Influence of chemistry and runout table parameters on hot coil collapse in C-Mn steels

The key metallurgical parameters affecting the incidence of coil collapse (soft slump) of C-Mn steels has been investigated using industrial data and laboratory simulation. Runout table (ROT) cooling/coiling simulations were performed on a Gleeble 1500D to study transformation before and during coiling of thin strip. For low C (< 0.07%) grades, coiling temperatures above 650 degrees C coupled with high nitrogen contents decreased the transformation end temperature Ar-1 and increased collapse. Coiling temperatures above the Ar-1 for ROT cooling increased both dilation and the time to complete transformation during coiling. These effects correlated with industrial conditions where a high frequency of coil collapse was observed.