Manufacturing method for thin-walled tailored steel blank material and hot-pressed member manufactured using the tailored blank material

Abstract

A manufacturing method of a thin-walled tailored blank material made of steel and a hot-pressed member made of the tailored blank material. A steel plate (10, 20) to be welded having an aluminum or aluminum alloy plating layer (12, 12', 22, 22') is used, and the composition of the shielding gas (50) and the composition of the welding wire (30) during the welding process are adjusted, and the welding speed and the welding wire feed speed are controlled to make the free aluminum content in the weld seam 0.1 to 4.0 wt.%, thereby preventing the formation of iron-aluminum intermetallic compounds in the weld seam during the tailored blank process, and at the same time, forming an appropriate amount of dispersed ferrite in the weld seam. The weld seam structure of the resulting tailored blank material is martensite + 1 to 15 vol.% dispersed ferrite + 0 to 5 vol.% retained austenite, and the weld seam structure of the hot-pressed member obtained by hot press forming is martensite + 0.1 to 10 vol.% dispersed ferrite.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a welded component, and more particularly to a method for manufacturing a thin-walled tailored blank made of steel, and a hot-pressed component manufactured using the tailored blank. [Background technology]

[0002] Lightweight, high-strength automotive steel sheets, coupled with national policies for energy conservation and emission reduction, have become a goal of the automotive industry in recent years, leading to an ever-increasing demand for high-strength, thin-walled automotive steel sheets. Compared to cold stamping, hot stamping technology plays an important role in achieving high-strength automotive steel sheets due to its advantages of significant weight reduction, good formability, and high dimensional accuracy. As public demands for automotive safety, reliability, and comfort increase, many automotive companies are striving to improve product quality by improving automotive structural design and adopting new manufacturing processes. Tailored blanks are steel sheets of the same or different materials, same or different thicknesses, and same or different coating layers that are welded together to meet the different material property requirements of each part. Laser-formed tailored blank hot stamping reduces vehicle weight, improves assembly precision, and simplifies assembly processes. At the same time, it incorporates the advantages of hot stamping to further improve the formability of steel sheets.

[0003] Hot-pressed products formed from laser-machined blanks have high strength, complex shapes, good formability, high dimensional accuracy, and low rebound. Depending on the surface condition, hot-pressed steel can be divided into bare steel and plated steel. During the actual hot-pressing process, the bare steel surface oxidizes at high temperatures, easily forming an oxide scale. During the stamping process, the oxide scale is extruded into the steel, forming surface defects that significantly affect its performance. Plated hot-pressed steel is gaining increasing attention because it protects the steel from oxidation compared to bare steel and eliminates the need for shot peening after hot pressing. Currently, hot-pressed steel with an aluminum or aluminum alloy plated layer is common, but this steel is unusable because the plated layer dissolves into the molten pool during welding, forming brittle and hard intermetallic compounds (Fe3Al, Fe2Al5, FeAl3) and ferrite, reducing the strength and ductility of the weld spot.

[0004] Chinese Patent CN101426612A discloses a "method for producing welded parts with good mechanical properties from rolled coated sheets," which uses aluminum-silicon coated steel sheets as raw materials to produce welded blanks containing only intermetallic compounds as a pre-coating. This method solves the problem of substandard weld seam strength and elongation caused by aluminum dissolving in the molten pool, but requires the coating to be ablated before welding the steel sheets, which increases capital investment and reduces production efficiency.

[0005] Chinese Patent CN102985216A discloses a "Method for Arc / Laser Hybrid Welding of Aluminum-Plated Steel Parts Using Gas Containing Nitrogen and / or Oxygen." This patent describes arc-laser hybrid welding of aluminum-plated parts, in which an additional gas, nitrogen or oxygen, is added to the shielding gas. The volume content of the additional gas is 1-20%. The function of the additional gas is to capture aluminum and form Al2O3 or AlN-based compounds, thereby preventing the formation of ferrite or other harmful intermetallic compounds. The formed aluminum oxide or aluminum nitride floats on the surface of the weld pool, preventing the aluminum from dissolving into the weld pool (paragraph 0015). The weld seam structure is fully martensitic. This patent reveals that when steel sheets with an aluminum or aluminum alloy coating are directly tailored to form a blank, the coating layer penetrates the weld pool during welding, reducing the strength of the weld spot after hot pressing. The spot elongation rate is around 1%, which means the tailored blank thermoformed parts may be damaged in a vehicle collision and fail to provide adequate safety protection.

[0006] Chinese Patent CN108025400A discloses a "laser welding method for manufacturing semi-finished plates from hardenable steel with an aluminum-based or aluminum-silicon-based plating layer," which uses tailored blanks made from differential strength hot-pressed steel plates, and the final weld seam structure is entirely martensitic.

[0007] Chinese Patent CN201380027064.4 discloses a "Weld-Notched Sheet Metal Part and Forming Method Thereof." This method uses aluminum-silicon-plated steel sheet as raw material and involves removing the entire aluminum-silicon plating before rewelding. This method also solves the problem of aluminum dissolving into the weld pool, resulting in substandard weld seam strength and elongation. However, controlling the depth of the plating removal is difficult, and incomplete plating removal, similar to the method disclosed in Chinese Patent CN101426612A, can be problematic. Removing too deep can damage the steel substrate, resulting in thinning of the material and inevitably degrading the spot properties after welding. Controlling the width of the plating removal is also problematic. If the removal width is narrower than the weld seam, elements from the plating will dissolve into the weld pool during welding, degrading the properties of the weld seam. However, if the removal width is wider than the weld seam, the weld heat-affected zone will not be protected by the plating, affecting the corrosion resistance of the spot.

[0008] Chinese Patent CN104023899A discloses a "tailored blank material, its manufacturing method, and a hot-pressed component using the tailored blank material." This patent uses a welding wire with a higher carbon and manganese content than the base material to weld an aluminum or aluminum alloy plated sheet. While this solves the weld seam quality problem, the weld seam structure transforms entirely to martensite during hot pressing, and the carbon and manganese contents of the welding wire are 0.1-0.8 wt.% and 1.5-7.0 wt.% higher than those of the base material. As is well known, hot-pressed steels inherently have high contents of elements such as carbon and manganese, and the welding wire disclosed in the patent is a high-carbon, high-manganese welding wire, making it difficult to manufacture.

[0009] Chinese Patent CN111230301A discloses a "method for manufacturing thin-walled steel welded or other high-strength components with an aluminum or aluminum alloy plating layer." However, this patent discloses welding aluminum or aluminum alloy plated sheets with a 1500 MPa strength using a welding wire with a lower carbon and manganese content than the base material, and the weld spot obtained using this method only has a 1500 MPa strength. If a hot-pressed component with a higher strength level is obtained using this method, when the weld spot of the hot-pressed component is stretched in a quasi-static process, the strength of the weld seam is lower than that of the base material, so the weld seam will break and cannot be used by automobile manufacturers. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a method for manufacturing thin-walled tailored steel blanks and hot-pressed components made from the tailored blanks. This method solves the problem of the coating layer melting into the molten pool during the tailored blank manufacturing process, resulting in poor weld seam quality in the hot-pressed tailored blanks. The hot-pressed components obtained from the tailored blanks have a quasi-static tensile fracture location in the base metal at the weld spot, a spot elongation of more than 4%, a weld seam strength greater than the tensile strength of the low-strength base metal, and a tensile fracture strain of more than 0.08 at a strain rate of 40-800 / s, meeting the needs of the automotive industry. [Means for solving the problem]

[0011] To achieve the above objectives, the technical solution of the present invention comprises: A method for manufacturing thin-walled steel tailored blanks, including the following steps: 1) Steel plate preparation before welding Two steel plates to be welded, each having the same or different strength levels, are subjected to surface cleaning before welding, the steel plates to be welded include a substrate and an aluminum or aluminum alloy plating layer on at least one surface thereof, the plating layer includes an intermetallic compound alloy layer in contact with the substrate and a metal alloy layer thereon, and the plating layer of the steel plates to be welded is not removed or thinned; 2) Setting the welding groove The groove of the steel plate to be welded should be set to 0.1-0.5 mm; 3) Welding process Welding is carried out using laser cladding, consumable electrode active gas arc welding (MAG welding) or laser-MAG hybrid welding; However, in laser cladding welding, the welding speed is 40-120 mm / s, and the welding wire feed speed is 2-8 m / min; In MAG welding, the welding speed is 300-800 mm / min; In laser MAG hybrid welding, the welding speed is 40-150 mm / s, and the welding wire feed speed is 2-10 m / min; The shielding gas is Ar+15~80vol.%CO2+1~10vol.%N2, and the shielding gas flow rate is 10~25L / min; The welding wire contains C, Mn, and Ni austenite stabilizing elements, and the differences obtained by subtracting the contents of the three elements in the welding wire from the contents of the corresponding elements in the steel plate A to be welded are represented by △C, △Mn, and △Ni, respectively, and the steel plate A to be welded is one of two steel plates to be welded that have the same strength level, or is the steel plate to be welded that has the lower strength level of two steel plates to be welded that have different strength levels; Tensile strength of steel plate A to be welded < 900 MPa, △C: -0.05 to 0.09 wt.%, △Mn: -0.5 to 1.4 wt.%, △Ni: 0 to 4.0 wt.%; or 900MPa≦tensile strength of steel plate A to be welded<1300MPa, △C: -0.1~0.09wt.%, △Mn: -2~1.4wt.%, △Ni: 0~4.0wt.%; or 1300MPa≦tensile strength of steel plate A to be welded<1700MPa, △C: -0.21 to -0.05wt.%, △Mn: -1.4 to 1.4wt.%, △Ni: 1.76 to 4.0wt.%; or Tensile strength of steel plate A to be welded ≥ 1700 MPa, △C: -0.26~-0.15 wt.%, △Mn: -1.4~0.7 wt.%, △Ni: 2.26~4.0 wt.%; The weld seam structure of the tailored blank material is martensite + 1 to 15 vol.% dispersed ferrite + 0 to 5 vol.% retained austenite, and the free aluminum content in the weld seam is 0.1 to 4.0 wt.%.

[0012] Preferably, in step 3), the CO2 content of the shielding gas is 15 to 50 vol.%.

[0013] Preferably, in step 3), the N2 content of the shielding gas is 2 to 4 vol.%.

[0014] Preferably, in step 3), the welding current for the MAG welding or laser-MAG hybrid welding is 110 to 130 A and the welding voltage is 18 to 25 V. Preferably, in step 3), the welding current for the MAG welding or laser-MAG hybrid welding is 110 to 125 A and the welding voltage is 18 to 25 V.

[0015] Preferably, in step 3), the welding speed of the laser-MAG hybrid welding is 60 to 150 mm / s, and the welding wire feed speed is 4 to 10 m / min.

[0016] Preferably, in step 3), the defocus amount in the laser build-up welding or laser MAG hybrid welding step is −10 to 10 mm, and the laser output range is 3 to 8 kW. Preferably, the defocus amount is −8 to 8 mm, and the laser output range is 4 to 8 kW.

[0017] Preferably, in the laser overlay welding or laser-MAG hybrid welding process of step 3), the minimum spot diameter output from the laser processing head is 0.3 to 1.6 mm. In this specification, those skilled in the art can select parameters that will result in a minimum spot diameter of 0.3 to 1.6 mm, taking into account actual conditions. For example, the ratio of the focal length of the focusing lens to the focal length of the collimating lens can be 0.75 to 4.0, the Rayleigh length can be 1.249 to 44.955, the diameter of the laser transmission optical fiber can be 0.2 to 0.8 mm, and the focusing angle can be 2.3 to 18.4 grads.

[0018] Preferably, in step 3), the welding is laser buildup welding, the welding speed is 40 to 120 mm / s, the welding wire feed speed is 2 to 8 m / min, the defocus amount is −8 to 8 mm, and the laser output range is 4 to 8 kW.

[0019] Preferably, in step 3), the welding is MAG welding, the welding speed is 400 to 800 mm / min, the welding current is 110 to 125 A, and the welding voltage is 18 to 25 V.

[0020] Preferably, in step 3), the welding is laser-MAG hybrid welding, the welding speed is 60 to 150 mm / s, the welding wire feed speed is 4 to 10 m / min, the defocus amount is -10 to 10 mm, the laser power range is 3 to 8 kW, the welding current is 110 to 130 A, and the welding voltage is 18 to 25 V.

[0021] Preferably, the welding wire has a diameter of 1.0 to 1.6 mm. Preferably, the thickness of the substrate is 0.5 to 3 mm.

[0022] Preferably, the plating layer is an aluminum alloy plating layer, and the components of the aluminum alloy plating layer are, by weight percentage: Si: 5-11%, Fe: 0-4%, and the balance is Al and other inevitable impurities. In one embodiment, the components of the aluminum alloy plating layer are, by weight percentage: Si: 8.5-10.5%, Fe: 1.5-2.5%, and the balance is Al and other inevitable impurities.

[0023] Preferably, the tensile strength of the steel plate A to be welded < 900 MPa, and its components are, by weight percentage: C: 0.06-0.1%, 0 < Si ≤ 0.1%, Mn: 0.5-1.0%, P < 0.03%, S < 0.01%, Al < 0.1%, 0 < Cr ≤ 0.1%, 0 < Ti ≤ 0.05%, and the balance is Fe and other inevitable impurities.

[0024] Preferably, the tensile strength of the steel plate A to be welded is 900 MPa or more and less than 1300 MPa, and its components are, by weight percentage: C: 0.06-0.15%, Si: 0.3-1.0%, Mn: 0.5-2.5%, P ≤ 0.10%, S ≤ 0.05%, Al: 0.02-0.30%, Cr: 0.05-0.5%, Nb: 0.02-0.20%, V ≤ 0.15%, Ti: 0.01-0.10%, Mo ≤ 0.5%, Ni ≤ 0.5%, B: 0.001-0.01%, and the balance is Fe and other inevitable impurities.

[0025] Preferably, the tensile strength of the steel plate A to be welded is 1300 MPa or more and less than 1700 MPa, and its components are, by weight percentage: C: 0.2-0.3%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P < 0.015%, S < 0.05%, Al < 0.1%, Ti < 0.2%, B: 0.0005-0.08%, Cr: 0.01-1%, Ni ≤ 0.24%, and the balance is Fe and other inevitable impurities.

[0026] Preferably, the tensile strength of the steel plate A to be welded is 1700 MPa or more, and its components are, in weight percent, C: 0.30 to 0.39%, Si: 0.05 to 0.6%, Mn: 0.5 to 2.5%, P≦0.015%, S≦0.01%, Al: 0.01 to 0.07%, Cr≦1.0%, Nb≦0.08%, V≦0.1%, Ti: 0.01 to 0.12%, Mo: 0.01 to 0.5%, Ni<0.25%, B: 0.0001 to 0.005%, N≦0.006%, with the balance being Fe and other unavoidable impurities.

[0027] Preferably, the welding wire has a composition, in weight percent, of 0.05-0.15% C, 0.5-1.9% Mn, 0-4% Ni, and the balance being Fe and other unavoidable impurities. In one embodiment, the Ni content of the welding wire is 0.5-4%. It should be understood that the selection of the C, Mn, and Ni contents of the welding wire must satisfy the conditions described above.

[0028] The present invention includes a thin-walled tailored steel blank obtained by the above manufacturing method. In one embodiment, the present invention provides a thin-walled tailored steel blank produced by welding two steel sheets having equal or different strength levels, the steel sheets including a base material and an aluminum or aluminum alloy plating layer on at least one surface thereof, the plating layer including an intermetallic compound alloy layer in contact with the base material and a metal alloy layer thereon, the weld seam structure of the thin-walled tailored steel blank being martensite + 1 to 15 vol.% dispersed ferrite + 0 to 5 vol.% retained austenite, and the free aluminum content in the weld seam is 0.1 to 4.0 wt.%.

[0029] Preferably, the thickness of the substrate is 0.5 to 3 mm. Preferably, the plating layer is an aluminum alloy plating layer, and the components of the aluminum alloy plating layer are, in weight percentage: Si: 5 to 11%, Fe: 0 to 4%, and the balance is Al and other inevitable impurities. In one embodiment, the components of the aluminum alloy plating layer are, in weight percentage: Si: 8.5 to 10.5%, Fe: 1.5 to 2.5%, and the balance is Al and other inevitable impurities.

[0030] Preferably, the two steel plates to be welded are independently selected from the following steel plates respectively: A steel plate with a tensile strength < 900 MPa, and its components are, in weight percentage: C: 0.06 to 0.1%, 0 < Si ≤ 0.1%, Mn: 0.5 to 1.0%, P < 0.03%, S < 0.01%, Al < 0.1%, 0 < Cr ≤ 0.1%, 0 < Ti ≤ 0.05%, and the balance is Fe and other inevitable impurities; A steel plate with a tensile strength of 900 MPa or more and less than 1300 MPa, and its components are, in weight percentage: C: 0.06 to 0.15%, Si: 0.3 to 1.0%, Mn: 0.5 to 2.5%, P ≤ 0.10%, S ≤ 0.05%, Al: 0.02 to 0.30%, Cr: 0.05 to 0.5%, Nb: 0.02 to 0.20%, V ≤ 0.15%, Ti: 0.01 to 0.10%, Mo ≤ 0.5%, Ni ≤ 0.5%, B: 0.001 to 0.01%, and the balance is Fe and other inevitable impurities; A steel plate with a tensile strength of 1300 MPa or more and less than 1700 MPa, and its components are, in weight percentage: C: 0.2 to 0.3%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P < 0.015%, S < 0.05%, Al < 0.1%, Ti < 0.2%, B: 0.0005 to 0.08%, Cr: 0.01 to 1%, Ni ≤ 0.24%, and the balance is Fe and other inevitable impurities; and A steel plate with a tensile strength of 1700 MPa or greater, containing, in weight percent, C: 0.30-0.39%, Si: 0.05-0.6%, Mn: 0.5-2.5%, P≦0.015%, S≦0.01%, Al: 0.01-0.07%, Cr≦1.0%, Nb≦0.08%, V≦0.1%, Ti: 0.01-0.12%, Mo: 0.01-0.5%, Ni<0.25%, B: 0.0001-0.005%, N≦0.006%, with the remainder being Fe and other unavoidable impurities.

[0031] Preferably, the weld seam structure of the thin-walled tailored steel blank is free of iron-aluminum intermetallic compounds and massive ferrite.

[0032] The present invention further provides a hot-pressed member manufactured from a thin-walled steel tailored blank obtained by the above manufacturing method, wherein the weld seam structure of the hot-pressed member is martensite + 0.1 to 10 vol.% dispersed ferrite, the tensile fracture position during the quasi-static process of the hot-pressed member is in the base material, the spot elongation is 4% or more, and the tensile fracture strain of the weld spot exceeds 0.08 when the strain rate of the weld spot is 40 to 800 / s.

[0033] Preferably, the ferrite content of the weld seam structure of the hot-pressed member according to the present invention is 0.5 to 5 vol.%.

[0034] Preferably, the ferrite in the weld seam structure of the hot-pressed part according to the invention is acicular.

[0035] Preferably, when the strain rate of the weld spot of the hot-pressed member according to the present invention is 40-800 / s, the tensile fracture strain of the weld spot is greater than 0.09.

[0036] Preferably, the weld seam structure of the hot-pressed parts according to the invention is free of iron-aluminum intermetallic compounds and massive ferrite.

[0037] The present invention further provides a hot-pressed member, the weld seam structure of which is martensite + 0.1-10 vol.% ferrite dispersed and distributed, the tensile fracture position of the hot-pressed member during the quasi-static process is in the base material, the spot elongation is 4% or more, and when the strain rate of the welding spot is 40-800 / s, the tensile fracture strain of the welding spot exceeds 0.08.

[0038] Preferably, the hot-pressed member is made from a thin-walled tailored steel blank material of the present invention, or is made from a thin-walled tailored steel blank material obtained by the manufacturing method of the present invention.

[0039] Preferably, the ferrite content of the weld seam structure of the hot-pressed member according to the present invention is 0.5 to 5 vol.%.

[0040] Preferably, the ferrite in the weld seam structure of the hot-pressed part according to the invention is acicular.

[0041] Preferably, when the strain rate of the weld spot of the hot-pressed member according to the present invention is 40-800 / s, the tensile fracture strain of the weld spot is greater than 0.09.

[0042] Preferably, the weld seam structure of the hot-pressed parts according to the invention is free of iron-aluminum intermetallic compounds and massive ferrite.

[0043] The present invention further provides a method for producing a hot-pressed member, the method comprising the step of hot-press quenching the thin-walled tailored blank made of steel of the present invention.

[0044] In one embodiment, after welding, the tailored blank plate is hot press quenched by heating at a temperature of 920 to 950°C for a heating time of 3 to 6 minutes and holding the pressure in a water-passing mold for 8 to 20 seconds.

[0045] Preferably, the method includes the steps of manufacturing a thin-walled tailored steel blank using a method for manufacturing a thin-walled tailored steel blank according to any one of the embodiments herein, and hot press quenching the manufactured thin-walled tailored steel blank.

[0046] Preferably, the weld seam structure of the hot-pressed member is martensite + 0.1 to 10 vol.% dispersed ferrite, the tensile fracture position in the quasi-static process of the hot-pressed member is in the base material, the spot elongation is 4% or more, and the tensile fracture strain of the weld spot exceeds 0.08 when the strain rate is 40 to 800 / s.

[0047] Preferably, the ferrite content of the weld seam structure of the hot-pressed member is 0.5 to 5 vol.%.

[0048] Preferably, the ferrite in the weld seam structure of the hot-pressed member is acicular. Preferably, the weld seam structure of the hot-pressed member is free of iron-aluminum intermetallic compounds and massive ferrite.

[0049] Preferably, when the strain rate of the welding spot of the hot-pressed member is 40 to 800 / s, the tensile fracture strain of the welding spot exceeds 0.09.

[0050] In the present invention, the substrate surface selected for the steel plate to be welded has a coating layer on at least one side, and the coating layer in the area to be welded of the steel plate to be welded is not removed or thinned before or during welding. The presence of an aluminum-containing coating layer causes the coating layer to dissolve in the molten pool, resulting in the formation of brittle and hard intermetallic compounds (Fe3Al, Fe2Al5, FeAl3) and excessive ferrite, which reduces the strength and ductility of the weld spot after hot pressing and makes it unusable. To improve the weld seam properties of the tailored blank material after hot pressing, the amount of free aluminum in the weld seam is controlled during the welding process to prevent the formation of iron-aluminum intermetallic compounds in the weld seam while simultaneously forming an appropriate amount of ferrite.

[0051] A ternary shielding gas consisting of argon, carbon dioxide, and nitrogen is used during the welding process. The volumetric content of N2 is 1-10%. N2 transports nitrogen to the weld seam. Meanwhile, aluminum and nitrogen react in the molten pool. The resulting AlN is dispersed throughout the molten pool due to vigorous stirring, and after hot pressing, it acts as a secondary phase particle, improving the strength of the weld seam. Meanwhile, free aluminum in the molten pool combines with nitrogen to form AlN, which controls the free aluminum concentration in the molten pool, preventing excessive ferrite precipitation and preventing the absence of ferrite in the weld seam at room temperature. However, if the proportion of N2 in the shielding gas is too high, the ductility of the weld spot decreases and nitrogen gas holes occur. The volume content of CO2 is 15~80%. CO2 increases the activity of the shielding gas in the welding area, increases the penetration rate of the plate material and the fluidity of the liquid metal, improves the uniformity of the composition of the molten pool metal, prevents uneven distribution of aluminum elements, ensures the uniformity of the composition of the weld seam, prevents striped structure caused by uneven composition, and especially prevents the formation of large ferrite due to aluminum aggregation, allowing the ferrite to be dispersed and distributed in the weld seam, making the properties of the weld seam more stable.

[0052] The welding wire used in the welding process contains elements such as carbon, manganese, and nickel, which expand the austenite phase region. The difference in the carbon, manganese, and nickel content between the weld seam and the steel plate being welded is controlled. On the one hand, these three elements expand the austenite phase region, compressing the high-temperature ferrite phase region and preventing excessive ferrite precipitation in the weld seam before the hot press die is closed, improving the strength of the weld seam. On the other hand, they lower the martensitic transformation start temperature of the weld seam and ensure the martensitic transformation rate.

[0053] Carbon is an important constituent element of welding wire, and affects the workability of the wire and the carbon equivalent of the weld seam. If the carbon content is too low, the austenite stability of the weld seam decreases, making it difficult to ensure the strength of the weld seam. If the carbon content is too high, the manufacturability of the welding wire decreases, and the plasticity and toughness of the weld seam decrease. Preferably, the C content of the welding wire may be 0.05 to 0.15%.

[0054] Manganese is an important constituent element of welding wire, improving the austenite stability of the weld seam and shifting the C curve to the right, thereby decreasing the critical cooling rate of martensite. Too high a manganese content affects the manufacturability of the welding wire and reduces the plasticity and toughness of the weld seam. Too low a manganese content reduces the hardenability of the weld seam and weakens the strengthening effect. Preferably, the manganese content of the welding wire is 0.5-1.9%.

[0055] Nickel, another important component of welding wire, can increase the stability of austenite in the weld seam, lower the critical Ms temperature, and improve the hardenability, strength, and toughness of the weld seam. If the nickel content is too high, the production cost of the welding wire increases, and the amount of retained austenite after hot pressing of the weld seam increases, affecting the strength of the weld seam. To ensure the strength of the weld seam, the nickel content of the welding wire can be adjusted according to the strength level of the plates to be welded. Preferably, the Ni content of the welding wire is 0-4%, for example, 0.5-4%.

[0056] The composition of the welding wire used in welding in the present invention is changed based on the composition of the steel plate to be welded, which is a low-strength steel. The composition of the welding wire can be changed appropriately for different strength levels of the steel plate to be welded, and the composition of each weld seam will necessarily change accordingly. Even if the structure of the weld seam after welding or hot pressing is the same, the mechanical properties exhibited by the weld seam will be different, so that the performance demands of the automotive industry for tailored blank plates with different strengths can be met.

[0057] This invention uses control of the components of the shielding gas and welding wire as a base, and also controls the welding speed and welding wire feed speed to vary the proportion of molten metal in the weld seam (weld seam metal formed after the welding wire is melted), making it possible to control the concentration of aluminum element dissolved in the weld seam of a tailored blank material, even if the steel sheet to be welded contains an aluminum or aluminum alloy plating layer.The concentration of free aluminum in the weld seam of a tailored blank material is controlled to 0.1 to 4.0 wt.% through the combined effects of the shielding gas, welding wire components, and welding process.

[0058] As is well known, Al is an element that promotes ferrite formation, and reducing the free Al in a weld seam weakens the ability to form ferrite. Therefore, by controlling the free Al content in the weld seam to 0.1 to 4.0 wt.%, it is possible to avoid the formation of excessive ferrite in the weld seam and ensure the strength of the weld seam. On the other hand, it is possible to avoid the formation of iron-aluminum intermetallic compounds in the weld seam, retain an appropriate amount of ferrite in the weld seam, and achieve a weld seam structure of martensite + 1 to 15 vol.% dispersed ferrite + 0 to 5 vol.% retained austenite at room temperature in tailored blank materials.

[0059] The present invention focuses on adjusting the weld seam structure of tailored blanks during their production process, primarily by adjusting the amount and morphology of ferrite and avoiding the formation of iron-aluminum intermetallic compounds and blocky ferrite during the welding process, so that the weld seam structure of the final tailored blank is martensite + 1-15 vol.% dispersed ferrite + 0-5 vol.% retained austenite. The tailored blank is then hot-pressed to form a hot-pressed part, where an appropriate amount of dispersed ferrite is retained below the weld seam of the hot-pressed part, and the final hot-pressed part has a weld seam structure of martensite + 0.1-10 vol.% dispersed ferrite.

[0060] The weld seam structure of the hot-pressed member of the present invention is martensite + 0.1-10 vol.% dispersed ferrite, which enhances the high-speed tensile strength of the weld spot, with the fracture strain exceeding 0.08 at a strain rate of 40-800 s. In contrast, the weld seam structure of conventional hot-pressed members is single martensite, with the fracture strain of the weld spot being approximately 0.07 at a strain rate of 40 s and approximately 0.058 at a strain rate of 800 s. This demonstrates the significantly increased high-speed tensile fracture strain of the hot-pressed member of the present invention. This is because martensite has high strength and hardness mechanical properties and poor deformability, while ferrite has good plasticity and toughness mechanical properties and strong deformability. Compared to weld spots with a single martensite weld seam structure, weld spots with a martensite + dispersed acicular ferrite weld seam structure provide more opportunities for harmonic deformation of the martensite when subjected to external forces. Furthermore, the substructure of martensite is primarily dislocations, and the presence of ferrite significantly reduces the internal dislocation density of martensite in the weld seam structure compared to weld spots with a single martensite structure. Since the accumulation of dislocations leads to the formation of microcracks, weld spots with a martensite + dispersed acicular ferrite structure have a significantly lower risk of microcrack formation compared to weld spots with a single martensite structure. Even if microcracks do form, the dispersed ferrite prevents their further growth and expansion. Therefore, weld spots with a martensite + dispersed acicular ferrite structure exhibit better deformability than weld spots with a single martensite structure, especially during high-speed tension.

[0061] This indicates that the hot-pressed parts manufactured by hot pressing from the tailored blank material obtained by the technical solution of the present invention have strong deformability at the weld seam during a collision, can absorb more energy, and have higher collision safety. However, the ferrite content in the weld seam of the hot-pressed part should not be too high, otherwise the strength and toughness of the weld seam will be reduced.

[0062] Tailored blanks are made on hot-formed steel sheets, and the strength of the weld seam after hot pressing is increased through the mutual cooperation and support of the welding wire components, welding process, and shielding gas. The tensile fracture position in the quasi-static process of the weld spot of the hot-pressed part obtained by hot press forming from the tailored blank material is in the base material, and the strength of the weld seam is greater than the strength of the base material, which is low-strength steel in the spot, and has good high-speed tensile properties, which meets the needs of the automobile production industry.

[0063] The beneficial effects of the present invention are as follows: In this invention, a tailored blank is made from a hot-pressed steel sheet having an aluminum or aluminum alloy plating layer. The welding speed and welding wire feed rate are controlled by adjusting the composition of the welding wire and using a ternary shielding gas. This reduces the amount of free aluminum in the weld seam of the tailored blank material and controls the free aluminum content in the weld seam to within the range of 0.1 to 4.0 wt.%. This prevents the formation of excessive ferrite in the weld seam and ensures the strength and toughness of the weld seam. It also prevents the formation of iron-aluminum intermetallic compounds in the weld seam, ensuring an appropriate amount of ferrite in the weld. The CO2 shielding gas prevents uneven distribution of aluminum, uniforms the composition of the weld seam, and prevents the formation of ferrite blocks due to aluminum aggregation, thereby stabilizing the properties of the weld seam. The hot-pressed components produced by hot press forming from the resulting tailored blank material have further improved weld seam strength due to the presence of AlN in the weld seam, and since the tensile fracture location during the quasi-static process of the weld spot is in the base material, it is clear that the weld seam strength exceeds that of the base material and meets the demands of the automotive production industry.

[0064] The present invention utilizes the cooperation and mutual support of the welding wire composition, welding process, and shielding gas composition and content to ensure that the weld seam structure of a tailored blank is martensite + 1-15 vol.% dispersed ferrite + 0-5 vol.% retained austenite. The weld seam structure of a hot-pressed part obtained by hot-pressing the tailored blank is martensite + 0.1-10 vol.% dispersed ferrite. Compared to hot-pressed parts with an entirely martensite weld seam structure, the high-speed tensile strength of the weld spots of the hot-pressed part of the present invention is significantly improved, with the weld spot fracture strain exceeding 0.08 at strain rates of 40-800 / s. In contrast, the weld seam structure of a conventional hot-pressed part is pure martensite, with the weld spot fracture strain being approximately 0.07 at a strain rate of 40 / s and approximately 0.058 at a strain rate of 800 / s. In other words, the thermoformed parts made from the tailored blank material obtained by the technical solution of the present invention not only have guaranteed mechanical properties in the quasi-static process, but also have better high-speed deformability, can absorb more energy during a collision, and have higher collision safety. [Brief explanation of the drawings]

[0065] [Figure 1] FIG. 1 is a schematic diagram of a laser cladding tailored blank according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a tensile strength curve diagram of the welding spot of the hot-pressed member obtained in Example 1 of the present invention in a quasi-static process. [Figure 3] FIG. 3 is a diagram showing the location of tensile fractures in the quasi-static process of the welding spot of the hot-pressed member obtained in Example 1 of the present invention. [Figure 4] FIG. 4 is a metallographic diagram of a welding spot of a hot-pressed member obtained in Example 1 of the present invention. [Figure 5] FIG. 5 shows the hardness distribution of the weld spots of the hot-pressed member obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0066] The present invention will be further described below with reference to examples and drawings. The present invention is not limited to the following embodiments, and anyone can create various other products based on the concept of the present invention. However, any technical solution having the same or similar features as the present invention, regardless of the shape or structure, falls within the scope of protection of the present invention.

[0067] Referring to FIG. 1, the laser cladding tailored blank of the present invention is produced by melting welding wire 30, steel sheets 10 and 20 to be welded with laser beam 40 under the protection of shielding gas 50; steel sheet 10 to be welded comprises a steel substrate 11 and plating layers 12, 12' thereon, and steel sheet 20 to be welded comprises a steel substrate 21 and plating layers 22, 22' thereon, the plating layers being aluminum or aluminum alloy plating layers.

[0068] Table 1 shows the components of the steel plate 10 to be welded, Table 2 shows the components of the steel plate 20 to be welded, Table 3 shows the components of the welding wire according to the present invention, Table 4 shows the tensile properties of the welding spots of the hot-pressed members in the quasi-static process, and Table 5 shows the high-speed tensile properties of the welding spots of the hot-pressed members.

[0069] The method for manufacturing a thin-walled tailored steel blank according to the present invention comprises the following steps: 1) Steel plate preparation before welding Take two steel plates to be welded that have the same or different strength levels, and clean the surfaces of the steel plates to be welded before welding; 2) Setting the welding groove The groove of the steel plate to be welded should be set to 0.1-0.5 mm; 3) Welding process Welding is performed on two steel plates using laser cladding, MAG welding, or laser-MAG hybrid welding.

[0070] The weight percentages of Si and Fe components in the aluminum alloy plating layers of the steel sheets to be welded in Examples 1 to 21 and Comparative Examples 1 and 2 are shown in Tables 1 and 2, with the remainder being Al and other unavoidable impurities; The strength levels of 500 MPa, 1000 MPa, 1500 MPa, and 1800 MPa in Examples 1 to 21 and Comparative Examples 1 and 2 are tensile strength levels of the steel sheets to be welded after hot pressing. The tensile strength ranges (measured according to ISO 6892) corresponding to these four strength levels are: 400 to 750 MPa for the 500 MPa level, 1000 to 1300 MPa for the 1000 MPa level, 1300 to 1700 MPa for the 1500 MPa level, and 1700 to 2150 MPa for the 1800 MPa level.

[0071] Example 1 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0072] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1800 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 4 kW, welding speed 80 mm / s, defocus amount 10 mm, welding wire feed rate 4 m / min, welding wire diameter 1.2 mm, shielding gas 48 vol.% Ar + 50 vol.% CO2 + 2 vol.% N2, gas flow rate 15 L / min.

[0073] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0074] After welding, the tailored blank plate was hot press quenched by heating at 945°C for 4 minutes and holding the plate in a water-passing mold for 10 seconds.

[0075] During the above-mentioned hot cycle, the tailored blank sheet was first austenitized. During this heating process, atoms in the coating layer and the steel diffused with each other, transforming the entire original coating layer into an intermetallic compound layer, the thickness of which was greater than that of the original coating layer. Furthermore, this layer had a high melting point and high hardness, preventing oxidation and decarbonization during the heating and holding stages of the substrate. During holding in the mold, martensitic transformation occurred in the tailored blank sheet.

[0076] The tensile curves of the quasi-static welding spot are shown in Figure 2. From Figure 2, it can be seen that the elongation rates of the hot-pressed parts are all above 4%, and the spot strength can meet the demands of the automotive industry.

[0077] The spot fracture locations are shown in Figure 3. From Figure 3, it can be seen that the fracture locations of the weld spots of the hot-pressed components during quasi-static tension are located on the base material.

[0078] The spot metallographic photograph is shown in Figure 4. The weld seam structure is martensite + 4.9 vol.% dispersed acicular ferrite, with no iron-aluminum intermetallic compounds or massive ferrite.

[0079] The spot hardness is shown in Figure 5. From Figure 5, it can be seen that the hardness of the weld seam of the hot-pressed member and the base material are in good agreement. The tensile properties of the weld spots of the hot-pressed member in the quasi-static process are shown in Table 4. The high-speed tensile properties of the weld spots of the hot-pressed member are shown in Table 5.

[0080] Example 2 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0081] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1800 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.1 mm, welding power 3 kW, welding speed 40 mm / s, defocus amount 0 mm, welding wire feed rate 2 m / min, welding wire diameter 1.0 mm, shielding gas 81 vol.% Ar + 15 vol.% CO2 + 4 vol.% N2, gas flow rate 10 L / min.

[0082] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0083] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0084] Example 3 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0085] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1500 MPa, thickness t = 1.6 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.5 mm, welding power 7 kW, welding speed 50 mm / s, defocus amount -10 mm, welding wire feed speed 8 m / min, welding wire diameter 1.2 mm, shielding gas 10 vol.% Ar + 80 vol.% CO2 + 10 vol.% N2, gas flow rate 25 L / min.

[0086] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0087] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0088] Example 4 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0089] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1500 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.4 mm, welding power 4.5 kW, welding speed 60 mm / s, defocus amount 5 mm, welding wire feed rate 5 m / min, welding wire diameter 1.2 mm, shielding gas 19 vol.% Ar + 80 vol.% CO2 + 1 vol.% N2, gas flow rate 20 L / min.

[0090] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0091] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0092] Example 5 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0093] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded and having an aluminum alloy plating layer (strength level 1000 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 1) and steel sheets 20 to be welded (strength level 1000 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 2) using a welding wire according to the present invention (welding wire composition shown in Table 3).The groove of the tailored blank sheet was set to 0.2 mm, and the welding power was 5 kW, the welding speed was 70 mm / s, the defocus amount was 7 mm, the welding wire feed rate was 4 m / min, the welding wire diameter was 1.2 mm, and the shielding gas was 49 vol.% Ar + 50 vol.% CO2 + 1 vol.% N2, and the gas flow rate was 17 L / min.

[0094] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0095] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0096] Example 6 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0097] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded and having an aluminum alloy plating layer (strength level 1000 MPa, thickness t = 2.0 mm, steel sheet composition shown in Table 1) and steel sheets 20 to be welded (strength level 1000 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 2) using a welding wire according to the present invention (welding wire composition shown in Table 3).The groove of the tailored blank sheet was set to 0.1 mm, and the welding power was 5 kW, the welding speed was 120 mm / s, the defocus amount was -5 mm, the welding wire feed rate was 7 m / min, the welding wire diameter was 1.0 mm, and the shielding gas was 40 vol.% Ar + 50 vol.% CO2 + 10 vol.% N2, and the gas flow rate was 22 L / min.

[0098] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0099] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0100] Example 7 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0101] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 500 MPa, thickness t = 1.6 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 8 kW, welding speed 100 mm / s, defocus amount -8 mm, welding wire feed rate 6 m / min, welding wire diameter 1.2 mm, shielding gas 46 vol.% Ar + 50 vol.% CO2 + 4 vol.% N2, gas flow rate 19 L / min.

[0102] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0103] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0104] Example 8 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0105] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 500 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 5 kW, welding speed 90 mm / s, defocus amount -6 mm, welding wire feed rate 5 m / min, welding wire diameter 1.2 mm, shielding gas 83 vol.% Ar + 15 vol.% CO2 + 2 vol.% N2, gas flow rate 21 L / min.

[0106] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0107] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0108] Example 9 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0109] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1500 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.4 mm, welding power 8 kW, welding speed 100 mm / s, defocus amount 3 mm, welding wire feed rate 3 m / min, welding wire diameter 1.6 mm, shielding gas 81 vol.% Ar + 18 vol.% CO2 + 1 vol.% N2, gas flow rate 23 L / min.

[0110] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0111] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0112] Example 10 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0113] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1500 MPa, thickness t = 1.75 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 8 kW, welding speed 88 mm / s, defocus amount -3 mm, welding wire feed rate 5 m / min, welding wire diameter 1.2 mm, shielding gas 74 vol.% Ar + 16 vol.% CO2 + 10 vol.% N2, gas flow rate 18 L / min.

[0114] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0115] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0116] Example 11 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0117] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1000 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.4 mm, welding power 5.5 kW, welding speed 80 mm / s, defocus amount -6 mm, welding wire feed rate 5.5 m / min, welding wire diameter 1.2 mm, shielding gas 58 vol.% Ar + 40 vol.% CO2 + 2 vol.% N2, gas flow rate 17 L / min.

[0118] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0119] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0120] Example 12 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0121] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded and having an aluminum alloy plating layer (strength level 1800 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and steel sheets 20 to be welded (strength level 1000 MPa, thickness t = 1.6 mm, steel sheet composition shown in Table 2) using a welding wire according to the present invention (welding wire composition shown in Table 3).The groove of the tailored blank sheet was set to 0.35 mm, and the welding power was 7.5 kW, the welding speed was 110 mm / s, the defocus amount was -7.5 mm, the welding wire feed rate was 7.5 m / min, the welding wire diameter was 1.4 mm, and the shielding gas was 51 vol.% Ar + 45 vol.% CO2 + 4 vol.% N2, and the gas flow rate was 19 L / min.

[0122] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0123] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0124] Example 13 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0125] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.7 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.25 mm, welding power 6.5 kW, welding speed 85 mm / s, defocus amount -5.5 mm, welding wire feed rate 5.5 m / min, welding wire diameter 1.2 mm, and shielding gas 65 vol.% Ar + 30 vol.% CO2 + 5 vol.% N2, gas flow rate 12 L / min.

[0126] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0127] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0128] Example 14 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0129] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1800 MPa, thickness t = 1.4 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 7.5 kW, welding speed 105 mm / s, defocus amount -4.5 mm, welding wire feed rate 8 m / min, welding wire diameter 1.0 mm, shielding gas 59 vol.% Ar + 35 vol.% CO2 + 6 vol.% N2, gas flow rate 14 L / min.

[0130] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0131] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0132] Example 15 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0133] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded and having an aluminum alloy plating layer (strength level 1500 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 1) and steel sheets 20 to be welded (strength level 1000 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 2) using a welding wire according to the present invention (welding wire composition shown in Table 3).The groove of the tailored blank sheet was set to 0.35 mm, and the welding power was 4.5 kW, the welding speed was 65 mm / s, the defocus amount was -7 mm, the welding wire feed rate was 4.5 m / min, the welding wire diameter was 1.2 mm, and the shielding gas was 67 vol.% Ar + 25 vol.% CO2 + 8 vol.% N2, with a gas flow rate of 11 L / min.

[0134] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0135] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0136] Example 16 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0137] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1000 MPa, thickness t = 1.8 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.2 mm, welding power 5.5 kW, welding speed 70 mm / s, defocus amount -6.5 mm, welding wire feed rate 5 m / min, welding wire diameter 1.2 mm, shielding gas 73 vol.% Ar + 20 vol.% CO2 + 7 vol.% N2, gas flow rate 16 L / min.

[0138] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0139] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0140] Example 17 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0141] For steel plate 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.2 mm, steel plate composition shown in Table 1) and steel plate 20 to be welded (strength level 500 MPa, thickness t = 1.4 mm, steel plate composition shown in Table 2) having an aluminum alloy plating layer, active gas protected MAG-ARC tailored blank was performed using a welding wire according to the present invention (welding wire composition shown in Table 3) with a groove of 0.4 mm in the tailored blank plate, a welding current of 110 A, a welding voltage of 22 V, a welding speed of 500 mm / s, a welding wire diameter of 1.2 mm, and a shielding gas of 76 vol.% Ar + 20 vol.% CO2 + 4 vol.% N2, and a gas flow rate of 13 L / min.

[0142] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0143] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0144] Example 18 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0145] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.7 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 4 kW, welding speed 60 mm / s, defocus amount -6.5 mm, welding wire feed rate 4 m / min, welding wire diameter 1.2 mm, shielding gas 56 vol.% Ar + 35 vol.% CO2 + 9 vol.% N2, gas flow rate 20 L / min.

[0146] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0147] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0148] Example 19 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0149] Laser-MAG composite tailored blanking was performed on steel plate 10 to be hot press welded (strength level 1000 MPa, thickness t = 1.2 mm, steel plate composition shown in Table 1) and steel plate 20 to be welded (strength level 500 MPa, thickness t = 1.3 mm, steel plate composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3).The groove of the tailored blank plate was 0.3 mm, and the welding power was 3 kW, the welding speed was 80 mm / s, the defocus amount was 2 mm, the MAG heat source current was 120 A, the voltage was 20 V, the welding wire feed speed was 6 m / min, the welding wire diameter was 1.2 mm, and the shielding gas was 78 vol.% Ar + 20 vol.% CO2 + 2 vol.% N2, and the gas flow rate was 24 L / min.

[0150] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0151] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile strength of the welded spots of the hot-pressed parts in the quasi-static process is shown in Table 4. The high-speed tensile strength of the welded spots of the hot-pressed parts is shown in Table 5.

[0152] Example 20 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0153] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1000 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 500 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.1 mm, welding power 5 kW, welding speed 85 mm / s, defocus amount -8.5 mm, welding wire feed rate 6 m / min, welding wire diameter 1.0 mm, shielding gas 40 vol.% Ar + 50 vol.% CO2 + 10 vol.% N2, gas flow rate 25 L / min.

[0154] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0155] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0156] Example 21 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0157] Laser cladding tailored blanks were performed on steel sheets 10 to be hot press welded (strength level 1500 MPa, thickness t = 1.2 mm, steel sheet composition shown in Table 1) and 20 to be welded (strength level 1500 MPa, thickness t = 1.5 mm, steel sheet composition shown in Table 2) having an aluminum alloy plating layer, using a welding wire according to the present invention (welding wire composition shown in Table 3), with a groove in the tailored blank sheet of 0.3 mm, welding power 5 kW, welding speed 83 mm / s, defocus amount -6 mm, welding wire feed speed 7 m / min, welding wire diameter 1.2 mm, shielding gas 40 vol.% Ar + 50 vol.% CO2 + 10 vol.% N2, gas flow rate 19 L / min.

[0158] After welding, a cross-sectional metallographic observation was carried out on the weld seam, and it was found that the weld seam was in good shape overall and there was no obvious spatter.

[0159] After welding, hot pressing was performed using the same hot pressing process as in Example 1. The tensile properties of the welded spots of the hot-pressed parts in the quasi-static process are shown in Table 4. The high-speed tensile properties of the welded spots of the hot-pressed parts are shown in Table 5.

[0160] Comparative Example 1 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0161] Tailor blanks were produced by solder welding on hot press welding target steel plate 10 (strength level 1500 MPa, thickness t = 1.5 mm, steel plate composition shown in Table 1) and welding target steel plate 20 (strength level 1500 MPa, thickness t = 1.5 mm, steel plate composition shown in Table 2) having an aluminum alloy plating layer. After welding, hot pressing was performed using the same hot pressing process as in Example 1. The weld seam structure of the hot pressed member obtained by solder welding was fully martensite. The results of high-speed tensile tests on the produced tailored blank hot pressed material are shown in Table 5, and the test was performed in accordance with the standard ISO / DIS 26203-2.

[0162] Comparative Example 2 The surface of the hot-formed steel plate to be welded was washed to remove oil stains, water stains, and other dirt from the surface, leaving the surface clean.

[0163] Hot press welding was performed on steel plate 10 (strength level 1500 MPa, thickness t = 1.5 mm, steel plate composition shown in Table 1) and steel plate 20 (strength level 1500 MPa, thickness t = 1.5 mm, steel plate composition shown in Table 2) with an aluminum alloy plating layer by overlay welding (welding wire composition shown in Table 3). The weld seam structure of the resulting hot press welding part was martensite + massive ferrite. The results of high-speed tensile tests on the weld spots are shown in Table 5, and the tests were performed in accordance with standard ISO / DIS 26203-2.

[0164] As can be seen from Tables 4 and 5, the tensile fracture position of the welded spot of the hot-pressed component obtained by the present invention during the quasi-static process is located in the base material, so the strength of the welded seam is greater than that of the low-strength base material, meeting the needs of the automotive production industry. The high-speed tensile strength of the welded spot is significantly improved, with the fracture strain of the welded spot exceeding 0.09 at a strain rate of 40-800 / s.

[0165] In Comparative Example 1, welding was performed using conventional solder welding, and the weld seam structure of the resulting weld spot was single martensite, with the fracture strain of the weld spot being approximately 0.07 when the strain rate was 40 / s and approximately 0.058 when the strain rate was 800 / s.

[0166] In Comparative Example 2, welding was performed by overlay welding, but the composition of the welding wire did not meet the requirements of the present invention, so the maximum fracture strain of the weld spot was 0.029. In other words, the thermoformed part manufactured from the tailored blank material obtained by the technical solution of the present invention not only ensures mechanical properties in the quasi-static process, but also has better high-speed deformability, can absorb more energy during a collision, and has higher collision safety.

[0167] [Table 1]

[0168] [Table 2]

[0169] [Table 3]

[0170] [Table 4]

[0171] [Table 5]

[0172] The weld seam structure of the tailored blank materials obtained in Examples 1 to 21 is martensite + 1 to 15 vol.% dispersed acicular ferrite + 0 to 5 vol.% retained austenite, and the free aluminum concentration of the weld seam is 0.1 to 4.0 wt.%. The tailored blank materials undergo a hot press forming process to become hot-pressed parts, and an appropriate amount of dispersed ferrite is retained below the weld seam of the hot-pressed part. The weld seam structure of the final hot-pressed part is martensite + 0.1 to 10 vol.% dispersed acicular ferrite, with no iron-aluminum intermetallic compounds or blocky ferrite.

Claims

1. A method for manufacturing a thin-walled steel tailored blank material, comprising the following steps: 1) Steel plate preparation before welding Two steel plates to be welded, which have the same or different strength levels, are taken, and the surfaces of the steel plates to be welded are cleaned before welding. The steel plate to be welded includes a substrate and an aluminum or aluminum alloy plating layer on at least one surface thereof, the plating layer including an intermetallic compound alloy layer in contact with the substrate and a metal alloy layer thereon, and the plating layer of the steel plate to be welded is not removed or thinned; 2) Setting the welding groove The groove of the steel plate to be welded is set to 0.1 to 0.5 mm; 3) Welding Welding is performed by laser cladding, MAG welding or laser-MAG hybrid welding; However, in laser cladding welding, the welding speed is 40 to 120 mm / s and the welding wire feed speed is 2 to 8 m / min, in MAG welding, the welding speed is 300 to 800 mm / min, and in laser-MAG hybrid welding, the welding speed is 60 to 150 mm / s and the welding wire feed speed is 4 to 10 m / min; Shielding gas: Ar + 15 to 80 vol. % CO ２ +1~10vol. %N ２ and the shielding gas flow rate is 10 to 25 L / min; The differences ΔC, ΔMn, and ΔNi obtained by subtracting the contents of the corresponding elements in the steel plate A to be welded from the contents of C, Mn, and Ni in the components of the welding wire satisfy the following conditions: Tensile strength of steel plate A to be welded <900 MPa, △C: -0.05 to 0.09 wt.%, △Mn: -0.5 to 1.4 wt.%, △Ni: 0 to 4.0 wt.%; or 900 MPa≦tensile strength of steel plate A to be welded<1300 MPa, △C: −0.1 to 0.09 wt.%, △Mn: −2 to 1.4 wt.%, △Ni: 0 to 4.0 wt.%; or 1300 MPa≦tensile strength of steel plate A to be welded<1700 MPa, △C: −0.21 to −0.05 wt.%, △Mn: −1.4 to 1.4 wt.%, △Ni: 1.76 to 4.0 wt.%; or Tensile strength of steel plate A to be welded ≧1700 MPa, △C: −0.26 to −0.15 wt. %, △Mn: −1.4 to 0.7 wt. %, △Ni: 2.26 to 4.0 wt. %; However, the steel plate A to be welded is one of two steel plates to be welded having the same strength level, or is the steel plate to be welded having the lower strength level of two steel plates to be welded having different strength levels; However, the weld seam structure of the tailored blank material is martensite + 1 to 15 vol. % dispersed ferrite + 0 to 5 vol. % retained austenite, and the free aluminum content in the weld seam is 0.1 to 4.0 wt. %.

2. In step 3), the CO ２ 2. The method for producing a thin-walled tailored steel blank according to claim 1, wherein the content is 15 to 50 vol. %.

3. In step 3), the N ２ 3. The method for producing a thin-walled tailored steel blank material according to claim 1, wherein the content is 2 to 4 vol. %.

4. 2. The method for manufacturing a thin-walled tailored steel blank according to claim 1, wherein the welding current for the MAG welding or laser-MAG hybrid welding is 110 to 130 A and the welding voltage is 18 to 25 V.

5. 2. The method for manufacturing a thin-walled tailored blank made of steel according to claim 1, wherein a defocus amount in the laser build-up welding or laser MAG hybrid welding process is −10 to 10 mm, a laser output range is 3 to 8 kW, and preferably, in the laser build-up welding or laser MAG hybrid welding process, a minimum spot diameter output from a laser processing head is 0.3 to 1.6 mm.

6. 2. The method for producing a thin-walled tailored steel blank according to claim 1, wherein the plating layer is an aluminum alloy plating layer, and the aluminum alloy plating layer contains, in weight percent, 5 to 11% Si, 0 to 4% Fe, and the remainder being Al and other unavoidable impurities.

7. The tensile strength of the steel plate A to be welded is less than 900 MPa, and its components are, in weight percent, C: 0.06 to 0.1%, 0 < Si ≤ 0.1%, Mn: 0.5 to 1.0%, P < 0.03%, S < 0.01%, Al < 0.1%, 0 < Cr ≤ 0.1%, 0 < Ti ≤ 0.05%, with the balance being Fe and other unavoidable impurities; or The tensile strength of the steel plate A to be welded is 900 MPa or more and less than 1300 MPa, and its components are, in weight percent, C: 0.06 to 0.15%, Si: 0.3 to 1.0%, Mn: 0.5 to 2.5%, P≦0.10%, S≦0.05%, Al: 0.02 to 0.30%, Cr: 0.05 to 0.5%, Nb: 0.02 to 0.20%, V≦0.15%, Ti: 0.01 to 0.10%, Mo≦0.5%, Ni≦0.5%, B: 0.001 to 0.01%, and the balance being Fe and other unavoidable impurities; or The tensile strength of the steel plate A to be welded is 1300 MPa or more and less than 1700 MPa, and its components are, in weight percent, C: 0.2 to 0.3%, Si: 0.1 to 0.5%, Mn: 0.5 to 2.5%, P<0.015%, S<0.05%, Al<0.1%, Ti<0.2%, B: 0.0005 to 0.08%, Cr: 0.01 to 1%, Ni≦0.24%, and the balance being Fe and other unavoidable impurities; or 2. The method for producing a thin-walled tailored steel blank according to claim 1, wherein the steel plate A to be welded has a tensile strength of 1700 MPa or more and contains, in weight percent, C: 0.30 to 0.39%, Si: 0.05 to 0.6%, Mn: 0.5 to 2.5%, P≦0.015%, S≦0.01%, Al: 0.01 to 0.07%, Cr≦1.0%, Nb≦0.08%, V≦0.1%, Ti: 0.01 to 0.12%, Mo: 0.01 to 0.5%, Ni<0.25%, B: 0.0001 to 0.005%, N≦0.006%, and the balance being Fe and other unavoidable impurities.

8. 2. The method for producing a thin-walled tailored blank made of steel according to claim 1, wherein the welding wire has components, in weight percent, of: C: 0.05 to 0.15%, Mn: 0.5 to 1.9%, Ni: 0 to 4%, preferably 0.5 to 4%, and the balance being Fe and other unavoidable impurities.

9. A thin-walled tailored blank made of steel is produced by welding two steel plates to be welded together having the same or different strength levels, the steel plates to be welded include a base material and an aluminum or aluminum alloy plating layer on at least one surface thereof, the plating layer includes an intermetallic compound alloy layer in contact with the base material and a metal alloy layer thereon, the weld seam structure of the thin-walled tailored blank made of steel is martensite + 1 to 15 vol. % dispersedly distributed ferrite + 0 to 5 vol. % retained austenite, and the free aluminum content in the weld seam is 0.1 to 4.0 wt. %.

10. One of the two steel plates to be welded having the same strength level, or the steel plate to be welded having the lower strength level of the two steel plates to be welded having different strength levels, is a steel sheet having a tensile strength of <900 MPa and containing, in weight percent, C: 0.06-0.1%, 0<Si≦0.1%, Mn: 0.5-1.0%, P<0.03%, S<0.01%, Al<0.1%, 0<Cr≦0.1%, 0<Ti≦0.05%, the balance being Fe and other unavoidable impurities; or a steel plate having a tensile strength of 900 MPa or more and less than 1300 MPa, and containing, in weight percent, C: 0.06-0.15%, Si: 0.3-1.0%, Mn: 0.5-2.5%, P≦0.10%, S≦0.05%, Al: 0.02-0.30%, Cr: 0.05-0.5%, Nb: 0.02-0.20%, V≦0.15%, Ti: 0.01-0.10%, Mo≦0.5%, Ni≦0.5%, B: 0.001-0.01%, and the balance being Fe and other unavoidable impurities; or a steel plate having a tensile strength of 1300 MPa or more and less than 1700 MPa, and containing, in weight percent, C: 0.2-0.3%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P<0.015%, S<0.05%, Al<0.1%, Ti<0.2%, B: 0.0005-0.08%, Cr: 0.01-1%, Ni≦0.24%, with the balance being Fe and other unavoidable impurities; or A steel plate having a tensile strength of ≥ 1700 MPa, the components of which are, in weight percent: C: 0.30-0.39%, Si: 0.05-0.6%, Mn: 0.5-2.5%, P≦0.015%, S≦0.01%, Al: 0.01-0.07%, Cr≦1.0%, Nb≦0.08%, V≦0.1%, Ti: 0.01-0.12%, Mo: 0.01-0.5%, Ni<0.25%, B: 0.0001-0.005%, N≦0.006%, and the balance being Fe and other unavoidable impurities.

10. The thin-walled tailored steel blank according to claim 9, wherein:

11. A thin-walled tailored steel blank material as described in claim 9, wherein the components of the welding wire are, in weight percent: C: 0.05 to 0.15%, Mn: 0.5 to 1.9%, Ni: 0 to 4%, preferably 0.5 to 4%, and the remainder being Fe and other unavoidable impurities.

12. A thin-walled tailored steel blank material as described in Claim 9, wherein the aluminum alloy plating layer has a composition, in weight percent, of: Si: 5 to 11%, Fe: 0 to 4%, and the remainder being Al and other unavoidable impurities.

13. A thin-walled tailored blank material made of steel as described in claim 9, wherein AlN is present in the weld seam.

14. A hot-pressed member, wherein the weld seam structure of the hot-pressed member is martensite plus 0.1 to 10 vol. % dispersed acicular ferrite, the tensile fracture position of the weld spot in a quasi-static process is in the base material, the spot elongation is 4% or more, and the tensile fracture strain of the weld spot exceeds 0.08 when the strain rate of the weld spot is 40 to 800 / s.

15. The hot-pressed member according to claim 14, wherein the hot-pressed member is produced by pressing a thin-walled tailored steel blank, the thin-walled tailored steel blank being formed from two steel plates to be welded having equal or different strength levels, the steel plates to be welded comprising a base material and an aluminum or aluminum alloy plating layer on at least one surface thereof, the plating layer comprising an intermetallic compound alloy layer in contact with the base material and a metal alloy layer thereon, the weld seam structure of the tailored blank being martensite + 1 to 15 vol. % dispersed ferrite + 0 to 5 vol. % retained austenite, and the free aluminum content in the weld seam is 0.1 to 4.0 wt. %.

16. One of the two steel plates to be welded having the same strength level, or the steel plate to be welded having the lower strength level of the two steel plates to be welded having different strength levels, is a steel sheet having a tensile strength of <900 MPa and containing, in weight percent, C: 0.06-0.1%, 0<Si≦0.1%, Mn: 0.5-1.0%, P<0.03%, S<0.01%, Al<0.1%, 0<Cr≦0.1%, 0<Ti≦0.05%, the balance being Fe and other unavoidable impurities; or a steel plate having a tensile strength of 900 MPa or more and less than 1300 MPa, and containing, in weight percent, C: 0.06-0.15%, Si: 0.3-1.0%, Mn: 0.5-2.5%, P≦0.10%, S≦0.05%, Al: 0.02-0.30%, Cr: 0.05-0.5%, Nb: 0.02-0.20%, V≦0.15%, Ti: 0.01-0.10%, Mo≦0.5%, Ni≦0.5%, B: 0.001-0.01%, and the balance being Fe and other unavoidable impurities; or a steel plate having a tensile strength of 1300 MPa or more and less than 1700 MPa, and containing, in weight percent, C: 0.2-0.3%, Si: 0.1-0.5%, Mn: 0.5-2.5%, P<0.015%, S<0.05%, Al<0.1%, Ti<0.2%, B: 0.0005-0.08%, Cr: 0.01-1%, Ni≦0.24%, with the balance being Fe and other unavoidable impurities; or A steel plate having a tensile strength of ≥ 1700 MPa, the components of which are, in weight percent: C: 0.30-0.39%, Si: 0.05-0.6%, Mn: 0.5-2.5%, P≦0.015%, S≦0.01%, Al: 0.01-0.07%, Cr≦1.0%, Nb≦0.08%, V≦0.1%, Ti: 0.01-0.12%, Mo: 0.01-0.5%, Ni<0.25%, B: 0.0001-0.005%, N≦0.006%, and the balance being Fe and other unavoidable impurities.

15. The hot-pressed part according to claim 14, wherein:

17. A hot-pressed member as described in claim 14, wherein the components of the welding wire used for welding are, in weight percent: C: 0.05 to 0.15%, Mn: 0.5 to 1.9%, Ni: 0 to 4%, preferably 0.5 to 4%, and the remainder being Fe and other unavoidable impurities.

18. A hot-pressed member as described in claim 15, wherein the components of the aluminum alloy plating layer are, in weight percent: Si: 5 to 11%, Fe: 0 to 4%, and the remainder being Al and other unavoidable impurities.

19. A hot-pressed member as described in claim 14, wherein AlN is present in the weld seam.

20. A hot-pressed member as described in claim 14, wherein the weld seam structure is free of iron-aluminum intermetallic compounds and massive ferrite.

21. 15. The hot-pressed part according to claim 14, wherein the ferrite content of the weld seam structure of the hot-pressed part is 0.5 to 5 vol. %.

22. 15. The hot-pressed member according to claim 14, wherein the weld spot of the hot-pressed member has a tensile fracture strain of more than 0.09 when the strain rate is 40 to 800 / s.

23. A method for manufacturing a hot-pressed member, the method comprising the steps of: manufacturing a thin-walled tailored steel blank by the method for manufacturing a thin-walled tailored steel blank according to any one of claims 1 to 8; and hot press quenching the manufactured thin-walled tailored steel blank.

24. The method according to claim 23, wherein the quenching by hot pressing is performed at a heating temperature of 920 to 950°C for 3 to 6 minutes, and the pressure is maintained for 8 to 20 seconds using a water-passing mold.

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