Influence of cooling rate on hot ductility of C-Mn-Al and C-Mn-Nb-Al steels

Tensile samples were cast in situ and cooled to test temperatures in the range 760 to 1100 degrees C, at cooling rates of 25, 60, and 200 K min(-1). In all cases, increasing the cooling rate to that undergone during thin slab casting caused the ductility to deteriorate. For C-Mn-Al steels this deterioration resulted from both a finer AlN precipitation as well as a finer dispersion of sulphides. In the case of C-Mn-Nb-Al steels, the inferior ductility arose because increasing the cooling rate caused more Nb to be held in solution before testing so that more of the detrimental strain induced Nb(CN) precipitation could occur during the test.