Study On The Wear Behaviour Of Steel With Nanobainite/Martensite Complex Microstructure

Recent years,nanobainitic steels have been widely studied for their excellent mechanical properties.The wear resistance of nano-bainite steel is proved to be excellent,but the heat treatment time of nano-bainite structure is too long.Therefore,nanometer bainite/martensite complex structure becomes the breakthrough of industrialization.However,the failure mechanism of the nanobainite/martensite multiphase structure under wear conditions is still unclear,such as the role of nanobainite,the influence of the amounts of nanobainite,and the competition between wear and contact fatigue.By preparing different quantities of nano-bainite/martensite multiphase structures,this study focuses on the influence of microstructure characteristics on the wear properties of multiphase structures and the failure mechanism.The main research results are as follows:(1)According to the composition design criteria of nano-bainitic steel,the ultra-high C and high Al type nano-bainite steel of “1.32C-0.49Si-1.46Al-1.31Cr” was designed.The nanobainite+martensite multiphase structures with different quantities of nanobainite were prepared,using the process of "short-time isothermal and quenching".The scale of bainite ferrite is below 100 nm,and the microstructure is mixed with spherical undissolved carbide and bulk residual austenite.With the increase of the number of nanobenite,the hardness of the multiphase structure decreases first and then increases,while the impact toughness increases first and then decreases.(2)The dry sliding wear behavior of multiphase structures was investigated under25,50 and 75 N loads.The results show that the number of nanobenite has almost no effect on the wear resistance of the multiphase structure under 25 N loads.Under the loads of 50 and 75 N,the specific wear decreases first and then increases with the increase of the number of nanobainite.The specimen obtained after isothermal 45 min has the lowest specific wear rate and the best wear resistance.The analysis of wear mechanism shows that the main failure mode of multiphase dry sliding wear is oxidation wear.(3)The rolling/sliding wear behavior of multiphase structures was investigated under conditions of 500 N+10% ratio and 1000 N+3% ratio.The results show that the wear resistance of the multiphase structure is better than that of the standard specimen GCr15.The wear resistance of the samples obtained after isothermal for 30 min and45min is the best under the two conditions,and the higher the load,the more obvious the advantage.The analysis of wear mechanism shows that the main failure mode of rolling sliding wear is contact fatigue spalling,followed by slight oxidation wear.(4)Compared with the single-phase structure,the multiphase structure has better dry-slip and rolling/sliping wear resistance,which is mainly attributed to the fact that nano-bainite and residual austenite can improve the strength and toughness of the multiphase structure and the presence of martensite in the multiphase structure can provide sufficient hardness.At the beginning of sliding or rolling sliding,martensite can resist the early wear of the surface;with the wear process,nano-bainite and residual austenite can slow down the crack initiation and hinder its propagation.In addition,the early nanocrystalline/nanocrystalline/amorphous process occurs in the wear process of nanocrystalline ferrite,which makes the surface hardness increase rapidly and increases the wear resistance.