Influence of Weld Heat Inputs on Reheat Cracking Sensitivity of Coarse-grained Heat Affected Zones in 2.25Cr1MoV Steel

Abstract

Reheat cracks have been detected many times in the welding coarse-grained heat affected zones(CGHAZ) of 2.25Cr1MoV reactor, but seldom been discovered after Y-groove reheat cracking test. Considering the difference of heat inputs between the two, the influence of weld heat inputs on reheat cracking sensitivity of CGHAZ in vanadium-modified 2.25Cr1Mo are studied by mean of Gleeble thermal simulation. Effect of heat inputs on microstructural, hardness, and high temperature ductility are discussed by microstructural observation, hardness test and fractographic analysis. The results show that the reheat cracking sensitivity of CGHAZ increases with increasing heat inputs within the range of 5~100 k J/cm. CGHAZ with heat input of 35 k J/cm is considered "highly susceptible" to reheat cracking at 675 ℃. The reheat cracking sensitivity is mitigated effectively by heat inputs limited to 25 k J/cm. The comprehensive analysis reveals that the high temperature ductility of the simulated CGHAZ is closely related to the hardness change after high temperature tensile test. Relatively high reduction of area(Ro A) is observed corresponds to softening phenomena, along with a mixed fracture mode of transgranular and intergranular. While the ductility of CGHAZ degraded obviously when second hardening occurs, along with a uniform fracture mode of intergranular microvoid coalescence.