Microstructure and mechanical properties of friction stir processed AISI 316L stainless steel. (15th February 2015)

• Record Type: Journal Article
• Authors: Hajian, M.; Abdollah-zadeh, A.; Rezaei-Nejad, S.S.; Assadi, H.; Hadavi, S.M.M.; Chung, K.; Shokouhimehr, M.
• Is Part Of: Materials & design. Volume 67(2015:Mar.)
• Page Start: 82
• Page End: 94
• Publication Date: 2015-02-15
• Subjects: Friction stir processing -- Austenitic stainless steel -- Grain refinement -- Microstructural characterization -- Mechanical properties; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2014.10.082
• Languages: English
• ISSNs: 0264-1275

Abstract

Highlights: 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. Abstract: Friction stir processing was used to refine the grain structure in 2 mm thick AISI 316L stainless steel sheets, with a pinless tool, at a constant traverse speed of 63 mm/min and relatively low rotational speeds of 200 and 315 rpm. Depending on the processing conditions, the initial grain size of 14.8 μm in the base metal was subsequently decreased to 0.8–2.2 μm 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.