Factors Causing Hydrogen Embrittlement of Cold-Drawn Pearlitic Steel Fractured Under Elastic/Plastic Region

Abstract

Factors causing hydrogen embrittlement of cold-drawn pearlitic steel fractured under plastic/elastic region have been investigated from the perspective of lattice defects. Tensile tests were conducted for hydrogen-charged specimens containing 1.5 and 4.0 mass ppm hydrogen to evaluate mechanical properties. The amount of tracer hydrogen, i.e., lattice defects in the specimens unloaded just before tensile fracture strength, was measured using a thermal desorption analysis. Specimens containing 1.5 and 4.0 mass ppm hydrogen fractured under plastic and elastic region, respectively. The specimen fractured under plastic region showed enhanced formation of lattice defects corresponding to vacancies, which directly caused embrittlement. In contrast, the specimen fractured under elastic region showed no enhancement to the formation of lattice defects. These results reveal that one of the factors causing hydrogen embrittlement under plastic region is due to hydrogen-enhanced strain-induced vacancies, whereas the factors causing hydrogen embrittlement under elastic region are due to others.