Effects of HFMI Treatment on the Boron-Alloyed Austenite Medium-Manganese Steel 140Mn6Cr3TiB Deposit: Enhanced Wear Resistance Induced by Heterogeneous Microstructure

This paper analyses the microstructure and properties of the titanium- and boron-alloyed high-carbon medium-manganese 140Mn6Cr3TiB steel deposit before and after high-frequency mechanical impact (HFMI) treatment. Nanoindentation revealed a distinct correlation between the phase composition and the deformation behaviour. The heterogeneous nature of the steel creates a "shield-and-buffer" effect, where the hard eutectic framework resists penetration and tough matrix prevents brittle failure. The synergistic interaction between the phases, i.e., the high hardness of boride-carbide phases with the high fracture toughness of the manganese-rich austenite, maintains a high tolerance to abrasion damage of the deposit. The HFMI treatment results in the formation of the strain-induced ε- and α’-martensites (~66% and 3–6%, respectively), a significant grains/crystallites refinement (down to 31–54 nm), and dislocation density (~2.2*1013–5.1*1013cm-2), which support essential hardening from HV0.2 = 5.17 GPa to HV0.2 ≈ 7.8 GPa. The HFMI treatment regime (load = 100 N, amplitude = 10 µm, and HFMI time = 60 s) was found to be optimal, which leads to the enhancement in wear resistance of 140Mn6Cr3TiB steel deposit that manifests itself by the decrease of the wear volume by ~4 times from 15.2 μm3 to 3.9 μm3 and in the decrease in the scratch track depths by ~30% (from ~0.52 μm to ~0.37 μm) in comparison with the initial deposit. The HFMI-hardening changed the wear mechanism of high-carbon medium-manganese titanium and boron-alloyed 140Mn6Cr3TiB steel hardfacing to the ploughing mechanism instead of the ‘wedge/pile-ups’ formation in the initial deposit. The obtained results confirm good efficiency and prospects of the medium-manganese steel hardfacing followed by the finishing HFMI treatment in the production of protective deposits of enhanced wear resistance and prolonged operation life.