Abstract
Eighty percent heavy cold thickness reduction and reversion transformation in the temperature range 700–950 °C for 60 s were performed to obtain the reverted ultrafine-grained (UFG) structure in 304 austenitic stainless steel. Through mechanical property experiments and transmission electron microscopy (TEM) of micro deformation of the UFG austenite structure, the tensile fractographs showed that for specimens annealed at 700–950 °C, the most frequent dimple sizes were approximately 0.1–0.3 μm and 1–1.5 μm. With the increase in annealing temperature, the dimple size distribution of nano-sized grains turned to micron-size. TEM micro deformation experiments showed that specimens annealed at 700 °C tended to crack quickly. In the grain annealed at 870 °C, partial dislocations were irregularly separated in the crystal or piled up normal to the grain boundaries; stacking faults were blocked by grain boundaries of small grains; twins held back the glide of the dislocations. In the grain annealed at 950 °C, the deformation twins were perpendicular to ε martensite. Fine grain was considered a strengthening phase in the UFG structure and difficult to break.
Highlights
Austenitic stainless steel (ASS) with its enhanced yield strength, high work hardening property, excellent weldability, and improved corrosion resistance has been put to use in many fields such as engineering applications and in everyday utensils [1,2,3]
It was found that the specimen annealed at 700 ◦ C during the micro deformation experiment tended to crack quickly. This may be attributed to the combined effect of the low ductility of the UFG and the existence of martensite
Nano-sized grains grew to micron-sized grains and the strengths decreased, while the elongation and average size of the dimples increased
Summary
Austenitic stainless steel (ASS) with its enhanced yield strength, high work hardening property, excellent weldability, and improved corrosion resistance has been put to use in many fields such as engineering applications and in everyday utensils [1,2,3]. The combination of high strength and high ductility in ultrafine-grained (UFG) structured ASS were achieved via operating severe deformation and reversion annealing treatment [4,5]. There are numerous recent papers discussing the deformation mechanisms in UFG steels from the microscopic or macroscopic view using conventional tensile testing and nanoindentation with TEM examination [4,5,6]. The ductile fracture of material consists of void nucleation and growth, which are governed by the motion of dislocations. A careful analysis of UFG of the fracture feature morphologies and the relation to the mechanical properties has been made in the ASS. TEM micro deformation tensile test of ASS with UFG structure deformation experiments were conducted to discuss the state of deformation mechanisms and fracture mechanisms
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