Microstructure and mechanical properties of friction stir processed AISI 316L stainless steel

•FSP can be used to produce bulk ultrafine grained structures in AISI 316L SS.•The main mechanism for grain structure refinement of FSP 316L SS is DDRX.•However, some evidences of CDRX and SRX were also observed.•The material flow was found to be near simple shear deformation (A/A‾ and C).•FSP sampl...

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Bibliographic Details
Published in:Materials in engineering 2015-02, Vol.67, p.82-94
Main Authors: Hajian, M., Abdollah-zadeh, A., Rezaei-Nejad, S.S., Assadi, H., Hadavi, S.M.M., Chung, K., Shokouhimehr, M.
Format: Article
Language:English
Subjects:
Austenitic stainless steel
Austenitic stainless steels
Base metal
Friction stir processing
Grain refinement
Grain structure
Heat resistant steels
Mechanical properties
Microstructural characterization
Microstructure
Stainless steels
Surface layer
Texture
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Summary:•FSP can be used to produce bulk ultrafine grained structures in AISI 316L SS.•The main mechanism for grain structure refinement of FSP 316L SS is DDRX.•However, some evidences of CDRX and SRX were also observed.•The material flow was found to be near simple shear deformation (A/A‾ and C).•FSP samples have an enhanced hardness and strength compared with the base metal. Friction stir processing was used to refine the grain structure in 2mm thick AISI 316L stainless steel sheets, with a pinless tool, at a constant traverse speed of 63mm/min and relatively low rotational speeds of 200 and 315rpm. Depending on the processing conditions, the initial grain size of 14.8μm in the base metal was subsequently decreased to 0.8–2.2μm in the processed areas. The microstructural characterizations by orientation imaging and transmission electron microscopy revealed that the grain structure evolution in the stir zone is primarily dominated by discontinuous dynamic recrystallization. The material flow was found to be near simple shear deformation and the developed textures were composed of a mixture of A/A‾ and C components of ideal simple shear textures. The mechanical properties were also evaluated by the longitudinal tensile tests and microhardness measurements. The obtained results showed that, despite a 50% decrease in ductility, the highest yield and ultimate tensile strength of the friction stir processed samples are respectively about 1.6 and 1.2 times higher than those of the base metal. In good agreement with the tensile properties, the increased hardness of the stir zone was attributed to the grain structure refinement.
ISSN:0261-3069
DOI:10.1016/j.matdes.2014.10.082