Formability eva‎luation and comparison of fine- and coarse-grained AISI 304 stainless steel

7/17/2023 12:00:00 AM

In this investigation, the effect of grain size on the formability of 304 austenitic stainless steel was studied. Thermomechanical processing (cold rolling and annealing) was used to create two different grain sizes. For this purpose, a 73% thickness reduction was applied to the as-received 304 stainless steel sheet followed by annealing at two temperatures of 1000 and 750 °C to achieve fine- and coarse-grained structures, respectively. The sample annealed at 750 °C for 90 min (with an average grain size of 1.9 μm) was used as the fine-grained sample and the sample annealed at 1000 °C for 90 min (with an average grain size of 35.5 μm) was used as the coarse-grained sample. Optical and scanning electron microscopy were used for the microstructural characterization. XRD measurements were performed on the specimens for phase identification. In order to investigate the formability, the tensile tests were performed in three directions of 0, 45 and 90 degrees to the rolling direction. The yield strength of as-received, fine-grained, and coarse-grained specimens was obtained 405, 305 and 733 MPa, respectively. So, the yield strength of the fine-grained specimen was almost twice that of the as-received specimen. But the total elongation decreased from 73% to 52%. Three different work hardening stage was observed for both fine- and coarse-grained specimens: 1- a sharp drop until reaching a minimum value, 2- a subsequent increase until reaching a maximum value, and 3- a decrease until the beginning of necking. The work-hardening rate of the coarse-grained specimen was higher than that of the fine-grained specimen, due to the higher transformation of austenite to martensite in the coarse-grained sample. In fact, with the grain refinement of austenite, its stability increases and the rate of transformation of austenite to martensite decreases. Also the uniform plastic strain and normal anisotropy coefficient (r) of the coarse-grained specimen were higher than that of the fine-grained specimen. This indicated that the formability of the coarse-grained specimen was better than that of the fine-grained specimen.

فولاد زنگ‌نزن آستنيتي 304 , عمليات ترمومكانيكي , كارسختي , خواص كششي , ناهمسانگردي , اندازه دانه

304 Austenitic Stainless Steel , Thermomechanical Processing , Work hardening , Tensile properties , Anisotropy , Grain Size

Saeedeh Afshar

Dr. Hossein Arabi, Dr. Bagher Mohammad Sadeghi