Thick cold-rolled hot-dipped aluminum-zinc steel plate with yield strength of 350 MPa

Abstract

The invention discloses a thick cold-rolled hot-dip aluminum-zinc steel plate with yield strength of 350 MPa. The thick cold-rolled hot-dip aluminum-zinc steel plate mainly solves the problems that the thickness range gt of an existing cold-rolled hot-dip aluminum-zinc steel plate with the thickness of 1.95-2.00 mm and the yield strength of 350 MPa is large; the thickness is 0.03 mm, the production cost is high, and the bending performance is poor. According to the technical scheme, a substrate of the thick cold-rolled hot-dip aluminum-zinc steel plate with the yield strength of 350 MPa comprises the following chemical components in percentage by weight: 0.17%-0.19% of C, 0.001%-0.054% of Si, 0.66%-0.76% of Mn, less than or equal to 0.025% of P, less than or equal to 0.025% of S, 0.010%-0.030% of Alt, 30%-38% of Mn / S and the balance of Fe and inevitable impurity elements. The thickness range of the cold-rolled hot-dipped aluminum-zinc steel plate with the thickness of 1.95-2.00 mm is smaller than or equal to 0.03 mm.

Description

Technical Field

[0001] The present invention relates to a cold-rolled hot-dip aluminum-zinc steel plate, in particular to a thick cold-rolled hot-dip aluminum-zinc steel plate with a yield strength of 350 MPa and a manufacturing method thereof, specifically to a low-cost cold-rolled hot-dip aluminum-zinc steel plate with a thickness of 1.95 to 2.00 mm and a yield strength of 350 MPa and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Thick-gauge hot-dip aluminum-zinc alloy coated steel plates are mainly used in the electrical cabinet industry due to their excellent corrosion resistance, paintability, processability and economy. In the electrical cabinet industry, the most commonly used thickness specification is 1.95~2.0mm.

[0003] The patent publication date is January 13, 2016, the publication number is CN105238999A, and the patent document is named "A 350MPa grade thick specification hot-dip galvanized steel and production method". It discloses a conventional aluminum-zinc alloy-coated steel plate with a carbon content of 0.07-0.10% and a niobium content of 0.03-0.05%, and its production cost is high.

[0004] The patent publication date is May 24, 2017, the publication number is CN106702267A, and the patent document is named "An iron-zinc coated steel plate with a yield strength of 350 MPa and a production method". It discloses a conventional iron-zinc coated steel plate with a carbon content of 0.075-0.09% and a niobium content of 0.011-0.023%, and its production cost is high.

[0005] The patent publication date is December 15, 2017, the publication number is CN107475625A, and the patent document is named "A cold-rolled steel sheet for electrogalvanizing with a yield strength ≥350MPa and a production method". It discloses a conventional electrogalvanized steel sheet with a carbon content of 0.01-0.16% and a manganese content of 0.9-1.1%, and its production cost is high.

[0006] The patent publication date is October 15, 2019, the publication number is CN110331336A, and the patent document named "350MPa grade low-alloy steel plate for steam generator and production method thereof" discloses a conventional hot-rolled steel plate with a manganese content of 1.3-1.5%, a molybdenum content of 0.45-0.60%, a niobium content of 0.50-0.70%, and a chromium content of 0.10-0.20%, and its production cost is high.

[0007] The patent publication date is December 15, 2017, the publication number is CN107475625A, and the patent document is named "A cold-rolled steel sheet for electrogalvanizing with a yield strength ≥350MPa and a production method". It discloses a conventional electrogalvanized steel sheet with a carbon content of 0.01-0.16% and a manganese content of 0.9-1.1%, and its production cost is high.

[0008] The patent publication date is December 10, 2019, the publication number is CN110551946A, and the patent document is named "A method for producing an economical 350MPa grade high-toughness structural steel". It discloses a hot-dip galvanized steel plate with a manganese content of 0.8-1.4% and a phosphorus content of 0.03-0.045%, and its production cost is high.

[0009] The patent publication date is December 24, 2019, the publication number is CN110607476A, and the patent document named "A method for manufacturing cold-rolled hot-dip galvanized high-strength structural steel with a yield strength of 350MPa" discloses a conventional electro-galvanized steel plate with a phosphorus content of 0.06-0.075% and a titanium content of 0.045-0.08%, and its production cost is high.

[0010] In the prior art, Nb, V, and Ti are usually used for strengthening, which has the problem of high production cost. At the same time, in the process of processing the C-type column of the electrical cabinet, it is first cut into narrow strips with a width of 50-200mm, and then each narrow strip is roll-formed. If the thickness deviation of each narrow strip is large, the length of the C-type column will be inconsistent; the thickness difference of the cold-rolled hot-dip aluminum-zinc steel plate required for processing the C-type column is required to be ≤0.03mm, and the prior art cannot meet this requirement. Summary of the invention

[0011] The purpose of the present invention is to provide a thick cold-rolled hot-dip aluminum-zinc steel plate with a yield strength of 350 MPa and a manufacturing method thereof, mainly to solve the technical problems that the existing cold-rolled hot-dip aluminum-zinc steel plate with a thickness of 1.95 to 2.00 mm and a yield strength of 350 MPa has a thickness range of >0.03 mm, high production cost and poor bending performance.

[0012] The technical solution adopted by the present invention is:

[0013] A thick cold-rolled hot-dip aluminum-zinc steel plate with a yield strength of 350 MPa, wherein the chemical composition of the substrate is as follows: C: 0.17% to 0.19%, Si: 0.001% to 0.054%, Mn: 0.66% to 0.76%, P≤0.025%, S≤0.025%, Alt: 0.010% to 0.030%, Mn / S is 30 to 38, and the remainder is Fe and unavoidable impurity elements.

[0014] The metallographic structure of the cold-rolled hot-dip aluminum-zinc steel sheet of the present invention is fine ferrite + free cementite + a small amount of pearlite, and the ferrite grain size level is I9-I11; the yield strength R of the cold-rolled hot-dip aluminum-zinc steel sheet with a thickness of 1.95-2.00 mm is P0.2 350~420MPa, tensile strength R m 420~500MPa, elongation after fracture A 80mm 18% to 25%; the thickness range of cold-rolled hot-dip aluminum-zinc steel sheet is ≤0.03mm; 180° bending test, d=0a is qualified, the outer surface of the cold-rolled hot-dip aluminum-zinc steel sheet does not peel off, and the base plate of the hot-dip aluminum-zinc steel sheet does not crack; the weight of the single-sided zinc layer of the cold-rolled hot-dip aluminum-zinc steel sheet is 60 to 75g / m 2 .

[0015] Cold-rolled and hot-dip aluminum-zinc steel plates meet the requirements for the preparation of C-shaped columns of electrical cabinets.

[0016] The reasons why the chemical composition of the substrate of the thick cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 350 MPa described in the present invention is limited to the above range are as follows:

[0017] Carbon: Carbon is the most economical solid solution strengthening element. As the carbon content increases, the strength of the steel matrix increases. Most of the existing technical solutions use Ti and P for strengthening. Since ferrophosphorus and ferrotitanium alloys contain more impurities, they form titanium oxides that are not easy to remove, affecting the castability of molten steel and the quality of slabs. Therefore, from the perspective of product quality and economy, the present invention has preferably set the carbon content at 0.17% to 0.19% through multiple tests.

[0018] Silicon: Silicon is a residual element in steel. No silicon alloy is added during the production process. The present invention limits Si to 0.001% to 0.054%.

[0019] Manganese: Manganese is an important solid solution strengthening element. Adding appropriate Mn can effectively improve the strength of steel plates. However, since manganese alloys are relatively expensive, it is necessary to comprehensively consider quality, strength, and cost to select an appropriate range. Since the affinity of manganese to sulfur is greater than that of iron to sulfur, manganese and sulfur form high-melting-point MnS (melting point 1600°C) to replace low-melting-point FeS (the eutectic melting temperature of Fe and FeS is 988°C), reducing the probability of FeS precipitation between crystals and reducing the hot brittleness of steel. When the Mn / S ratio is less than 20, cold bending cracking is prone to occur. When the Mn / S ratio is greater than 38, the production cost increases significantly. The applicant has found that when the Mn / S ratio is 30 to 38, economical cost and excellent bending performance can be obtained. The present invention considers bending performance and cost. After multiple tests, the preferred range of manganese content is determined to be 0.66% to 0.76%.

[0020] Sulfur: S in the present invention is an impurity element. According to the actual steelmaking production capacity and the impact of desulfurization on the cost, the present invention limits S to ≤ 0.025%.

[0021] Phosphorus: P in the present invention is an impurity element. According to the actual steelmaking production capacity and the impact of dephosphorization on the cost, the present invention limits P to ≤ 0.025%.

[0022] Aluminum: In addition to being the main deoxidizing element, Al added to steel can combine with N in steel to form AlN. When the Al content is greater than 0.030%, excessive aluminum will increase costs. When the Al content is less than 0.10%, it is easy to cause insufficient deoxidation of molten steel, resulting in high inclusions in the steel, and cracking is prone to occur during processing. Therefore, the addition range of aluminum in steel is controlled to ensure deoxidation while minimizing production costs. The present invention sets Al: 0.010% to 0.030%.

[0023] Manganese-sulfur ratio: In order to obtain a more uniform yield strength in the plate width direction, the manganese-sulfur ratio is beneficial to the uniformity of the structure, and is also beneficial to obtaining economical cost and excellent bending performance. The present invention sets the ratio of the weight content of manganese to the weight content of sulfur in the steel, Mn / S, to preferably 30 to 38.

[0024] A method for manufacturing a thick cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 350 MPa, the method comprising:

[0025] The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows: C: 0.17% to 0.19%, Si: 0.001% to 0.054%, Mn: 0.66% to 0.76%, P≤0.025%, S≤0.025%, Alt: 0.010% to 0.030%, Mn / S is 30 to 38, and the remainder is Fe and unavoidable impurity elements;

[0026] The continuous casting slab is heated to 1170-1220° C. in a heating furnace and then hot rolled. The hot rolling is a two-stage rolling process. The finishing temperature of the finishing rolling is 850-870° C. and the finishing rolling reduction rate is 90%-91%. After finishing rolling, the thickness of the hot-rolled steel plate is controlled to be 3.6-4.0 mm, the convexity of the hot-rolled steel plate is 0.010-0.035 mm, the laminar cooling adopts the front-stage cooling, and the coiling temperature is 520-560° C. to obtain the hot-rolled steel coil;

[0027] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, cooled to room temperature after plating, coated with a fingerprint-resistant film, and the coil is obtained to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.95-2.00 mm. The cold rolling reduction rate is 50%-55%. The heating temperature of the hardened strip steel after cold rolling in the horizontal continuous annealing furnace is 720-740°C, the temperature of the soaking section is 781-790°C, and the annealing time of the strip steel in the soaking section is 55-65s; the strip steel is directly put into the zinc pot for hot-dip galvanizing; the temperature of the strip steel entering the zinc pot is 550-600°C; the weight of the single-side zinc layer of the cold-rolled hot-dip galvanized steel sheet is controlled to be 60-75g / m 2 .

[0028] Furthermore, the speed of the strip passing through the zinc pot is controlled to be 55-65m / min, and the hot-dip aluminum-zinc coating effect is best.

[0029] The reasons for the production process adopted by the present invention are as follows:

[0030] 1. Setting of finishing rolling and coiling temperature

[0031] The composition of the present invention is predicted to have an A3 phase line temperature of 847.5° C. In order to obtain a steel plate with a certain strength, high formability and flatness, preferably, the hot rolling process is: the finishing temperature of the finishing rolling is 850-870° C., and the coiling temperature is 520-560° C.

[0032] 2. Setting of convexity of hot rolled steel plate

[0033] The convexity of the hot-rolled steel plate is crucial to the thickness uniformity of the aluminum-zinc steel coil in the width direction. The smallest possible convexity is beneficial to reducing the thickness range. However, if the convexity is too small, it will affect the rolling stability of the acid rolling unit. After many tests, the convexity of the hot-rolled steel plate is set to 0.010-0.035mm. Preferably, when the width of the hot-rolled steel plate is 800-1000mm, the convexity of the hot-rolled steel plate is 0.010-0.030mm; when the width of the hot-rolled steel plate is 1001-1300mm, the convexity of the hot-rolled steel plate is 0.015-0.035mm.

[0034] 3. Setting the temperature of the heating section of the horizontal continuous annealing furnace

[0035] In order to make the steel plate fully recover recrystallization, a horizontal continuous annealing furnace is used to heat the steel plate, and the heating temperature is controlled at 720℃~740℃.

[0036] The metallographic structure of the cold-rolled hot-dip aluminum-zinc steel sheet produced by the above method is fine ferrite + free cementite + a small amount of pearlite, and the ferrite grain size grade is I9~I11; the yield strength R of the 1.95~2.00mm thick cold-rolled hot-dip aluminum-zinc steel sheet is P0.2 350~420MPa, tensile strength Rm 420~500MPa, elongation after fracture A 80mm 18% to 25%; the thickness range of cold-rolled hot-dip aluminum-zinc steel sheet is ≤0.03mm; 180° bending test, d=0a is qualified, the outer surface of the cold-rolled hot-dip aluminum-zinc steel sheet does not peel off, and the base plate of the hot-dip aluminum-zinc steel sheet does not crack; the weight of the single-sided zinc layer of the cold-rolled hot-dip aluminum-zinc steel sheet is 60 to 75g / m 2 .

[0037] Compared with the prior art, the present invention has the following positive effects: 1. The steel plate of the present invention can achieve the high thickness accuracy required by the C-shaped column, and the thickness range is ≤0.03mm. 2. The method of the present invention adopts a conventional acid rolling unit, and the cold rolling reduction rate is 50-55%, the unit load is small, and the manufacturing process is simple. 3. The steel plate of the present invention has good economy, and only economic elements carbon and manganese are added to achieve high strength and low cost. It is particularly easy to implement in the actual smelting production process, and the production cost is greatly reduced compared with the existing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a metallographic structure photograph of the cold-rolled hot-dip aluminum-zinc steel sheet of Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with Examples 1 to 5, as shown in Tables 1 to 4.

[0040] Table 1 shows the chemical composition (by weight percentage) of the substrate of the cold-rolled hot-dip aluminum-zinc steel sheet according to an embodiment of the present invention, with the remainder being Fe and unavoidable impurities.

[0041] Table 1 Chemical composition of the substrate of the cold-rolled hot-dip aluminum-zinc steel sheet according to the embodiment of the present invention, unit: weight percentage.

[0042]

[0043]

[0044] Through converter smelting, a continuous casting billet meeting the required chemical composition is obtained, with a thickness of 210 to 240 mm, a width of 800 to 1300 mm, and a length of 5000 to 10000 mm.

[0045] The continuous casting slab is heated to 1170-1220°C in a heating furnace and then hot rolled. The hot rolling is a two-stage rolling process, the rough rolling is 5 continuous rolling, the finishing rolling is 7 continuous rolling, the finishing rolling end temperature is 850-870°C, the finishing rolling reduction rate is 90%-91%, the convexity of the hot rolled steel plate is 0.010-0.035mm, the laminar cooling adopts the front section cooling, the coiling temperature is 520-560°C to obtain the hot rolled steel coil; the hot rolling process control is shown in Table 2.

[0046] Table 2 Hot rolling process control parameters of the embodiment of the present invention

[0047]

[0048] After the hot-rolled steel coil is unrolled, it is pickled, cold rolled, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, cooled to room temperature after plating, coated with a fingerprint-resistant film, and the coil is obtained to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.95-2.00 mm. The cold rolling reduction rate is 50%-55%. The heating temperature of the hardened strip after cold rolling in the horizontal continuous annealing furnace is 720℃-740℃, the soaking section temperature is 781-790℃, and the annealing time of the strip in the soaking section is 55-65s; the strip is directly put into the zinc pot for hot-dip galvanizing; the temperature of the strip entering the zinc pot is 550℃-600℃, and the speed of the strip passing the zinc pot is 55-65m / min. The process control parameters of cold rolling, annealing, and hot-dip galvanizing are shown in Table 3.

[0049] Table 3 Control parameters of pickling and hot-dip aluminum-zinc process of the present invention

[0050]

[0051] The cold-rolled hot-dip aluminum-zinc steel sheet produced by the above method is Figure 1 The metallographic structure of cold-rolled hot-dip aluminum-zinc steel sheet is fine ferrite + free cementite + a small amount of pearlite, and the ferrite grain size grade is I9~I11; the yield strength R of 1.95~2.00mm thick cold-rolled hot-dip aluminum-zinc steel sheet P0.2 350~420MPa, tensile strength R m 420~500MPa, elongation after fracture A 80mm 18% to 25%; the thickness range of cold-rolled hot-dip aluminum-zinc steel sheet is ≤0.03mm; 180° bending test, d=0a is qualified, the outer surface of the cold-rolled hot-dip aluminum-zinc steel sheet does not peel off, and the base plate of the hot-dip aluminum-zinc steel sheet does not crack; the weight of the single-sided zinc layer of the cold-rolled hot-dip aluminum-zinc steel sheet is 60 to 75g / m 2 .

[0052] The hot-dip aluminum-zinc steel sheet obtained by the present invention is subjected to a tensile test according to "GB / T228.1-2010 Metallic Material Tensile Test Part 1: Room Temperature Test Method"; a bending test is conducted according to "GB / T232-2010 Metallic Material Bending Test Method", a 180° bending test, d=0a, and the outer surface of the cold-rolled hot-dip aluminum-zinc steel sheet does not have a coating peeling, and the hot-dip aluminum-zinc steel sheet substrate does not crack, which is qualified. The mechanical properties and coating properties of the cold-rolled hot-dip aluminum-zinc steel sheet are shown in Table 4.

[0053] Table 4 Performance parameters of the cold-rolled hot-dip aluminum-zinc steel sheet of the present invention

[0054]

[0055] The examples 1 to 5 of the present invention show that in the 180° bending test, d=0a, the coating on the outer surface of the cold-rolled hot-dip aluminum-zinc steel sheet does not peel off, and the hot-dip aluminum-zinc steel sheet substrate does not crack. When used to manufacture electrical cabinets, no cracking defects occur during bending, meeting the use requirements.

[0056] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 350 MPa, wherein the chemical composition weight percentage of the substrate is: C: 0.17% to 0.19%, Si: 0.001% to 0.054%, Mn: 0.66% to 0.76%, P≤0.025%, S≤0.025%, Alt: 0.010% to 0.030%, Mn / S is 30 to 38, and the balance is Fe and unavoidable impurity elements; the yield strength R of the cold-rolled hot-dip aluminum-zinc steel sheet with a thickness of 1.95 to 2.00 mm P0.2 350~420MPa, tensile strength R m 420~500MPa, elongation after fracture A 80mm 18% to 25%; the thickness range of cold-rolled hot-dip aluminum-zinc steel sheet is ≤0.03mm; 180° bending test, d=0a is qualified; the weight of single-sided zinc layer of cold-rolled hot-dip aluminum-zinc steel sheet is 60 to 75g / m 2 .

2. The thick cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 350 MPa as claimed in claim 1, characterized in that: The metallographic structure of cold-rolled hot-dip aluminum-zinc steel sheet is fine ferrite + free cementite + a small amount of pearlite, and the ferrite grain size grade is I9~I11.

3. The method for manufacturing a thick cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 350 MPa as claimed in claim 1, characterized in that: The method includes: The molten steel is continuously cast to obtain a continuous casting slab, wherein the chemical composition of the molten steel is as follows: C: 0.17% to 0.19%, Si: 0.001% to 0.054%, Mn: 0.66% to 0.76%, P≤0.025%, S≤0.025%, Alt: 0.010% to 0.030%, Mn / S is 30 to 38, and the remainder is Fe and unavoidable impurity elements; The continuous casting slab is hot rolled after passing through a heating furnace. The hot rolling is a two-stage rolling process. The finishing temperature of the finishing rolling is 850-870°C and the finishing rolling reduction rate is 90%-91%. After finishing rolling, the thickness of the hot rolled steel plate is controlled to be 3.6-4.0 mm. The laminar cooling adopts the front stage cooling. The coiling temperature is 520-560°C to obtain the hot rolled steel coil. The hot-rolled steel coil is unrolled and then pickled, cold rolled, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, air-cooled to room temperature after plating, coated with a fingerprint-resistant film, and the coil is obtained to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.95-2.00 mm. The cold rolling reduction rate is 50%-55%. The heating temperature of the hardened strip after cold rolling in the horizontal continuous annealing furnace is 720-740°C, the temperature of the soaking section is 781-790°C, and the annealing time of the strip in the soaking section is 55-65s; the strip is directly put into the zinc pot for hot-dip galvanizing; the temperature of the strip entering the zinc pot is 550°C-600°C.

4. The manufacturing method according to claim 3, characterized in that: The speed of the strip passing through the zinc pot is 55-65m / min.

5. The manufacturing method according to claim 3, characterized in that: The metallographic structure of cold-rolled hot-dip aluminum-zinc steel sheet is fine ferrite + free cementite + a small amount of pearlite, and the ferrite grain size grade is I9~I11.

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