Investigations Of The Aging Of High Manganese Steel

The purpose of this work is searching methods of optimizing the manufacturing technology of high manganese steel crossing by means of researching the aging treatments of high manganese steel. As an excellent material of wear-resistant materials, high manganese steel has been used extensively in railway crossing and other fields, meanwhile as metastable material, the tendency of precipitated carbide is existed even under room temperature, precipitation decomposition will occur once given energy, separate out carbide and changes of microstructure and properties is aroused.In this paper, the research object is high manganese steel used for crossing. The changes of microstructure and properties of high manganese steel after heating aging, deformation aging and strain induced aging were investigated by means of metallography, SEM , XRD as well as TEM. At the same time , the work hardening mechanism and rolling contact fatigue property of high manganese steel were investigated.The results shows that, during heating aging high manganese steel immediately separate out carbide once aged at 400℃for a short time, and the property is seriously embrittlement, the optimum aging temperature for high manganese steel crossing is 350℃.During deformation aging, firstly low temperature recovery is taken place in deformation high manganese steel and its hardness vale decreased , and then precipitation decomposition is taken place , its hardness vale increased and decreased again. During strain induced aging, high manganese steel separate out carbide in the conditions of 1800MPa contact stress and 100℃for 40 hours, and precipitation decomposition is accomplished. In the process of aging of high manganese steel, the temperature of accomplishing precipitation decomposition is gently decreased with additional mechanical energy increased. Meanwhile another results shows that, the main work hardening mechanism of high manganese steel in compressed state is twins work hardening .The temperature rising of high manganese steel crossing work surface during service is about 150℃. The rolling contact fatigue life of high manganese steel used for crossing is about 1.2×106 cycles under 1800MPa contact stress, the overload quantity is 5Mt which is much lower than that of practical high manganese steel crossing. The contact surface is failed by means of fatigue spalling.The hardened layer is only depth of 1.5mm and the maximum hardness vale is about 700HV.