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Wire arc additive manufacturing (WAAM) is an efficient technique for producing medium to large‐size components, due to its accessibility and sustainability in fabricating large‐scale parts with high deposition rates, employing low‐cost and simple equipment, and achieving high material efficiency. Consequently, WAAM has garnered attention across various industrial sectors and experienced significant growth, particularly over the last decade, as it addresses and mitigates challenges within production markets. One of the primary limitations of WAAM is its thermal history during the process, which directly influences grain formation and microstructure heterogeneity in the resulting part. Understanding the thermal cycle of the WAAM process is thus crucial for process improvement. Typically, fabricating a part using WAAM results in a microstructure with three distinct zones along the build direction: an upper zone (thin surface layer) with fine grains, a middle zone dominated by undesirably long and large columnar grains covering more than 90% of the produced part, and a lower zone with smaller to intermediate columnar grains closer to the substrate material. These zones arise from variations in cooling rates, with the middle zone exhibiting the lowest cooling rate due to 2D conduction heat transfer. Consequently, producing a component with a microstructure comprising three different zones, with a high fraction of large and long columnar grains, significantly impacts the final mechanical properties. Therefore, controlling the size and formation of these grain zones plays a key role in improving WAAM. The aim of this work is to investigate the formation of undesired columnar grains in austenitic stainless steel 316L during WAAM and propose a simple hybrid technique by combining WAAM with a hot forging process (with or without interlayer cooling time). This approach targets the disruption of the solidification pattern of columnar grain growth during deposition progression and aims to enhance the microstructure of WAAM components.

Coke drums are critical units in the delayed coking process to produce lightweight oil products from heavy residual oil. The fulfillment of the designed coke drum lifetime is often obstructed by low-cycle fatigue damage over cyclic thermal and mechanical loading. Considering the tremendous cost of drum replacement and production loss due to shutdown, the coke drum lifetime extension is of great economic significance in the oil and gas industry. A research project regarding coke drum fabrication and repair was initiated in the Manufacturing & Materials Joining Innovation Center (MA2JIC) at the Ohio State University in 2016. The project includes two phases of work. The first phase of the study (2016∼2019) focused on the external weld repair of coke drum materials, while the ongoing second phase of the study (2019∼2023) addressed coke drum fabrication and repair. A novel low-cycle fatigue testing approach was developed using Gleeble thermo-mechanical simulator and was applied to evaluating the performance of coke drum base materials and welded joints under cyclic deformation. The project goal is to improve the fundamental understanding of materials and joint performance that allows the optimization of coke drum design, fabrication, and repair. In this technical paper, the key methodologies and achievements of the project will be introduced, and some future work will be proposed for the next step.

Temper bead (TB) welding is often used as an alternative to post weld heat treatment (PWHT) for repair of pressure vessels and piping in the nuclear power industry. Historically, qualification of TB welding procedures has employed the Charpy V-notch test to ensure acceptable heat-affected-zone (HAZ) impact properties. The 2004 Edition of ASME Section IX provided a new provision in QW-290 that allows temper bead qualification using a peak hardness criterion. The peak hardness provision is appropriate for industries such as oil and gas, where peak allowable hardness is specified to ensure adequate resistance to sulfide stress cracking in sour service environments. However, a peak hardness criterion is not appropriate where impact properties are specified for resistance to brittle fracture during low temperature conditions that can occur during certain postulated accident scenarios at a nuclear power plant.

Work at the Electric Power Research Institute (EPRI) and The Ohio State University (OSU) show that a hardness drop protocol can be used to demonstrate acceptable impact properties in the HAZ of a temper bead weld. This paper presents a quantitative correlation between hardness measurements and HAZ microstructures with presumed optimum impact properties using a hardness drop approach. The overarching goal is to develop a hardness test protocol for temper bead weld procedure qualification for applications where impact properties are specified.

In-service welding simulations were carried out using a multiphysics finite element analysis (FEA). Calculated data as temperature and thermal cycles were validated by comparing them with experimental welding results carried out in a carbon steel pipe attached to a water loop. Two in-service welding cases were tested using the GMAW-P process with and without the assistance of induction preheating. The molten zone of weld macrographs and the simulated models were matched with excellent accuracy. The great agreement between the simulation and experimental molten zone generated a maximum error in the peak temperature of 1%, while in the cooling curve, the error was about 10% at lower temperatures. A higher hardness zone appeared in the weld’s toe within the CGHAZ, where the maximum induction preheating temperature achieved was 90°C with a power of 35 kW. Induction preheating reduced the maximum hardness from 390 HV to 339 HV.

The Hyper Duplex Stainless Steel HDSS enhanced corrosion resistance and toughness relies upon high alloying to obtain a balanced ferrite and austenite volume and pitting resistance equivalent number PREn. However, during welding, sigma phase precipitates might form, hindering corrosion and mechanical performance. Therefore, a kinetics model is developed to avoid the sigma phase's formation during welding and validated using physical simulation, finite element analysis (FEA), welding, and SEM characterisation. The sigma phase kinetics model produced calculated and validated temperature-time-transformation (TTT) and continuous-cooling-transformation (CCT) curves from which a 4°C/s cooling rate was found as a cooling rate threshold for sigma phase formation in this new material. Three-layered gas tungsten arc welding GTAW cladded mockup with 53 beads produced 24°C/s minimum cooling rate. Moreover, microscopy, mechanical, and corrosion testing attested it as a sigma-free weld.

GTAW welding with pulsed current has been misinterpreted in some of the classic literature and scientific articles. General conclusions are presented, stating that its use provides greater penetration compared to the use of constant current and that the simple pulsation of the current promotes beneficial metallurgical effects. Therefore, this manuscript presents a critical analysis of this topic and adopts the terminology of thermal pulsation for the situation where the weld undergoes sensitive effects, regarding grain orientation during solidification. For comparison purposes, an index called the form factor (ratio between the root width and the face width of the weld bead) is adopted. It is shown that the penetration of a welding with pulsed current can be worse than constant current depending on the formulation of the adopted procedure. Moreover, metallurgical effects on solidification, such as grain orientation breakage, only occur when there is adequate concatenation between the pulsation frequency and the welding speed. Finally, a thermal simulation of the process showed that the pulsation frequency limits the welding speed so that there is an overlap of the molten pool in each current pulse, and continuity of the bead is obtained at the root. For frequencies of 1 Hz and 2.5 Hz, the limit welding speed was 3.3 mm/s and 4.1 mm/s, respectively.