Ferrite decomposition in austenitic stainless steel weld metals

AbstractResidual ferrite decomposition in several common austenitic stainless steel weld metals, with or without molybdenum additions, has been investigated. It is shown that ferrite decomposes in α and chromium rich α′ phase at temperatures below about 490°C, whereas it transforms to σ at temperatures above 540°C. At temperatures between 490 and 540°C, α + α′ and α + σ transformations occur simultaneously. These transformations are accompanied by precipitation of carbides and in molybdenum bearing alloys by Mo containing phases such as R. Using the LSW (Lifshitz, Slyozov, Wagner) theory of diffusion controlled coarsening, the apparent activation energy for α → α + α′ decomposition is estimated (Q = 67 kJ mol−1) and a general equation giving the particle size of α′ as a function of aging time and temperature is derived. This equation is used to predict the kinetics of embrittlement owing to α + α′ decomposition at low temperatures.