Structural stability of dissimilar weld joints of steel P91

Abstract

The present paper addresses the issue of carbon and nitrogen redistribution in weld joints between creep resistant chromium steels. The redistribution of carbon and nitrogen was measured using the wave dispersive X-ray method. The conditions of the long term diffusion annealing process were: temperature 575, 625, and 700°C; and time 10, 100, 1000, and 5000 h. It was ascertained that carbon and nitrogen diffused from the low alloy steels to the high alloy steel P91. The carbon diffusion coefficients in the individual steels in 15128/P91 and SK3STC/P91 weld joints, the ratio between the thermodynamic activity coefficients of carbon in the joints, the diffusion interaction parameters β^Cr _C, and their temperature dependencies were estimated from carbon concentration curves. The present paper also contains a microstructure analysis of decarburised and carburised zones in the weld joints studied.