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Abstract Slow strain rate, fatigue crack growth rate, and fracture toughness (respectively SSRT, FCGR, and FT) tests in high pressure gaseous hydrogen are used in evaluating hydrogen embrittlement (HE) susceptibility of pipelines steels welds. The applicability of these tests to pipeline service conditions in stress-based design (below YS) or up to 5% strain in strain-based design is limited. SSRT demonstrates effects of HE at loading above UTS. FCGR and FT tests quantify resistance to propagation of existing cracks but cannot characterize susceptibility to HE crack nucleation. We present HE susceptibility results generated using the delayed hydrogen cracking test (DHCT), standardized as AMPP TM21453-2023. DHCT applies a constant tensile load below or slightly above the material YS on flat gauge section specimens subjected to electrolytic charging with hydrogen. HE susceptibility is quantified by the time to failure and the mechanical energy for crack nucleation and growth to critical size. The paper draws a parallel between the HE phenomena introduced by the SSRT, FCGR, FT tests and DHCT, in terms of hydrogen absorption and transportation effects on the crack nucleation and propagation mechanisms. The mechanical energy introduced by these tests and the resulting failure mechanisms are compared and discussed. 

Abstract The objective of this study was to investigate the applicability of the delayed hydrogen cracking test (DHCT), standardized as AMPP TM21453, for evaluating hydrogen embrittlement (HE) susceptibility in pipeline steel welds. A comparative analysis of the HE mechanisms induced by the DHCT and the slow strain rate test (SSRT) was performed by quantifying the mechanical energy of crack nucleation and propagation in failures induced by these tests. The DHCT applies a static tensile load below the material yield strength (YS) in an electrochemically generated atomic hydrogen environment. Test results of X65 PSL2 steel welds demonstrated that the DHCT generates low-energy HE failures, associated with brittle QC and IG mechanisms, and can differentiate the effects of microstructure and weld profile-induced stress concentration on HE susceptibility. SSRT, performed in atomic hydrogen, induced brittle failures at plastic strains below 2%, showing potential application for evaluating HE susceptibility in pipeline welds for strain-based design service. Analysis of published results from SSRT in high-pressure gaseous hydrogen revealed that the related failure mechanism absorbs mechanical energy of up to three orders of magnitude higher than the DHCT. This was attributed to the large magnitude of plastic strain generated at loading above the material UTS, which is necessary for absorbing a sufficient amount of hydrogen to initiate HE failures. 

Abstract This study sought to evaluate the solidification cracking susceptibility in filler metals designed for wire arc additive manufacturing (WAAM) of a functionally graded pipe component for the harsh service conditions in olefin furnaces. Three filler metals corresponding to the outer diameter (OD), inner diameter (ID), and bulk (Core) regions of the tubular cross-section were developed based on previous modeling work. Cast pin tear testing (CPTT) was performed in this study to rank the solidification crack susceptibility among the three filler metals. CPTT samples were subsequently characterized by scanning electron microscopy (SEM) to propose potential mechanisms for the differences in crack susceptibility observed between the filler metals. Large, blocky Cr-rich carbides forming during solidification were identified as potential bad actors for solidification cracking susceptibility. The nature/amount of liquid ahead of the formation of these carbides was proposed to play a critical role in the difference in crack susceptibility observed among the three filler metals. 

Abstract Tungsten heavy alloys are used in demanding high pressure die casting applications due to their high temperature strength, high thermal conductivity, and low thermal expansion. High cost limits applications to small sintered die inserts and manual gas tungsten arc weld repairs. A new tungsten heavy alloy consumable, Anviloy wire, was developed for automated cladding of hot work tool steel dies. Literature regarding characterization of tungsten heavy alloy die steel clads was lacking. Understanding base metal dilution effect on clad microstructure is critical but required new sample preparation methods. An Anviloy wire-H13 clad was made using hot wire gas tungsten arc cladding and analyzed with metallography. Samples were found to have grain boundary M₆C carbide phase as-welded with the help of an alkaline sodium picrate etchant. An isothermally aged arc crucible melted sample of the same composition was characterized using metallography, scanning electron microscopy, and transmission electron diffraction. The clad representative arc crucible melted sample was subjected to isothermal aging at 725°C for 100 hours. Isothermal aging resulted in precipitation of a high volume fraction of intermetallic platelets. Using a new carbon extraction replica sample preparation method involving two chemical polishing steps, transmission electron diffraction of precipitates indicated they were mu phase intermetallic. 

Abstract 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. 

Abstract 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. 

Ductility dip cracking (DDC) remains a persistent challenge in multipass welds of high-chromium nickel-based alloys used in the nuclear power generation industry. While dynamic recrystallization (DRX) has been observed to arrest DDC crack growth and has been associated with weld regions that experience less DDC, there exists no quantitative relationship between the extent of recrystallization in a microstructure and DDC susceptibility. This research examines the influence of intragranular carbides on DRX behavior and establishes an experimental relationship between DDC susceptibility and extent of recrystallization in high-chromium nickel-based weld metals, novel contributions for this alloy system. In this work, the DRX behavior of the weld metal of high-chromium nickel-based filler metals (FM-52, FM-52M, FM-52i, and FM-52xl) was investigated under controlled thermo-mechanical conditions, and its effect on DDC susceptibility was established. Weld metal specimens were subjected to uniaxial deformation at 1100 °C to a true strain of 2% at strain rates of 10−3/s and 10−4/s using a Gleeble 3800TM. Recrystallization was quantified using electron backscatter diffraction (EBSD) via grain orientation spread (GOS) analysis and dislocation–precipitate interactions were examined using transmission electron microscopy (TEM). Strain-to-fracture (STF) testing at 950 °C was employed to assess DDC susceptibility as a function of the extent of recrystallization and grain surface area. All tested weld metals exhibited increased recrystallization and grain refinement, as the strain rate decreased from 10−3/s to 10−4 s. The FM-52i weld metal specimens exhibited the highest grain refinement under high temperature deformation, followed by the FM-52xl, FM-52, and FM-52M weld metals with a percent reduction in average grain surface area of 51.22%, 41.66%, 35.48%, and 24.40%, respectively. The FM-52i weld metal specimens also exhibited the highest recrystallization response, followed by FM-52M, FM-52xl, and FM-52 weld metals at 75%, 40%, 39% and 21% recrystallized, respectively. Weld metals containing strong carbide formers experienced higher recrystallization responses than those without due to precipitate–carbide interactions. All tested weld metals experienced drastic reductions in DDC response with increasing extent of recrystallization and decreasing average grain surface areas. DRX in STF specimens was observed to facilitate uniform plastic strain accumulation, lowering overall DDC susceptibility compared to non-recrystallized specimens.