Study Of Microstructure And Mechanical Properties Of Quenched-partitioned Medium Manganese Wear-resistant Steels

In order to reduce the cracking and wear failure in the martensitic medium manganese steels due to its insufficient toughness and plasticity,in this paper,a certain volume fraction of retained austenite is introduced into the matrix of martensitic medium manganese steels using the quenching-partitioning(Q&P)process.The micro structure is observed by OM,SEM.The morphology,distribution and volume fraction of retained austenite are analysed by means of TEM,EBSD and XRD analysis.The hardeness,strengh and plasticity of the steels are tested using the hardness tester and the universal tensile testing machine.The wear resistance of the steels is measured by abrasive wear testing machine.The effect of the cooling rate on the phase transformation behavior and the effect of the quenching-partitioning(Q&P)process on the microstructure,strength and wear properties of medium manganese steels are researched.Then the following conclusions are reached:(1)After being austenitized fully and then cooled to room temperature at different cooling rates(0.05℃/s～30℃/s),the Ti-free medium manganese steels undergoes only martensitic transformation.When the test steels is cooled to below Ms at a slower cooling rate(0.05℃/s),the volume fraction of retained austenite increase to 12vol.%,due to"carbon partitioning" occurred in the formed martensite which improves the stability of austenite.And the vickers hardness y of Ti-free medium manganese steels and cooling rate x accord with a double exponential decay relationship:y=-42.23 exp(-x/4.75)-38.27 exp(-x/0.17)+573.76(2)After Q&P treatment,both Ti-free and Ti-bearing medium manganese steels obtain a mixed micro structure composed of martensite and retained austenite.The maximum volume fraction of retained austenite in Q&P treated Ti-free steels is 19.7vol.%,while that in Q&P treated Ti-bearing steels is only 12.5vol.%,because the existence of(Ti,Mo)C precipitates in Ti-bearing steels reduced the diffusion rate of carbon atom.Significant TRIP effect of retained austenite is observed during the tensile testing.Best comprehensive mechanical properties is obtained in Ti-free medium manganese steels while the quenching temperature is 220℃ and partitioning temperature is 350℃,with yield strength of 914MPa,tensile strength of 1526MPa,and elongation of 15.5%.(3)The wear mechanism of Ti-free medium manganese steels is plastic deformation and fatigue spalling,while that of Ti-bearing medium manganese steels is mainly micro-cutting and fatigue failure.The stress induced martensitic transformation of retained austenite during the wear process improves the wear resistance.The wear resistance of Ti-bearing medium manganese steels is 1.7 times higher than that of Ti-free medium manganese steels,mainly because the(Ti,Mo)C particles in the matrix of Ti-bearing medium manganese steels hinders the abrasive sliding.