Effect of Hydrogen Content on Cold Crack Susceptibility of Various Steels with the Implant Test

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Susceptibilities of various plain carbon steels and alloy steels to cold crack are estimated by the implant test. Furthermore, fractographic investigation is also made on fracture surfaces obtained by the implant test. Main conclusions are as follows: (1) Increase in applied stress decreases an area of intergranular fracture mode in HY130, 1<1/4>Cr-1/2Mo and 2<1/4>Cr-1Mo steels. (2) In weldable high strength and low carbon alloy steels nearly linear relations between lower critical stress and maximum hardness of HAZ are obtained in each hydrogen content but results are rather scattering. (3) Being estimated by an "embrittlement index I" (I=NTS-LCS/NTS), susceptibility of alloy steels to cold crack is increased according to a following order ; 3.5% Ni<SM50<9% Ni<2<1/4>Cr-1Mo<1<1/4>Cr-1/2Mo<HT80<HY130<SCM4≒SNCM8 steel. (4) Based on results in this study, the authors propose a following formula for a estimation of lower critical stress affected by hydrogen embrittlement in weldable high strength steels such as SM50, HT60, HT80 and HY130 and low carbon alloy steels such as 3.5% Ni, 9% Ni, 1<1/4>Cr-1/2Mo and 2<1/4>Cr-1Mo steels, which is determined by a regression analysis. σ_cr=-268P_<CM>-23.3logH_<JIS>+138 (heat input ; 17kJ/cm, without preheating)
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