Study On Both Strength And Plasticity With The Austempering Structure Of A High Carbon Content Hypoeutectoid Steel

With the development of long-span bridge construction in China,the demand of 2000 MPa high strength / plastic bridge cable is increasingly urgent.At present,the high carbon(hypereutectoid carbon content)alloy steel used for high strength / plastic bridge cables is processed by sorbite heat treatment combined with drawing deformation.The production process is complex and the cost is high.In this paper,the idea of controlling the transformation process of steel to form bunchy bainite structure is introduced into the research of high strength/ plastic bridge cable,which provides theoretical support for the development of new processing technology of high strength / plastic bridge cable.In this paper,the effects of both heating oxidation and austenitizing at high temperature and then austempering on the microstructure and mechanical properties of a hypoeutectoid carbon structural steel with higher carbon content(Fe-0.71C-0.13Si-0.43Mn-0.08Cr)were studied,especially the formation characteristics of bunchy bainite structure and its influence on mechanical properties.The results show that the experimental steel is in a relatively slow oxidation state under the condition of heating at 900-930? and holding time less than 15 min,the oxide scale is thin and easily to be removed by pickling.After austenitizing at 930? and then austempering at280? for 10 min,the microstructure mainly consists of fine bunchy bainite,the tensile strength and elongation of the sample without surface oxide scale can reach 1953 MPa and 24.52%,respectively,while that of the sample with surface oxide scale can reach 1764 MPa and 16.26%,respectively,it still has high strength and plasticity.The fine microstructure observation results show that the bainitic ferrite strips composed of fine bunchy bainite consist of a series of subunits with the width of nanometer scale,and the internal crystal defect is dislocation entanglement which is characteristic of martensite like transformation.The process of austenitization of 930? and then short isothermal time at austempering temperature in the air used in hypoeutectoid carbon structural steel with higher carbon content has outstanding engineering application value in the development of new processing technology for the bridge cable with high strength / plasticity.