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KR-102963135-B1 - Laser welding method and laser weld joint

KR102963135B1KR 102963135 B1KR102963135 B1KR 102963135B1KR-102963135-B1

Abstract

The present invention provides a laser welding method and a laser welded joint for preventing cracks and obtaining a welded joint with excellent toughness of the weld metal. The laser welding method involves butting steel materials having a chemical composition in which, in mass%, C: 0.04 to 0.15%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, Ti: 0.050% or less, O: 0.010% or less, N: 0.008% or less, satisfying a carbon equivalent Ceq represented by the following formula (1) of 0.30 to 0.45, and the remainder being Fe and unavoidable impurities, and then coating the surface of the steel materials, including the weld line, with a flux of a predetermined composition and laser welding from thereon to produce a welded joint. Ceq=[C]+[Mn]/6+[Si]/24+[Cu]/20+[Ni]/40+[Cr]/5+[Mo]/4 (1)

Inventors

  • 다카다 아츠시
  • 오카베 타카토시

Assignees

  • 제이에프이 스틸 가부시키가이샤

Dates

Publication Date
20260508
Application Date
20230508
Priority Date
20220905

Claims (6)

  1. A laser welding method in which steel materials are butted together, the surface of the steel materials including the weld line is coated with flux, and a laser beam is irradiated from above to join them. The chemical composition of the above steel is, in mass %, C: 0.04~0.15%, Si: 0.05~1.00%, Mn: 0.50–2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, Ti: 0.050% or less, O: 0.010% or less, and, N: Contains 0.008% or less, Randomly Cu: 1.00% or less, Ni: 2.00% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.20% or less, V: 0.20% or less, Ca: 0.005% or less, REM: 0.050% or less, and, B: Contains at least one type selected from 0.0030% or less, and The remainder consists of Fe and inevitable impurities, along with, The above steel has a carbon equivalent Ceq in the range of 0.30 to 0.45 as represented by the following formula (1), and In addition, the above flux has a component index X represented by the following formula (2) in the range of 0.5 to 2.5, and α, represented by the following equation (3), is in the range of 0.2 to 1.1, and A laser welding method in which β, represented by the following equation (4), is in the range of 0.2 to 2.5. Ceq=[C]+[Mn]/6+[Si]/24+[Cu]/20+[Ni]/40+[Cr]/5+[Mo]/4 (1) X＝{(CaO)＋(MgO)＋(CaF 2 )＋0.5(MnO)＋(B 2 O 3 )}/{(SiO 2 )＋0.5(Al 2 O 3 )＋0.5(TiO 2 )｝ (2) α=[Al]/(0.025+0.05×log 0.1 β={[Ti]+(TiO 2 )/2000}/(0.025+0.05×log 0.1 Here, [element] in each of the above formulas represents the content (mass%) of the corresponding element of the steel, and (component) represents the content (mass%) of the corresponding component of the flux, and if the corresponding element or component is not contained, it is set to 0.
  2. In paragraph 1, A laser welding method in which the plate thickness of the above steel is 6 to 50 mm.
  3. In paragraph 1, A laser welding method in which the laser welding output of the above laser welding is 5 to 80 kW and the welding speed is in the range of 0.3 to 2.0 m/min.
  4. In paragraph 2, A laser welding method in which the laser welding output of the above laser welding is 5 to 80 kW and the welding speed is in the range of 0.3 to 2.0 m/min.
  5. A laser welded joint welded by a laser welding method described in any one of paragraphs 1 to 4, The chemical composition of the weld metal, in mass %, C: 0.04~0.15%, Si: 0.05~1.00%, Mn: 0.50–2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, Ti: 0.060% or less, O: 0.009~0.050%, and, N: Contains 0.010% or less, Optionally, Cu: 1.00% or less, Ni: 2.00% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.20% or less, V: 0.20% or less, Ca: 0.005% or less, REM: 0.050% or less, and, B: Contains at least one type selected from 0.0030% or less, and The remainder consists of Fe and inevitable impurities, along with, The carbon equivalent Ceq represented by the following formula (5) is in the range of 0.30 to 0.45, and The mass ratio of the Al content to the O content in the above weld metal is in the range of 0.2 to 1.1, and A laser welded joint in which the mass ratio of the Ti content to the O content in the weld metal is in the range of 0.2 to 2.5. Ceq=[C]+[Mn]/6+[Si]/24+[Cu]/20+[Ni]/40+[Cr]/5+[Mo]/4 (5) Here, [element] of the weld metal in the above equation (5) represents the content (mass%) of the element, and if the element is not contained, it is set to 0.
  6. In paragraph 5, A laser welded joint in which the absorbed energy V E -20 of a V-notch Charpy impact test at a test temperature of -20℃ of the weld metal is 27J or more.

Description

Laser welding method and laser weld joint The present invention relates to a laser welding method for steel used in a low-temperature environment of -20°C and a laser welded joint. In this specification, “x to y” indicating a numerical range represents x or greater and y or less, and includes boundary values. High-energy density beam welding, such as laser welding and electron beam welding, features greater penetration depth, faster welding speeds, and the elimination of the need for post-weld deformation correction compared to conventional arc welding. Due to these characteristics, high-energy density beam welding is known as a highly efficient welding method. Since these high-energy density beam welding processes are fundamentally controlled automatically, they do not require skilled workers compared to arc welding. Furthermore, they offer advantages such as minimal weld deformation, which eliminates the need for post-weld correction work. Therefore, against the backdrop of the recent surge in demand for labor savings and full automation in manufacturing sites, the widespread adoption of high-energy density beam welding in the actual construction of thick steel plates is anticipated. Meanwhile, the weld metal formed by laser welding is created by melting the base material of the weldment with the energy of laser light and then solidifying it. Typically, the chemical composition of the weld metal produced by laser welding is nearly identical to that of the base material, making it difficult to achieve high toughness of the weld metal. Regarding this point, Patent Document 1 discloses that oxygen is incorporated into the shielding gas along with adjusting the composition of the base material. It also states that low-temperature toughness of the weld metal can be achieved by controlling the elemental composition ratio of Al/O in the weld metal to 0.5 to 1.2. In addition, Patent Document 2 discloses a laser welding method and a flux for laser welding, wherein the surface of a workpiece is coated with flux for welding. The technology states that deep penetration can be obtained without using a low vacuum atmosphere, and high-temperature cracking can also be effectively suppressed. Furthermore, Patent Document 2 discloses that regarding the flux components, the total content of an additive component selected from manganese dioxide, alumina, magnesium oxide, titanium oxide, and silica sand is 30 mass% or more. FIG. 1 is a schematic diagram showing one embodiment of a laser welding method according to the present invention. FIG. 2 is a three-sided schematic diagram showing a test specimen with a side groove used for a Charpy impact test of a laser welded joint according to the present invention, where (a) is a side view, (b) is a front view, and (c) is a bottom view. Figure 3 is a graph showing the relationship between the flux component index X and the penetration depth of the laser welding method according to the present invention. (Form for carrying out the invention) Suitable embodiments of the present invention will be described below. The present embodiment is a laser welding method for producing a welded joint by laser welding butt-joint steel materials together. In addition, the plate thickness of the butt-joint steel materials is preferably 6 to 50 mm from the perspective of weldability. More preferably, it is 8 to 45 mm. [Chemical composition of steel] First, the chemical composition of the steel used contains, in mass%, C: 0.04 to 0.15%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, Ti: 0.050% or less, O: 0.010% or less, and N: 0.008% or less. In addition, the steel is made of a steel having a chemical composition in which the carbon equivalent Ceq represented by the following formula (1) satisfies 0.30 to 0.45, and the remainder consists of Fe and unavoidable impurities. Ceq=[C]+[Mn]/6+[Si]/24+[Cu]/20+[Ni]/40+[Cr]/5+[Mo]/4 (1) Here, [element] of the steel in the above formula (1) represents the content (mass%) of the element, and if the element is not contained, it is set to 0. The reasons for limiting the chemical composition of the steel are as follows. Hereinafter, "%" in the chemical composition refers to "mass%". [C: 0.04~0.15%] C is an effective element for improving the strength of steel at a low cost, and in this embodiment, a content of 0.04% or more is required. On the other hand, if the content exceeds 0.15%, the weld metal hardens, and toughness decreases. Therefore, the C content is limited to a range of 0.04 to 0.15%. In addition, preferably, it is in the range of 0.06 to 0.12%. More preferably, it is in the range of 0.07 to 0.10%. [Si: 0.05~1.00%] Si acts as a deoxidizing element and contributes to the improvement of steel strength. To obtain such effects, a content of 0.05% or more is required. On the other hand, if the content exceeds 1.00%, a hard secondary phase (striated martensite) is formed in the weld metal, which lowers the toug