Controllable Martensite Transformation and Strain-Controlled Fatigue Behavior of a Gradient Nanostructured Austenite Stainless Steel

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.

Nanostructured Metals with an Excellent Synergy of Strength and Ductility: A Review

“…The resulting deformation amount, rate, and temperature from the surface to the interior all exhibit gradient changes, thereby a gradient nanostructure forms on the metal surface. The involved deformation methods include SMAT [ 144 , 145 , 146 , 147 ], surface mechanical grinding treatment (SMGT) [ 136 , 148 ], surface mechanical rolling technique (SMRT) [ 149 , 150 , 151 , 152 ], and other plastic deformation technologies (such as laser shock peening, shot peening, etc.) [ 153 , 154 ].…”

The Effect of Initial Texture on the Plastic Deformation of Gradient Aluminum

“…To attain such microstructures, substantial effort has been devoted to modifying severe plastic deformation processing methods, which allow for the development of unique grain structures and a subsequent increase in strength and ductility. Various severe plastic deformation methods such as surface mechanical attrition treatment (SMAT) [ 8 ], surface mechanical rolling treatment (SMRT) [ 9 ], surface mechanical grinding treatment SMGT [ 10 , 11 ], high-pressure torsion (HPT) [ 12 ], and equal-channel angular pressing (ECAP) [ 13 , 14 ] can be used to produce different types of gradient microstructures with distinct grain size distributions and grain size spatial distributions. However, relatively less attention has been paid to the inevitable induced texture or texture gradient that accompanies severe plastic deformation processing.…”

Influence of Plastic Strain Control on Martensite Evolution and Fatigue Life of Metastable Austenitic Stainless Steel

“…However, in the case of materials undergoing a strong cyclic hardening, such as metastable austenitic stainless steels, the majority of fatigue life investigations are performed under stress control or under strain control at constant total strain amplitude [11]. This is caused mainly by the fact that these materials yield a significant secondary cyclic hardening caused by the martensitic phase transformation (e.g., [12,13]). This hardening behavior impedes the performance of fatigue tests under strain control at constant plastic strain amplitude since the cyclic stress vs. plastic strain hysteresis loop is changing from cycle to cycle due to the influence of hardening.…”