Kinetics and mechanism of grain growth during welding in niobium-stabilized 17% chromium stainless steels

Stabilized 17% chromium stainless steels have adequate corrosion resistance in numerous industrial environments. Their use as materials of construction has been limited by their poor toughness, notably in the heat-affected zone. This embrittlement has been attributed to the large grain size as well as the accompanying grain-boundary precipitates. The present study was undertaken to determine the kinetics of grain growth in the heat-affected zone. Using relatively simple models to describe the grain-growth process, the kinetic parameters were estimated, which allowed a mechanism for grain growth in this material to be proposed. It was found that the poor toughness could not be attributed to coarse grain size alone, but was also related to the cooling rate after welding. The embrittlement is caused by dispersion hardening through minute niobium carbonitrides which occur in the heat-affected zone close to the fusion boundary.