The study on laser composite processing of pre-controlled crack in low carbon steel

Abstract

To improve the initial velocity and damage effect of the pre-controlled fragments, and to ameliorate the processing method of the fragment shells, this study describes the laser composite experiment for processing low-carbon steel controlled-fragmentation by prefabricated cracks, and the cracks are used to realize the manufacture of pre-controlled fragments with low-carbon steel as the shell. The objective of this paper is to study the processing of prefabricated cracks on the surface of low carbon steel and the fracture mode of cracks. In the research, firstly, the low carbon steel was laser cladding brittle materials to modify the surface and obtain a brittle cladding layer, afterwards, laser alloying treatment was performed on the modified area to make the melting zone morphology uniform and symmetrical, and finally after the laser deep penetration treatment, metal cracks meeting the requirements were produced in the melting zone under the influence of multiple factors. The formation process and fracture mode of this kind of crack were studied, and the results show that the increase in carbon equivalent of the weld caused by the addition of alloy materials is the main reason for the cracks. The melting zone after laser treatment produced changes in metallographic structure, and the main structure in the melting zone is lath martensite, with an average hardness of 700–1000 HV, and cold cracks were produced under large residual stress. Research on the fracture surface found that the upper middle part of the melting zone containing Fe2W phase is the origin of cracks, its fracture feature is mainly quasi-cleavage fracture, and the crack propagation zone in the lower half of the melting zone is characterized by intergranular fracture. The crack ends in the heat-affected zone with lower hardness. This research has realized the controllable prefabricated crack manufacturing on the surface of low-carbon steel and provides technical and theoretical support for laser manufacturing of low carbon-steel controlled fragmentation.