Effects of preheating-induced interlaminar microstructural evolution on performance of fiber laser welded high strength low alloy steel

In this study, the induction preheating was adopted to improve the microstructure and performance of the high strength low alloy steel butt joints with 20 mm thickness. The induction preheating could effectively change thermal cycles of the interlaminar zones, which was beneficial to restrain the formation of the interlaminar martensite and inhibit the microstructural inhomogeneity. As the preheating temperature increased, cooling rates of the interlaminar zones slowed down. As a consequence, the time for carbon diffusion outward the austenite increased, the martensite transformation was inhibited and the ferrite transformation was promoted in the interlaminar zone, led to remarkable decrease of the amount of the martensite–ferrite interfaces. The fluctuation of hardness was effectively smoothed due to the elimination of the interlaminar martensite. Cracks occurred at the martensite–ferrite interfaces under cyclic stresses were greatly reduced, which resulted in significant increase of the fatigue life of the welded joint. Galvanic reactions caused by different potentials of the martensite and the ferrite were restrained, which effectively decreased the corrosion rates of the interlaminar zones and enhanced the corrosion resistance of the welded joints.