EFFECTIVENESS OF HOT TENSILE TEST IN SIMULATING STRAIGHTENING IN CONTINUOUS-CASTING

The extent to which the hot tensile test can be used to assess the relationship of steel composition to the incidence of transverse cracking in continuous casting has been examined. The influence of S, Ca, Ti, and Nb on the hot ductility of C-Mn-Al steels was investigated for the temperature range 700-1100-degrees-C and the results were compared with available commercial data on the effect of these elements on transverse cracking. Three different heat treatments that were carried out before straining have been examined: (i) reheating hot rolled plate to 1330-degrees-C; (ii) in situ casting of tensile samples; and (iii) as for (ii) followed by reheating to 1330-degrees-C. After these treatments, the samples were cooled directly to test temperature at a cooling rate of 100 K min-1 and strained to failure at a strain rate of 2 x 10(-3) s-1. All heat treatments showed that Nb gave the worst ductility in accordance with its known propensity to favour transverse cracking. Reheating hot rolled plate was found to be the simplest and most successful method for examining the influence of the microalloying additions Al and Nb (and probably V) on ductility in relation to the transverse cracking problem. Although in situ casting is a difficult technique and tends to suppress the relative changes in ductility with composition, it is the only method that can be used to assess the influence of elements such as Ti and S which do not return or dissolve fully into solution on reheating. The hot ductility curves are discussed in relation to the precipitation and grain sizes generated by the various treatments.