Evolution of strengthening mechanisms in ODS 316L steel during plastic straining

Cyclic behavior of 316L steel predicted by means of finite element computations

Cyclic hardening/softening behavior of 316L stainless steel at elevated temperature including strain-rate and strain-range dependence: Experimental and damage-coupled constitutive modeling

The formation of ferromagnetic α′-martensite in 316L austenitic stainless steel poses a significant threat to the structural integrity of hydrogen-related components, particularly under mechanical loading and hydrogen exposure. This study compares and analyses four advanced magnetic non-destructive testing techniques, magnetic Barkhausen noise, magnetic incremental permeability, eddy current testing, and Magnetic Flux Leakage (MFL) via Nitrogen-Vacancy center (NV-center) magnetometry, for their ability to detect α′-martensite in plastically deformed 316L specimens. Energy-dispersive X-ray diffraction was used as a reference to quantify near-surface α′-martensite content, while finite element simulations of plastic strain and residual stress provided supporting mechanical context. Among the tested methods, NV-center magnetometry exhibited a very strong linear correlation with XRD-based martensite quantification (r = 0.99), reflecting its sensitivity to plastic strain, which closely governs α′-martensite formation. Other techniques showed lower correlations (r < 0.4), with magnetic incremental permeability notably influenced by mechanical stress rather than martensite content. In addition to its sensitivity, NV-center MFL also demonstrated excellent spatial resolution, fast acquisition, and high robustness, making it a promising technique for α′- martensite detection in 316L components. • NV-center magnetometry shows high sensitivity to α′-martensite in 316L steel. • NV-center method achieves strong correlation (r = 0.99) with XRD measurements. • NV-center offers high spatial resolution and fast magnetic flux leakage mapping. • MBN and MIP techniques mainly respond to mechanical stress, not martensite content. • NV-center magnetometry is promising for hydrogen system integrity monitoring.

Investigation of the irradiation effects in additively manufactured 316L steel resulting in decreased irradiation assisted stress corrosion cracking susceptibility

Flat specimen of 316L steel was cyclically pre-deformed with constant plastic strain amplitude to early stage of fatigue life relevant to the period of cyclic strain localization and fatigue crack initiation. To document slip activity and reversibility/irreversibility of persistent slip bands (PSBs) in situ experiments in the high-resolution SEMFEG under special imaging conditions were performed. The half-and full-cycle slip activity and distribution of plastic strain within PSBs in individual grains were investigated via slip steps generated in half-and full-cycle deformation after intermediate vibration polishing. After completion of in situ tests the surface topography in identical locations was quantitatively documented using atomic force microscopy (AFM).

Low cycle fatigue (LCF) regime was experimentally studied for a 316L steel additively manufactured by laser‐powder bed fusion (L‐PBF), a material widely used in sectors that require a reliable durability analysis. Material cyclic elastoplastic behavior is described by the Chaboche–Voce combined plasticity model, which displayed a great degree of accuracy. The fatigue life was modeled by both invoking the Manson–Coffin curve and other simplified models derived from static properties of the material; some of which showed remarkably good accuracy. A quantitative comparison with a wrought‐processed 316L steel displayed a markedly different cyclic elastoplastic response but comparable fatigue strengths.

Numerical simulation and experiment analysis of angular distortion and residual stress in hybrid laser-magnetic welding

Non-proportional hardening models for predicting mean and peak stress evolution in multiaxial fatigue using Tanaka’s incremental plasticity concepts

The austenitic stainless steel 316L is used for numerous components due to its excellent corrosion resistance. However, forming of components influences the microstructure and can thus change the corrosion resistance of the steel. In this context, the corrosion rate of the steel 316L is determined for the case of uniform corrosion of various cold-rolled con­ditions by ageing tests in 0.5 M H2SO4. The microstrain, the martensite fraction, and the residual-stress state are quantified using X-ray diffraction. The surface roughness is measured by laser scanning microscopy. Three different model equations are derived by means of multiple regression to predict the corrosion rate as a function of the specimen properties. The analysis shows that a particularly simple model equation, which predicts the corrosion rate only via the plastic strain, shows insufficiently large deviations from the experimentally determined corrosion rates. However, a low divergence to the experimental results with a mean deviation of less than 4% is achieved by using a model equation that takes microstructural parameters and the surface ratio into account. Within this model equation, an increased corrosion rate is achieved with higher microstrain and residual compressive stress of the austenite phase as well as a higher surface-area ratio. A higher fraction of martensite is found to lower the corrosion rate.

Polycrystal modelling of fatigue: Pre-hardening and surface roughness effects on damage initiation for 304L stainless steel

Atomic force microscopy (AFM) and focused ion beam technique (FIB) were adopted to study the early stages of surface relief evolution in 316L steel and polycrystalline copper fatigued with constant plastic strain amplitudes at different temperatures (316L steel at 93, 173 and 573 K; copper at 83, 173 and 295 K). Qualitative and quantitative data on the morphology and shape of persistent slip markings (PSMs), occurrence of extrusions and intrusions and the kinetics of extrusion growth are reported. They are discussed in relation with recent physically based theories of surface relief formation leading to fatigue crack initiation.

High plastic Zr–Cu–Fe–Al–Nb bulk metallic glasses for biomedical applications

AFM study of surface relief evolution in 316L steel fatigued at low and high temperatures

Stability of austenitic 316L steel against martensite formation during cyclic straining

Materials for the components of advanced nuclear reactors are expected to undergo harsh operational conditions, in which high temperature levels (of the order of 650°C or higher) and severe mechanical stresses provide conditions for creep deformation to be significant as to become a key factor limiting the lifetime of the material. At the same time, components in nuclear power plants are subject to cycles of start-up and shut-down, due to operations of maintenance, refuelling, variations in demand and emergency stops. These conditions, characterized by removal of mechanical loads only or both mechanical loads and temperature, trigger a time-dependent recovery of the plastic strain accumulated during creep deformation, known as anelasticity. The studies herein presented were aimed at investigations on the creep performance and on the impact of stress transients on the creep behaviour of the materials, due to the anelastic response. These transient tests, carried out by imposing stages of load removal, were concentrated at simulating the in-service conditions. Specific goals were set for each material. For the 316H, the anelastic response under partial unloading conditions was investigated, in an effort to determine the magnitude of the back stress, which is the driving force for anelastic recovery, stemming from basic physical mechanisms within the crystalline domains. The Oxide Dispersion Strengthened (ODS) 316L steel had its mechanical properties characterised, with particular focus on the creep response, analysed under the scope of performance requirements established by structural integrity code for materials in nuclear applications. And, finally, the behaviour in full load removal transients was characterised for the MA956 ferritic ODS steel, in order to study its anelastic response. It was observed that, for the 316H, partial unloading stages produce the same recovery effect on the microstructure, provided that the drop in stress is accompanied by change in the dominant creep mechanism from dislocation-based to diffusion-controlled. Moreover, the heterogeneous dislocation arrangement model of back stress was successfully applied for calculating the intragranular stresses and, along with neutron diffraction measurements of intergranular stresses, found good correspondence with the anelastic behaviour of the material. As for the ODS 316L, creep properties at 650°C were found to comply with the RCC MR code for the stress levels tested, but its creep performance fell short of a conventional 316L. HR TEM surveys on the oxides and a pilot diffusion-bonding study showed the effects of particle growth and how they influence the mechanical response of this alloy. And, in the case of the MA956, the investigations suggested that anelasticity is absent in this ODS steel. Although a more detailed approach is required, all the results obtained provided evidence that most of the grains in this material are resisting creep deformation. The outcomes of the investigations are the deepening of the understanding of the potential for recovery of steels subject to creep deformation, in terms of the basic microstructural features, and how they influence the creep response. From these studies, better materials assessment procedures may be envisaged.