PSI - Issue 54

Magdalena Eškinja et al. / Procedia Structural Integrity 54 (2024) 123–134 M. Eškinja et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 7. Permeation current as function of time for a) HMoS and b) LMoS.

3.5. Influence of double quenching and tempering (Q&T) on HE behaviour of high Mo steel High Mo steel showed lower diffusion coefficient and higher quantity of strong traps, what makes it ideal candidate for pipeline material. This steel has high strength and at the same time, as it was shown, it is susceptible to HE. Considering this fact, the strategy of changing microstructural features should be undertaken to improve HMoS steel and make it HE resistant. To decrease the strength of steel double quench and tempering procedure (Q&T) in case of HMoS was used, and results are graphically denoted in Figure 8. Change of heat treatment from single to double Q&T increased resistance of the steel to HE and improved mechanical performance exhibiting decrease of HE susceptibility to half of its starting value.