Strain Criterion of Reheat Cracking in 2.25Cr1Mo0.25V Steel

Coarse-grained heat-affected zone (CGHAZ) simulation specimens of 2.25Cr1Mo0.25V steel welded joint were prepared with different parameters, and the optimal thermal simulation parameters were determined by comparing hardness, grain size and microstructure with those of the actual joint CGHAZ. And then the CGHAZ specimen was simulated with the optimal parameters. The stress relaxation behavior of the specimen at 675℃ was studied, the reheat cracking process was analyzed, and the reheat cracking strain criterion was obtained. The results show that the optimal thermal simulation parameters were listed as follows:heat input of 30 kJ·cm^-1, preheating temperature of 200℃, heating rate of 1 000℃·s^-1, peak temperature of 1 320℃, time on peak temperature of 1 s. The microstructure of the obtained CGHAZ specimen consisted of lath bainite, with grain size of grade 4.5. The stress relaxation behaviors of CGHAZ specimen were similar under different initial stresses. The critical failure creep strains were all about 0.31%. The critical failure creep strain can be regarded as the reheat cracking strain criterion, and can be used to evaluate the post-welding heat treatment process of the steel as the creep strain demarcation point for characterizing the sensitivity of CGHAZ reheat crack.