TEM And HRTEM Characterization Of 304&316l Stainless Steel With Nano And Microcrystalline Dual Phase

The 304,316L-stainless steel with nano/micro-crystalline structure were prepared by an aluminothermic reaction method.The material was about 120 mm in diameter and 15 mm in thickness.the microstructural evolution of the stainless steel was studied after rolled by considering different thickness reduction followed by annealing for different time.By analyzing the nanocrystalline austenite grain size and its volume fraction and grain size.The mechanism of microstructure evolution is raised in accordance with the research results.1.After rolling 304 stainless steel at 1000°c with thickness reduction of 40% and then rolled with different thickness reduction 40%,60%and 80% at 700°c,when the thickness reduction is less than or equal 60% the nanocrystalline phase increasing with the increase of the thickness reduction.When rolled with thickness reduction 80% most of nanograins was converted to submicron grains and microcrystalline grains.The volume fraction of nanocrystalline after rolled with 40%,60% and 80% was 21.7%,30.4and 8.9 % and the volume fraction of submicron crystalline was 18.7%,24.7%and 32.2% respectively.2.304 stainless steel after rolled at 1000°c with thickness reduction 40% then rolled at 700°c with thickness reduction 40% and then followed by annealing for 1h and 8h the result shows that by increasing the annealing time most of nanocrystalline was fade and the submicron-crystalline also was decreased.The volume fraction of nanocrystalline was 23.6% and 3.1% and the volume fraction of submicron crystalline was 27.2% and 24.7% respectively.In the case where the sample was rolled with thickness reduction 60% and then followed annealing for 1h the volume fraction of nanocrystalline and submicron crystalline was 7.3% and 38.6% respectively.3.The 316 L stainless steel processed by aluminum thermic reaction after being characterized by TEM and HRTEM the result shows that the cast steel contains micro and nanocrystal dual phase.after firstly rolled at 800°C 60%and then at 600°C with thickness reduction 75% the nanocrystalline grain grew up and appeared submicron grain,the average grain size of nanocrystalline after rolling was 25 nm and the average of submicron grain was 137 nm.4.The 316 Lstainleess steel after rolled and then followed by annealing for different time the nanocrystalline decreased with the decreasing of the annealing time however,the submicron crystalline was increased synchronously with the annealing time which is not the case at 40 min due to the broken of submicron grains to nanograin.HRTEM image shows the width of stacking faults inside the grain.