DEVELOPMENT OF DUAL-PHASE STEELS FROM PLAIN CARBON SHEET STEELS

An attempt has been made to develop dual-phase (d-p) steels from cold- rolled plain carbon sheet steels. Three plain carbon sheet steels with carbon content of 0.075, 0.095 and 0.2 wt.% have been selected. Inter critical heat treatments at 740 degrees C and holding times of 0.5, 1, 1.5, 2, 3, 4, 5, 8, 10, 15, and 30 minutes at this temperature follow ed by fast water quenching were used. A good combination of strength a nd ductility of d-p steels has been observed for the heat treatment cy cle of 740 degrees C for 1.5 minutes and WQ. D-p steel with 0.075 wt.% carbon has shown an ultimate tensile strength of 560 MPa and a ductil ity (uniform elongation) of 16% whereas the starting material i.e. pla in carbon cold rolled sheet steel, has a UTS of 382 MPa and a ductilit y of 5.5%. Similar improvements have been observed for other steels. T hese improvements in the mechanical properties are explained on the ba sis of the cold work energy and the kinetics of austenitisation during intercritical annealing.