Modulation of the local grain structure in laser beam welds to inhibit the propagation of centerline hot cracks

Abstract

The morphology and the size of the grains of a weld result from the solidification rate and the temperature gradient during solidification. The heat input and the velocity of the welding process directly affect these quantities. The laser power, the welding velocity and the beam diameter were periodically modulated to achieve a periodical change of the solidification conditions during welding. It leads to a continuous change of the type of grain structure over the welded length. The metallographic analysis of welds in close edge position shows the periodical interruption of centerline cracks at local changes of the grain structure.