Prevention of weld metal hydrogen cracking in high-strength multipass welds

Welding modern high-strength steel with low carbon and impurity contents, preheat may be dictated by cracking sensitivity of the weld metal instead of the HAZ. Standard EN 1011 does not provide the user with any unified methodology for the calculation of safe preheat for weld metal. The few calculation formulae that apply to multipass welds can give greatly varying predictions. This article studies controlling factors that govern transverse hydrogen cracking in high-strength multipass weld metal. The experiments comprised heavily restrained Y- and U-groove multipass cracking tests of SMAW and SAW welds. The objectives were the assessment of hydrogen cracking risk by defining the Crack — No Crack boundaries in terms of safe line description giving the desired lower-bound estimates, and to derive predictive equations capable of giving reliable estimates of the required preheat/interpass temperature T ₀/T _i for the avoidance of cracking. Equations were derived to assess the weld critical hydrogen content H _cr corresponding to the Crack — No Crack conditions as a function of either weld metal P _cm, yield strength R _p0.2 or maximum hardness HV _5(max). For the calculation of safe T ₀/T _i estimates, a formula incorporating weld metal strength as linear functions of either CET or weld HV _5(max), weld build-up thickness a _w in the form of tanh expression and weld diffusible hydrogen H _d in terms of combined [In / powerlaw] expression, was found descriptive.