15 Effect of Strain-Induced Martensite on Hydrogen Charged Trip Steel

The effects of strain-induced martensite were investigated on hydrogen charged TRIP sheet steel. Tensile samples were pre-strained 5% at -20 °C, 23 °C, and 102 °C to create three distinct microstructures with 10.5%, 5.5%, and 0.5% strain-induced martensite, respectively, and subsequently charged with low levels of hydrogen (1–2 ppm) and tested to failure at room temperature. Ductility loss was observed in all charged TRIP steel and martensite fracture was observed as the predominant microstructural damage. Untempered strain-induced martensite has been shown to be susceptible to hydrogen embrittlement; however, ductility loss did not scale accordingly with greater strain-induced martensite in charged microstructures. Plasticity was observed in hydrogen charged samples, indicating that an incubation time was required for hydrogen accumulation in martensite before fracture occurred.