Effect Of Cr Element On The Transformation Structure And Performance Of Pearlite

High carbon pearlite steel wire has high strength and excellent toughness,and is widely used in major fields such as bridge suspension cables,vehicle tires and large buildings.Microalloyed high-carbon hot-rolled wire rod is the raw material for the production of ultra-high-strength pearlitic steel wire,and its structure has an important influence on the control of the final structure and performance of the steel wire.In this paper,two Fe-C-Mn-Si quaternary alloy systems containing Cr and Cr free are the research objects,and the effect of Cr element on the structure and properties of pearlite transformation under different austenitization states and eutectoid transformation conditions is studied.And analyze the distribution behavior and interaction of alloying elements in Fe₃C and-Fe two phases.The study found that during the eutectoid transformation process,the pearlite isothermal transformation kinetics curve is S-shaped.As the transformation time increases,the pearlite transformation rate first increases and then decreases;as the isothermal transition temperature decreases,the lamella spacing and pellet size of pearlite are reduced;and the finer the pearlite lamella spacing,the smaller the pellet size,which is conducive to the improvement of material strength and plasticity.The Cr element can significantly delay the phase transformation process of pearlite,reduce the transformation temperature,and refine the pearlite lamella spacing;the addition of Cr element can reduce the transformation speed,narrow the transformation temperature range,and improve the uniformity of the transformation structure,and increase its strength and plasticity.In the pearlite transformation,Cr is mainly concentrated in the cementite phase,and its solubility in the ferrite phase is negligible;Mn is distributed in both cementite/ferrite phases,but Mn element tends to be enriched in cementite,and as the transformation temperature increases,the degree of enrichment of Mn in the cementite phase continues to increase;the addition of Cr element can hinder the enrichment of Mn in the cementite phase.When the transformation temperature increases,this hindering effect is continuously enhanced;while the Si element is mainly concentrated in the ferrite phase and is basically insoluble in the cementite phase,and its distribution behavior is hardly affected by the Cr element and the transformation temperature.In the austenitizing transformation of pearlitic steel,low heating temperature and short holding time will increase the volume fraction of degraded pearlite structure formed by isothermal transformation,which will significantly reduce the strength of the material;since the carbides formed by the element Cr are difficult to dissolve,under the condition of short-term austenitization at low temperature,the Cr-containing steel has a greater tendency to form short flake or granular pearlite;increasing the austenitization temperature can reduce the pearlite lamella spacing,while the austenitizing holding time has almost no effect on the pearlite lamella spacing;while the austenitizing temperature and Cr element have no significant effect on the elongation,and the elongation is maintained at about 5%-6%;the best austenitizing temperature for Cr-free steel is 1050℃,and the best austenitizing temperature for Cr-containing steel is 1000℃.