Controlled cold rolling effect on microstructure and mechanical properties of Ce-modified SAF 2507 super duplex stainless steel

Abstract

Controlled cold rolling impacts on microstructure and mechanical properties of the rare earth Ce-modified SAF 2507 super duplex stainless steel (SDSS) are investigated towards a better application and development prospective over the pristine SDSS. Rolling was performed at room temperature with the deformation level in a range of 30% -90%. A large amount of dislocations into the ferrite phase turned out, and their density increased with the deformation. While, emergence of dislocation plugs group, ferrite grains get refined to nanometer scale during the deformation process. In addition to deformed bands within austenite, formation of α′-martensitic phases and significant increment in their volume fraction are detected and attributed to deformation-induced martensitic transformation. Elongation of the ferrite and austenite microstructures along the deformation direction under the action of high strain also resulted in fibers formation gradually. Correspondingly, significant increase in the strength index while decrement in the plasticity index are observed. Moreover, cold rolling deformation not only affects the tensile fracture morphology but also switches it from a typical ductile to a ductile and quasi-cleavage mixed fracture.

Microstructural Evolution Induced Mechanical Property Enhancement in Cryogenically Rolled Ce‐Modified SAF2507 Super Duplex Stainless Steel

“…Compared to a scarcely reported cold rolling of SAF2507 (Zhou et al [12] ), the cryogenic deformation of the SDSS has not been reported in literature to the best of our knowledge. Aiming to a cost-effective processing and superior thermal processing performances, Ce-modified SAF2507 SDSS (Ce-SAF2507) with an increased N content is selected in the present study.…”

“…Furthermore, comparison of strain analysis for cold (Zhou et al [ 12 ] ) and cryogenically rolled Ce‐SAF2507 shows similar trends, i.e., increase in strain with the deformation level. However, it is important to note that the strain accumulation of ferrite is lower (20 × 10 −4 ) than that of the room‐temperature cold rolling (52 × 10 −4 ), which is rather intriguing.…”

“…Cryogenic rolling has been found superior in deformation‐induced martensitic transformation over the cold‐rolling at room temperature. Previous studies (Zhou et al [ 12 ] ) shows the martensitic transformation rate reached only 71.3% under 90% deformation at room temperature. However, cryogenic rolling can reduce austenite to less than 10% leading to higher martensite volume fraction and significantly improves the strength and hardness to meet higher industrial production needs.…”

“…Furthermore, the extent of martensitic transformation was found significantly lower than in the metastable austenite stainless steel. The Ce‐modified SAF2507 was cold‐rolled in a latest work of Zhou et al [ 12 ] . Along with the formation of strain‐induced martensite phase, increase in the strength index and decrease in the plasticity index were observed.…”

Impacts of Stress Relief Treatments on Microstructure, Mechanical and Corrosion Properties of Metal Active-Gas Welding Joint of 2205 Duplex Stainless Steel

“…This is because ferrite’s stacking fault energy is higher than austenite’s. In the process of surface plastic deformation, a large number of dislocations are more likely to form in ferrite, resulting in dislocation proliferation and entanglement [ 30 , 31 ]. Dislocation densities of ferrite and austenite were lower in specimen 4 than in specimen 1.…”