Microstructure related enhancement in wear resistance of tool steel AISI D2 by applying laser heat treatment followed by ultrasonic impact treatment

The surface layers of tool steel AISI D2 were modified by laser heat treatment (LHT) conducted using the solid state fiber-laser, by ultrasonic impact treatment (UIT) and by the combined LHT + UIT process. The paper is focused on the establishing the correlation between the microstructure, hardness and wear resistance of the modified layers. XRD analysis and TEM observations show that the LHT process results in the formation of microstructure comprised submicronic ferrite/austenite grains, martensitic needles and secondary carbides while the combined LHT + UIT process leads to the formation ultra-fine grained structure (~ 80-250 nm) with grain boundaries fixed with fine secondary carbides (~ 20 nm), and some areas of martensitic feathers. The observed microstructural features and phase compositions are shown to affect the wear resistance of the AISI D2 steel surface measured both in quasi-static and dynamic conditions. The modified layers demonstrate almost double, triple and four times decrease in the wear losses in dynamic conditions with regard to the initial surface after the LHT, UIT, and combined LHT + UIT processes, respectively. Theoretical evaluations of the wear resistance W− 1th using the Archard expression correlate well with the experimental data W− 1exp, especially when the local plasticity characteristics δН describing the retained plasticity was taken into account.