Explore the vast range of titles available.

AISI 316 stainless steel (SS316) is an attractive material for industrial applications. Welding of this alloy can lead to severe distortion that often results in dimensional inaccuracies. With the help of specially designed fixture and clamping mandrels, tungsten inert gas (TIG) welding on SS316 pipes is employed to investigate the effect of liquid nitrogen on the circumferential distortion, weld penetration and delta-ferrite distribution in different welding zones. The experimental results reveal that the presence of trailing heat sink in TIG welded butt joint has almost zero distortion at a distance of 30 mm from the weld centerline and 64% decrement in residual circumferential distortion at the center of the weld bead. A metallurgical microscope is used to find the weld penetration, (fusion zone) FZ and (heat affected zone) HAZ. The results illustrate that increase in current and the presence of intensive cooling media yield deeper penetration in TIG welding. Liquid nitrogen (LN 2 ) also constricts the FZ and HAZ. Instead of evaluating delta-ferrite contents using the ferrite number technique, a MATLAB ® code for image processing is developed to evaluate the delta-ferrite distribution in the different regions of a single-pass weldment. Delta-ferrite contents are maximum in the presence of intensive cooling media near HAZ and increase with an increase in the current value. Hence, TIG welding with LN 2 as trailing heat sink is the most suitable scheme to weld industrial pipes owing to its higher weld penetration, higher delta-ferrite contents and minimum circumferential distortion.

Four different AISI 304L austenitic stainless steels with chromium equivalent-to-nickel equivalent (Creq/Nieq) ratios of 1.57, 1.59, 1.62, and 1.81 were chosen for this study. The influence of chemical composition on solid-state formation of delta ferrite phase during hot deformation was investigated. Compression tests were performed at temperature, strain, and strain rate ranges of 1200 to 1300 °C, 10 to 70%, and 0.1 to 10 s−1, respectively. Increasing the temperature, strain, and strain rate led to increased formation of delta ferrite. The results show that the formation of delta ferrite during hot deformation is also strongly dependent on chemical composition. The higher the Creq/Nieq ratio, the higher the tendency for the formation of delta ferrite. The observed behavior may be attributed to plastic deformation-induced formation of crystallographic defects such as dislocations affecting the diffusion rate.

In the present research work, an effort has been made to examine the effect of the ERNiCrCoMo-1 filler on solidification mechanism, microstructural characterization, welded joint integrity, and residual stresses of the dissimilar welded joint (DWJ) of martensitic grade P92 steel and Ni-based superalloy Inconel 617 for advanced ultra-supercritical (A-USC) power plant application. Weld joints have been fabricated for V groove geometry by using the multipass gas tungsten arc welding (GTAW) process. The multiple aspects of the welded joint structural integrity have been tested by performing the tensile test, microhardness tests and Charpy impact test. The ERNiCrCoMo-1 weld solidified in austenitic mode with columnar and cellular dendrites in the interior region, while columnar dendrites were observed near the interface region. The unmixed zone (UZ) formation was noticed at the ERNiCrCoMo-1 filler weld and P92 steel interface, while the UZ gets eliminated at Inconel 617 interface. The microstructural observation near the interface showed that migrated grain boundaries were observed frequently near the lower region of the weld metal (WM), while at the interface of the P92 steel and ERNiCrCoMo-1 filler welds, higher density of soft δ ferrite patches for the capping and backing passes were observed. The energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) results confirmed the presence of the Cr- and Mo-enriched M23C6 precipitates, Mo-enriched M6C and Ti-enriched Ti(C, N) precipitates in the WM. Acceptable mechanical properties were obtained at room temperature. The Charpy impact toughness (CIT) was observed 98 ± 5 J and 108 ± 3 J for WM with V notch at the top and root region, respectively. The dramatic reduction in CIT was after the postweld heat treatment (PWHT) was attributed to the evolution of the carbide particles in interdendritic areas. Tensile strength results of the cross-weld specimen showed the tensile strength value marginally lower than the P92 steel but significantly lower than the Inconel 617 base metal in both as-welded (AW) and PWHT condition along with fracture in the week region of P92 steel. The failure from the region of P92 steel instead of the ERNiCrCoMo-1 filler WM confirmed that the welded joint was safe for A-USC power plants boiler application. A significant heterogeneity in microhardness was seen along the weldments with a peak hardness of 445 ± 8 in P92 CGHAZ and a lower hardness of 181 HV in the peninsula. The increase in microhardness of the WM as a result of PWHT was attributed to the evolution of the carbide particles in the WM. Through thickness residual stresses variation was also measured for both WM and HAZ region and the effect of the PWHT on the magnitude and nature of the residual stresses were also performed. Hence the work provides insight into welding procedure development, microstructural evolution in the WM and HAZ, variation in mechanical properties, and residual stresses variation for the welded joint of P92 steel and Inconel 617 alloy.

The most relevant criticalities of parts produced by material extrusion additive manufacturing technologies are lower mechanical properties than standard material performances, the presence of pores caused by the manufacturing method, and issues related to the interface between layers and rods. In this context, heat treatments can be considered an effective solution for tailoring the material behavior to different application fields, especially when using precipitation hardening stainless steels. In this work, aging treatments were conducted on parts realized using three different extrusion-based processes: Atomic Diffusion Additive Manufacturing, bound metal deposition, and fused filament fabrication. Two conditions of direct aging (H900 and H1150) were considered with the aim of comparing the response of properties in the opposite conditions of peak-aged and overaged. The hardness tests revealed that H900 aging significantly influenced hardness (max increase of 52%), and porosity (− 34.3% with respect to the as-sintered condition). On the other hand, the H1150 aging decreased the hardness (− 18% max) and porosity (− 32.2% max). Substantial differences among the microstructures due to grain size and δ-ferrite were illustrated. A statistical test was included to better highlight the influence of the heat treatment on the investigated properties.

The tungsten inert gas welded P91 steel welded joints were subjected to the two different type of heat treatments including the postweld direct tempering (PWDT) and re-austenitizing based tempering (PWNT) treatment. The microstructure of weld fusion and heat affected zone (HAZ) were characterized in different heat treatment conditions using optical microscope and scanning electron microscope. For as-welded joint, a great heterogeneity was observed in microstructure and mechanical properties across the weldments. The Charpy toughness of the as-welded joint was measured much lower than the minimum recommended value of 47J and it was measured 8±5J. The PWHTs have found a beneficial effect in decreasing the microstructure heterogeneity across the welded joint and improving the mechanical properties. The PWDT resulted in a drastic improvement in the Charpy impact toughness of the welded joint and it was measured 59±5J which was higher than the minimum required value of 47J but still inferior than the base metal. The δ ferrite still remained in overlap zone of the weld fusion zone. The PWNT treatment resulted in homogeneous microstructure and hardness variation across the welded joint in transverse direction and Charpy impact toughness (149±6J) exceeded than that achieved in base metal.

Directed energy deposition (DED), one of the additive manufacturing (AM) technologies, was used to realize AISI 316L specimens. The role of substrate preheating on the microstructure, hardness, surface roughness, and mechanical properties of AISI 316L samples was studied using two groups of deposited samples on a cold substrate and a preheated one. The cooling rate in each specimen was determined using primary cellular arm spacing (PCAS). It is found that the thermal gradient and cooling rate in the samples produced on the preheated substrate are lower. However, in both cases, the cooling rate decreased as the deposition height increased. The phase composition analysis confirmed that the lower cooling rate in the preheated samples resulted in a lower residual δ-ferrite content. The deeper microstructural analysis also confirmed the formation of non-metallic inclusions during the building process. However, the quantity of these inclusions was lower in the samples realized on the cold substrate. Preheating the base plate had a negligible effect on the surface roughness of the AISI 316L cubes. The tensile results demonstrated that the samples produced using the cold base plate had better mechanical performance than those deposited on the preheated base plate. All in all, using a preheated substrate led to a lower thermal gradient, lower cooling rate, larger PCAS, higher inclusion content, higher oxygen pick-up, and lower nitrogen pick-up that strongly affected the mechanical characteristics of the AISI 316L samples.

In this paper, different pre-weld microstructures of clam steel were obtained by heat treatment, and the seamless connection of the test steel was achieved by EBW welding. The microstructure and fracture morphology of the samples were observed by optical microscope and scanning electron microscope, and the composition of the second phase particles was detected by EDS. The results show that the joint microstructure was mainly composed of the melting zone and HAZ zone. The δ ferrite was detected in the melting zone, and the HAZ zone with fine grains was filled with carbides in and along the grain boundaries. B and N are mainly distributed on the grain boundary, and C exists in the form of a precipitated phase on the grain boundary and in the form of a solid solution in the grain.

In 316L austenitic stainless steel, the presence of ferrite phase severely affects the non-magnetic properties. 316L austenitic stainless steel with low-alloy type (L-316L) and high-alloy type (H-316L) has been studied. The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy (HT-CLSM). There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions. In L-316L steel, ferrite morphology appears as the short rods with a ferrite content of 6.98%, forming a dual-phase microstructure consisting of austenite and ferrite. Conversely, in H-316L steel, the ferrite appears as discontinuous network structures with a content of 4.41%, forming a microstructure composed of austenite and sigma (σ) phase. The alloying elements in H-316L steel exhibit a complex distribution, with Ni and Mo enriching at the austenite grain boundaries. HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes: L-316L steel solidifies in an FA mode, whereas H-316L steel solidifies in an AF mode. These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases, respectively. The solidification mode observed by experiments is similar to the thermodynamic calculation results. The L-316L steel solidified in the FA mode and showed minimal element segregation, which lead to a direct transformation of ferrite to austenite phase (δ → γ) during phase transformation after solidification. Besides, the H-316L steel solidified in the AF mode and showed severe element segregation, which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction (δ → σ + γ).

Purpose This paper aims to provide a comparison between the mechanical performance and microstructural aspects of stainless steel 17-4 PH processed using, respectively, two technologies: atomic diffusion additive manufacturing (ADAM) and metal fused filament fabrication (MFFF). Design/methodology/approach Different tensile specimens have been printed using an industrial system and a consumer three-dimensional (3D) printer, varying two main 3D printing parameters. Mechanical and microstructural tests are executed to make a comparison between these two technologies and two different feedstock material, to identify the main differences. Findings These 3D printing processes make parts with different surface quality, mechanical and microstructural properties. The parts, printed by the industrial system (ADAM), showed lower values of roughness, respect those produced using the 3D consumer printer (MFFF). The different sintering process parameters and the two debinding methods (catalytic or solvent based) affect the parts properties such as porosity, microstructure, grain size and amount of δ-ferrite. These proprieties are responsible for dissimilar tensile strength and hardness values. With the aim to compare the performances among traditional metal additive technology, MFFF and ADAM, a basic analysis of times and costs has been done. Originality/value The application of two metal extrusion techniques could be an alternative to other metal additive manufacturing technologies based on laser or electron beam. The low cost and printing simplicity are the main drivers of the replacements of these technologies in not extreme application fields.

The solidification path and the σ-phase precipitation mechanism in the S31254 (UNS designation) steel are investigated thanks to Quenching during Directional Solidification (QDS) experiments accompanied by scanning electron microscopy observations and electron backscattered diffraction (EBSD) analysis. Considering experimental conditions, the γ-austenite is found to be the primary solidifying phase (1430 °C), followed by δ-ferrite (1400 °C, ≈ 87 pct solid fraction). The σ-phase appears in the solid-state through the eutectoid decomposition of the δ-ferrite: δ → σ + γ2 (1210 °C), whereas the σ-phase is predicted to form from the austenite at 1096 °C in equilibrium conditions. The resulting temperatures of solidification path and phase transformation are compared with Gulliver–Scheil model and equilibrium calculations predicted using Thermo-Calc© software. It is shown that the thermodynamics calculations agree with experimental results of solidification path. The EBSD analysis show that the δ-ferrite has δNW2 ORs with the σ-phase.