Some effects of heat treatment on grain boundary chemistry and precipitation in type 316 steel

Abstract

The effects of solution treatment temperature and cooling rate, carbon content, and aging at 600°C on the precipitation and grain boundary composition of AISI type 316 stainless steel were investigated. No matrix precipitation was observed even in a high carbon cast aged for 1000 h. Carbides of M₂₃C₆ type were the only precipitates observed and these formed on grain boundaries. Nucleation of a second phase in these solution treated specimens was difficult, despite the carbon supersaturation. The grain boundary regions were investigated using high spatial resolution X-ray analysis to show that chromium depleted and nickel enriched zones formed when grain boundary carbides occurred. The behaviour of molybdenum was more complex; it segregated strongly to grain boundaries either during a slow cool from the solution treatment temperature or during aging, but was also incorporated into any carbides that formed.

MST/890