1994 Volume 34 Issue 6 Pages 528-535
The metallurgical structure and hot ductility of continuous casting steels mainly depends on temperature history after solidification. The usual hot ductility tests do not reproduce the actual temperature path of continuous casting steels during current production processes because the deformation is achieved on tensile specimens reheated from room temperature. A laboratory hot tensile test on in situ solidified sample 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. The tensile test is then achieved at the required temperature after a rate controlled cooling. In comparison with other tests, the notched specimens offer a great interest in producing very depressive hydrostatic stress, significant triaxiality and so, favouring microvoid growth and coalescence. The late step being quickly reached when the specimen notched zone has a poor ductility.
Experiments in the range of 700 to 1100°C are achieved on a set of C-Mn steels and Nb-V microalloyed steels to establish influence of the temperature path on hot ductility. The results show some significant differences on the ductility curves between tests performed on in situ solidified specimens. It is found that the differences are mainly related to segregation distribution, austenite grain size, ferrite formation kinetics and dynamic precipitation of niobium/vanadium carbonitrides.
