THERM`.. - MECHANICAL TREATMENT OF MARAGING STEELS

Abstract

In the present investigation thermo-mechanical treatment comprised of marforming i.e., cold working in the martensftic condition followed by maraging at 450 and 520°G respectively. It was observed that with increase of prior deformation i.e., upto 47 per cent reduction the hardness peak shifts towards lesser aging per-iod. The variation of hardness with aging time for any fixed aging temperature shows a maxima, which shifts towards lesser aging period, when temperature is increased. For any constant aging period the hardness of Fe'.l8Ni and Pe-19Ni maraging steels increases linearly with increase of prior cold deformation. However, for Fe-25Ni steel there is discontinuity in this linearity at about 8 per cent deformation. This is related to the different degree of work hardening of the martensite and the retained austenite in conjunction with the precipitation.- It is striking to note that the absence of maraging does not reveal this subtle hardening difference