Microstructure of ASTM A-36 Steel Laser Beam Weldments

Abstract

The effect of the laser welding process on the microstructure of ASTM A-36 steel is to produce a bainitic fusion zone and a refined ferrite/pearlite heat-affected zone. The formation of these microstructural constituents results in improved mechanical properties such as in strength and toughness as compared to the base plate. The stress-relief heat treatment of 1175°F/1 h breaks up and spherodizes the carbide films present at the bainite lath boundaries. This significantly increases the impact energy the material can absorb down to low temperatures. The results of this study indicate that laser welding can be used to produce weldments with good mechanical properties in low-carbon steels such as A-36 where the high cooling rates refine the microstructure without the formation of the embrittling martensite that would be found in high-carbon steels. The toughness of the A-36 laser beam weldments can be increased further through the use of a stress relief anneal which coarsens and spherodizes the bainitic carbides.