Effects of accelerated cooling after rolling and of additions of Ni and Nb on the microstructure and mechanical behaviour of 0.1 wt% C steels

The study of the microstructure is necessary so as to investigate the effects of the parameters of interrupted accelerated cooling (IAC) on the mechanical behaviour of 0.1 wt % C, Ti or Nb + Ti microalloyed steels. The paper deals with larger variations of the cooling rate and of the finish cooling temperature than are usual in industrial practice. The work establishes : 1) the favourable effects of the highest cooling rate and for the Nb-free materials of a lower than usual finish cooling temperature, 2) the unsuitable character of a 0.4 wt% addition of Ni in, IAC samples and 3) the chief advantage of a 0.0015 wt% microaddition of Nb. The metallurgical origins of these results are detailed