Welding method of low-cost 980MPa-grade hot-dip galvanized dual-phase steel in acid rolling process

Abstract

The invention discloses low-cost 980MPa-grade hot-dip galvanized dual-phase steel and a welding method for an acid rolling process of the low-cost 980MPa-grade hot-dip galvanized dual-phase steel. The dual-phase steel comprises the following chemical components: C, Si, Mn, Cr, Nb, Ti, P, S, Als, N, B and the balance of Fe and inevitable impurities. According to the welding method, after a connecting material selected for welding and a raw material steel coil are sheared, welding faces of the connecting material and the raw material steel coil are aligned and located on the same horizontal plane, then welding wires are added for welding, after welding, welding lines are subjected to post-welding annealing and polishing treatment, and the quality of the welding lines is checked by measuring the thickness of the welding lines and conducting a cup convex test. According to the method, good welding seam quality can be obtained, meanwhile, the cold rolling reduction rate is adjusted according to the thickness of the strip steel, stable and efficient production of the acid rolling procedure is ensured, and then batch stable production of the low-cost 980 MPa-grade hot-dip galvanized dual-phase steel is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled strip production, and in particular relates to a method for producing low-cost 980MPa grade hot-dip galvanized duplex steel products by adopting a combined acid rolling unit and a hot-dip galvanizing unit. Background Art

[0002] The development trend of the modern automobile industry is to make it as lightweight as possible to reduce fuel consumption and emissions while ensuring safety performance. Dual-phase steel has the advantages of good strength and plasticity, high work hardening rate, etc., and has become one of the most widely used advanced high-strength steels. Dual-phase steel is the most widely used advanced high-strength steel at present. 980MPa-grade products have become one of the most important products used by automobile companies. At the same time, with the continuous improvement of corrosion resistance requirements, the proportion of galvanized sheets is increasing. The balanced galvanizing process of 980MPa-grade hot-dip galvanized dual-phase steel is in the bainite transformation zone (about 460°C). When designing the composition, a certain amount of alloy elements needs to be added to ensure hardenability and inhibit the formation of bainite, which brings certain difficulties to the hot rolling process (welding, rolling load, etc.). The welding process commonly used in the prior art is: Prior art 1 (CN 112025081A) discloses a method for welding QP980 and above ultra-high strength steel using a laser welder, comprising the following steps: 1) adjusting the working process of the laser welder, first adjusting the inlet section, then adjusting the outlet section, and finally adjusting the middle section; 2) adjusting the position of the shielding gas nozzle; 3) adjusting the transverse blowing pressure; 4) selecting transition material; 5) using a water cooling device to cool down; 6) optimizing welding parameters; 7) using a QCDS weld detection system to monitor the weld quality in real time; 8) optimizing the preheating and annealing device; 9) equipment maintenance before production welding, and realizing the production of QP980 with poor weldability and a carbon equivalent of more than 0.575%, but it does not introduce the production rhythm, transition material material, raw material specifications and plate shape, strip head / tail processing method, gas protection and weld quality evaluation, which is not conducive to guiding the whole process production. At the same time, due to different strengths and steel types, there are large differences in welding processes.

[0003] Prior art 2 (CN104842056A) discloses a weld plasticizing device and process for ultra-high strength dual-phase steel laser welded plates. The weld of the ultra-high strength dual-phase steel welded plates is placed between a heat-conducting material and a cooling plate to ensure the flatness of the welded plate while using an electromagnetic chuck to accurately position and assemble the materials; the high-frequency heating coil is turned on to adjust the output power to ensure an output temperature of 800-850°C, and the insulation time is 3-5 minutes to austenitize the weld structure; a cooling plate filled with coolant is used to cool the welded plates. The cooling plate is used to quickly cool the weld of the ultra-high strength dual-phase steel tailor-welded plate; the output power of the high-frequency heating coil is adjusted to ensure the output temperature of 250-300℃, and the heat preservation time is 5-30s; the coolant flow rate is reduced, the output power of the high-frequency heating coil is increased, the output temperature is ensured to be 300-380℃, and the heat preservation time is 10-90s, and the weld is locally distributed; the output power of the high-frequency heating coil is reduced to zero; the weld of the ultra-high strength dual-phase steel tailor-welded plate is quickly cooled to room temperature using a cooling plate filled with coolant. The average grain size of the weld obtained is 1.5μm-4.0μm, and the cupping value of the ultra-high strength dual-phase steel tailor-welded plate is 7.3-9.9mm, which is 43% higher than the cupping value of the tailor-welded plate. It did not provide detailed descriptions of the production rhythm, transition material material, specifications and plate shape, strip head / tail processing, key welding process parameters (welding wire, laser power, welding speed, wire feeding process, etc.), and the equipment was specially modified, which is not conducive to the use of conventional units to complete the welding of acid-rolled raw materials.

[0004] Therefore, how to obtain a low-cost welding method for 980MPa grade hot-dip galvanized dual-phase steel that ensures a stable and efficient pickling process has become a difficult problem that urgently needs to be solved. Summary of the invention

[0005] Based on this, in view of the deficiencies of the above-mentioned prior art, a method for producing a low-cost 980MPa grade hot-dip galvanized duplex steel product using a combined pickling mill and a hot-dip galvanizing mill and a welding method thereof are provided.

[0006] In order to achieve the above purpose, the following technical solutions are adopted: The invention provides a low-cost 980MPa grade hot-dip galvanized dual-phase steel. The chemical composition of the dual-phase steel comprises, by weight percentage, C: 0.05%-0.12%, Si: 0.25%-0.50%, Mn: 2.00%-2.40%, P≤0.018%, S≤0.009%, Als: 0.010%-0.065%, N≤0.0065%, Cr: 0.30%-0.70%, Nb: 0.015%-0.040%, Ti: 0.025-0.050%, B: 0.0010-0.0050, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the remaining elements are Fe and inevitable impurities.

[0007] In some embodiments, the chemical composition of the dual-phase steel includes, by weight percentage, C: 0.07%~0.10%, Si: 0.30%~0.45%, Mn: 2.05%~2.35%, P≤0.012%, S≤0.006%, Als: 0.025%~0.060%, N≤0.0045%, Cr: 0.33%~0.58%, Nb: 0.018%~0.033%, Ti: 0.028%~0.048%, B: 0.0025%~0.0045%, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the balance is Fe and unavoidable impurities.

[0008] The present invention also provides a welding method for the above-mentioned low-cost 980MPa grade hot-dip galvanized dual-phase steel acid rolling process, wherein the welding material and the raw steel coil are sheared, the welding surfaces of the welding material and the raw steel coil are aligned and on the same horizontal plane, and then welding wire is added for welding, and the weld is annealed and polished after welding, and the weld quality is checked by measuring the weld thickness and cupping test; The carbon equivalent of the selected connecting material needs to be controlled by the carbon equivalent formula, which is: Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14(%).

[0009] The difference in yield strength between the connecting material and the low-cost 980MPa grade hot-dip galvanized duplex steel before and after welding is within 1.7 times.

[0010] In some embodiments, the carbon equivalent of the selected connecting material is controlled in the range of 0.50% to 1.0%.

[0011] In some embodiments, the weld is heat treated through a thermal cycle after welding, with a power of 48 kW, a frequency of 35 kHz, a weld heat treatment current compensation amount of 0 to 15%, and a heating rate of ≤20°C / s during the heating process of the weld heat treatment. During cooling, the weld is cooled to below 280°C at a cooling rate of ≤15°C / s and then air-cooled.

[0012] In some embodiments, the step of "cutting the welding selected connecting material and the raw steel coil" includes: when cutting, the cutting length of the steel coil is controlled according to the following requirements, and welding is performed after ensuring the plate shape and surface quality; Use double-cut shears to cut a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the strip thickness t<3.25mm, the cutting amount is 9.0m, and when the strip thickness 3.25mm≤t<4.25mm, the cutting amount is 7.5m. Ensure that the defects at the head and tail of the strip can be completely removed and will not deteriorate the welding quality.

[0013] In some embodiments, the shear blade gap ranges from 0.25mm to 0.45mm; the shear blade gap is controlled according to the thickness of the steel strip according to the following requirements: when the strip thickness is ≤3.25mm, the shear blade gap is 0.25mm, and the shear blade gap increases by 0.05mm for every 0.5mm increase in strip thickness; the shear blade is replaced according to a cycle of ≤5500t or a shearing number of ≤9000 times. After each replacement of the shear blade, the side gap of the shear blade should be calibrated to ensure that the sheared end face is smooth and straight, without burrs, delamination and other defects.

[0014] In some embodiments, the welding process parameters are: laser power 14±0.5KW, welding speed 2.5~3.5±0.5m / min; wherein, when the raw material thickness is ≤3.25mm, the welding speed is 3.5±0.5m / min, and the speed decreases by 0.5m / min for every 0.5mm increase in thickness; the welding speed compensation range is 0~18%; after welding, the weld needs to be cleaned with a rolling wheel, the rolling wheel pressure is ≤65KN, and the rolling wheel height is 0 mm ~6.5mm.

[0015] In some embodiments, the welded steel is subsequently pickled and cold rolled; wherein the pickling step is: The i-Box type acid tank is used to clean the iron oxide scale on the surface of the strip steel. The acid concentration of the 1# acid tank is 45g / L~70g / L, the acid concentration of the 2# acid tank is 75 g / L~100g / L, and the acid concentration of the 3# acid tank is 105 g / L~140g / L. The acid temperature is 60℃~80℃, and the pickling speed is 60m / min~180m / min. The pickling speed is 180m / min when the strip steel thickness is 2.25mm, and the pickling speed decreases by 15m / min for every 0.25mm increase in thickness. After that, the residue on the surface of the strip steel is removed by rinsing, and the pH value of the rinsing agent is ≥5.0. Finally, it is dried at a drying temperature of 80~150℃.

[0016] In some embodiments, the cold rolling step is: after pickling, the hot-rolled coil is cold-rolled into a thin strip steel of 0.90mm-2.40mm, and the cold rolling reduction rate is 43%-60%. As the thickness of the cold-rolled finished material increases, the cold rolling reduction rate gradually decreases. For every 0.3mm increase in the thickness of the cold-rolled thin strip steel, the raw material thickness is adjusted accordingly, and the cold rolling reduction rate is reduced by about 3.5%. The present invention has the following beneficial technical effects: This scheme provides a low-cost 980MPa grade hot-dip galvanized duplex steel acid rolling process welding method, the material, plate shape, surface quality, shearing effect, welding parameters (wire selection, laser power, welding speed, wire feeding speed, etc.) of the raw materials, and the evaluation of welding effect are described in detail to obtain good weld quality. At the same time, the cold rolling reduction rate is adjusted according to the thickness of the strip to ensure the stable and efficient production of the acid rolling process, thereby realizing the low-cost 980MPa grade hot-dip galvanized duplex steel batch stable production. This method can also be extended to the same type of units to produce 980MPa grade hot-dip galvanized duplex steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 Schematic diagram of weld quality after welding according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0020] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are only illustrative. Although only a few embodiments are described in detail in the present invention, it is easy for those skilled in the art to appreciate that multiple modifications are feasible without actually departing from the teaching of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, changes and deletions may be made to the design, operating conditions and parameters of the following exemplary embodiments.

[0021] Based on the above purpose, in a first aspect of an embodiment of the present invention, a low-cost 980MPa grade hot-dip galvanized dual-phase steel comprises, by weight percentage, the following chemical compositions: C: 0.05%~0.12%, Si: 0.25%~0.50%, Mn: 2.00%~2.40%, P≤0.018%, S≤0.009%, Als: 0.010%~0.065%, N≤0.0065%, Cr: 0.30%~0.70%, Nb: 0.015%~0.040%, Ti: 0.025~0.050%, B: 0.0010~0.0050, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the remaining elements are Fe and unavoidable impurities.

[0022] The preferred low-cost 980MPa grade hot-dip galvanized dual-phase steel has the following chemical components, by weight percentage: C: 0.07%~0.10%, Si: 0.30%~0.45%, Mn: 2.05%~2.35%, P≤0.012%, S≤0.006%, Als: 0.025%~0.060%, N≤0.0045%, Cr: 0.33%~0.58%, Nb: 0.018%~0.033%, Ti: 0.028%~0.048%, B: 0.0025%~0.0045%, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the balance is Fe and unavoidable impurities.

[0023] The second aspect of the embodiment of the present invention discloses a low-cost 980MPa grade hot-dip galvanized duplex steel acid rolling process welding method, wherein the welding material and the raw steel coil are selected for welding and the welding surfaces of the connecting material and the raw steel coil are aligned and on the same horizontal plane, and then welding wire is added for welding, and the weld is subjected to post-weld annealing and grinding after welding, and the weld quality is checked by measuring the weld thickness and cupping test; since the 980MPa grade hot-dip galvanized duplex steel has a high alloy content and poor welding performance, the weld needs to be supplemented with welding wire, and the diameter of the welding wire is 0.9mm; the material of the welding wire is determined to be YGW12 with reference to the JIS Z 3312 standard, and the YGW12 welding wire is a flux-cored welding wire for hard facing surfacing, which can fill the part of the weld below the strip steel, improve the performance of the special steel weld area, and eliminate the blank area between the gaps.

[0024] Among them, the carbon equivalent of the selected connecting material needs to be controlled by the carbon equivalent formula, which is: Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14(%). After calculation, the carbon equivalent of the selected connecting material is controlled in the range of 0.50%~1.0%. The difference in yield strength between the connecting material and the low-cost 980MPa grade hot-dip galvanized duplex steel before and after welding is within 1.7 times, that is, the yield strength of the higher-strength strip in the two steel coils before and after welding should not be higher than 1.7 times the yield strength of the lower-strength steel strip. The surface requirements of the hot-rolled raw material are visually normal hot-rolled iron oxide scale, no excessive defects and no water accumulation, and also need to have a good plate shape. The thickness range of the hot-rolled raw material for welding is 2.25mm~4.25mm, and the width range is 800mm~1300mm.

[0025] The step of "cutting the welding selected connecting material and the raw steel coil" includes: when cutting, the cutting length of the steel coil is controlled according to the following requirements, and welding is performed after ensuring the plate shape and surface quality; Use double-cut shears to cut a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the strip thickness t<3.25mm, the cutting amount is 9.0m, and when the strip thickness 3.25mm≤t<4.25mm, the cutting amount is 7.5m. The operator needs to inspect each incoming roll and ensure that the defects at the head and tail of the strip can be completely removed without deteriorating the welding quality.

[0026] Among them, the surface straightness of the strip is ≤230umit, the sickle bend is ≤18mm / 10m, and the convexity (hc-h40) is ≤120μm. The jump range of the welding machine thickness is ≤1.6H1 (H1 is the thickness of the thin steel strip, in mm), and the width jump is ≤270mm (≤135mm on each side).

[0027] The shear blade clearance range is 0.25mm~0.45mm; the shear blade clearance is controlled according to the thickness of the steel strip according to the following requirements. When the strip thickness is ≤3.25mm, the shear blade clearance is 0.25mm. For every 0.5mm increase in strip thickness, the shear blade clearance increases by 0.05mm; the shear blade is replaced according to a cycle of ≤5500t or a shearing number of ≤9000 times. After each replacement of the shear blade, the side clearance of the shear blade should be calibrated to ensure that the sheared end face is smooth and straight, without burrs, delamination and other defects.

[0028] The welding process parameters are: laser power 14±0.5KW, welding speed 2.5~3.5±0.5 m / min, wire feeding speed 2.0~3.0±0.5 m / min; among them, when the raw material thickness is ≤3.25mm, the welding speed is 3.5±0.5m / min, and the speed decreases by 0.5m / min for every 0.5mm increase in thickness; the welding speed compensation range is 0~18%; when the raw material thickness is ≤3.25mm, the wire feeding speed is 3.0±0.5m / min, and the speed decreases by 0.5m / min for every 0.5mm increase in thickness; the wire feeding speed compensation range is 0~15%; after welding, the weld needs to be cleaned with a rolling wheel, the rolling wheel pressure is ≤65KN, the rolling wheel height is 0mm ~6.5mm, and due to the high alloy content of 980MPa grade hot-dip galvanized duplex steel, the weld needs to be heat treated to improve its weld quality.

[0029] After welding, the weld is heat treated through a thermal cycle with a power of 48kW, a frequency of 35kHz, and a weld heat treatment current compensation amount of 0-15%. During the heating process of the weld heat treatment, the heating rate is required to be ≤20℃ / s, and during cooling, the cooling rate is ≤15℃ / s to below 280℃ and then air-cooled.

[0030] After post-weld annealing and grinding, the weld surface must be smooth and free of cracks, and the weld area must not have defects such as inclusions, incomplete penetration, and misalignment. In addition, the weld quality must be checked through weld thickness and cupping tests.

[0031] The thickness of the weld (t1) is 1.06~1.30 times the thickness of the raw material (1.06t≤t1≤1.30t, where t is the raw material thickness); when taking weld samples for cupping test, at least 3 points should be inspected. When making width jump connection, a crescent bend test is required, and the transition of width jump steel coil can be carried out only after no problem is found in the test.

[0032] The strip is straightened by the tensioning machine, tensioned by the tension machine, and the strip position is adjusted by the deviation correction roller (keeping the strip in the center of the equipment) to avoid damage and downtime caused by warping and other strip shape problems and strip deviation and collision with equipment. The strip is adjusted by the pre-pickling loop to ensure the smooth progress of the pickling process.

[0033] The welded steel is subsequently pickled and cold rolled; wherein the pickling step is: The i-Box type acid tank is used to clean the iron oxide scale on the surface of the strip steel. The acid concentration of the 1# acid tank is 45g / L~70g / L, the acid concentration of the 2# acid tank is 75 g / L~100g / L, and the acid concentration of the 3# acid tank is 105 g / L~140g / L. The acid temperature is 60℃~80℃, and the pickling speed is 60m / min~180m / min. The pickling speed is 180m / min when the strip steel thickness is 2.25mm, and the pickling speed decreases by 15m / min for every 0.25mm increase in thickness. After that, the residue on the surface of the strip steel is rinsed and the pH value of the rinse agent is ≥5.0. Finally, it is dried at a drying temperature of 80~150℃.

[0034] In some embodiments, the cold rolling step is: after pickling, the hot-rolled coil is cold-rolled into a thin strip steel of 0.90mm-2.40mm, and the cold rolling reduction rate is 43%-60%. As the thickness of the cold-rolled finished material increases, the cold rolling reduction rate gradually decreases. For every 0.3mm increase in the thickness of the cold-rolled thin strip steel, the raw material thickness is adjusted accordingly, and the cold rolling reduction rate is reduced by about 3.5%. 7 stands are used for cold rolling. In order to obtain a good plate shape, the reduction rate of the last pass is maintained at 5~8%, and the remaining passes are autonomously allocated by a computer. Example 1 The tail of a low-cost 980MPa grade hot-dip galvanized duplex steel coil with a specification of 3.50mm×1180mm (chemical composition: 0.093%C, 0.43%Si, 2.28%Mn, 0.008%P, 0.003%S, 0.038%Als, 0.55%Cr, 0.030%Nb, 0.045%Ti, 0.0030%B, 0%Ni, 0%V, 0%Mo, 0.0026%N, and a carbon equivalent of 0.677%) was cut for 7.5m and then connected with a low-cost 780MPa grade hot-dip galvanized duplex steel coil with a specification of 3.65mm×1150mm. After the steel coil head is sheared for 7.5m, the welding current is 13.5kW and the wire feeding speed is 3.0m / min. The weld seam after welding by the above welding process is smooth and flat, without nodules, weld scars, weld penetration and other defects. After the cupping test, there is no cracking along the weld seam, and the crescent bend effect is good. There is no belt breakage caused by the weld seam during pickling and cold rolling. The acid concentrations of the acid tanks were 65g / l, 88g / l and 123g / l, the acid temperature was 77°C, the pickling speed was 103m / min, and the drying temperature was 90°C. The cold rolling reduction ratios were 50% and 52%, respectively, and the strip shape and surface quality after pickling were good.

[0035] Example 2 The tail of a low-cost 980MPa grade hot-dip galvanized duplex steel coil with a specification of 4.25mm×1050mm (chemical composition: 0.088%C, 0.42%Si, 2.33%Mn, 0.010%P, 0.003%S, 0.045%Als, 0.028%Nb, 0.55%Cr, 0.043%Ti, 0.0031%B, 0Ni, 0%V, 0%Mo, 0.0024%N, and its carbon equivalent is 0.682%) was cut to 7.5m and then connected with a low-cost 980MPa steel coil with a specification of 4.00mm×1100mm. Grade 2 hot-dip galvanized duplex steel (0.089%C, 0.38%Si, 2.30%Mn, 0.09%P, 0.002%S, 0.033%Als, 0.52%Cr, 0.032%Nb, 0.044%Ti, 0.0040%B, 0Ni, 0%V, 0%Mo, 0.0027%N, with a carbon equivalent of 0.669%) steel coil head sheared 7.5m, and then welded at a welding current of 14.0kW and a wire feeding speed of 2.5m / min. The weld after welding by the above welding process is smooth and flat, without nodules, weld scars, weld penetration and other defects. The cupping test did not show cracking along the weld, and the crescent bend effect was good. There was no belt breakage caused by the weld during pickling and cold rolling. The acid concentrations of the acid tanks were 55 g / l, 90 g / l and 110 g / l, the acid temperature was 75 ° C, the pickling speed was 75 m / min, and the drying temperature was 92 ° C. The cold rolling reduction rates were 43% and 44%, respectively, and the plate shape was good after cold rolling.

[0036] Example 3 The tail of a low-cost 980MPa grade hot-dip galvanized duplex steel coil with a specification of 3.25mm×1200mm (chemical composition: 0.095%C, 0.40%Si, 2.18%Mn, 0.006%P, 0.003%S, 0.045%Als, 0.028%Nb, 0.55Cr, 0.045%Ti, 0.0042%B, 0Ni, 0%V, 0%Mo, 0.0026%N, and its carbon equivalent is 0.658%) was cut for 7.5m and then cut into a 5.5mm×1450mm After the DC03 (chemical composition is 0.0026%C, 0.01%Si, 0.08%Mn, 0.005%P, 0.002%S, 0.035%Als, 0.040%Ti, 0Ni, 0%V, 0%Mo, 0.00225N, and its carbon equivalent is 0.019%) steel coil head is cut 2.0m, and the welding current is 13.9kW with a wire feeding speed of 3.5m / min. The welding wire is fed at a speed of 3.5m / min. The weld quality after welding by the above welding process is not good, and cracks along the weld appear in the cupping test. Production is carried out after changing the connecting material.

[0037] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope of the embodiments disclosed in the claims. Although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0038] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the above embodiments of the present invention, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A low-cost 980MPa grade hot-dip galvanized duplex steel, characterized in that: The chemical composition of the dual-phase steel includes, by weight percentage, C: 0.05%-0.12%, Si: 0.25%-0.50%, Mn: 2.00%-2.40%, P≤0.018%, S≤0.009%, Als: 0.010%-0.065%, N≤0.0065%, Cr: 0.30%-0.70%, Nb: 0.015%-0.040%, Ti: 0.025-0.050%, B: 0.0010-0.0050, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the remaining elements are Fe and unavoidable impurities.

2. The low-cost 980MPa grade hot-dip galvanized dual-phase steel according to claim 1, characterized in that: The chemical composition of the dual-phase steel includes, by weight percentage, C: 0.07%~0.10%, Si: 0.30%~0.45%, Mn: 2.05%~2.35%, P≤0.012%, S≤0.006%, Als: 0.025%~0.060%, N≤0.0045%, Cr: 0.33%~0.58%, Nb: 0.018%~0.033%, Ti: 0.028%~0.048%, B: 0.0025%~0.0045%, Ni≤0.05%, V≤0.01%, Mo≤0.01%, and the balance is Fe and unavoidable impurities.

3. A welding method for the low-cost 980MPa grade hot-dip galvanized dual-phase steel pickling process as claimed in claim 1 or 2, characterized in that: After the welding connection material and the raw steel coil are sheared, the welding surfaces of the connection material and the raw steel coil are aligned and on the same horizontal plane, and then welding wire is added for welding, and the weld is annealed and polished after welding, and the weld quality is checked by measuring the weld thickness and cupping test; The carbon equivalent of the selected connection material needs to be controlled by the carbon equivalent formula, which is: Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14(%); The difference in yield strength between the connecting material and the low-cost 980MPa grade hot-dip galvanized duplex steel before and after welding is within 1.7 times.

4. The welding method according to claim 3, characterized in that: The carbon equivalent of the selected connecting material is controlled in the range of 0.50%~1.0%.

5. The welding method according to claim 3, characterized in that: After welding, the weld is heat treated through a thermal cycle with a power of 48kW, a frequency of 35kHz, and a weld heat treatment current compensation amount of 0-15%. During the heating process of the weld heat treatment, the heating rate is required to be ≤20℃ / s, and during cooling, the cooling rate is ≤15℃ / s to below 280℃ and then air-cooled.

6. The welding method according to claim 3, characterized in that: The step of "cutting the welding selected connecting material and the raw steel coil" includes: when cutting, the cutting length of the steel coil is controlled according to the following requirements, and welding is performed after ensuring the plate shape and surface quality; Use double-cut shears to cut a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the strip thickness t<3.25mm, the cutting amount is 9.0m, and when the strip thickness 3.25mm≤t<4.25mm, the cutting amount is 7.5m. Ensure that the defects at the head and tail of the strip can be completely removed and will not deteriorate the welding quality.

7. The welding method according to claim 6, characterized in that: The shear blade clearance range is 0.25mm~0.45mm; the shear blade clearance is controlled according to the thickness of the steel strip according to the following requirements. When the strip thickness is ≤3.25mm, the shear blade clearance is 0.25mm. For every 0.5mm increase in strip thickness, the shear blade clearance increases by 0.05mm; the shear blade is replaced according to a cycle of ≤5500t or a shearing number of ≤9000 times. After each replacement of the shear blade, the side clearance of the shear blade should be calibrated to ensure that the sheared end face is smooth and straight, without burrs, delamination and other defects.

8. The welding method according to claim 3, characterized in that: The welding process parameters are: laser power 14±0.5KW, welding speed 2.5~3.5±0.5 m / min; among them, when the raw material thickness is ≤3.25mm, the welding speed is 3.5±0.5m / min, and the speed decreases by 0.5m / min for every 0.5mm increase in thickness; the welding speed compensation range is 0~18%; after welding, the weld needs to be cleaned with a rolling wheel, the rolling wheel pressure is ≤65KN, and the rolling wheel height is 0 mm ~6.5mm.

9. The welding method according to claim 3, characterized in that: The welded steel is subsequently pickled and cold rolled; wherein the pickling step is: The i-Box type acid tank is used to clean the iron oxide scale on the surface of the strip steel. The acid concentration of the 1# acid tank is 45g / L~70g / L, the acid concentration of the 2# acid tank is 75 g / L~100g / L, and the acid concentration of the 3# acid tank is 105 g / L~140g / L. The acid temperature is 60℃~80℃, and the pickling speed is 60m / min~180m / min. The pickling speed is 180m / min when the strip steel thickness is 2.25mm, and the pickling speed decreases by 15m / min for every 0.25mm increase in thickness. After that, the residue on the surface of the strip steel is rinsed and the pH value of the rinse agent is ≥5.

0. Finally, it is dried at a drying temperature of 80~150℃.

10. The welding method according to claim 9, characterized in that The cold rolling steps are as follows: after pickling, the hot-rolled coil is cold-rolled into a thin strip steel of 0.90mm-2.40mm, and the cold rolling reduction rate is 43%-60%. As the thickness of the cold-rolled finished material increases, the cold rolling reduction rate gradually decreases. For every 0.3mm increase in the thickness of the cold-rolled thin strip steel, the raw material thickness is adjusted accordingly, and the cold rolling reduction rate is reduced by about 3.5%.

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