Detecting oxygen content in commercially pure titanium (CP-Ti) is essential, especially in additive manufacturing processes where contamination is problematic. Traditional analyses are expensive and require significant amounts of material. In titanium, oxygen content corresponds to increasing β transus temperatures. Differential scanning calorimetry (DSC) was used on titanium materials to determine β transus temperatures, which were confirmed by independent oxygen analyses, and used in CALPHAD modeling. Analysis suggested DSC could be a less expensive method of determining oxygen content in CP-Ti.
Submerged arc welding (SAW) with multiple wires is used in pipe mills due to high deposition rates. The finite element method has been used previously for thermal modeling of multi-wire SAW. However, these calculations are time-consuming, making them impractical for shop floor applications. This study introduces a novel semi-analytical thermal model for multi-wire SAW, which reduces the computational time from several hours to approximately 4 min when run in GPU using CUDA implementation. The proposed model assumes a superposition of a series of semi-ellipsoidal heat sources and uses the Green function approximation leading to a simplified expression. Experimental validation for a tandem SAW demonstrated an average error of 8
Porosity during welding of aluminum alloys is critical as it affects the mechanical properties and functionality of the part. In the present study, commonly used filler wires of aluminum–silicon alloys ER4043 and ER4047 in two diameters of 1.2 mm and 1.6 mm were studied in the purview of porosity, distortion, and mechanical properties in the welding of 6061-T6 alloy. A semi-analytical model was used to understand the impact of filler wire and process parameters on the porosity evolution. The model predictions matched qualitatively with the experimental observations and trends. The study found that using ER4047 wire of 1.6 mm thickness with Precision Pulse® waveform produces industry-standard weld quality with almost zero porosity, superior mechanical properties, and negligible distortion levels while improving the productivity for thicknesses up to 3 mm of 6061-T6 base material. This information is crucial for the automotive industry as it seeks to increase the use of aluminum in vehicles.
Fracture toughness and temper embrittlement susceptibility are pivotal factors influencing the mechanical integrity of hydroprocessing reactors within oil refineries and chemical plants. Moreover, they exert a notable impact on the minimum allowed pressurization temperature (MPT), thereby affecting the startup and shutdown times. Enhanced fracture toughness at low temperatures and heightened resistance to temper embrittlement lead to a lower permissible MPT setting. Temper-embrittlement is the reduction in fracture toughness due to a metallurgical change that can occur in some low-alloy steels as a result of prolonged exposure in the temperature range of about 650 degrees F to 1070 degrees F (345 degrees C to 575 degrees C). This change causes an upward shift in the ductile-to-brittle transition. Although the loss of toughness is not evident at operating temperature, equipment afflicted by temper embrittlement becomes susceptible to brittle fracture during start-up and shutdown processes. This paper includes a literature review and describes the variability in fracture toughness of 2.25Cr 1Mo steel plate material as a function of temperature. Additionally, it presents a case history where high variability was reported in weld deposits. Factors affecting fracture toughness and tempering embrittlement are analyzed and recommendations to maximize fracture toughness and reduce temper embrittlement susceptibility are included. Finally, the paper touches upon technology limitations as dictated by contemporary manufacturing practices. The characterization process incorporates optical microscopy, scanning electron microscopy, hardness, chemistry, impact testing and crack tip opening displacement measurements.
Stainless steel pipe welds for service applications in corrosive environments typically use gas tungsten arc welding (GTAW) and require the use of an inert backing gas in order to minimize or prevent root bead contamination and oxidation. This adds significant cost and complexity to the welding of stainless steel pipe due to access restrictions, personnel safety, and/or economic factors. In this work, waveform-controlled gas metal arc welding (GMAW) was used for no-backing gas (NBG) welding of Type 304L austenitic stainless steel. Pitting corrosion behavior locally in the backside heat-affected zone and root bead weld metal was characterized using a syringe cell setup for cyclic potentiodynamic polarization (CPP) measurements. The CPP results indicate that the NBG welds have a similar pitting corrosion resistance as compared to reference GTAW and GMAW welds made with pure argon purging and an argon-oxygen mixture backing gas. The repassivation potential of the NBG welds was comparable to the reference welds, while the pitting potential was slightly lower. Weld bead appearance, weld metal ferrite, and heat tint oxidation were also characterized, and discussed with regard to the observed pitting corrosion resistance.
