Effects of Ni and Cr contents on fatigue crack growth properties of SUS316-based stainless steels in high-pressure gaseous hydrogen

Abstract

Fatigue crack growth tests were carried out in high-pressure gaseous hydrogen at 90 MPa at room temperature for SUS316-based stainless steels containing different amounts of Ni and Cr, and the effects of these alloying elements on fatigue crack propagation were investigated. The fatigue crack growth rate of the SUS316-based steels with a Ni content lower than 12 mass% was accelerated in hydrogen gas with decreasing Ni content. The Cr content had little effect on the fatigue crack growth rate in hydrogen gas. The combined effect of the Ni and Cr contents on the fatigue crack growth rate was closely related to Md30 and a modified Ni equivalent, [Ni]+0.37[Cr], where [Ni] and [Cr] are the Ni and Cr contents, respectively. The fatigue crack growth rate in the second region in the da/dN-δK relationship for SUS316-based stainless steels can be estimated with the Paris equation, da/dN = C (δK) m, and C = 8 10 -11 exp (0.0235 Md30) in steels with Md30 < -95°C. No clear degradation ascribable to high pressure hydrogen gas was observed in steels with Md30 < -95°C or [Ni]+0.37[Cr] ≥ 17.5 mass%. Fatigue cracks propagated mainly in the γ phase, and the α deformation induced martensite phase sometimes became the crack propagation path in tested steels with low γ phase stability. Faceted fracture surfaces consisting of the {111}γ plane and α ? martensite were observed at the fatigue fracture surfaces and considered to be formed as a result of hydrogen gas embrittlement at or near the interphase boundaries between the two phases, where the hydrogen concentration was considered to be high. © 2012 ISIJ.