IN-SITU SOLIDIFIED HOT TENSILE TEST AND HOT DUCTILITY OF SOME PLAIN CARBON-STEELS AND MICROALLOYED STEELS

The metallurgical structure and hot ductility of continuous casting st eels mainly depends on temperature history after solidification. The u sual hot ductility tests do not reproduce the actual temperature path of continuous casting steels during current production processes becau se the deformation is achieved on tensile specimens reheated from room temperature. A laboratory hot tensile test on in situ solidified samp le has been achieved to investigate the thermomechanical properties of steels directly after solidification, without a cooling step down to room temperature. The basic principle of this test consists in melting a sample of the studied steel to obtain a notched tensile specimen. T he tensile test is then achieved at the required temperature after a r ate controlled cooling. In comparison with other tests, the notched sp ecimens offer a great interest in producing very depressive hydrostati c stress, significant triaxiality and so, favouring microvoid growth a nd coalescence. The late step being quickly reached when the specimen notched zone has a poor ductility. Experiments in the range of 700 to 11 00-degrees-C are achieved on a set of C-Mn steels and Nb-V microall oyed steels to establish influence of the temperature path on hot duct ility. The results show some significant differences on the ductility curves between tests performed on reheated specimens and tests perform ed on in situ solidified specimens. It is found that the differences a re mainly related to segregation distribution, austenite grain size, f errite formation kinetics and dynamic precipitation of niobium/vanadiu m carbonitrides.