Effect of α′ Martensite Content Induced by Tensile Plastic Prestrain on Hydrogen Transport and Hydrogen Embrittlement of 304L Austenitic Stainless Steel

Effects of microstructural changes induced by prestraining on hydrogen transport and hydrogen embrittlement (HE) of austenitic stainless steels were studied by hydrogen precharging and tensile testing. Prestrains higher than 20% at 20 °C significantly enhance the HE of 304L steel, as they induce severe α′ martensite transformation, accelerating hydrogen transport and hydrogen entry during subsequent hydrogen exposure. In contrast, 304L steel prestrained at 50 and 80 °C and 316L steel prestrained at 20 °C exhibit less HE, due to less α′ after prestraining. The increase of dislocations after prestraining has a negligible influence on apparent hydrogen diffusivity compared with pre-existing α′. The deformation twins in heavily prestrained 304L steel can modify HE mechanism by assisting intergranular (IG) fracture. Regardless of temperature and prestrain level, HE and apparent diffusivity ( D app ) increase monotonously with α′ volume fraction ( f α ′ ). D app can be described as log D app = log ( D α ′ s α ′ / s γ ) + log [ f α ′ / ( 1 − f α ′ ) ] for 10 % < f α ′ < 90 % , with D α ′ is diffusivity in α′, s α ′ and s γ are solubility in α′ and austenite, respectively. The two equations can also be applied to these more typical duplex materials containing both BCC and FCC phases

Numerical analysis of hydrogen transport into a steel after shot peening

Surface peening is a potential method of suppressing hydrogen embrittlement (HE). But experimental observations in literatures have shown that it can suppress HE of steels exposed to a mild hydrogen-containing environment, but in a severe hydrogen-containing environment it enhances HE. To explain this from the perspective of hydrogen transport and concentration, this paper gives a numerical analysis of hydrogen transport into a PSB1080 high strength steel after shot peening (SP) focusing on the combined effect of residual compressive stress and SP plastic deformation on diffusion. The diffusion model established by Oriani and Sofronis et al. is used, which considers the effect of the increase of trap sites due to plastic strain and assumes that the populations of hydrogen in trap sites and in normal lattice sites are in equilibrium. The results were related to experimental observations. In mild hydrogen-containing environment, the increase of trap sites due to SP can significantly reduce the apparent hydrogen diffusivity, thus suppress the transport and resulting hydrogen concentration level in normal lattice sites. As a result, hydrogen trapped at grain boundaries is reduced, and HE mechanism changes from HEDE to simultaneous HELP and HEDE. Intergranular fracture is suppressed thus reducing HE. And the suppression of hydrogen transport increases with increasing shot velocity, as a faster shot gives rise to more severe plastic deformation. In severe hydrogen-containing environment, SP deformation has little influence on diffusivity but significantly increases trapped hydrogen, leading to irreversible hydrogen blisters hence enhancing HE. Keywords: Hydrogen diffusion, Hydrogen embrittlement, Shot peening, Trap sites, Plastic deformatio

Surface Grain Refinement of 304L Stainless Steel by Combined Severe Shot Peening and Reversion Annealing Treatment

The present study proposes a novel method, i.e., combined severe shot peening (SP) and reversion annealing treatment, to grain-refine the surface layers of 304L austenitic stainless steel. Steel specimens were shot-peened at 0.7 MPa for 30 min, introducing 40% vol. α′ martensite, and then were annealed at 700 or 800 °C for different durations (30 s). As annealing reversed α′ martensite to austenite, the obtained surface layers consist of fully austenitic ultrafine grains. The smallest grain size obtained is about 500 nm at the top surface. SP elevates the microhardness to more than 500 HV. Although the grain-refined surface layers produced by the combined method are not as hard as that treated by only SP, they are harder (e.g., the specimen annealed at 700 °C for 30 s using a heating rate of 50 °C/s exhibited a peak microhardness of 400 HV) than the untreated surface layer (225 HV) due to grain refinement. Moreover, due to the absence of α′ martensite, they have higher corrosion resistance in H2SO4 solution than that treated by only SP

Hepatoprotective Effects of Rosmarinic Acid on Ovalbumin-Induced Intestinal Food Allergy Mouse Model

Rosmarinic acid (RA) has been proven to exert antianaphylaxis in atopic dermatitis, asthma, and allergic rhinitis. The aim of this study was to determine the hepatoprotective effects of RA on ovalbumin (OVA) challenge-induced intestinal allergy. The results exhibited that RA could relieve anaphylactic symptoms, decrease diarrhea, and prevent hypothermia in allergic mice. Moreover, the elevation of OVA specific IgE (OVA-sIgE), histamine, and mouse mast cell proteinases (mMCP-1) in the serum of OVA challenged mice were remarkably inhibited by RA. OVA challenge resulted in notable increases in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) activities, liver malondialdehyde (MDA) and nitic oxide (NO) levels, and a remarkable decrease in liver superoxide dismutase (SOD) activity and glutathione (GSH) level. RA treatments succeeded in improving these biochemical parameters and promote the redox homeostasis. Cytokine expression evaluation showed that RA effectively enhanced the expression of anti-inflammatory cytokines (IL-10 and FOXP-3) in the liver of OVA-challenged mice. Meanwhile, the elevation of pro-inflammatory cytokines (TNF-α, IL-4, IL-6, mMCP-1, and iNOS) were remarkably inhibited by RA. These findings suggest that RA possesses hepatoprotective effects on OVA challenge-induced liver injury. The anti-oxidative and anti-inflammatory activities of RA potentially play vital roles in this process