Grain refinement effect on cryogenic tensile ductility in a Fe–Mn–C twinning-induced plasticity steel

Cryogenic mechanical properties of twinning-induced plasticity steels of various grain sizes were investigated by the tensile tests. Specimens with coarse grain sizes, e.g. 10, 23 and 37 μm, showed a brittle fracture at 123 K. The embrittlement was suppressed by a grain refinement to 3.5 μm by cold rolling and recrystallization. Furthermore, a grain refinement to 460 nm by warm caliber rolling suppressed the embrittlement more effectively compared with the grain refinement via cold rolling and recrystallization treatment. The grain refinements improved the tensile elongation, yield strength, and ultimate tensile strength significantly at 123 K. It was found that the suppression of the embrittlement was caused by the reductions in the amount of ε-martensite.