RAPID SOLIDIFICATION OF 17-7-PH STAINLESS-STEEL - HEAT-TREATMENT RESPONSE

Commercial grade 17-7 PH stainless steel has been rapidly solidified ( RS) by chill block melt spinning to result in an improvement in Vicker s microhardness by 88 per cent, refinement in grain size by a factor o f 9 and a significant suppression in delta-ferrite and carbide phases as compared to conventionally processed (CP) 17-7 PH steel. In order t o study heat treatment response three different routes of hardening he at treatments were applied to RS 17-7 PH steel ribbons. These were (i) direct isochronal ageing, (ii) conventional double hardening treatmen t and (iii) direct conditioning coupled with isochronal ageing. Conven tionally peak aged (PA) melt spun ribbons were found to be (a) 46 per cent harder than CP 17-7 PH steel after identical heat treatment and ( 6) 43 per cent harder than direct isochronally PA (at 973 degrees K) r ibbons. Direct isochronally PA 17-7 PH steel ribbons showed a precipit ation of M(23)C(16) predominantly at grain boundaries with a plate lik e morphology (plates 140 to 300 nm long and 70 to 140 nm wide).