Low-cost 780MPa-grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method

Abstract

The invention discloses a low-cost 780MPa-grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method, which comprises the following steps of: welding according to the lap amount, the compensation amount, the welding speed, the welding pressure, the welding temperature and the welding current which are calculated according to a formula; welding surfaces of the joining material and the raw material steel coil are aligned and are positioned on the same horizontal plane for welding, and the welding seam quality is checked by measuring the thickness of the welding seam and performing a cup convex test after welding. According to the narrow lap welding method, welding parameters are determined through a calculation formula, the material (carbon equivalent and plate shape), thickness / width transition, surface quality, shearing process and quality of raw materials are controlled, a welding seam with good quality is obtained, and stable and efficient production of the hot galvanizing process is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled strip production, and in particular relates to a narrow lap welding method suitable for a low-cost 780MPa grade hot-dip galvanized duplex steel hot-dip galvanizing process. Background Art

[0002] As energy and environmental issues become increasingly prominent, energy conservation and environmental protection have become inevitable issues in the development of the automotive industry. Reducing the weight of vehicles by reducing the thickness of automotive steel is considered an effective way to promote the sustainable development of the automotive industry. Dual-phase steel is the most widely used advanced high-strength steel. 780MPa-grade products have become important products used in the automotive field. At the same time, with the continuous improvement of corrosion resistance requirements, the proportion of galvanized sheets is increasing. The hot-dip galvanizing process requires 460°C galvanizing (in the bainite transformation zone). A certain amount of alloying elements needs to be added in the alloy design to ensure hardenability and inhibit the formation of bainite, which reduces the weldability of the strip and brings certain difficulties in the acid rolling process and galvanizing production (welding, rolling load, etc.).

[0003] The existing narrow lap welding method for hot-dip galvanizing of duplex steel does not clarify the material and specification of the transition material, which is not conducive to ensuring the welding quality of products of different materials and specifications, or the welding process is relatively general without detailed division, which is not conducive to efficient production and obtaining good quality welds.

[0004] Therefore, how to describe the welding process in detail and efficiently produce and obtain good quality welds in the narrow lap welding method of hot-dip galvanized duplex steel hot-dip galvanizing process has become a difficult problem that urgently needs to be solved. Summary of the invention

[0005] Based on this, the above-mentioned shortcomings of the prior art provide a low-cost 780MPa grade hot-dip galvanized duplex steel hot-dip galvanizing process narrow lap welding method. The material, plate shape, surface quality, shearing effect, welding parameters, welding effect evaluation, etc. of the raw materials are described in detail, and the stable production of low-cost 780MPa grade hot-dip galvanized duplex steel is achieved.

[0006] In order to achieve the above purpose, the following technical solutions are adopted: The present invention provides a low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method, welding is performed according to the overlap amount, compensation amount, welding speed, welding pressure and welding current calculated according to the following formulas 1)-5); L=0.4T+0.6(1) Y=0.08T+0.86(2) V = -2T + 15.5 (3) P=3T+8(4) I=T+9(5) Among them, T is the thickness of welding material, in mm; L is the overlap amount, in mm; Y is the compensation amount, in mm; V is the welding speed, in m / min; P is the welding pressure, in kN; I is the welding current, in kA.

[0007] In some embodiments, the chemical composition of the dual-phase steel includes, by weight percentage: C: 0.05%~0.11%, Si: 0.20%~0.40%, Mn: 1.70%~2.30%, P≤0.017%, S≤0.008%, Als: 0.010%~0.080%, N≤0.008%, Cr: 0.35%~0.75%, Nb: 0.01%~0.05%, and the balance is Fe and unavoidable impurities.

[0008] In some embodiments, the chemical composition of the dual-phase steel includes, by weight percentage: C: 0.070%-0.095%, Si: 0.25%-0.36%, Mn: 2.05%-2.25%, Al: 0.025%-0.065%, P≤0.012%, S≤0.006%, N≤0.004%, Nb: 0.010%-0.035%, Cr: 0.50%-0.70%, and the balance is Fe and unavoidable impurities.

[0009] In some embodiments, the overlap amount is 0.80 mm to 1.30 mm, the compensation amount is 0.90 mm to 1.10 mm, the welding speed is 9.0 m / min to 14.5 m / min, the welding pressure is 9.5 KN to 17.0 KN, and the welding current is 9.5 KA to 12.0 KA.

[0010] In some embodiments, 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 placed on the same horizontal plane for welding, and after welding, the weld quality is checked by measuring the weld thickness and cupping test; The carbon equivalent of the selected connection material and raw steel coil needs to be controlled by the carbon equivalent formula, which is: ; The tensile strength of the higher strength steel before and after welding shall not exceed 3.0 times the tensile strength of the lower strength steel.

[0011] In some embodiments, the carbon equivalent of the connecting material and the raw steel coil is controlled in the range of 0.22% to 0.60%.

[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 shears to cut off a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the raw material thickness t<1.2mm, the amount of strip tail resection is 15.0m, and the amount of strip head resection is 8.0m; when 1.2mm≤raw material thickness t<2.0mm, the amount of strip tail resection is 12.0m, and the amount of strip head resection is 6.0m; when the raw material thickness ≥2.0mm, the amount of strip tail resection is 10.0m, and the amount of strip head resection is 4.5m; and ensure that the defects of the head and tail of the strip can be completely removed without deteriorating the welding quality.

[0013] In some embodiments, the measured weld thickness needs to be 0.85 to 1.50 times the thickness of the weld material.

[0014] In some embodiments, when the weld is sampled for the cupping test, at least three points are inspected. If the crack is in the heat affected zone and the crack is perpendicular to the weld direction, the weld is judged to be qualified; if the crack coincides with the weld, the weld quality is judged to be unqualified.

[0015] In some embodiments, the plate shape of the connecting material and the raw steel coil is ≤15IU, and the curvature is ≤25mm 2 / 10m; the thickness range of the welded cold-hardened coil is 0.50mm~3.00mm, of which the thickness ratio of the two steel coils is ≤1.5; the width range of the welded cold-hardened coil is 850~1500mm, of which the width transition of the two steel coils is ≤200mm, that is, the single-side width transition is ≤100mm.

[0016] The present invention has the following beneficial technical effects: The low-cost 780MPa grade hot-dip galvanized duplex steel hot-dip galvanizing process narrow lap welding method of the present invention obtains a weld with good quality by controlling the material (carbon equivalent, plate shape) of the raw materials, thickness / width transition, good surface quality, shearing process and quality, and key welding processes (welding current, welding speed, welding machine pressure, overlap amount, compensation amount, etc.), thereby ensuring stable and efficient production of the hot-dip galvanizing process. 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 This is a strip welding effect diagram of a narrow lap welding method using a low-cost 780 MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process 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 objectives, a first aspect of an embodiment of the present invention proposes that the present invention provides a low-cost 780MPa grade hot-dip galvanized duplex steel hot-dip galvanizing process narrow lap welding method.

[0022] Narrow lap welding is a type of resistance welding. In this welding method, the edges of two metal sheets are overlapped, and the width of the overlapped part is narrow. Then pressure is applied through electrodes and current is passed through. The resistance heat of the metal under the action of the current is used to heat and melt the metal in the overlapping part under pressure to form a welded joint.

[0023] The embodiment of the present invention performs welding according to the overlap amount, compensation amount, welding speed, welding pressure and welding current calculated according to the following formulas 1)-5); L=0.4T+0.6(1) Y=0.08T+0.86(2) V = -2T + 15.5 (3) P=3T+8(4) I=T+9(5) Among them, T is the thickness of welding material, in mm; L is the overlap amount, in mm; Y is the compensation amount, in mm; V is the welding speed, in m / min; P is the welding pressure, in kN; I is the welding current, in kA.

[0024] Specifically, the overlap amount is 0.80 mm to 1.30 mm (when the thickness of the welding material is 0.50 mm, the welding pressure is 0.80 mm, and the overlap amount increases by 0.20 mm for every 0.5 mm increase in the thickness of the welding material); the compensation amount is 0.90 mm to 1.10 mm (when the thickness of the welding material is 0.50 mm, the compensation amount is 0.90 mm, and the compensation amount increases by 0.1 mm for every 1.25 mm increase in the thickness of the welding material); the welding speed is 9.0 m / min to 14.5 m / min (when the thickness of the welding material is 0.50 mm, the welding speed is 14.5 m / min, and the welding speed decreases by 1.0 m / min for every 0.5 mm increase in the thickness of the welding material); the welding pressure is 9.5 KN to 17.0 KN (when the thickness of the welding material is 0.50 mm, the welding pressure is 9.5 kN, and the welding pressure increases by 1.5 kN for every 0.5 mm increase in the thickness of the welding material); and the welding current is 9.5 KA ~12.0KA (when the thickness of welding material is 0.50mm, the welding current is 9.5kA, and the welding current increases by 0.5kA for every 0.5mm increase in the thickness of welding material).

[0025] In some embodiments, the chemical composition of the dual-phase steel includes, by weight percentage: C: 0.05%~0.11%, Si: 0.20%~0.40%, Mn: 1.70%~2.30%, P≤0.017%, S≤0.008%, Als: 0.010%~0.080%, N≤0.008%, Cr: 0.35%~0.75%, Nb: 0.01%~0.05%, and the balance is Fe and unavoidable impurities.

[0026] Preferably, the chemical composition of the dual-phase steel includes, by weight percentage: C: 0.070%-0.095%, Si: 0.25%-0.36%, Mn: 2.05%-2.25%, Al: 0.025%-0.065%, P≤0.012%, S≤0.006%, N≤0.004%, Nb: 0.010%-0.035%, Cr: 0.50%-0.70%, and the balance is Fe and unavoidable impurities.

[0027] The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method of the present invention selects the connecting material for welding and the raw steel coil for shearing, and aligns the welding surfaces of the connecting material and the raw steel coil and places them on the same horizontal plane for welding. After welding, the weld quality is checked by measuring the weld thickness and cupping test. The weld after welding cannot have defects such as inclusions, incomplete penetration, misalignment, etc. after inspection. In addition, the weld quality needs to be further checked by weld thickness, cupping test, etc.

[0028] The carbon equivalent of the selected connection material and raw steel coil needs to be controlled by the carbon equivalent formula, which is: ; The tensile strength of the higher strength steel before and after welding must not exceed 3.0 times the tensile strength of the lower strength steel. The plate shape of the connecting material and the raw steel coil is ≤15IU, and the curvature is ≤25mm 2 / 10m; the thickness range of the welded cold-hardened coil is 0.50mm~3.00mm, of which the thickness ratio of the two steel coils is ≤1.5; the width range of the welded cold-hardened coil is 850~1500mm, of which the width transition of the two steel coils is ≤200mm, that is, the single-side width transition is ≤100mm.

[0029] In some embodiments, the carbon equivalent of the connecting material and the raw steel coil is controlled in the range of 0.22% to 0.60%.

[0030] 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; Before welding the tail of the previous steel coil and the next steel coil, a double shear is used to cut off a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the raw material thickness t<1.2mm, the cutting amount of the strip tail is 15.0m, and the cutting amount of the strip head is 8.0m; when 1.2mm≤raw material thickness t<2.0mm, the cutting amount of the strip tail is 12.0m, and the cutting amount of the strip head is 6.0m; when the raw material thickness ≥2.0mm, the cutting amount of the strip tail is 10.0m, and the cutting amount of the strip head is 4.5m; at the same time, the operator shall determine the cutting length according to the actual situation of the incoming material to ensure that the defects of the strip head and tail can be completely removed and will not deteriorate the welding quality.

[0031] In some embodiments, the measured weld thickness needs to be 0.85 to 1.50 times the thickness of the welding material (0.85t≤t1≤1.50t, where t is the material thickness).

[0032] In some embodiments, when the weld is sampled for the cupping test, at least 3 points are inspected. If the crack is in the heat-affected zone and the crack is perpendicular to the weld direction, the weld is judged to be qualified; if the crack coincides with the weld, the weld quality is judged to be unqualified. In addition, two welds are not allowed in a large coil, otherwise it is judged to be unqualified. When performing width jump connection, a crescent bend test is required. Only after the test is found to be problem-free can the transition of the width jump steel coil be carried out.

[0033] The cupping test (also known as the Erichsen cupping test or the Erichsen cupping test) is a test method used to evaluate the ductility and formability of metal sheets and strips. The test measures the maximum deformation that the sheet can withstand by pressing a hemispherical punch into a metal sheet specimen fixed in a die at a certain speed until the specimen breaks.

[0034] Test equipment and devices The cupping test equipment mainly includes a punch, a die and a blank holder. The punch is generally hemispherical with a specific radius (such as 20mm), the die has a circular opening for placing the sample, and the blank holder is used to fix the edge of the sample during the test to prevent the edge material from excessively flowing during the test and affecting the test results. The entire test equipment is usually powered by a hydraulic or mechanical drive system, which enables the punch to punch the sample at a stable speed (such as 0.05 - 0.2mm / s).

[0035] Material performance evaluation For metal sheets, the cupping test is an important means of evaluating the quality of the sheet. Through this test, the forming limit of the sheet can be understood, providing a reference for subsequent processing techniques (such as stamping, deep drawing, etc.). For example, in automobile manufacturing, the stamping parts of the car body need to have good ductility, and the cupping test can be used to screen out metal sheets suitable for body stamping.

[0036] Example The tail of a low-cost 780MPa grade hot-dip galvanized duplex steel coil (chemical composition: 0.092%C, 0.28%Si, 2.22%Mn, 0.011%P, 0.002%S, 0.043%Als, 0.026%Nb, 0.61%Cr, 0.0030%N, carbon equivalent: 0.237%) with a size of 1.00mm×1450mm was cut to 15.0m and then connected to a 590MPa steel coil with a size of 1.30mm×1400mm. Grade cold-rolled dual-phase steel (0.090%C, 0.50%Si, 1.50%Mn, 0.010%P, 0.005%S, 0.041%Als, 0.25%Cr, 0.0026%N, carbon equivalent is 0.40%) steel coil head shear 6.0m, welding current 10.5kA with 12.5m / min speed, overlap 0.90mm, compensation 1.00mm, welding pressure 12.5kN. Figure 1As shown in the figure, the weld after welding with the above welding process is flat and smooth, without nodules, weld scars, weld penetration and other defects. After the cupping test, there is no cracking problem along the weld, and the crescent bend effect is good. There is no belt breakage accident caused by the weld during the hot-dip galvanizing annealing and finishing process.

[0037] Comparative Example The tail of a low-cost 780MPa grade hot-dip galvanized duplex steel coil (chemical composition: 0.085%C, 0.32%Si, 2.05%Mn, 0.008%P, 0.003%S, 0.036%Als, 0.62%Cr, 0.026%Nb, 0.0025%N, and its carbon equivalent is 0.226%) with a specification of 2.00mm×1350mm was sheared for 10.0m, and then the head of a DC05 coil (chemical composition: 0.0018%C, 0.01%Si, 0.04%Mn, 0.005%P, 0.002%S, 0.033%Als, 0.072%Ti, 0.0028%N, and its carbon equivalent is 0.0221%) with a specification of 2.10mm×1315mm was sheared for 4.5m. After that, the welding current was 11.0kA, the speed was 11.5m / min, the overlap was 1.10mm, the compensation was 1.00mm, and the welding pressure was 14.0kN. The weld quality after welding by the above welding process was poor, and the cupping test showed cracks along the weld, and the production needed to be carried out after changing the connecting material.

[0038] 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.

[0039] 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 780MPa grade hot-dip galvanized duplex steel hot-dip galvanizing process narrow lap welding method, characterized in that: Welding is performed according to the overlap amount, compensation amount, welding speed, welding pressure and welding current calculated according to the following formulas 1)-5); L=0.4T+0.6(1) Y=0.08T+0.86(2) V = -2T + 15.5 (3) P=3T+8(4) I=T+9(5) Among them, T is the thickness of welding material, in mm; L is the overlap amount, in mm; Y is the compensation amount, in mm; V is the welding speed, in m / min; P is the welding pressure, in kN; I is the welding current, in kA.

2. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 1, characterized in that: The chemical composition of the dual-phase steel includes, by weight percentage, C: 0.05%~0.11%, Si: 0.20%~0.40%, Mn: 1.70%~2.30%, P≤0.017%, S≤0.008%, Als: 0.010%~0.080%, N≤0.008%, Cr: 0.35%~0.75%, Nb: 0.01%~0.05%, and the balance is Fe and unavoidable impurities.

3. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 2, characterized in that: The chemical composition of the dual-phase steel includes, by weight percentage, C: 0.070%-0.095%, Si: 0.25%-0.36%, Mn: 2.05%-2.25%, Al: 0.025%-0.065%, P≤0.012%, S≤0.006%, N≤0.004%, Nb: 0.010%-0.035%, Cr: 0.50%-0.70%, and the balance is Fe and unavoidable impurities.

4. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 1, characterized in that: The overlap amount is 0.80 mm ~ 1.30 mm, the compensation amount is 0.90 mm ~ 1.10 mm, the welding speed is 9.0 m / min ~ 14.5m / min, the welding pressure is 9.5KN ~ 17.0KN, and the welding current is 9.5 KA ~ 12.0 KA.

5. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 3, 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 placed on the same horizontal plane for welding, and after welding, the weld quality is checked by measuring the weld thickness and cupping test; The carbon equivalent of the selected connection material and raw steel coil needs to be controlled by the carbon equivalent formula, which is: ； The tensile strength of the higher strength steel before and after welding shall not exceed 3.0 times the tensile strength of the lower strength steel.

6. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 5, characterized in that: The carbon equivalent of the connecting material and raw steel coil is controlled in the range of 0.22%~0.60%.

7. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 5, 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 shears to cut off a certain length of the steel strip to ensure the plate shape and surface quality before welding. When the raw material thickness t<1.2mm, the amount of strip tail resection is 15.0m, and the amount of strip head resection is 8.0m; when 1.2mm≤raw material thickness t<2.0mm, the amount of strip tail resection is 12.0m, and the amount of strip head resection is 6.0m; when the raw material thickness ≥2.0mm, the amount of strip tail resection is 10.0m, and the amount of strip head resection is 4.5m; and ensure that the defects of the head and tail of the strip can be completely removed without deteriorating the welding quality.

8. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 5, characterized in that: The measured weld thickness needs to be 0.85~1.50 times the thickness of the welding material.

9. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 5, characterized in that: When taking weld samples for cupping test, at least 3 points shall be inspected. If the crack is in the heat affected zone and the crack is perpendicular to the weld direction, the weld is judged to be qualified; if the crack coincides with the weld, the weld quality is judged to be unqualified.

10. The low-cost 780MPa grade hot-dip galvanized dual-phase steel hot-dip galvanizing process narrow lap welding method according to claim 5, characterized in that: The shape of the connecting material and the raw steel coil is ≤15IU, and the curvature is ≤25mm 2 / 10m; the thickness range of the welded cold-hardened coil is 0.50mm~3.00mm, of which the thickness ratio of the two steel coils is ≤1.5; the width range of the welded cold-hardened coil is 850~1500mm, of which the width transition of the two steel coils is ≤200mm, that is, the single-side width transition is ≤100mm.

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