Maraging steels with 18wt%Ni and 10wt%Co are precipitation hardenable steels selected for special applications. These steels are quenched and aged in the 480 - 600ºC range. Ti and Mo are added to precipitate during aging as fine Ni3(Ti,Mo) and Fe2Mo particles. Aging at high temperatures causes overaging due to coarsening of particles and austenite formation. SAE 4340 is a typical low alloy medium carbon steel for quenching and tempering. The best combination of mechanical properties is attained by quenching and tempering in the 650 - 670ºC range. These two steels are selected for services where an optimum combination of mechanical strength, toughness and fatigue resistance is required. In this work, the austenitizing temperature in the quenching treatment was varied in order to evaluate the effects on microstructure and mechanical properties of both steels. The results showed that the effect of previous austenite grain size on the toughness was different in the two steels analyzed.
Keywords:
maraging 300 steel; SAE 4340 steel; quenching and tempering; previous austenite grain size
