The effects of thermal treatment on the austenitic grain size and mechanical properties of 18 Pct Ni maraging steels

Abstract

A technique has been developed for controlling the austenitic grain size of 18 pct Ni maraging steels by thermal treatment alone. This treatment has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7 in both cases. The process of grain size refinement requires thermal cycling from a temperature belowM _f to a temperature considerably above the austenitizing temperature. The minimum austenitic grain size attainable depends on the prior strain in the material as well as the thermal treatment. While significant grain size refinement can be attained by one cycle to the proper temperature, the attainment of the minimum uniform grain size requires several cycles. The effects of austenitic grain size on tensile properties have been investigated both at room temperature and at elevated temperatures. The prior austenitic grain size has a small but measurable effect on the mechanical behavior of aged material at room temperature. The austenitic grain size has a significant effect on the ultimate tensile strength at 1600°F.