ARC WELDED JOINT OF Zn PLATED STEEL SHEET

Abstract

Provided is a welded joint that suppresses occurrences of blow holes in initial parts and final parts in a Zn plated steel sheet and reduces the occupancy ratio for blow holes in the welded part as a whole. The arc welded joint is obtained by the method of arc-welding Zn-based plated steel sheets, in which a blowhole occupancy over the entirety of the welding length is less than 30%.

1 . An arc welded joint obtained by the following method of arc-welding Zn-based plated steel sheets, in which a blowhole occupancy over the entirety of the welding length is less than 30%,
 the method of arc-welding comprising:   setting an inter-sheet gap within a range of 0.2 to 1.5 mm;   performing welding by moving a welding means along an overlaid portion of the steel sheets to be welded and joined;   a first step of moving the welding means at a first welding speed from a welding start point, and applying a first welding heat input to perform welding;   a second step of, after the first step, moving the welding means at a second welding speed, and applying a second welding heat input to perform welding; and   a third step of, after the second step, stopping the movement of the welding means, and performing welding for 0.1 to 2 seconds at a position where the welding means is stopped, wherein   the first step includes a welding section welded under conditions where the first welding speed is smaller than the second welding speed, and the first welding heat input is larger than the second welding heat input, and   the third step includes performing welding at a welding current and a welding voltage lower than those used in the second step.   
     
     
         2 . The arc welded joint according to  claim 1 , wherein a starting end portion corresponding to a welding section after the first step is a region covering 10 to 40% of the entirety of a welding length, and a terminal end portion corresponding to a welding section after the third step is a region covering 10 to 20% of the entirety of the welding length. 
     
     
         3 . The arc welded joint according to  claim 1 , wherein the first step includes starting welding at one end of the overlaid portion, and performing welding toward the other end, the welding heat input in the first step being more than 1.2 times of the welding heat input in the second step. 
     
     
         4 . The arc welded joint according to  claim 1 , wherein the first step includes performing welding at the welding start point located inwardly separated from the one end of the overlaid portion toward the end, and then turned around to perform welding from the end toward the other end,
 the welding toward the one end being performed at a welding speed smaller the welding speed in the second step and with a welding heat input more than 1.2 times of the second welding heat input, and   the welding toward the other end being performed at the same welding speed as the second welding speed.   
     
     
         5 . The arc welded joint according to  claim 1 , wherein the Zn-based plated steel sheets each have a hot-dipped layer consisting of, by mass %, Al: 4.0 to 22.0%, Mg: 0.05 to 10.0%, Ti: 0 to 0.10%, B: 0 to 0.05%, Si: 0 to 2.0%, Fe: 0 to 2.5%, and the remainder being Zn and unavoidable impurities. 
     
     
         6 . The arc welded joint according to  claim 1 , wherein the Zn-based plated steel sheets each have a plating deposition amount per side of 20 to 250 g/m2, and a sheet thickness of 1.6 to 6.0 mm.