The effect of in-service work hardening and crystallographic orientation on the micro-scratch wear of Hadfield steel

This work presents the micro-scratch wear analysis of a sample of Hadfield steel previously used in a jaw crusher machine. The in-service work hardening material derived from dynamic high loads during the abrasive contact on the steel surface. The scratch resistance of hardened samples was evaluated by micro-scratch tests on a cross-section surface. Scratches were made on a deformed layer and on an undeformed material. In the undeformed region, the two crystallographic planes 001 and 111 were analyzed. The scratch tests were performed under various normal loads (from 20 mN to 250 mN) with a diamond cone stylus of 60° and a 5 μm radius. The electron microscopy techniques (FEG, FIB, and EBSD) were applied to characterize the microstructure, the wear micromechanisms, and the change of the submicrostructure due to scratches and crystallography. Additionally, an optical interferometry analysis was done for the topography characterization of the scratches. The microhardness profile analysis showed a variation of the hardness values from 300 to 700 HV0.3, which resulted from the twinned grains found near the worn surface. Low loads (20 mN and 50 mN) corresponded to mild wear regime, with a wear regime transition at 100 mN. A severe wear regime corresponded to higher loads (150 mN, 200 mN, and 250 mN). A significant variation of the friction coefficient along with the severely hardened layer for low normal loads was not observed. On the other hand, high loads resulted in significant variations of the friction coefficient, without correlation with microhardness profile. Additionally a strong relationship was observed between the scratch wear and the individual grain crystallographic orientation. For scratches in the (001) plane microploughing was established as the predominant wear micromechanism, whereas for (111) plane microcutting was identified as the micromechanism responsible for wear, presenting a higher friction coefficient than for the (001) plane.