Study on microstructure and tensile properties of high nitrogen Cr-Mn steel processed by CMT wire and arc additive manufacturing

A designed Cr-Mn-N wire with 0.99 wt% of nitrogen content (HNS0.99) was used to make high nitrogen austenite stainless steel parts by introducing CMT wire and arc additive manufacturing (CMT-WAAM) method. The solidification behaviour, microstructure evolution, inclusions and tension properties were studied both in the as-built and post heat treatment conditions. Excellent tension properties parts with high nitrogen content were successfully produced. Ferrite-austenite (FA) and austenite-ferrite (AF) solidification models were revealed in the as-built microstructure of two different areas, inner layer area (ILA) and partial melting area (PMA), respectively, and the former predominated the microstructure. Amorphous inclusion islands and microspherical inclusions made by MnO were found. The increasing density of the latter in 0.1-1 μm diameters was detrimental to the tensile properties because the matrix-inclusion surfaces acted as the preferred nucleation sites for Cr2N during heat treatment. Due to the stable austenite and the nitrogen work hardening effect, planer dislocation-arrays predominated the dislocation slip model which, to some extent, diminished the strength anisotropy in different directions. However, the ferrite dendrites caused the diversity of UTS and elongation by acting as tunnels for cracks in the horizontal direction samples

Microstructure and mechanical properties of TOP-TIG-wire and arc additive manufactured super duplex stainless steel (ER2594)

As the excellent combination of mechanical properties and corrosion resistance for super duplex stainless steel, a prospective method – Wire and Arc Additive Manufacturing – for fabricating this material was proposed, and a wall component was deposited in this study. The microstructure of the as-deposited wall was carefully analyzed along with the variation of mechanical properties. The results revealed that, in the wall-body, the austenite/ferrite phase balance was broken by the overgrowing the austenite phase. During this process, the intergranular secondary austenite leading the increase of austenite phase together with some contributions made by the precipitation of intragranular secondary austenite. Propagation of the intermetallic phases, chi and sigma phase, was not the major reason for the low impact toughness in the last layer area and the root region. Instead, the presence of CrN and “inclusions” (Cr2N and impurities) took the main responsibility not only in the impact toughness but also the ductility. The anisotropic analysis revealed that the UTS and elongation appeared distinct difference in vertical and horizontal direction samples. The varieties in YS were eliminated by the nitrogen work hardening effect to a large extent

Element partitioning and electron backscatter diffraction analysis from feeding wire to as-deposited microstructure of wire and arc additive manufacturing with super duplex stainless steel

The redistribution of alloying elements and the crystallographic characterizations in wire and arc additive manufactured (WAAM) super duplex stainless steel (SDSS) was investigated from the wire to the final as-deposited structure. The results showed that elemental partitioning between austenite and ferrite was suppressed in the last layer and the solidified droplet. The high Ni content but low Cr and N contents in the initial state of the intragranular austenite (IGA) confirmed the predominance of the chromium nitrides acted as the nucleation sites. Gathering of nitrogen was found more distinct in the coarsening IGA, Widmanstätten austenite (WA) than the grain boundary austenite (GBA). The columnar epitaxial ferrite presented a strong texture in the deposition direction, while the and orientations was found in the austenite. Random orientations of the intragranular secondary austenite was revealed. The Rotated Cube texture of the austenite grains were consumed by the “recrystallization” textures (Brass, Rotated Brass, Cu, R, E, and F) caused by the austenite reformation. The low-angle interphase boundaries between austenite and ferrite were predominated in the as-deposited wall, and, at which, the K–S orientation took the crucial part. A Taylor factor analysis revealed that through fabrication via additive process, the austenite became oriented “harder” and contributed most to good mechanical properties. The textured microstructure contributed about a 2.6% higher engineering strain in the Z direction and a 27.8 MPa higher yield strength in the X direction

Problems in Welding of High Nitrogen Steel: A Review

High nitrogen steel (HNS) has an excellent tensile strength and impact property due to the solid solution strengthening of nitrogen, which provides a good application prospect in many fields. Fusion welding is one of the main processing methods of HNS, but the process is prone to spatters, serious nitrogen losses, N2 porosities, and poor performances of joints, resulting in the failure of large-scale engineering applications of HNS. In this work, the development of HNS welding is reviewed, and the problems including the droplet transfer instability, N2 porosities, nitrogen losses and poor mechanical properties due to high nitrogen content are discussed. According to previous welding experiences, the adoption of a welding method with a low heat input is proposed, which utilizes powders instead of wires, optimizes compositions in the shielding gas and feeding materials in order to solve the above problems, and improves the mechanical properties of the weld

Transparent Wood Developed by Impregnating Poplar with Epoxy Resin Assisted by Silane Coupling Agent

Biodegradable transparent wood was fabricated by introducing epoxy resin E51 modified with the silane coupling agent (KH550) into bleached poplar veneer. The light transmittance of transparent wood was modulated by KH550 content. The silane coupling agent KH550 was able to change the compatibility of epoxy resin and wood substrate, thereby affecting the performance of transparent wood. In this study, the effect of KH550 on the properties of transparent wood and its mechanism were investigated. The light transmittance, tensile strength, and elongation at break of transparent wood showed an increasing and then decreasing trend with increased KH550 dosage. When the mass ratio of the coupling agent KH550 to the epoxy resin was 1:20, the transparent wood made by impregnating wood substrate with epoxy resin modified by KH550 had the best performance, with the fast degradation starting temperature of 338 °C, 81.07% light transmittance at λ = 780 nm, 59.92 MPa tensile strength, and 3.47% elongation at break. This work provides a new way for preparing high performance transparent wood

Transparent Wood Developed by Impregnating Poplar with Epoxy Resin Assisted by Silane Coupling Agent

Biodegradable transparent wood was fabricated by introducing epoxy resin E51 modified with the silane coupling agent (KH550) into bleached poplar veneer. The light transmittance of transparent wood was modulated by KH550 content. The silane coupling agent KH550 was able to change the compatibility of epoxy resin and wood substrate, thereby affecting the performance of transparent wood. In this study, the effect of KH550 on the properties of transparent wood and its mechanism were investigated. The light transmittance, tensile strength, and elongation at break of transparent wood showed an increasing and then decreasing trend with increased KH550 dosage. When the mass ratio of the coupling agent KH550 to the epoxy resin was 1:20, the transparent wood made by impregnating wood substrate with epoxy resin modified by KH550 had the best performance, with the fast degradation starting temperature of 338 °C, 81.07% light transmittance at λ = 780 nm, 59.92 MPa tensile strength, and 3.47% elongation at break. This work provides a new way for preparing high performance transparent wood

Investigation of dendrite growth, Nb segregation during laser IN718 deposition via volume of fluid-phase field modeling

In this work, a macro-micro VOF-PF (Volume of Fluid-Phase field) model is established to simulate the heat transfer, dendrite growth and Nb segregation during the laser IN718 deposition. According to calculated heat transfers, G increases, while Vp decreases, and the corresponding G×Vp decreases from top to bottom in the molten pool. The calculated the primary dendrite arm spacing (PDAS) using the PF model increases from top to bottom. Compared with other models, the calculated PDAS using the PF model considering the liquid-metal flow is closest to experiment measurements. During the dendrite growth, Nb is enriched in the interdendritic region, and finally is distributed in the droplet shape. The calculated actual solute distribution coefficient Cmin/Cmax decreases from 0.584 to 5.548 with the decrease of G×Vp, which follows the equilibrium solidification theory. According to dc/dy=G/ml, the liquidus slope ml is calculated as 0.05322wt.%/μm very close to the theoretical value 0.05394wt.%/μm. The simulated Nb concentrations in the matrix γ and Laves phases are 3.97wt.%, 13.3wt.% respectively, which are in good agreements with experimental 3.7wt.% and 13wt.%

A Tryptophan-Deficient Diet Induces Gut Microbiota Dysbiosis and Increases Systemic Inflammation in Aged Mice

The gut microflora is a vital component of the gastrointestinal (GI) system that regulates local and systemic immunity, inflammatory response, the digestive system, and overall health. Older people commonly suffer from inadequate nutrition or poor diets, which could potentially alter the gut microbiota. The essential amino acid (AA) tryptophan (TRP) is a vital diet component that plays a critical role in physiological stress responses, neuropsychiatric health, oxidative systems, inflammatory responses, and GI health. The present study investigates the relationship between varied TRP diets, the gut microbiome, and inflammatory responses in an aged mouse model. We fed aged mice either a TRP-deficient (0.1%), TRP-recommended (0.2%), or high-TRP (1.25%) diet for eight weeks and observed changes in the gut bacterial environment and the inflammatory responses via cytokine analysis (IL-1a, IL-6, IL-17A, and IL-27). The mice on the TRP-deficient diets showed changes in their bacterial abundance of Coriobacteriia class, Acetatifactor genus, Lachnospiraceae family, Enterococcus faecalis species, Clostridium sp genus, and Oscillibacter genus. Further, these mice showed significant increases in IL-6, IL-17A, and IL-1a and decreased IL-27 levels. These data suggest a direct association between dietary TRP content, the gut microbiota microenvironment, and inflammatory responses in aged mice models