Thick-gauge galvanized low-alloy high-strength steel strip with yield strength of 500 MPa and production method of thick-gauge galvanized low-alloy high-strength steel strip

Abstract

The invention discloses a thick galvanized low-alloy high-strength steel strip with yield strength of 500MPa and a production method thereof. The provided low-alloy high-strength steel strip comprises the following chemical components in percentage by mass: 0.09 to 0.11 percent of C, 0.02 to 0.04 percent of Si, 1.0 to 1.1 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.020 to 0.040 percent of Alt, 0.05 to 0.06 percent of Nb, 0.01 to 0.02 percent of Ti, 0.01 to 0.02 percent of V, 0.0008 to 0.0015 percent of Ca, less than or equal to 0.0050 percent of N and the balance of Fe. The mechanical properties meet the requirements that the yield strength ReL is 500-620 MPa, the tensile strength Rm is 530-690 MPa, the yield ratio is larger than or equal to 0.85, the ductility A80 is larger than or equal to 13%, and the characteristics of high safety, low energy consumption and corrosion resistance of automobiles are met.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a thick-gauge galvanized low-alloy high-strength steel strip with a yield strength of 500 MPa and a production method thereof. Background Art

[0002] In recent years, in order to meet the needs of the contemporary automobile manufacturing industry for safety, energy saving, weight reduction, corrosion resistance, and high-end development, domestic and foreign steel companies that have the ability to produce galvanized low-alloy high-strength steel strips have accelerated the development of galvanized low-alloy high-strength steel for automobiles. In the manufacture of automotive equipment, chassis, trunk floors, seats, engine compartments, and other structural parts or reinforcements with higher strength requirements all require good deformation resistance, that is, a higher yield strength with an appropriate yield-to-strength ratio. Therefore, in order to meet the demand for raw materials for lightweighting in the automotive manufacturing industry, high-grade galvanized low-alloy high-strength steel came into being, and the demand has increased year by year.

[0003] Galvanized low alloy high strength steel is a high strength steel series product developed for automotive structural parts and reinforcements. Its unique strengthening and toughening mechanism is: adding strong carbide forming elements such as Nb or Ti to low carbon ferritic steel, forming carbides or nitrides through reasonable rolling and galvanizing annealing process, and precipitating on the ferrite matrix, thereby improving the strength of the steel while retaining some toughness. The galvanized low alloy high strength steel strip with a yield strength of 500MPa is used in automotive structural parts to meet the automotive industry's requirements for high safety, low energy consumption and corrosion resistance. Summary of the invention

[0004] The present invention aims to provide a thick gauge yield strength 500MPa grade galvanized low alloy high strength steel strip and its production method. The thick gauge yield strength 500MPa grade galvanized low alloy high strength steel strip of the present invention has the characteristics of high strength with appropriate yield strength ratio, good weldability, corrosion resistance, etc., which meets the requirements of high safety, low energy consumption and corrosion resistance of automobiles. Mechanical properties meet: yield strength R eL : 500~620MPa (preferably 545MPa or more), tensile strength R m : 530~690MPa (preferably 610MPa or more), yield strength ratio ≥ 0.85 (preferably ≥ 0.88), elongation A 80 ≥13% (preferably elongation A 80 ≥15%). The specific technical scheme of the present invention is as follows.

[0005] In one aspect, the present invention provides a thick gauge galvanized low alloy high-strength steel strip with a yield strength of 500 MPa, wherein the chemical composition thereof is as follows by mass percentage: C: 0.09-0.11%, Si: 0.02-0.04%, Mn: 1.0-1.1%, P≤0.020%, S≤0.010%, Alt: 0.020-0.040%, Nb: 0.05-0.06%, Ti: 0.01-0.02%, V: 0.01-0.02%, Ca: 0.0008-0.0015%, N≤0.0050%, and the remainder is Fe and unavoidable impurities;

[0006] The mechanical properties of the thick specification yield strength 500MPa grade galvanized low alloy high strength steel strip meet the following requirements: yield strength R eL : 500~620MPa, tensile strength R m : 530~690MPa, yield strength ratio ≥0.85, elongation A 80 ≥13%.

[0007] In some embodiments, the mechanical properties of the thick gauge yield strength 500 MPa grade galvanized low alloy high strength steel strip meet the following requirements: yield strength R eL ≥545MPa, tensile strength R m ≥610MPa, yield strength ratio ≥0.88, elongation A 80 ≥15%.

[0008] In some embodiments, the method for producing the thick gauge 500 MPa grade galvanized low alloy high strength steel strip comprises the following processes: smelting and continuous casting - hot rolling - pickling and cold rolling - continuous hot dip galvanizing and skin pass.

[0009] In some embodiments, the smelting and continuous casting process includes: molten iron pretreatment - converter - LF refining - slab continuous casting, wherein oxygen blowing decarburization and heating are performed in the converter top and bottom combined blowing smelting, and aluminum iron, manganese iron, etc. are added during the converter steel tapping process for deoxidation and alloying, and the P and S components are controlled to prevent the molten steel from being overoxidized, and the steel tapping temperature is ≥1600°C; LF out-of-furnace refining adopts the LF full-process argon blowing process, and the target composition is adjusted according to the molten steel composition, and the molten steel composition for the casting machine is C: 0.09-0.11%, Si: 0.02~0.04%, Mn: 1.0~1.1%, P≤0.020%, S≤0.010%, Alt: 0.020~0.040%, Nb: 0.05~0.06%, Ti: 0.01~0.02%, V: 0.01~0.02%, Ca: 0.0008~0.0015%, N≤0.0050%; the slab continuous casting superheat is controlled at 25~30℃, and the pulling speed is controlled at 0.55~0.80m / min.

[0010] In some embodiments, the hot rolling process includes: heating of the ingot - rough rolling - finishing rolling - coiling, wherein the ingot is in the furnace for 180 to 250 minutes, the furnace temperature is 1210 to 1270°C, the rough rolling is carried out by a 3+3 mode 2-stand rolling mill, the finishing rolling is carried out by a 7-stand rolling mill, the finishing rolling start temperature is 980 to 1000°C, the finishing rolling final temperature is 860 to 910°C, and the thickness of the hot rolled steel strip is 4.0 to 5.0 mm; cooling adopts laminar cooling equipment, and the coiling temperature is 610 to 620°C.

[0011] In some embodiments, the pickling cold rolling process includes: pickling the hot-rolled steel strip to remove surface iron oxide scale, and then cold rolling it through a 5-stand cold rolling mill with a cold rolling reduction rate of 50-60% and a thickness of 1.8-2.5 mm.

[0012] In some embodiments, the continuous hot-dip galvanizing and skin-passing process includes: uncoiling the cold-hardened steel strip and welding it for continuous production, the furnace zone speed is 50-90 m / min, the soaking temperature is 755-785°C, slowly cooling to 620-630°C, and then cooling to 450-460°C, the zinc pot temperature is 450-460°C, the skin-passing elongation is 0.5-0.9%, and the tensile elongation is ≤0.3%.

[0013] Another aspect of the present invention provides a method for producing a thick gauge 500 MPa grade galvanized low alloy high strength steel strip, which comprises the following processes: smelting and continuous casting - hot rolling - pickling and cold rolling - continuous hot dip galvanizing and skin pass; wherein:

[0014] The smelting and continuous casting process comprises: molten iron pretreatment - converter - LF refining - slab continuous casting, wherein oxygen blowing decarburization and heating are carried out in the converter top and bottom combined blowing smelting, aluminum iron, manganese iron and the like are added in the converter steel tapping process for deoxidation and alloying, P and S components are controlled to prevent overoxidation of molten steel, and the steel tapping temperature is ≥1600°C; LF out-of-furnace refining adopts LF full-process argon blowing process, and the target composition is adjusted according to the molten steel composition, and the molten steel composition for the casting machine is C: 0.09-0.11%, Si: 0.02 ~0.04%, Mn: 1.0~1.1%, P≤0.020%, S≤0.010%, Alt: 0.020~0.040%, Nb: 0.05~0.06%, Ti: 0.01~0.02%, V: 0.01~0.02%, Ca: 0.0008~0.0015%, N≤0.0050%; the slab continuous casting superheat is controlled at 25~30℃, and the pulling speed is controlled at 0.55~0.80m / min;

[0015] The hot rolling process comprises: heating of the casting billet - rough rolling - finishing rolling - coiling, wherein the casting billet is in the furnace for 180-250 minutes, the furnace temperature is 1210-1270°C, the rough rolling adopts 3+3 mode 2-stand rolling mill, the finishing rolling adopts 7-stand rolling mill, the finishing rolling start temperature is 980-1000°C, the finishing rolling final rolling temperature is 860-910°C, and the hot rolled steel strip thickness is 4.0-5.0mm; the cooling adopts laminar cooling equipment, and the coiling temperature is 610-620°C;

[0016] The pickling cold rolling process comprises: pickling the hot-rolled steel strip to remove the surface iron oxide scale, and then cold rolling it through a 5-stand cold rolling mill, with a cold rolling reduction rate of 50-60% and a thickness of 1.8-2.5 mm;

[0017] The continuous hot-dip galvanizing and skin-passing process comprises: uncoiling the cold hardened steel strip and welding it for continuous production, the furnace zone speed is 50-90 m / min, the soaking temperature is 755-785° C., slowly cooling to 620-630° C., then cooling to 450-460° C., the zinc pot temperature is 450-460° C., the skin-passing elongation is 0.5-0.9%, and the straightening elongation is ≤0.3%.

[0018] The beneficial effect of the present invention is to provide a thick gauge yield strength 500MPa grade galvanized low alloy high strength steel strip and its production method. The thick gauge yield strength 500MPa grade galvanized low alloy high strength steel strip of the present invention has the characteristics of high strength, appropriate yield strength ratio, good weldability, corrosion resistance, etc., which meets the requirements of high safety, low energy consumption and corrosion resistance of automobiles. Mechanical properties meet: yield strength R eL : 500~620MPa, tensile strength R m : 530~690MPa, yield strength ratio ≥0.85, elongation A 80 ≥13%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a microstructure photograph of the thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa obtained in Example 1. DETAILED DESCRIPTION

[0020] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0021] Example

[0022] According to the above smelting and continuous casting production process requirements, the actual slab chemical composition is shown in Table 1.

[0023] Table 1: Chemical composition of the present invention (wt%)

[0024] Example C Si Mn P S Alt Nb Ti V Ca N 1 0.09 0.02 1.05 0.015 0.006 0.021 0.055 0.011 0.015 0.0008 0.0045 2 0.09 0.04 1.08 0.014 0.008 0.025 0.050 0.015 0.012 0.0011 0.0044 3 0.10 0.03 1.10 0.018 0.005 0.032 0.060 0.014 0.010 0.0012 0.0023 4 0.11 0.02 1.09 0.013 0.002 0.033 0.058 0.020 0.018 0.0009 0.0025 5 0.10 0.03 1.01 0.014 0.007 0.038 0.051 0.018 0.015 0.0014 0.0038

[0025] According to the above hot rolling process requirements, the hot rolling thickness is 4.0 to 5.0 mm, and the actual process is shown in Table 2.

[0026] Table 2: Hot rolling process of the embodiment of the present invention

[0027]

[0028]

[0029] According to the above pickling cold rolling, hot dip galvanizing and skin finishing process requirements, the cold rolling thickness is 1.8 to 2.5 mm, and the actual hot dip galvanizing and skin finishing processes are shown in Table 3.

[0030] Table 3: Hot-dip galvanizing and skin-passing process of the present invention

[0031]

[0032] The mechanical properties of the steel strip according to the embodiment of the present invention were tested, and the test results are shown in Table 4.

[0033] Table 4: Mechanical properties of the steel strips in the embodiments of the present invention

[0034]

[0035] It can be seen from the data in Table 4 that the mechanical properties of the thick-gauge yield strength 500MPa grade galvanized low-alloy high-strength steel strip provided by the present invention can meet the following requirements: yield strength R eL : 548~574MPa, tensile strength R m : 613~642MPa, yield strength ratio: 0.88~0.92, elongation A 80 : 15.0~18.0%. The steel strip products obtained by the above process have been used by users and have suitable performance and can be promoted for use.

[0036] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A thick gauge galvanized low alloy high strength steel strip with a yield strength of 500MPa, characterized in that: The chemical composition of the thick gauge yield strength 500MPa grade galvanized low alloy high strength steel strip is calculated by mass percentage as follows: C: 0.09-0.11%, Si: 0.02-0.04%, Mn: 1.0-1.1%, P≤0.020%, S≤0.010%, Alt: 0.020-0.040%, Nb: 0.05-0.06%, Ti: 0.01-0.02%, V: 0.01-0.02%, Ca: 0.0008-0.0015%, N≤0.0050%, and the rest is Fe and unavoidable impurities; The mechanical properties of the thick specification yield strength 500MPa grade galvanized low alloy high strength steel strip meet the following requirements: yield strength R eL : 500~620MPa, tensile strength R m : 530~690MPa, yield strength ratio ≥0.85, elongation A 80 ≥13%.

2. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 1, characterized in that: The mechanical properties of the thick specification yield strength 500MPa grade galvanized low alloy high strength steel strip meet the following requirements: yield strength R eL ≥545MPa, tensile strength R m ≥610MPa, yield strength ratio ≥0.88, elongation A 80 ≥15%.

3. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 1 or 2, characterized in that: The production method of the thick-gauge yield strength 500MPa-grade galvanized low-alloy high-strength steel strip comprises the following processes: smelting and continuous casting - hot rolling - pickling and cold rolling - continuous hot-dip galvanizing and skin-passing.

4. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 3, characterized in that: The smelting and continuous casting process comprises: molten iron pretreatment - converter - LF refining - slab continuous casting, wherein oxygen blowing decarburization and heating are carried out in the converter top and bottom combined blowing smelting, aluminum iron, manganese iron and the like are added in the converter steel tapping process for deoxidation and alloying, P and S components are controlled to prevent overoxidation of molten steel, and the steel tapping temperature is ≥1600°C; LF out-of-furnace refining adopts LF full-process argon blowing process, and the target composition is adjusted according to the molten steel composition, and the molten steel composition for the casting machine is C: 0.09-0.11%, Si: 0.02 ~0.04%, Mn: 1.0~1.1%, P≤0.020%, S≤0.010%, Alt: 0.020~0.040%, Nb: 0.05~0.06%, Ti: 0.01~0.02%, V: 0.01~0.02%, Ca: 0.0008~0.0015%, N≤0.0050%; the slab continuous casting superheat is controlled at 25~30℃, and the pulling speed is controlled at 0.55~0.80m / min.

5. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 3, characterized in that: The hot rolling process includes: heating of the ingot - rough rolling - finishing rolling - coiling, wherein the ingot is in the furnace for 180 to 250 minutes, the furnace temperature is 1210 to 1270°C, the rough rolling is carried out by a 3+3 mode 2-stand rolling mill, the finishing rolling is carried out by a 7-stand rolling mill, the finishing rolling start temperature is 980 to 1000°C, the finishing rolling final temperature is 860 to 910°C, and the thickness of the hot rolled steel strip is 4.0 to 5.0 mm; cooling is carried out by laminar cooling equipment, and the coiling temperature is 610 to 620°C.

6. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 3, characterized in that: The pickling cold rolling process comprises: pickling the hot-rolled steel strip to remove the surface iron oxide scale, and then cold rolling it through a 5-stand cold rolling mill, with a cold rolling reduction rate of 50-60% and a thickness of 1.8-2.5 mm.

7. The thick gauge galvanized low alloy high strength steel strip with a yield strength of 500 MPa according to claim 3, characterized in that: The continuous hot-dip galvanizing and skin-passing process comprises: uncoiling the cold hardened steel strip and welding it for continuous production, the furnace zone speed is 50-90 m / min, the soaking temperature is 755-785° C., slowly cooling to 620-630° C., then cooling to 450-460° C., the zinc pot temperature is 450-460° C., the skin-passing elongation is 0.5-0.9%, and the straightening elongation is ≤0.3%.

8. A method for producing a thick gauge 500 MPa grade galvanized low alloy high strength steel strip, comprising the following processes: Smelting and continuous casting - hot rolling - pickling and cold rolling - continuous hot-dip galvanizing and skin-passing; of which: The smelting and continuous casting process comprises: molten iron pretreatment - converter - LF refining - slab continuous casting, wherein oxygen blowing decarburization and heating are carried out in the converter top and bottom combined blowing smelting, aluminum iron, manganese iron and the like are added in the converter steel tapping process for deoxidation and alloying, P and S components are controlled to prevent overoxidation of molten steel, and the steel tapping temperature is ≥1600°C; LF out-of-furnace refining adopts LF full-process argon blowing process, and the target composition is adjusted according to the molten steel composition, and the molten steel composition for the casting machine is C: 0.09-0.11%, Si: 0.02 ~0.04%, Mn: 1.0~1.1%, P≤0.020%, S≤0.010%, Alt: 0.020~0.040%, Nb: 0.05~0.06%, Ti: 0.01~0.02%, V: 0.01~0.02%, Ca: 0.0008~0.0015%, N≤0.0050%; the slab continuous casting superheat is controlled at 25~30℃, and the pulling speed is controlled at 0.55~0.80m / min; The hot rolling process comprises: heating of the casting billet - rough rolling - finishing rolling - coiling, wherein the casting billet is in the furnace for 180-250 minutes, the furnace temperature is 1210-1270°C, the rough rolling adopts 3+3 mode 2-stand rolling mill, the finishing rolling adopts 7-stand rolling mill, the finishing rolling start temperature is 980-1000°C, the finishing rolling final rolling temperature is 860-910°C, and the hot rolled steel strip thickness is 4.0-5.0mm; the cooling adopts laminar cooling equipment, and the coiling temperature is 610-620°C; The pickling cold rolling process comprises: pickling the hot-rolled steel strip to remove the surface iron oxide scale, and then cold rolling it through a 5-stand cold rolling mill, with a cold rolling reduction rate of 50-60% and a thickness of 1.8-2.5 mm; The continuous hot-dip galvanizing and skin-passing process comprises: uncoiling the cold hardened steel strip and welding it for continuous production, the furnace zone speed is 50-90 m / min, the soaking temperature is 755-785° C., slowly cooling to 620-630° C., then cooling to 450-460° C., the zinc pot temperature is 450-460° C., the skin-passing elongation is 0.5-0.9%, and the straightening elongation is ≤0.3%.

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