvanized low-alloy high-strength steel strip according to claim 3, characterized in that: The acid rolling process: the acid rolling reduction rate is ≥50%.

6. The method for manufacturing a high-strength grade single-steel multi-grade galvanized low-alloy high-strength steel strip according to any one of claims 3 to 5, characterized in that: The continuous hot-dip galvanizing process includes a preheating section, a heating section, a second heating section, a soaking section, a slow cooling section, a fast cooling section and a zinc pot entry process; for products with a yield strength of 420MPa≤ and a yield strength of <460MPa, the second heating section and the soaking temperature are controlled at 760-820°C, and the speed of the steel strip furnace zone is controlled at 60-110m / min; for products with a yield strength of 460MPa≤ and a yield strength of <500MPa, the second heating section and the soaking temperature are controlled at 730-770°C, and the speed of the steel strip furnace zone is controlled at 80-115m / min; for products with a yield strength of ≥500MPa, the second heating section and the soaking temperature are controlled at 690-750°C, and the speed of the steel strip furnace zone is controlled at 60-85m / min.

7. The method for manufacturing a high-strength grade single-steel multi-grade galvanized low-alloy high-strength steel strip according to any one of claims 3 to 5, characterized in that: The skin-passing process: for products with a yield strength of 420MPa≤ and a yield strength of <460MPa, the skin-passing machine elongation is controlled at 0.8-1.6%; for products with a yield strength of 460MPa≤ and a yield strength of <500MPa, the skin-passing machine elongation is controlled at 1.0-1.3%; for products with a yield strength of ≥500MPa, the skin-passing machine elongation is controlled at 0.3-0.6%.

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