Fracture resistance in hardfaced metal for continuous casting rollers and hot rolling mill work rolls

Abstract

Continuous casting machine rolls and hot rolling mill work rolls are susceptible to surface cracking under dynamic loading. The fracture resistance of homogeneous metal compositions used for their manufacture and hardfacing is determined by the work of crack initiation. This is evaluated by separating the work of crack initiation from the work of crack propagation. Research on the dynamic fracture process of heterogeneous multilayer composites hardfaced on hot rolling mill work rolls confirmed that crack arrest at the interface between strong and ductile layers occurs by a delamination mechanism, ensuring high impact toughness. Furthermore, it was found that homogeneous steel compositions with cast and plastically deformed structures used for the manufacture and hardfacing of continuous casting machine rollers and work rolls exhibit a linear relationship between fatigue crack growth rate and stress intensity factor range. This linear relationship deviates in heterogeneous hardfaced metal structures, where the fatigue crack propagation rate varies and exhibits regions of abrupt deceleration. Similar behavior is observed in welded joints of steels with different compositions and mechanical properties. The study also revealed that in cases where there are significant differences in the structure and thermophysical properties between the hardfacing layer and the base material of continuous casting machine rollers, a sharp drop in the level of axial tensile stresses at the fusion boundary leads to the arrest of surface fatigue cracks. In the absence of such a drop in stress, the crack changes direction and slows down, but does not stop. In addition, the application of variable composition hardfacing technology to hot rolling mill work rolls not only reduces uneven wear along the roll barrel, but also increases resistance to surface cracking.