Microstructural Evolution and Mechanical Properties of Ultrafine/nano Structured AISI 321 Stainless Steel Produced by Thermo mechanical Processing

The mechanical properties and microstructural developments of 321 stainless steel during thermomechanicalprocess were investigated. The repetitive cold rolling and subsequent annealing wereconducted to achieve nanocrystalline structure in an AISI 321 stainless steel. Heavily cold rolling at−20°C was conducted to form martensite in metastable austenitic steel. The process was followed byannealing treatment at 700–850 °C for 0.5–30 min. The effects of process parameters such as “reductionpercentage”, “annealing temperature”, and “annealing time” on the microstructural development werealso investigated. Microstructural evolutions were conducted using feritscope, X ray diffraction andscanning electron microscope (SEM). The mechanical properties were determined by hardness (Vickersmethod) and tensile test. The results indicated that more thickness reduction made more martensiteformation, leading to the rise of hardness. In addition, mechanical evaluations after heat treatmentsrevealed that decreasing austenite grain size to 0.7 μm resulted in hardness and strength increment byadapting Hall Petch equation.