Effect of Low Transformation Temperature Welding Consumable on Microstructure, Mechanical Properties and Residual Stress in Welded Joint of A516 Carbon Steel

The microstructure, mechanical properties and residual stress of flux-cored arc welded ASTM A516-70N carbon steel using a Mn-based low-temperature transformation (LTT) welding consumable were investigated. Microstructural analysis with X-ray diffraction, an electron backscattered diffractometer and a field-emission scanning electron microscope showed that the LTT weld metal was made up of ferrite, austenite, martensite, and bainite with phase fractions 50.5%, 0.2%, 40.2% and 9.1%, respectively. The increase in hardness and the decrease in absorbed impact energy of the LTT weld metal compared with conventional consumable welds were confirmed to be due to the relatively high fraction of martensite phase in the weld metal. The welding residual stress distributions in three coupons (LTT, conventional and postweld heat-treated conventional weld) were compared by the results using instrumented indentation testing. The LTT weld coupon showed compressive residual stress distributed in the weld metal and heat-affected zone (HAZ), confirming previous studies in which this residual stress was attributed to a martensitic phase transformation at relatively low temperature. PWHT in the conventionally welded coupon considerably reduced the tensile residual stress distributed in the weld metal and HAZ. The LTT consumable, however, showed a significant advantage in welding residual stress, even compared with the heat-treated conventional consumable.

Effect of boron and manganese on hot crack resistance and toughness for flux cored arc weldments of 550 MPa grade tensile strength

The hot crack resistance and mechanical properties of flux cored arc (FCA) welds were investigated with three kinds of welding consumables having different boron (B) and manganese (Mn) contents for high strength carbon steel. The hot crack resistance measured from self-restraint testing strongly depended on the amount of B in the welding consumable. Welding consumable with higher B contents resulted in longer total crack length and an increased number of cracks. Boron was intensely detected near the grain boundary of the weld centerline by secondary ion mass spectrometry (SIMS) analysis, and precipitated with boron carbide (Fe23(C,B)6), as analyzed by transmission electron microscopy (TEM). This promoted hot crack propagation in the high strength carbon steel welds. However, removing B from the welding consumable decreased the low temperature toughness for root and face weld metal due to the growth of Ferrite Side Plate (FSP) in comparison with welding consumables having more B or Mn contents. The addition of Mn in the weld metal suppressed the formation of FSP and increased the low temperature toughness. Therefore, the minimization of B and the supplement of Mn successfully achieved hot crack resistance and low temperature toughness for high strength carbon steel welds of 550 MPa tensile strength.

Effects of High Toughness and Welding Residual Stress for Unstable Fracture Prevention

Unstable fractures generally occur in brittle materials under low-temperature service conditions. Toughness and welding residual stress are the main factors that should be evaluated when defining a brittle crack propagation path. In this study, a rainbow welding technique was proposed and confirmed as being significantly useful in preventing unstable fractures in weld joints. The residual compressive stress in the crack front was particularly useful for decreasing the possibility of brittle fracture. The objective was to examine the effect of high welding consumable toughness welding residual stress, especially for avoiding brittle fracture through welding residual compressive stress.

Mechanical System and Template-Matching-Based Position-Measuring Method for Automatic Spool Positioning and Loading in Welding Wire Winding

Welding wire is a major type of welding consumable, which needs to be winded onto spools for sale. Currently, the winding process is accomplished manually due to obstacles such as automatic spool loading and clamping. When loading the spool, the angular position of the spool is a prerequisite for matching the drive rod on the spindle and drive bore on the spool. Therefore, this paper proposes a template-matching method combined with area-based matching and feature-point detection to measure the angular position of the spool, and presents a mechanical system that can rotate the spool to match the drive rod and push the spool onto the spindle. A novel feature-point distribution density (FPDD) method was developed to accelerate the matching process and improve matching reliability by pre-locating the searching area. The robustness and accuracy of the template-matching-based measuring method were validated using a built prototype of the mechanical system. The comparison result shows that the proposed method was superior in robustness, accuracy, and speed, and it was efficient for automatic spool loading in the welding wire winding process.

Experimental investigations on red ochre for application in welding consumable development

This paper investigates the thermophysical, physicochemical, and surface properties of mineral waste red ochre, assessing suitability for application in welding consumable development. Red ochre is an anhydrous iron oxide derived from tailings of iron ore haematite. High iron and silica concentration makes it suitable for various engineering applications. Iron in the electrode coatings is known to increase arc stability, bead smoothness, and also it enhances slag detachability along with smoothening bead profile. The red ochre has been characterized for the properties of weight loss, density, specific heat, enthalpy, thermal conductivity, and diffusivity. Structural analysis of red ochre powder has been done using Fourier transformed infrared spectroscopy and X-ray diffraction. BET (Brunauer, Emmett, and Teller) surface area analysis has been done to estimate the surface properties, which include pore radius and specific surface area. The shielded metal arc welding electrodes have been developed by adding red ochre in a fixed proportion, and produced welds have been examined for visual defects, microstructure, and microhardness.

Development of Optimized Welding Consumable for Joining Type 410 Martensitic Stainless Steel

Type 410 martensitic stainless steel is used in some downstream hydro-processing installations, due to its good resistance to sulfide corrosion and chloride stress corrosion cracking. Industry experience with Type 410 steel welds, using generic welding consumables, has shown difficulties in meeting the weld metal and HAZ hardness and toughness requirements. Recent research has pointed out the wide composition specifications of Type 410 base metal and welding consumables as the leading cause for significant hardness and toughness variations, related to exceeding the A1 temperature during PWHT and formation of fresh martensite, and to retention of significant amounts of delta ferrite. Predictive equations for the A1 temperature and the content of retained delta ferrite were used to identify optimal composition for Type 410 welding consumables with delta ferrite content below 20% and A1 temperature close to the upper end of the ASME specified PWHT range. Experimental metal core filler wire was manufactured and tested to validate the A1 temperature and delta ferrite content. A test weld in Type 410 steel was produced with the new filler wire and subjected to PWHT, metallurgical characterization, and mechanical testing. The weld metal and HAZ properties met the corresponding NACE and ASME hardness and toughness requirements.

Advanced SAWL Developments and Optimizations for High Toughness, Low Hardness and Sour Environment

Natural gas exploitation has been increasing progressively and the pipeline community are facing more challenging demands to ensure safe and reliable operations. In that direction, gas fields in very harsh environments are demanding material and welding procedure selections to comply with a combination of important requirements such as toughness at low temperature, sour environment, very low hardness, manual ultrasonic inspection (for UOE longitudinal weld soundness assurance) and others. Looking forwarding big challenges, Tenaris Confab has been successfully working to continue improving the know how regarding plate to pipe mechanical properties behavior, through steel selection using TMCP plates, welding consumables definition and process control to assure material performance. Considering this scenario, the main challenge is to comply with a combination of toughness and hardness requirements, assuring the material soundness through manual ultrasonic testing after 48h. These combination lead to a careful selection of welding consumable to add the right content of alloy element at the welding pool aiming a specific weld metal chemical composition after dilution. The alloy element selection has to be considered due to the aimed final microstructure at the weld metal, i.e. increases acicular ferrite, in order to achieve the toughness, hardness and manual ultrasonic performance for delayed hydrogen cracking (DHC); it is important to avoid grain boundary ferrite (GBF) nucleation. High wall thickness and high heat input increases residual stress after pipe welding, high residual stress combined to poor microstructure and hydrogen, is a perfect scenario for DHC. To avoid hydrogen cracks, a robust pipe forming process and welding concept is needed to give enough energy to diffuse hydrogen out from weld metal. Quality controls were applied to strict hydrogen content such as welding consumable specifications, evaluating the correlation curve between flux moisture and diffusible hydrogen, flux temperature control and others. As a result of those actions, good mechanical properties were achieved and overcoming the hydrogen cracking performance during automatic and manual ultrasonic testing confirm a robust pipe forming and welding procedure for demanding projects.