Deformed nanotwins promoted by grain refinement in austenitic stainless steel and its characteristics
Introduction
Metastable austenitic stainless steels have been widely used in the engineering field due to their outstanding mechanical properties and excellent corrosion resistance [1], [2]. Therefore, it is significant interest to pursue the stainless steel with high strength and excellent ductility. Then, the grain refinement of the microstructure has aroused extensive research interest [3]. Various severe plastic deformation technology, such as, equal channel angular pressing [4], accumulative roll bonding [5], and high-pressure torsion [6] have been successfully applied to obtain nano/ultrafine grained stainless steels with high strength. Despite the strength of the nano/ultrafine grained stainless steels was significantly improved [7], it required at the same time undesirable compromises to ductility. The ductility of nano/ultrafine grained stainless steel is lower than the conventional coarse grained one. The nano/ultrafine microstructures could inhibit accumulating and accommodating ability of the dislocations in nano/ultrafine grained stainless steels, which will decrease its corresponding capability of plastic deformation [8]. Recently, a new conception that combined severe plastic deformation and reversed transformation annealing approach was adopted to obtain nano/ultrafine grained metastable austenitic stainless steels [9]. It was found that metastable austenitic stainless steel with bimodal microstructures fabricated by cold rolling and reversed transformation exhibited excellent mechanical strength and high ductility [10]. The strain-induced α′-martensite transformation and deformation twinning enhanced the work-hardening ability and the ductility of metastable austenitic stainless steels [11]. In addition, accommodating more dislocations and secondary twinning inside the nanotwins during deformation process also could improve ductility and hardening ability for annealed nanotwinned steel based on microstructure observations [12]. Therefore, the formation mechanism and thermal stability of nanotwins during severe plastic deformation and subsequent reversed transformation in annealing process both are very important. Recent noteworthy and important findings demonstrated that high density nanotwins could stabilize nanostructured microstructures, which should be thermally induced grain boundary relaxation phenomenon from the nanotwins [13]. Based on the above discussion, this study will investigate the effect of the grain refinement on the formation of nanotwins during twice severe plastic deformation and reversed transformation annealing, as well as the thermal stability of secondary deformation nanotwins during reversed transformation annealing. Moreover, we also compared the effect of the grain refinement and nanotwins on the tensile properties of austenitic stainless steels.
Section snippets
Experimental
The solid solution 316L austenite stainless steel with chemical composition (wt.%) C 0.025, Cr 17.01, Ni 12.03, Mn 1.40, P 0.028, S 0.003, Si 0.40, Mo 2.05 and balance Fe was used. Then the samples were firstly rolled to 95% thickness reduction at room temperature, then were annealed at 800 °C for and 250 s for sufficient reversed transformation The samples were second rolled to 90% thickness reduction at room temperature, then were further annealed at 800 °C for and 200 s. The dog-bone-shaped
Results and discussion
The homogenized 316L stainless steel has coarse grained austenitic phase in Fig. 1. Some annealed twins are observed. It is obvious that different grain orientation affects the corrosion resistance in metallographic etching. Based on metallographic observation, the calculated average grain size of solid solution 316L austenite stainless steel is 31 μm.
Fig. 2 shows the XRD patterns of cold rolled and annealed 316L stainless steels. The solid solution annealed stainless steel has narrow half
Conclusion
The effect of grain refinement on deformed nanotwins during severe plastic deformation and reversed transformation in annealing process was investigated, moreover, the mechanical properties were also evaluated comparatively. The main conclusions were as follows:
- 1)
The grain refinement promoted the forming of nanotwins in metastable austenitic stainless steel, especially for nano/ultrafine grained austenitic stainless steel.
- 2)
Thermal stability of deformed nanotwins in nano/ultrafine grained
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References (21)
- et al.
Mater. Sci. Eng. R Rep.
(2009) - et al.
Corros. Sci.
(2020) Scr. Mater.
(2003)- et al.
Acta Mater.
(2011) - et al.
Acta Mater.
(2015) - et al.
Acta Mater.
(2010) - et al.
Mater. Sci. Eng. A
(2011) - et al.
Mater. Sci. Eng. A
(2010) - et al.
Mater. Sci. Eng. A
(2020) - et al.
Materialia
(2019)
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