Abstract
Gradient nanostructured (GNS) surface layer with a controllable martensite fraction has been synthesized on 316L austenitic stainless steel by means of surface mechanical rolling treatment (SMRT) with temperature being controlled. The mean grain size is in the nanometer scale in the near-surface layer and increases gradually with depth. In addition, the volume fraction of martensite decreases from ~85% to 0 in the near-surface layer while the SMRT temperature increases from room temperature to 175 °C. Fatigue experiments showed that the strain-controlled fatigue properties of the GNS samples are significantly enhanced at total strain amplitudes ≥0.5%, especially in those with a dual-phase surface layer of austenite and pre-formed martensite. Analyses on fatigue mechanisms illustrated that the GNS surface layer enhances the strength-ductility synergy and suppresses the formation of surface fatigue defects during fatigue. In addition, the dual-phase structure promotes the formation of martensite and stacking faults, further enhancing fatigue properties at high strain amplitudes.
Highlights
As an important structural material with superior corrosion resistance and deformability, 316L stainless steel is widely used in industries such as nuclear power and petrochemistry [1]
Gradient nanostructured (GNS) surface layers with different martensite fractions were formed on 316L austen
GNS itic surface layers with martensite fractions were formed on 316L austenitic stainless steel bydifferent means of surface mechanical rolling treatment (SMRT) with temperature being controlled
Summary
As an important structural material with superior corrosion resistance and deformability, 316L stainless steel is widely used in industries such as nuclear power and petrochemistry [1]. It was typically found that the fatigue properties of SPD materials were significantly decreased under strain-controlled mode or at high stress amplitudes in low-cycle fatigue (LCF) regime, mostly due to their significantly decreased ductility [3,6]. Significantly enhanced strain-controlled fatigue properties were detected in the GNS 316L stainless steel, with an increase of more than 30 times than the CG sample in fatigue life at a total strain amplitude of 0.30% [14]. Enhanced strain-controlled fatigue properties were obtained in dual-phase steels containing martensite and ferrite [17,18]. By forming nanolaminated ferrite-cementite or martensite-austenite structure in a multi-phase steel, the fatigue strength was further enhanced in the LCF regime, due to the decelerated crack opening and growth process during fatigue [19]. Straincontrolled fatigue behavior of the GNS samples was studied at strain amplitudes ≥ 0.5%
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