Internal corner-crack in continuous casting 40Cr billets produced by basic oxygen furnace-LF refinery-continuous casting from a factory was analyzed from processing procedure and continuous casting equipment as well as observing microstructure by hot hydrochloric acid

metallographic microscope

and electron probe-energy spectrum analysis.It is found that there is absent of abnormal microstructure and particle segregation around the defects.Solidification process of continuous casting mould was simulated by the Anysys software.The results show that the internal corner-crack is generated in the mould during solidification process

which is attributed to the formation of apparent hot spot zone at the off-corner of the billet resulted from unevern heat flow in the mould resulting in the formation of thermal stress.The defects are related with the composition of liquid steel

optimization of processing parameters as well as transition fillet.Through strictly controlling processing parameters and optimizing design of transition fillet on mould

the internal corner-crack less than 1.0 level is controlled to 89.68%.