Effect Of Si On Microstructure And Impact Wear Properties Of Bainitic Steel

Mn-Si-Cr series bainitic steels have been widely used in rail transit,mining,construction machinery and other fields.Recently,higher strength and impact toughness are required in some applied environments,especially those impact wear condition.Si addition may result in the formation of filmy retained austenite,corresponding to higher impact toughness.Therefore,the effect of Si addition on microstructure and properties under different processing was studied for Mn-Si-Cr series large parts.Air cooling plus tempering and austempering treatment were designed and optimized.Related impact wear performances were checked.The results are listed as follows:1.Si content has big effect on continous cooling transformation and austempering transformation for Mn-Si-Cr series baintic steels.Its addition can increase undercooled austenitestability,reduce Bs and Ms,and make B/M complex phase transformation intervalmove downward.Furthermore,the addition can prolong incubation period of bainitic transformation and result in more lath bainite.2.Weight percentage of Si has large effect on microstructure and mechanical properties.(1)The transformation microstructureconsists of lath bainite plus granular bainite when isothermlly treated from 340? to 360? and the transformation products are mainly granular bainite from 380? to 400? for G1.While for G2,the isothermal products are always lath CFB structure in the range of 340? to 400?.Compared with G1 microstructure,G2 CFB show higher strength,hardness and elongation.(2)G1 and G2 has B/M duplex structure and CFB after QT treatment respectively,both of which demonstrate good strength and toughness match.While it is noted that CFB has better general properties with 1710 MPa,79.28 J,73.26 J and 62.73 J at 20?,-20? and-60? respectively.3.G1 and G2 show obviously different wear resistance.(1)Wear loss of G1 and G2 under QT condition decreases at first and then increases with impact load increment,and both have the smallest wear weight loss at 3 J load.Compared with Mnl3 steel,G1 has better impact abrasive wear resistance under 1-2 J impact load and while G2 shows better under 1-4 J.(2)Work hardening layer thickness of G1 and G2 under QT condition rises with impact load increment.CFB of G2 shows heavier harden layer and surface hardness than G1 under the same condition.4.CFB microstructure is more conducive to wear performance improvement than B/M duplex in as-used alloy composition system.