Carbon redistribution during long-term operation of weld joints of creep-resisting chrome steels

The paper deals with C and N redistribution in weld joints of creep-resisti ng chrome steels. The C and N redistribution were measured by means of wave -disperse X-ray method. The condition of long-term diffusion annealing were realised as follows: temperature 575, 625 and 700 degrees C; time 10, 100, 1000 and 5000 hours. It was estimated that C and N diffused from the low a lloy steels to the high alloy steel P91. The errors of the measured nitroge n concentration curves were so high that the quantitative evaluation of nit rogen concentration curves was impossible. The carbon diffusion coefficient s in individual steels of 15128/P91 and SK3STC/P91 weld joints, the ratio b etween thermodynamic activity coefficients of carbon in joints, diffusion i nteraction parameters beta(C)(Cr), and their temperature dependences have b een estimated from the measured carbon concentration curves.