Effect of grain refinement on tensile properties in Fe-25Cr-1N alloy

Nickel-free austenitic stainless steel (Fe-25Cr-1N) was produced by solution nitriding, and then the grain size was variously controlled by the two-step phase transformation method. Mechanical property of the steel with different grain size was investigated by means of tensile testing to clarify the effect of grain size on the strength, elongation and fracture surface. The as-solution-nitrided material with a coarse grain size caused brittle intergranular fracture on the way of uniform deformation before the onset of local necking deformation. As a result of grain refinement, intergranular fracture was markedly suppressed, and this leads to the enlargement of elongation as well as increase in yield strength and tensile strength. The suppression mechanism of intergranular fracture was discussed on the basis of dislocation pile-up model together with the experimental results of TEM observation for dislocation substructure in tensile-deformed materials. It was then concluded that the stress concentration at grain boundary is reduced by grain refinement, and this contributed to the suppression of intergranular fracture and enlargement of elongation in the grain-refined material