Corrosion Behavior and Mechanical Properties of AISI 316 Stainless Steel Clad Q235 Plate

Recent Advances in Additive Manufacturing of Soft Magnetic Materials: A Review

Additive manufacturing (AM) is an attractive set of processes that are being employed lately to process specific materials used in the fabrication of electrical machine components. This is because AM allows for the preservation or enhancement of their magnetic properties, which may be degraded or limited when manufactured using other traditional processes. Soft magnetic materials (SMMs), such as Fe-Si, Fe-Ni, Fe-Co, and soft magnetic composites (SMCs), are suitable materials for electrical machine additive manufacturing components due to their magnetic, thermal, mechanical, and electrical properties. In addition to these, it has been observed in the literature that other alloys, such as soft ferrites, are difficult to process due to their low magnetization and brittleness. However, thanks to additive manufacturing, it is possible to leverage their high electrical resistivity to make them alternative candidates for applications in electrical machine components. It is important to highlight the significant progress in the field of materials science, which has enabled the development of novel materials such as high-entropy alloys (HEAs). These alloys, due to their complex chemical composition, can exhibit soft magnetic properties. The aim of the present work is to provide a critical review of the state-of-the-art SMMs manufactured through different AM technologies. This review covers the influence of these technologies on microstructural changes, mechanical strengths, post-processing, and magnetic parameters such as saturation magnetization (MS), coercivity (HC), remanence (Br), relative permeability (Mr), electrical resistivity (r), and thermal conductivity (k).

Pulsed TIG Cladding of a Highly Carbon-, Chromium-, Molybdenum-, Niobium-, Tungsten- and Vanadium-Alloyed Flux-Cored Wire Electrode on Duplex Stainless Steel X2CrNiMoN 22-5-3

The hardfacing process aims to increase the life span of structural components in the petrochemical, mining, nuclear and automotive industries. During operation, these components are subject to demands of abrasion wear, cavitation erosion and corrosion. Duplex stainless steels are characterized by high mechanical characteristics and corrosion resistance, but poor behavior to abrasive wear and cavitation erosion. The improvement in wear resistance is possible by selecting and depositing a special alloy on the surface using a joining technique that ensures a metallurgical bonding between the layer and the substrate. The experimental investigations carried out in this work demonstrate the ability of the TIG pulsed welding process to produce layers with good functional properties for engineering surfaces. The "Corodur 65" alloy was deposited on a duplex-stainless-steel substrate, X2CrNiMoN22-5-3, using a series of process parameters that allowed for the control of the cooling rate and heat input. The properties of the deposited layers are influenced not only by the chemical composition, but also by the dilution degree value. Since the deposition of layers through the welding operation can be considered as a process with several inputs and outputs, the control of the input parameters in the process aims at finishing the granulation and the structure in the fusion zone as well as limiting the segregation phenomena. The aim of this work is to investigate the microstructural characteristics of the iron-based alloy layer, Corodur 65, deposited via pulsed current TIG welding on duplex X2CrNiMoN22-5-3 stainless-steel substrates.

Experimental Investigation of Cobalt Deposition on 304 Stainless Steel in Borated and Lithiated High-Temperature Water

The radioactive corrosion products ⁵⁸Co and ⁶⁰Co in the primary loops of pressurized water reactors (PWRs) are the main sources of radiation doses to which workers in nuclear power plants are exposed. To understand cobalt deposition on 304 stainless steel (304SS), which is the main structural material used in the primary loop, the microstructural characteristics and chemical composition of a 304SS surface layer immersed for 240 h in borated and lithiated high-temperature water containing cobalt were investigated with scanning electron microscopy (SEM), X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectrometry (GD-OES), and inductively coupled plasma emission mass spectrometry (ICP-MS). The results showed that two distinct cobalt deposition layers (an outer layer of CoFe₂O₄ and an inner layer of CoCr₂O₄) were formed on the 304SS after 240 h of immersion. Further research showed that CoFe₂O₄ was formed on the metal surface by coprecipitation of the iron preferentially dissolved from the 304SS surface with cobalt ions from the solution. The CoCr₂O₄ was formed by ion exchange between the cobalt ions entering the metal inner oxide layer and (Fe, Ni) Cr₂O₄. These results are useful in understanding cobalt deposition on 304SS and have a certain reference value for exploring the deposition behavior and mechanism of radionuclide cobalt on 304SS in the PWR primary loop water environment.

Influence of Vanadium Micro-Alloying on the Microstructure of Structural High Strength Steels Welded Joints

The inter-critically reheated grain coarsened heat affected zone (IC GC HAZ) has been reported as one of the most brittle section of high-strength low-alloy (HSLA) steels welds. The presence of micro-alloying elements in HSLA steels induces the formation of microstructural constituents, capable to improve the mechanical performance of welded joints. Following double welding thermal cycle, with second peak temperature in the range between Ac1 and Ac3, the IC GC HAZ undergoes a strong loss of toughness and fatigue resistance, mainly caused by the formation of residual austenite (RA). The present study aims to investigate the behavior of IC GC HAZ of a S355 steel grade, with the addition of different vanadium contents. The influence of vanadium micro-alloying on the microstructural variation, RA fraction formation and precipitation state of samples subjected to thermal cycles experienced during double-pass welding was reported. Double-pass welding thermal cycles were reproduced by heat treatment using a dilatometer at five different maximum temperatures of the secondary peak in the inter-critical area, from 720 °C to 790 °C. Although after the heat treatment it appears that the addition of V favors the formation of residual austenite, the amount of residual austenite formed is not significant for inducing detrimental effects (from the EBSD analysis the values are always less than 0.6%). Moreover, the precipitation state for the variant with 0.1 wt.% of V (high content) showed the presence of vanadium rich precipitates with size smaller than 60 nm of which, more than 50% are smaller than 15 nm.

Quantification of Residual Stress Relief by Heat Treatments in Austenitic Cladded Layers

The effect of the heat treatment on the residual stresses of welded cladded steel samples is analyzed in this study. The residual stresses across the plate’s square sections were determined using complementary methods; applying diffraction with neutron radiation and mechanically using the contour method. The analysis of the large coarse grain austenitic cladded layers, at the feasibility limits of diffraction methods, was only made possible by applying both methods. The samples are composed of steel plates, coated on one of the faces with stainless steel filler metals, this coating process, usually known as cladding, was carried out by submerged arc welding. After cladding, the samples were submitted to two different heat treatments with dissimilar parameters: one at a temperature of 620 °C maintained for 1 h and, the second at 540 °C, for ten hours. There was some difference in residual stresses measured by the two techniques along the surface of the coating in the as-welded state, although they are similar at the welding interface and in the heat-affected zone. The results also show that there is a residual stress relaxation for both heat-treated samples. The heat treatment carried out at a higher temperature showed sometimes more than 50% reduction in the initial residual stress values and has the advantage of being less time consuming, giving it an industrial advantage and making it more viable economically.

Recrystallization and Grain Growth of AISI 904L Super-Austenitic Stainless Steel: A Multivariate Regression Approach

AISI 904L is a super-austenitic stainless steel that is remarkable for its mechanical properties and high corrosion resistance, which strictly depend on its chemical composition and microstructural features. The recrystallization process and grain growth phenomena play key roles in achieving high levels of material quality, as often requested by customers for specific applications. In this paper, the evolution of the microstructure and hardness values after cold rolling and subsequent annealing is reported, with the aim of optimizing the thermomechanical treatment conditions and improving the efficiency of the production process. The investigation was focused on three different cold reduction ratios (50%, 70% and 80%), while combining different annealing temperatures (950, 1050 and 1150 °C) and soaking times (in the range of 20–180 s. The test results were organized using a data analysis and statistical tool, which was able to show the correlation between the different variables and the impacts of these on recrystallization and grain growth processes. For low treatment temperatures, the tested soaking times led to partial recrystallization, making this condition industrially unattractive. Instead, for the higher temperature, full recrystallization was achieved over a short time (20–40 s), depending on the reduction ratio. Regarding the grain growth behavior, it was found to be independent of the reduction ratio; for each treatment temperature, the grain growth showed a linear trend as a function of the soaking time only. Moreover, the static recrystallization kinetics were analyzed using a statistical analysis software program that was able to provide evidence indicating the most and least influential parameters in the process. In particular, taking into consideration the hardness values as output data, the temperature and soaking time were revealed to have major effects as compared with the reduction ratio, which was excluded from the statistical analysis. The prediction approach allowed us to formulate a regression equation in order to correlate the response and terms. Moreover, a response optimizer was used to predict the best solution to get as close as possible to the hardness target required by the market.

Heat Treatment of Steels

Steels represent an interesting family of materials, both from a scientific and commercial point of view, considering the many innovative applications they can be used for [...]

Optimization of Open Die Ironing Process through Artificial Neural Network for Rapid Process Simulation

The open die forging sequence design and optimization are usually performed by simulating many different configurations corresponding to different forging strategies. Finite element analysis (FEM) is a tool able to simulate the open die forging process. However, FEM is relatively slow and therefore it is not suitable for the rapid design of online forging processes. A new approach is proposed in this work in order to describe the plastic strain at the core of the piece. FEM takes into account the plastic deformation at the core of the forged pieces. At the first stage, a thermomechanical FEM model was implemented in the MSC.Marc commercial code in order to simulate the open die forging process. Starting from the results obtained through FEM simulations, a set of equations describing the plastic strain at the core of the piece have been identified depending on forging parameters (such as length of the contact surface between tools and ingot, tool’s connection radius, and reduction of the piece height after the forging pass). An Artificial Neural Network (ANN) was trained and tested in order to correlate the equation coefficients with the forging to obtain the behavior of plastic strain at the core of the piece.

Heat Treatment Effect on Microstructure Evolution in a 7% Cr Steel for Forging

Well-defined heat-treatment guidelines are required to achieve the target mechanical properties in high-chromium steels for forgings. Moreover, for this class of materials, the microstructure evolution during heat treatment is not clearly understood. Thus, it is particularly important to assess the steel microstructure evolution during heat treatment, in order to promote the best microstructure. This will ascertain the safe use for long-term service. In this paper, different heat treatments are considered, and their effect on a 7% Cr steel for forging is reported. Results show that, following the high intrinsic steel hardenability, significative differences were not found versus the cooling-step treatment, although prior austenite grain size was significantly different. Moreover, retained austenite (RA) content is lower in double-tempered specimens after heat treatments at higher temperatures.