Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Grade E Steel

In order to meet the new requirement of heavy haul trains to properties ofthe coupler, this paper adopts grade E steels used by the coupler of heavy haultrains as experiment materials, explores the effect of preparation normalizing+quenched-tempered heat treatment, preparation normalizing+secondaryquenching+tempering and preparation normalizing+and tempering betweenquenching+tempering heat treatment on microstructure and mechanicalproperties of grade E steels to improve the mechanical properties of grade E steelby changing heat treatments. Experiment results are shown as follow:Firstly, fix hardening temperature and tempering temperature and explorethe effect of normalizing temperature on the microstructure and mechanical ofgrade E steels. Experimental results show that normalizing heat treatment canmake microstructure refined, but the normalizing temperature is too high andeasily to make the microstructure coarse, and improve the strength and-40℃impact toughness. The strength increases and then decreases, plasticity show atrend of increasing and-40℃impact toughness decreases and then increaseswith normalizing temperature increasing from880℃to960℃. The bestnormalizing temperature is920℃after compositing all kinds of mechanicalproperties.Secondly, fix the normalizing temperature and explore the effect ofhardening temperature and tempering temperature on the microstructure andproperties of grade E steels. Experimental results show that the effect ofhardening temperature on the strength of grade E steels, but the effect on theirplasticity and-40℃impact toughness is more obvious. The strength increases,the plasticity and-40℃impact toughness both decrease with hardeningtemperature increasing from860℃to920℃. When the hardening temperatureis over920℃, the strength decreases, the plasticity and toughness increase slightly. The strength and hardness both decrease, the plasticity and toughnessincrease with the tempering temperature increasing from560℃to640℃. Theoptimized technology of normalizing+hardening and tempering is920℃normalizing+900℃hardening+580℃tempering. The yield strength andtensile strength under this technology are respectively912.0MPa and984.0MPa,the elongation and reduction of area are respectively17.6%and54.3%, theimpact toughness of-40℃is33.0J, and the hardness is284.0.Finally, fix the normalizing temperature, hardening temperature andtempering temperature and explore the effect of secondary hardening temperatureand holding time of rapid austenitizion after middle tempering on themicrostructure and mechanical of grade E steels. The strength, plasticity and the-40℃impact toughness all increase and then decrease with the secondaryhardening temperature increasing from800℃to880℃. The strength and the-40℃impact toughness both reach maximum with secondary hardeningtemperature820℃. The plasticity is the best with secondary hardeningtemperature840℃. The strength and the-40℃impact toughness bothincrease and then decrease and plasticity decreases and then increases withholding time of rapid austenitizion increasing from20min to80min. Thestrength is the highest when the holding time is60min, and the impact toughnessreaches maximum when holding time is40min.The best heat treatment after optimization is920℃normalizing+900℃hardening+640℃tempering+820℃hardening+580℃tempering, in the640℃tempering treatment the temperature is increased to820℃afterholding2h, and in the820℃hardening, the holding time is40min. Themechanical properties of grade E steels under this technology are shown that theyield strength and tensile strength are respectively904.1MPa and967.1MPa,the-40℃impact toughness is80.2J, the elongation and reduction of area arerespectively18%and51.6%, and the brinell hardness is294.