EDGE CRACKING IN HOT-ROLLED COILS OF SEMI-KILLED STEELS

Various processing parameters leading to edge cracking in hot-rolled c oils are described, along with a study of the effect of these paramete rs on the occurrence of edge cracking during commercial production of semi-killed hot-rolled coils, High-temperature tensile testing reveale d that ductility decreased with a decrease in test temperature from 85 0 to 750 degrees C and improved with a further drop in temperature, Th is phenomenon is attributed to the closed-packed structure of single-p hase austenite at higher temperatures, which transforms to ferrite + a ustenite at the intermediate temperature range, Edge cracking was freq uently observed in hot-rolled coils that were finish rolled within thi s intermediate temperature range, Optical microscopy revealed large fe rrite grains near edges of the coil as well as at inner surfaces of cr acks caused by decarburization at higher temperatures, A minimum manga nese/sulfur ratio of 12 to 8 for a sulfur level of 0.03 to 0.04 %, pro per teeming practice, adequate soaking, and a finish rolling temperatu re above 875 degrees C resulted in overall improvement in the edge qua lity of hot-rolled coils.