Hydrogen Embrittlement of Submicrocrystalline Ultra-Low Carbon Steel Produced by High-Pressure Torsion Straining

Abstract

The tensile property and hydrogen embrittlement (HE) behavior in the submicrocrystalline ultra-low carbon steel produced by HPT straining were investigated. Elongated grains with 300 nm thickness and 600 nm length with high dislocation density were formed by the HPT straining at a rotation-speed of 0.2 rpm under a compression pressure of 5 GPa. The engineering tensile strength of the HPT processed ultra-low carbon steel for > 5 turns was 1.9 GPa, which is similar to the value of maraging high-alloy steels. The elongation increased with strain (at 5 to 10 turns), is caused by the reduction of the stress concentration due to the existence of continuously recrystallized grains. HE occurred in the HPT processed specimen for 5 turns with high tensile strength of 1.9 GPa under hydrogen atmosphere. However, its HE was suppressed via recovery process by annealing at low temperature while maintaining the high strength.

Effect of Lattice Defects on Tribological Behavior for High Friction Coefficient under TCP Added PAO Lubrication in Nanostructured Steels

“…17) After the HPT process, low temperature annealing at 200°C for 1 h was performed to control the dislocation density in the sample while keeping the grain size. 18) The annealed sample was referred to as HPT + A.…”

Influence of Hydrogen on Local Mechanical Properties of Pure Fe with Different Dislocation Densities Investigated by Electrochemical Nanoindentation

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Hydrogen Embrittlement Mechanism of Ultrafine-grained Iron with Different Grain Sizes

“…It should be noted that HPT processing can produce ultrafine grains of less than 1 μm by applying a large amount of strain even for pure metals without contaminated by impurities. Mine et al 31) and Todaka et al 32) conducted tensile tests of HPT-processed Fe-0.01 mass% C after hydrogen charging and small punch tests of HPT-processed ultra-low carbon steel in a hydrogen environment, respectively, to investigate hydrogen-induced changes in their mechanical properties. While those results suggested that hydrogen embrittlement more likely occurs in the specimens with smaller grain sizes, the fracture mechanism has not been fully discussed, and thus the effect of grain boundaries on hydrogen embrittlement of iron is not clear yet.…”