Study on the nucleation mechanism of hard particles in high boron and high carbon alloy by laser-induced arc welding

Abstract

It is an effort to improve the phenomenon of thick boron-carbon compound forming, during the process of arc surfacing of high boron and high carbon alloy. This paper deals with the refinement of hard particles, in order to improve the microstructure of the surfacing layer. The comparison of microstructure and hard particles composition between laser arc composite surfacing layer and arc surfacing layer confirmed that hard particles of both are (Fe, Cr)7(B, C)3 and (Fe, Cr)2B. Also, the results show that in the cross section of the arc surfacing layer, the hard particles are in the shape of long strips, hexagonal and regular quadrangular blocks. But the size of hard particles decreases and follows a uniform distribution under laser induction. The wear resistance of laser arc composite surfacing layer is obviously improved. This may be due to that thick hard particles were broken into smaller units by pulsed laser stirring molten pool, thus providing more nucleating particles for the formation of hard particles. At the same time, the thick hard particles were melt down by high energy laser beam, which improves the temperature gradient and forces hard particles to grow uniformly.