Exceptionally high strength and good ductility in an ultrafine-grained 316L steel processed by severe plastic deformation and subsequent annealing
Introduction
The 316L stainless is a frequently used material in both medicine and industry due to its excellent properties, such as a good corrosion resistance and the low susceptibility to neutron absorption [1]. The main crystalline phases in 316L steel are the face-centered cubic (fcc) γ-austenite and the body-centred cubic (bcc) α′-martensite. The good ductility of γ-austenite is usually accompanied by a relatively low strength which can limit its applications under high loads. At the same time, the high strength α′-martensite with bcc structure exhibits low ductility. Therefore, the ability to process 316L steel with high strength and good ductility is a challenging task.
The strength of ductile austenitic steels can be increased by grain refinement using severe plastic deformation (SPD) techniques such as high-pressure torsion (HPT) and hydrostatic extrusion [2], [3]. However, during SPD there is a simultaneous phase transformation from γ-austenite to α′-martensite [2]. It was suggested that annealing after SPD may yield fine austenite grains [4], [5] so that a combination of high strength and good ductility is feasible. The present research was initiated to study the tensile properties of samples processed by HPT and annealed at different temperatures. Our study shows that a combination of HPT-processing and subsequent annealing to 1000 K yields an exceptional combination of high strength and good elongation to failure by comparison with the available literature data for 316L steel.
Section snippets
Material and methods
316L stainless steel samples with a coarse-grained single phase γ-austenite structure were HPT-processed for 20 turns at room temperature (RT) with an applied pressure of 6.0 GPa and rotation speed of 1 rpm. The thickness and the diameter of the HPT-processed disks were ∼0.75 mm and ∼10 mm, respectively. In former studies, the microstructure and the phase composition evolution during HPT processing and subsequent annealing were investigated in detail [2], [5]. Differential scanning calorimetry
Results and discussion
The yield strength, the ultimate tensile strength, the uniform elongation and the elongation to failure for the initial coarse-grained sample, for the HPT-processed specimens and for the samples annealed to 740 and 1000 K were determined from the tensile stress-strain curves (not shown) and the evolution of these data is plotted in Fig. 1. In order to explain the changes in the tensile properties of 316L steel during annealing, the evolution of the γ-austenite fraction, the grain size and the
Conclusions
- 1.
HPT processing dramatically increased the yield strength while the elongation to failure significantly decreased. The extremely high strength and limited ductility of the HPT-processed sample were attributed to the high fraction of α′-martensite, the small grain size and the high dislocation density.
- 2.
DSC annealing of the HPT-processed sample to a moderate temperature of 740 K led to a pronounced embrittlement and strength reduction. The reduction of ductility was most probably caused by the
Acknowledgements
The authors are indebted to the Hungarian Scientific Research Fund, OTKA, Grant No. K 109021 for financial support. Three of the authors were supported by the European Research Council under ERC Grant Agreement No. 267464-SPDMETALS (PHRP, YH and TGL). Park would like to acknowledge support from the NRF-2016-Fostering Core Leaders of the Future Basic Science Program/Global Ph.D. Fellowship Program (2016H1A2A1909161).
References (12)
- et al.
Microstructure, phase composition and hardness evolution in 316L stainless steel processed by high-pressure torsion
Mater. Sci. Eng., A
(2016) - et al.
Mechanical properties and corrosion resistance of ultrafine grained austenitic stainless steel processed by hydrostatic extrusion
Mater. Des.
(2017) - et al.
Suppression of twinning and phase transformation in an ultrafine grained 2GPa strong metastable austenitic steel: Experiment and simulation
Acta Mater.
(2015) - et al.
High temperature thermal stability of nanocrystalline 316L stainless steel processed by high-pressure torsion
Mater. Sci. Eng., A
(2017) - et al.
Property enhancement in Type 316L stainless steel by spray forming
Mater. Sci. Eng., A
(1991) - et al.
Tensile properties of a nanocrystalline 316L austenitic stainless steel
Scr. Mater.
(2005)
Cited by (31)
Supreme tensile properties in precipitation-hardened 316L stainless steel fabricated through powder cold-consolidation and annealing
2024, Materials Science and Engineering: AMicro/nano incremental material removal mechanisms in high-frequency ultrasonic vibration-assisted cutting of 316L stainless steel
2023, International Journal of Machine Tools and ManufactureTailoring a high-strength Al–4Cu alloy through processing of powders by up to 100 turns of high-pressure torsion
2023, Materials Science and Engineering: ABody-thorough ultrahigh strength and ductility of austenitic 316L stainless steel by industry-applicable 3-axis stress-released impact
2023, Materials Science and Engineering: ATensile and fatigue properties of the binder jet printed and hot isostatically pressed 316L austenitic stainless steel
2023, Materials Science and Engineering: AHeterostructured stainless steel: Properties, current trends, and future perspectives
2022, Materials Science and Engineering R: ReportsCitation Excerpt :Additionally, the uniform tensile ductility of the bimodal sample was 35% compared to 30% in the UFG sample. The limited ductility in UFG materials is mainly due to the instability of fine grains, which is related to the limited capacity to store dislocations within fine grains [596,597]. The above results are in line with the observation reported by Flipona et al. for a bimodal 316 L SS [46].