Laser surface alloying of C-B-W-Cr powders on nodular cast iron rolls

Abstract

The laser surface alloying technique was used to form wear resistant layers on nodular cast iron rolls with C-B-W-Cr powder. The microstructure, element distribution, crack propagation, phases, microhardness distribution and wear behaviors of the layer were investigated. Results indicate that the alloyed layer had pores and cracks, composing of dendrites and eutectics with a hyper-eutectic structure. Solid solution, martensite, retained austenite and a lot of carbides co-existed in the alloyed layer, improving the microhardness from 500HV 0.05 of the substrate to an average of 1201HV 0.05 of the alloyed layer. Wear results at ambient and 500 °C indicate that the wear resistance of the layer was almost 1.6 times of that of the nodular cast iron substrate after sliding for 904.32 m. The improvement in wear resistance is believed to be the combined results of the grain refining effect, the solution strengthening effect, the distribution of the hard phases, the work hardening effect of the retained austenite, and the good bonding between these hard phases and the Fe-based matrix. Comparisons among different alloyed layers (different powders alloyed on different rolls) indicated that rolls with a low content of carbon and alloying elements, and alloying powders with tough bonding components are good to obtain a dense and defect-free alloyed layer and a large wear resistance improvement of the substrate.