The effect of phase transformation in the plastic zone on the hydrogen-assisted fatigue crack growth of 301 stainless steel

The effects of rolling and stress ratio (R) on the fatigue crack growth rates (FCGRs) of AISI 301 stainless steel (SS) in gaseous hydrogen were investigated. Accelerated fatigue crack growth occurred for the solution-annealed (SA) and cold rolled (CR) specimens tested in gaseous hydrogen, and especially for the CR specimen at high R. Moreover, a sufficiently high ΔK and/or Kmax were required to activate hydrogen-assisted fatigue crack growth of the 301 SS. Fatigue crack growth within a narrow α′ martensite layer was responsible for the rapid FCGRs of the specimens in hydrogen. The plastic zone size, identified by hardness distributions, was much larger than the region that underwent phase transformation.