316H stainless steel, due to its excellent high-temperature mechanical properties, is widely used in high-temperature and high-pressure environments such as nuclear power plants and chemical plants. Under these extreme conditions, the fatigue properties of the material are critical to the safe operation of equipment. The Masing behavior, as an important cyclic plastic behavior, determines the stress-strain response of the material under cyclic loading, which is crucial for predicting its fatigue life. However, the current research on the Masing behavior of 316H stainless steel at high temperatures is insufficient, and there is a lack of in-depth understanding of its cyclic deformation behavior and damage mechanism.
The Masing behavior is a phenomenon in metallic materials under cyclic loading: when hysteresis loops at different strain amplitudes are translated to align the lowest points, if they can completely overlap, the material exhibits Masing behavior. The Masing behavior reflects the stability of the material's microstructure under cyclic loading. If the dislocation structure remains stable during the fatigue process, the material usually exhibits Masing behavior; otherwise, non-Masing behavior.
Methods
Prof. Bing-Bing Li and Prof. Xu Chen from Tianjin University conducted a systematic study on the low-cycle fatigue behavior of 316H stainless steel at 650°C using a series of experimental and analytical methods.
First, a series of strain-controlled low-cycle fatigue tests were conducted to obtain cyclic stress-strain response curves at different strain amplitudes.
Then, the microstructure of the fatigued samples was characterized using electron backscatter diffraction (EBSD) to analyze local plastic deformation, grain orientation, and grain boundary characteristics.
In addition, the dislocation microstructure was observed using transmission electron microscopy (TEM), and the carbide precipitation was analyzed.
Finally, the cyclic deformation mechanism and damage mechanism of 316H stainless steel were revealed by combining the analysis results of macroscopic mechanical properties and microstructure.
Highlights
The Masing behavior transition of 316H stainless steel at 650°C was revealed, and it was found that it exhibits non-Masing behavior at strain amplitudes lower than 0.6% and Masing behavior at strain amplitudes larger than 0.6%.
The flow stress decomposition mechanism during cyclic hardening, stabilization, and softening stages was analyzed in depth, and the influence of dislocation configuration evolution on the Masing behavior was clarified.
The microstructure characteristics of 316H stainless steel during high-temperature fatigue, such as local plastic deformation, grain classification, and carbide precipitation, were accurately characterized.
The evolution of crack initiation and propagation characteristics and the dominant damage mechanism were systematically studied, and it was found that intergranular damage is dominant at high strain amplitudes.
This research provides new ideas and methods for predicting and evaluating the fatigue life of 316H stainless steel at high temperatures. The research results can provide theoretical guidance for the design and optimization of 316H stainless steel applications in high-temperature environments such as nuclear power plants, thereby improving equipment safety and reliability. This research also has reference significance for the fatigue performance research of other high-temperature alloys.
Fig. 3. (a)-(d) Dislocation microstructures in the region adjacent to grain boundary of the fractured samples at the strain amplitude of 0.2%, 0.4%, 0.6% and 1.0%; (e) precipitation at grain boundaries; (f) EDS results of precipitation along the line AB in (e). elemental variations from point A to point B.
Editor: Dr. Jun-Jing He
