C - Chemistry – Metallurgy – 21 – D
Patent
C - Chemistry, Metallurgy
21
D
148/47
C21D 1/30 (2006.01) C21D 3/06 (2006.01) C21D 9/50 (2006.01) C21D 11/00 (2006.01)
Patent
CA 1189427
ABSTRACT OF THE DISCLOSURE: A method for postweld heat treatment (hereinafter referred to as PWHT) for multilayer welding, in which the terminating point of the PWHT is judged correctly to pre- clude cracking due to insufficient treatment or uneco- nomical excessive treatment, the method comprising; determining the residual hydrogen concentration directly beneath the final welded layer immediately after comple- tion of welding; determining a crack-preventing critical hydrogen concentration to obtain a ratio of the critical hydrogen concentration to the residual hydrogen concen- tration; determining the value of a product of a hydrogen diffusivity coefficient during the heat treatment and a holding time where a hydrogen concentration currently occurring in the heat treatment reaches the critical hydrogen concentration, on the basis of the relation of a ratio of the current hydrogen concentration to the residual hydrogen concentration and a sum of a parameter of hydrogen diffusion to be determined depending upon the welding conditions and the above-mentioned product; measuring the temperature of the heat treatment at a suitable point of the weld; and terminating the heat treatment at a time point when a time-integrated value of a hydrogen diffusivity coefficient at the measured temperature exceeds the value of the above-mentioned product.
370283
Iwai Kenji
Takahashi Eiji
Kobe Steel Ltd.
Riches Mckenzie & Herbert Llp
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