Structural changes in 12–2.25% Cr weldments – an experimental and theoretical approach

Abstract

In welds between low alloy and 12% Cr-steels, a depletion of carbon occurs in the material of lower carbon activity, the low alloy steel, during post weld heat treatment. A carbon depleted zone is formed along the fusion boundary. This zone consists of large ferritic grains and affects the creep strength of the material by promoting type IIIa cracking.In this work the absence of carbides in the carbon depleted zone is verified by transmission electron microscopy, and identified as the cause of the grain growth. A computer simulation of the diffusion processes with the DICTRA software shows good agreement with experimental microprobe carbon content measurements. The simulations could also predict the types of carbides appearing in the weld zone. Methods for reducing the carbon depletion by varying the weld and heat treatment parameters are identified.