If I am not wrong primary reason behind this cracking is poor creep ductility to accomodate thermal strain, as a result disbondment occur at the grain boundary. stress induced/ stress relaxation/ stress relief/ creep embrittlement/ low creep ductility cracking etc. What I understand from this article that Cr-Mo-V is prone to Reheat Cracking during H.T or in-service below critical temperature range only.
I missed out this article earlier but finally I caught it. There are certain steels that are prone to reheat cracking: Reheat cracking from the bismuth addition are a form of liquid metal embrittlement. Moreover, the reheat cracks are typically found in the coarse-grained region of the heat affected zone (HAZ) of a weldment. The undesirable effects of introducing reheat cracks is of special concern because the nature of these micro cracks is that they may not be detected by routine nondestructive testing such as radiography. The PWHT practice cannot only introduce cracks that may go undetected but also degrade notch toughness thereby reducing the tolerance for cracks.PWHT have the desirable effect of out gassing hydrogen, but in certain steels, it may introduce reheat cracking and/or reduction in notch toughness.Sometimes the critical level of 20 Rockwell C is satisfactory. Hardness is sometimes used as an index of susceptibility to SCC. PWHT reduce the residual stresses which is important in controlling distortion, residual stresses also prevents the risk of SCC(Stress Corrosion Cracking).The Reheat Cracking is a potential issue with low alloys steel, the 300 series SS and super alloys such as Alloy 800H 2.
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