Effect of chemical composition on microstructure and mechanical properties of laser weld metal of high-tensile-strength steel

Laser beam welding (LBW) and laser-arc hybrid welding are expected to be applied towelding of high-strength steel plates over 780 MPa, because they have advantages such as low distortion and a narrow heat-affected zone. This research examined the relationship between the chemical composition of high-strength steel plates and the microstructure and mechanical properties of the weld metal with the aim of improving the toughness of welded joints of high-strength steels by the LBW process. The results revealed that weld metal toughness is strongly dependent on the carbon (C) content of the steel plates, and excellent toughness can be obtained in weld metals with low C contents having an almost fully lower bainite structure without formation of slender martensite austenite constituent (MA). Based on these results, a guideline for appropriate alloying element design for high-strength steels for LBW was proposed, targeting mechanical properties of tensile strength >= 980 MPa and toughness vE (-40 degrees C)>= 47 J.