Dual roles of pearlite microstructure to interfere/facilitate gaseous hydrogen-assisted fatigue crack growth in plain carbon steels

Fatigue crack growth of two carbon steels with different pearlite volume fractions were studied in pressurized gaseous hydrogen environment. Notably, pearlite was found to mitigate hydrogen-assisted fatigue crack acceleration. This positive impact of pearlite was ascribed to ferrite/cementite lamellar aligned perpendicularly to the cracking direction, which functioned as barriers to intermittently arrest the crack propagation. Meanwhile, brittle delamination fracture ensued in the pearlite lamellar lying parallel to the crack-plane increased the crack growth rate and compromised the above positive effect to some extent. The material behavior is rationalized in light of fractographical observations and microstructural analyses of the crack-wake.

Automated summary

This study investigates the fatigue crack growth behavior of two carbon steels with different pearlite volume fractions in a pressurized gaseous hydrogen environment. The results show that pearlite can mitigate the accelerated crack growth caused by hydrogen. This is mainly attributed to the perpendicular alignment of ferrite/cementite lamellar in pearlite to the cracking direction, which acts as barriers to intermittently arrest crack propagation. However, the presence of pearlite lamellar parallel to the crack-plane leads to brittle delamination fracture, increasing the crack growth rate and compromising the mitigating effect of pearlite.