980MPa-grade reinforced plastic dual-phase steel for continuous annealing and narrow lap welding method for continuous annealing process of 980MPa-grade reinforced plastic dual-phase steel

Abstract

The invention discloses 980MPa-grade reinforced plastic dual-phase steel for continuous annealing and a narrow lap welding method of a continuous annealing process of the 980MPa-grade reinforced plastic dual-phase steel. The 980MPa-grade reinforced plastic dual-phase steel comprises the following chemical components in percentage by weight: 0.16 to 0.20 percent of C, 0.60 to 1.00 percent of Si, 2.00 to 2.50 percent of Mn, 0.10 to 0.40 percent of Cr, 0.010 to 0.035 percent of Nb, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.015 to 0.055 percent of Ti, 0.0010 to 0.0040 percent of B, 0.010 to 0.035 percent of Als and less than or equal to 0.005 percent of N. And the balance of Fe and inevitable impurities. According to the method, the joining material and the raw material steel coil are sheared and then welded, and the welding seam quality is checked by measuring the welding seam thickness and performing a cup drawing test after welding; therefore, the technical problems of instability and low production efficiency in the production process in the prior art are effectively solved, and the purpose of ensuring stable and efficient hot galvanizing process production of the reinforced plastic dual-phase steel for 980MPa-grade continuous annealing is achieved.

Description

Technical Field

[0001] This invention relates to the field of cold-rolled sheet and strip production technology, and in particular to a 980MPa grade continuously annealed reinforced duplex steel and a narrow lap welding method for the continuous annealing process of the 980MPa grade continuously annealed reinforced duplex steel. Background Technology

[0002] Duplex steel, due to its excellent strength, ductility, and processing properties, has become the most widely used advanced high-strength steel. However, it is prone to stretching cracks during the stamping of complex parts. The ductile elongation after fracture (A) of 980MPa grade cold-rolled duplex steel... 80 The requirement of ≥10% is insufficient for complex parts. It is necessary to introduce a certain amount of retained austenite to induce the TRIP effect and achieve high plasticity, thereby increasing the elongation after fracture (A). 80 A value of ≥13% is required to meet the stamping requirements of complex parts, such as automotive A-pillar reinforcement plates and seat rails, which require high yield strength to resist deformation.

[0003] Patent document CN108311779A discloses a narrow lap welding method for 600MPa grade duplex steel. The technical solution employs a narrow lap welding machine on a continuous annealing production line. The tail end of the front coiled strip and the head end of the rear coiled strip are sheared at the inlet. Then, the tail end of the front coiled strip and the head end of the rear coiled strip are lapped together. Appropriate current, pressure, and speed are selected, and the welding wheel, via a moving frame, compacts the lap joint. Low pressure is used when the strip thickness is below 0.8mm, and high pressure is used when it is above 0.8mm, resulting in a high-strength weld that allows for continuous strip production. However, this invention lacks a transition material, and all lap welding examples involve welding the same type of steel, which is detrimental to production scheduling.

[0004] Patent document CN112958930A discloses a welding method for high-carbon equivalent strip steel during continuous annealing. The technical solution involves welding multiple steel coils end-to-end together during continuous annealing, followed by continuous annealing. The adjacent steel coils being welded have different carbon equivalents, namely high-carbon equivalent strip steel and low-carbon equivalent strip steel. This invention application only discloses the welding carbon equivalent and the use of high- and low-carbon equivalent products in cross-production, without specifying the transition material, specifications, or welding process. This is detrimental to ensuring the welding quality of dissimilar materials and products with different specifications.

[0005] Patent document CN104842056A discloses a narrow lap welding process for cold-rolled duplex steel strip. The technical solution utilizes a narrow lap resistance welding machine to weld the cold-rolled duplex steel strip. The welding process conditions are: welding current of 9–26 kA, welding speed of 6–13 m / min, welding wheel pressure of 6.5–13 kN, and the lap distance between the tail of the front coil and the head of the rear coil is 0.4–2.0 mm, with a compensation amount of 0.25–0.7 mm. The welding process in this invention application is not conducive to efficient welding production and obtaining high-quality welds. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a 980MPa graded annealing reinforced duplex steel that can ensure stable and efficient production of hot-dip galvanized steel.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 980MPa continuous annealing reinforced plastic dual-phase steel, the chemical composition of which, by weight percentage, includes C: 0.16-0.20%, Si: 0.60-1.00%, Mn: 2.00-2.50%, Cr: 0.10-0.40%, Nb: 0.010-0.035%, P≤0.020%, S≤0.010%, Ti: 0.015-0.055%, B: 0.0010-0.0040%, Als: 0.010%-0.035%, N≤0.005%; the remaining elements are Fe and unavoidable impurities.

[0008] As a further improvement to the above scheme, its chemical composition, by weight percentage, includes C: 0.16–0.20%, Si: 0.60–1.00%, Mn: 2.00–2.50%, Cr: 0.15–0.60%, Nb: 0.015–0.030%, P≤0.010%, S≤0.005%, Ti: 0.025–0.040%, B: 0.0020–0.0035%, Als: 0.015%–0.030%, N≤0.0035%; the remaining elements are Fe and unavoidable impurities.

[0009] The present invention also discloses a narrow lap welding method for the continuous annealing process of the above-mentioned 980MPa grade reinforced plastic duplex steel. The narrow lap welding method uses connecting materials to weld the 980MPa grade continuous annealing reinforced plastic duplex steel. The connecting material steel coil and the raw material steel coil are cut and then welded. After welding, the weld quality is checked by measuring the weld thickness and cupping test. Among them, the tensile strength of the higher-strength strip in the two steel coils before and after welding should not exceed 2.5 times the tensile strength of the lower-strength strip; The carbon equivalent of the connecting material used in welding is controlled within the range of 0.10 to 0.50% according to the following formula: Ceq=C+Si / 30+Mn / 20+2P+4S.

[0010] As a further improvement to the above scheme: double-cut shearing is adopted for shearing steel coils; when the thickness of the raw strip is <1.5mm, the tail removal amount is 16.0mm and the head removal amount is 12.0mm; when the thickness of the raw strip is ≥1.5mm and <2.2mm, the tail removal amount is 14.0mm and the head removal amount is 10.5mm; when the thickness of the raw strip is ≥2.2mm, the tail removal amount is 12.0mm and the head removal amount is 9.0mm.

[0011] As a further improvement to the above scheme: the shape of the raw material steel coil is ≤16IU, and the curvature is ≤26mm² / 10m; the thickness range of the welded cold-hardened coil is 0.90~2.50mm, and the width range is 900~1250mm; the thickness ratio of the two steel coils is ≤1.8, the width transition between the two steel coils is ≤200mm, and the width transition on one side is ≤100mm.

[0012] As a further improvement to the above scheme: during the welding process, the welding current is 11.5~13.5KA, the welding speed is 6.0~10.0m / min, the welding pressure is 9.0~15.0KN, the overlap is 1.10~1.50mm, and the compensation is 1.00~1.30mm.

[0013] As a further improvement to the above scheme: when the thickness of the raw strip is 0.90 mm, the welding current is 11.5 kA, and the welding current increases by 0.5 kA for every 0.4 mm increase in thickness; when the thickness of the raw strip is 0.90 mm, the welding speed is 10.0 m / min, and the welding speed decreases by 1.0 m / min for every 0.4 mm increase in thickness; when the thickness of the raw strip is 0.90 mm, the welding pressure is 9.0 kN, and the welding pressure increases by 1.5 kN for every 0.4 mm increase in thickness; when the thickness of the raw strip is 0.90 mm, the overlap is 1.10 mm, and the overlap increases by 0.10 mm for every 0.4 mm increase in thickness; when the thickness of the raw strip is 0.90 mm, the compensation is 1.00 mm, and the compensation increases by 0.10 mm for every 0.8 mm increase in thickness.

[0014] As a further improvement to the above scheme: the thickness of the weld is 0.75 to 1.50 times the thickness of the raw strip steel; when sampling the weld for cupping test, at least 3 points should be inspected. If the crack is in the heat-affected zone and the crack is perpendicular to the weld direction, the weld is considered qualified. If the crack coincides with the weld, the weld quality is considered unqualified. Furthermore, no two welds are allowed in a large roll, otherwise it is considered unqualified.

[0015] The beneficial effects of this invention are as follows: This invention controls the composition of the 980MPa grade continuously annealed reinforced duplex steel according to a specific ratio, and welds it before continuous annealing using the following method: cutting the connecting material and raw material steel coils before welding; after welding, the weld quality is checked by measuring the weld thickness and performing a cupping test; the tensile strength of the higher-strength strip in the two steel coils before and after welding should not exceed 2.5 times the tensile strength of the lower-strength strip; the carbon equivalent of the connecting material used in welding is controlled within the range of 0.10% to 0.50% according to the carbon equivalent formula: Ceq=C+Si / 30+Mn / 20+2P+4S. This effectively solves the technical problems of unstable production and low production efficiency in existing technologies, achieving the goal of providing a method that ensures stable and efficient production of the hot-dip galvanizing process for 980MPa grade continuously annealed reinforced duplex steel. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the weld quality after welding according to the present invention. Detailed Implementation

[0017] To facilitate understanding of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0018] The 980MPa continuous annealing reinforced plastic dual-phase steel disclosed in this invention has the following chemical composition by weight percentage: C: 0.16-0.20%, Si: 0.60-1.00%, Mn: 2.00-2.50%, Cr: 0.10-0.40%, Nb: 0.010-0.035%, P≤0.020%, S≤0.010%, Ti: 0.015-0.055%, B: 0.0010-0.0040%, Als: 0.010%-0.035%, N≤0.005%; the remaining elements are Fe and unavoidable impurities. The present invention discloses a narrow lap welding method for the continuous annealing process of 980MPa grade reinforced ductile duplex steel. This method uses a connecting material to weld the 980MPa grade continuously annealed reinforced ductile duplex steel. The connecting material coil and the raw material coil are sheared before welding. After welding, the weld quality is checked by measuring the weld thickness and performing a cupping test. The tensile strength of the higher-strength strip in the two coils before and after welding should not exceed 2.5 times the tensile strength of the lower-strength strip. The carbon equivalent of the connecting material used in welding is controlled within the range of 0.10-0.50% according to the following formula: Ceq=C+Si / 30+Mn / 20+2P+4S(%). This invention controls the carbon equivalent, plate shape, thickness and width transition, surface quality, shearing process and quality, and key welding processes including welding current, welding speed, welding machine pressure, lap length, and compensation amount of the connecting material. Figure 1 As shown, a weld with a smooth surface and no cracks was obtained, and the weld area was free of defects such as inclusions, incomplete penetration, and misalignment. This ensures stable and efficient production of the hot-dip galvanizing process and can provide guidance for the production of 980MPa-class continuous annealing reinforced duplex steel in similar units at home and abroad.

[0019] Based on actual needs, the composition of the 980MPa grade continuous annealing reinforced plastic dual-phase steel can be further optimized. In the optimized scheme, its chemical composition by weight percentage includes C: 0.16-0.20%, Si: 0.60-1.00%, Mn: 2.00-2.50%, Cr: 0.15-0.60%, Nb: 0.015-0.030%, P≤0.010%, S≤0.005%, Ti: 0.025-0.040%, B: 0.0020-0.0035%, Als: 0.015%-0.030%, N≤0.0035%; the remaining elements are Fe and unavoidable impurities.

[0020] In the narrow lap welding method disclosed in this invention, when selecting raw steel coils, the surface of the raw material must be free from severe dents, scratches, and wrinkles. Visually normal hot-rolled iron oxide scale must be present, and defects exceeding standards are not allowed. Simultaneously, the waviness and warping of the steel coils to be welded should not be excessive. The sheet shape of the raw steel coil is ≤16 IU, and the curvature is ≤26 mm² / 10 m. The thickness range of the cold-hardened coil to be welded is 0.90–2.50 mm, and the width range is 900–1250 mm. The thickness ratio of the two steel coils is ≤1.8, the width transition between the two steel coils is ≤200 mm, and the single-sided width transition is ≤100 mm.

[0021] The narrow lap welding method of this invention requires shearing of both the connecting steel coil and the raw material steel coil before welding. Before welding, the tail of the preceding steel coil and the following steel coil are double-cut to remove a certain length to ensure the plate shape and surface quality before welding. The shearing process is limited according to the thickness of the raw material strip. Specifically, when the thickness of the raw material strip is <1.5mm, the tail removal is 16.0mm and the head removal is 12.0mm; when the thickness of the raw material strip is ≥1.5mm and <2.2mm, the tail removal is 14.0mm and the head removal is 10.5mm; when the thickness of the raw material strip is ≥2.2mm, the tail removal is 12.0mm and the head removal is 9.0mm. Operators determine the cutting length based on the actual condition of the incoming material to ensure that defects at the head and tail are completely removed without deteriorating the welding quality.

[0022] In the narrow lap welding method of the present invention, key welding process parameters are controlled. The welding current is 11.5 - 13.5 KA, the welding speed is 6.0 - 10.0 m / min, the welding pressure is 9.0 - 15.0 KN, the lap amount is 1.10 - 1.50 mm, and the compensation amount is 1.00 - 1.30 mm. And the parameters of the above welding process are segmented and defined according to the thickness range of the raw strip steel. Specifically, when the thickness of the raw strip steel is 0.90 mm, the welding current is 11.5 KA, and for every 0.4 mm increase in thickness, the welding current increases by 0.5 KA; when the thickness of the raw strip steel is 0.90 mm, the welding speed is 10.0 m / min, and for every 0.4 mm increase in thickness, the welding speed decreases by 1.0 m / min; when the thickness of the raw strip steel is 0.90 mm, the welding pressure is 9.0 KN, and for every 0.4 mm increase in thickness, the welding pressure increases by 1.5 KN; when the thickness of the raw strip steel is 0.90 mm, the lap amount is 1.10 mm, and for every 0.4 mm increase in thickness, the lap amount increases by 0.10 mm; when the thickness of the raw strip steel is 0.90 mm, the compensation amount is 1.00 mm, and for every 0.8 mm increase in thickness, the compensation amount increases by 0.10 mm.

[0023] After the narrow lap welding is completed, the weld seam needs to be annealed and polished after welding. The surface is required to be smooth and crack-free, and there should be no defects such as inclusions, incomplete penetration, and misalignment in the weld seam area. In addition, the weld quality needs to be inspected by measuring the weld thickness and performing a cupping test to ensure that the thickness of the weld seam is 0.75 - 1.50 times the thickness of the raw strip steel.

[0024] When sampling the weld seam for the cupping test, at least 3 points should be inspected. If the crack is in the heat-affected zone, or the crack is perpendicular to the weld seam direction and the crack is perpendicular to the weld seam direction, the weld seam is judged to be qualified. If the crack coincides with the weld seam, the weld quality is judged to be unqualified; and there are not allowed to be two weld seams in one large coil, otherwise it is judged to be unqualified. When making a width jump connection, a crescent bend experiment needs to be carried out, and only after passing the test can the transition of the width jump steel coil be carried out.

[0025] Example: A 12.0mm tail section was cut from a 1.20mm*1050mm coil of 980MPa grade continuously annealed reinforced duplex steel (chemical composition: 0.185%C, 0.85%Si, 2.24%Mn, 0.28%Cr, 0.010%P, 0.003%S, 0.023%Nb, 0.28%Als, 0.033%Ti, 0.0024%B, carbon equivalent 0.357%). Then, a 1.30mm*1100mm diameter... The strip of a 590MPa grade continuously annealed reinforced duplex steel coil (0.168%C, 0.92%Si, 1.79%Mn, 0.005%P, 0.002%S, 0.042%Als, 0.032%Ti, 0.0030%B, with a carbon equivalent of 0.306%) was sheared to a length of 16.0mm. Welding was performed using a welding current of 12.0kA at a speed of 9.0m / min, with an overlap of 1.20mm and a compensation of 1.10mm, and a welding pressure of 10.5kN. The weld seam produced by this welding process was smooth and free of defects such as nodules, weld scars, and burn-through. No cracking along the weld seam was observed after cupping tests, and the crescent bend effect was good. No strip breakage caused by the weld seam occurred during hot-dip galvanizing annealing and finishing processes.

[0026] Comparative Example: A 10.5mm tail section was cut from a 1.70mm*1000mm coil of 980MPa grade continuously annealed reinforced duplex steel (chemical composition: 0.178%C, 0.93%Si, 2.22%Mn, 0.010%P, 0.002%S, 0.25%Als, 0.038%Ti, 0.020%Nb, 0.28%Cr, 0.0020%B, with a carbon equivalent of 0.348%). A 0.50mm diameter section was then... A 14.0mm section of a 1470mm thick DC04 steel coil (chemical composition: 0.0028% C, 0.02% Si, 0.10% Mn, 0.009% P, 0.003% S, 0.034% Al, 0.060% Ti, carbon equivalent: 0.033%) was cut off from the end. Welding was performed using a current of 8.0kA, a welding speed of 13.0m / min, an overlap of 1.10mm, a compensation of 1.10mm, and a welding pressure of 10.0kN. The weld quality after this welding process was poor; cupping tests showed cracks along the weld. Production was then resumed after changing the connecting material.

Claims

1. 980MPa grade continuous annealing reinforced plastic dual-phase steel, characterized in that: Its chemical composition, by weight percentage, includes C: 0.16–0.20%, Si: 0.60–1.00%, Mn: 2.00–2.50%, Cr: 0.10–0.40%, Nb: 0.010–0.035%, P≤0.020%, S≤0.010%, Ti: 0.015–0.055%, B: 0.0010–0.0040%, Als: 0.010%–0.035%, N≤0.005%; the remaining elements are Fe and unavoidable impurities.

2. The 980MPa cascade reinforced duplex steel as described in claim 1, characterized in that: Its chemical composition, by weight percentage, includes C: 0.16–0.20%, Si: 0.60–1.00%, Mn: 2.00–2.50%, Cr: 0.15–0.60%, Nb: 0.015–0.030%, P≤0.010%, S≤0.005%, Ti: 0.025–0.040%, B: 0.0020–0.0035%, Als: 0.015%–0.030%, N≤0.0035%; the remaining elements are Fe and unavoidable impurities.

3. A narrow lap welding method for the continuous annealing process of 980MPa reinforced duplex steel as described in claim 2, characterized in that: The narrow lap welding method uses a connecting material to weld 980MPa grade continuous annealing reinforced plastic duplex steel. The connecting material steel coil and the raw material steel coil are cut before welding. After welding, the weld quality is checked by measuring the weld thickness and cupping test. Among them, the tensile strength of the higher-strength strip in the two steel coils before and after welding should not exceed 2.5 times the tensile strength of the lower-strength strip; The carbon equivalent of the connecting material used in welding is controlled within the range of 0.10 to 0.50% according to the following formula: Ceq=C+Si / 30+Mn / 20+2P+4S.

4. The narrow lap welding method for the continuous annealing process of reinforced duplex steel for 980MPa continuous annealing as described in claim 3, characterized in that: Double-cut shearing is used for steel coils; when the thickness of the raw strip is <1.5mm, the tail removal amount is 16.0mm and the head removal amount is 12.0mm; when the thickness of the raw strip is ≥1.5mm and <2.2mm, the tail removal amount is 14.0mm and the head removal amount is 10.5mm; when the thickness of the raw strip is ≥2.2mm, the tail removal amount is 12.0mm and the head removal amount is 9.0mm.

5. The narrow lap welding method for the continuous annealing process of reinforced duplex steel for 980MPa continuous annealing as described in claim 3, characterized in that: The raw material steel coil has a plate shape ≤16IU and a curvature ≤26mm² / 10m; the thickness of the welded cold-hardened coil ranges from 0.90 to 2.50mm and the width ranges from 900 to 1250mm; the thickness ratio of the two steel coils is ≤1.8, the width transition between the two steel coils is ≤200mm, and the width transition on one side is ≤100mm.

6. The narrow lap welding method for the continuous annealing process of reinforced duplex steel for 980MPa continuous annealing as described in claim 3, characterized in that: During the welding process, the welding current is 11.5~13.5KA, the welding speed is 6.0~10.0m / min, the welding pressure is 9.0~15.0KN, the overlap is 1.10~1.50mm, and the compensation is 1.00~1.30mm.

7. The narrow lap welding method for the continuous annealing process of reinforced duplex steel for 980MPa continuous annealing as described in claim 6, characterized in that: The welding current is 11.5 kA when the thickness of the raw strip is 0.90 mm, and the welding current increases by 0.5 kA for every 0.4 mm increase in thickness. The welding speed is 10.0 m / min when the thickness of the raw strip is 0.90 mm, and the welding speed decreases by 1.0 m / min for every 0.4 mm increase in thickness. The welding pressure is 9.0 kN when the thickness of the raw strip is 0.90 mm, and the welding pressure increases by 1.5 kN for every 0.4 mm increase in thickness. The overlap is 1.10 mm when the thickness of the raw strip is 0.90 mm, and the overlap increases by 0.10 mm for every 0.4 mm increase in thickness. The compensation is 1.00 mm when the thickness of the raw strip is 0.90 mm, and the compensation increases by 0.10 mm for every 0.8 mm increase in thickness.

8. The narrow lap welding method for the continuous annealing process of reinforced duplex steel for 980MPa continuous annealing as described in claim 3, characterized in that: The thickness of the weld should be 0.75 to 1.50 times the thickness of the raw strip steel. When sampling the weld for cupping tests, at least 3 points should be inspected. If the crack is in the heat-affected zone and perpendicular to the weld direction, the weld is considered qualified. If the crack coincides with the weld, the weld quality is considered unqualified. Furthermore, no two welds are allowed in a large roll; otherwise, it is considered unqualified.

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