The Microstructure And Wear Resistance Of Manganese Steel

High manganese steel has long history and wide application showing an excellent wear resistance under the severe impact wearing condition. But under middle and small loading conditions, its wear resistance was very low comparing with the martensitic steels. At present, many low-alloy wear-resistant steels had been developed to replace the high manganese steel at home and abroad. At home some steels can reach the requirements of strength and hardness, but generally had low toughness and wear resistance due to the inhomgeneous distribution of the composition and the lack of optimum process and equipment.In this study, the new type medium manganese steels with different carbon content were used as experimental materials, which were processed by two kinds of heat treatment:One is the traditional QT process to obtain martensitic medium manganese steels, and another is the ART-annealed to obtain ultrafine ferrite/austenite lamellar duplex structure. Microstructures, mechanical properties and wear resistances of medium manganese steels processed under different heat treatment conditions were examined by SEM, XRD, EBSD and AFM. It was found that the microstructure of martensitic medium manganese steels mainly included tempering martensite and a small amount of some dioxides. With increasing of carbon content, strength, hardness, uniform elongation, the wear resistance of martensitic medium manganese steels increase gradually, but area reduction and impact toughness (under-40C) decrease. Under the similar carbon content, the wear resistance of the medium manganese steel was similar to foreign advanced wear-resistant steel, and both showing wear mechanism of microscopic cutting wear. In ART-annealed medium manganese steel, ferrite and austenitic laths were arranged in parallel and alternate mode, which could be much clearer with increasing of annealing time. After annealing at650℃, the residual austenite content, the strength, the ductility and the wear resistance of dual phase medium manganese steel increase with increasing of annealing time. In the studied range of annealing time, and the best wear performance were obtained in the specimens with6hours annealing at650℃, Rm:1080MPa, At:37.5%, Rm*At:40.5GPa%. Meanwhile, after annealing at675℃, the strength and the wear resistance of studied steel increase with annealing time as well, but the variations of residual austenite content, the ductility and combined mechanical properties (Rm*AT and Rm*AU) first rise and then decline, which results in the best performance of steels annealed with10minutes. Similar to the martensitic structure steels, the wear mechanism of dual phase medium manganese steels is microscopic cutting wear as well. In general, the wear resistance of dual phase medium manganese steels is better than the martensitic under same carbon content, and the wear resistances of all of the steel increase with the increasing of austenite fraction.Based on the analysis on the relationship among microstructure, mechanical properties and wear resistance, it was found that the strength, the ductility and the wear resistances of dual phase medium manganese steels were strongly dependent on the austenite fraction, which were ascribed to the phase transformation induced plasticity and phase transformation induced hardenability stemming from the large volume fraction of austenite.