Effect of Cr/Mn segregation on pearlite—martensite banded structure of high carbon bearing steel

Abstract

The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling. With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed. The formation causes of an abnormal banded structure and the elimination methods were analyzed. Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet. Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200°C, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased. Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate. This distinct white band is composed of martensitic phases. The formation of this abnormal pearlite—martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements. Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.