Increasing the welding interpass temperature (IT) can reduce the welding time and cost of welding but may degrade the quality of the welded joint. The objective of the present study was to analyze ...the effects of the IT on microstructure and Charpy V-notch (CVN) impact energy of coarse-grain heat-affected zone (CGHAZ) of an AISI 4130 steel welded pipe. The welding was computationally simulated using finite element method. The CGHAZ was physically simulated and evaluated via optical and scanning electron microscopy, electron backscatter diffraction analysis, Vickers microhardness, and CVN impact. The numeric model had an accuracy of 97.5% (difference in the simulated and measured maximum temperatures), with a simulated cooling rate equal to the measured value. An increase in IT changed the microstructure from bainite (B) and martensite (IT 315 °C) to B, ferrite with aligned martensite–austenite–carbide (AC), and pro-eutectoid ferrite (FP) (IT 400 °C), followed by ferrite AC, FP, ferrite with non-aligned martensite-austenite-carbide, and ferrite–carbide aggregate (IT 475 and 550 °C). These changes in microstructure significantly impacted the effective grain size and grain boundary character distribution, which directly influenced CVN impact energy of the CGHAZ. IT = 315 °C exhibited the highest CVN impact energy (89 J), and ITs ≥ 400 °C did not satisfy the ASME 31.3 code. Therefore, indiscriminately increasing the IT is unsuitable method for reducing the welding cost for AISI 4130 steel pipes.
Welding costs associated with the laying of pipes for deepwater oil and gas extraction can be reduced using high interpass temperatures (ITs). However, a high IT can decrease the mechanical ...properties of the heat-affected zone (HAZ) of welded joints. With the use of high strength-toughness steels, this decrease may be an acceptable trade-off. Therefore, it is necessary to evaluate the influence of high ITs on the HAZ. The influence of the IT on the coarse-grain HAZ (CGHAZ) and intercritically reheated coarse-grain HAZ (ICCGHAZ) of an API 5L X70 pipe joint welded by gas metal arc welding was investigated. The welding was numerically simulated using finite element method software. The microstructure of the HAZ was predicted using thermodynamic simulation software. The CGHAZ and ICCGHAZ were also physically simulated and evaluated via optical microscopy and scanning electron microscopy, dilatometry, and Vickers microhardness and Charpy V-notch (CVN) impact tests. The increase in IT led to a decrease in CGHAZ microhardness but did not affect the ICCGHAZ. The CVN energies obtained for all ITs (CGHAZ and ICCGHAZ) were higher than that set by the DNVGL-ST-F101 standard (50 J). These results show that increasing the IT is an interesting and effective method to reduce welding costs. In addition, thermodynamic simulation proved to be a valid method for predicting the phases in the HAZ of API 5L X70 pipe welded joints.
With the aim of reducing pipe-laying costs through the application of more efficient welding techniques, this study evaluated the influence of an interpass temperature (IT) higher than 230 °C ...(Petrobras N-133 IT standard specific limit) on the microstructure, Vickers microhardness, and Charpy V-notch (CVN) impact energy of the simulated coarse-grained and intercritically reheated coarse-grained heat-affected zones (CGHAZ and ICCGHAZ, respectively) of a clad API 5L X65 pipe gas metal arc welded joint. The welding was computationally simulated using Sysweld®, a commercially finite element method (FEM) software. In response to an increase in the IT, the microstructure of the CGHAZ transformed from martensite to lath and granular bainite, which led to a decrease in the microhardness. Conversely, the microstructure of the ICCGHAZ transformed from needle-like to elongated grains of ferrite in response to an increased IT, but this change did not significantly influence the microhardness. The increase in the IT led to the formation of a dot-shape and necklace-type martensite-austenite (M-A) constituent (
IT
≥ 360 °C); however, it did not compromise the CVN impact energy of the CGHAZ because all ITs were higher than that set by the DNVGL-ST-F101 standard (45 J). For the ICCGHAZ, an increased IT led to the formation of block-like and massive M-A, which decreased the CVN impact energy and did not meet the DNVGL-ST-F101 standard at
IT
= 420 °C. Therefore, an increase in the IT up to 360 °C can serve as an alternative strategy to reduce the welding cost.
Additive manufacturing (AM) has transformed the way of manufacturing metallic parts due to its ability of rapid prototyping, customization, reduced waste, and cost-effectiveness for small-batch ...manufacturing, and it has been increasingly replacing milling and molding processes. Directed energy deposition and powder-based fusion AM are the major classes of metal AM technologies, which are already well-established to print high-volume and small complex parts, respectively. However, the increasing demand for the fabrication of small devices, due to the miniaturization trend that is occurring in several industries fields, requires the development of specialized metal AM systems with the ability to increase the resolution of the printed parts. Thus, micro-metal additive manufacturing (MMAM) systems are now being developed using a scaling-down approach of the currently well-established metal AM technologies. In this review, a state-of-art analysis of the existing body of knowledge including the existing MMAM technologies, process parameters, and main results associated with MMAM was compiled and critically discussed. A surface texture index is defined, and a comparison of the trade-off between surface finishing and the building rate was performed considering the metal AM processes and the already developed scaled-down technologies. Additionally, other important aspects of the process (e.g., cost-related, health, environmental risks) are discussed.
In recent years, efforts have been focused on the development of metal additive manufacturing (AM) processes to address the growing trend of miniaturization in industries such as aerospace and ...electronics. Thus, new technologies have been developed based on a downscaled approach using direct energy deposition (DED) processes, now referred to as μ-DED. In this context, the development of a downscaled DED prototype based on gas metal arc (GMA) working with micrometric wires (μ-GMA) has the potential to unify the positive characteristics of GMA-based DED, increasing the complexity of the design and resolution of the produced parts. Therefore, this work focuses on developing a μ-GMA prototype and assessing its technical feasibility. This paper describes the development of the μ-GMA prototype, characterizes the metallic transfer mode, and statistically analyzes the effect of deposition parameters on bead width and height. Additionally, microstructural analysis, Vickers microhardness, and reduced Young's modulus tests were performed. The μ-GMA prototype demonstrated the capability to deposit beads with an approximate width of 1 mm, nearly 5 times thinner than standard GMA-based DED deposition, with a build rate of 30 cm3/h, which is lower than GMA-based DED but higher than other μ-DED processes. Furthermore, the mechanical properties of the μ-GMA depositions are comparable to regular GMA-based DED parts.
This work aimed to develop a microstructure-predicting methodology (MPM) using coupled physical-FEM-thermodynamic simulation to predict the influence of cooling time from 800 to 500 °C (t8/5 – 15, ...30, 80, and 210 s) on the microstructure and mechanical behavior of the coarse grain heat-affected zone (CGHAZ) of a Cr-Mo low alloy steel welded joint. The MPM was experimentally validated. The MPM certainly predicted that the increase of t8/5 caused a remarkable change in CGHAZ microstructure (martensite and bainite to ferrite with aligned and non-aligned martensite-austenite-carbide M-A-C) and also decreases the Vickers microhardness. The MPM and experimental data show that the use of welding parameters that increases t8/5 (reducing the cooling rate) can jeopardize the welded joint behavior. Besides, the MPM proved to be a suitable tool for estimating the microstructure and microhardness of the CGHAZ.
Os tratamentos térmicos de têmpera e particionamento (Q&P) vem sendo largamente estudados, uma vez que tem sido relatado na literatura uma melhora nas propriedades mecânicas dos aços após esses ...tratamentos. Busca-se, então, analisar os efeitos do mesmo, em aços API usados no revestimento de poços de petróleo; e na condução de óleo e gás (aço API 5CT e aço API 5L, respectivamente). Esses tratamentos têm como objetivo a formação de uma microestrutura que consiste, normalmente, numa matriz martensítica com considerável teor de austenita retida (ɤR ). Desta forma, foi desenvolvida uma rota de tratamentos Q&P, empregando-se diferentes temperaturas de particionamento, em três aços API com aplicações na indústria petrolífera. As influências desses tratamentos nas propriedades mecânicas dos aços foram analisadas, via ensaios de tração, impacto Charpy e microdureza Vickers, e comparadas com os resultados obtidos ao se utilizar a rota habitual de tratamentos térmicos, de têmpera e revenimento (Q&T). Foram observadas melhoras na ductilidade, razão elástica e tenacidade ao impacto dos aços.
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