Showing papers on "Shielded metal arc welding published in 2014"

Residual stress distributions in welded stainless steel sections

Abstract: Residual stress magnitudes and distributions in structural stainless steel built-up sections have been comprehensively investigated in this study. A total of 18 test specimens were fabricated from hot-rolled stainless steel plates by means of shielded metal arc welding (SMAW). Two grades of stainless steel were considered, namely the austenitic grade EN 1.4301 and the duplex grade EN 1.4462. Using the sectioning method, the test specimens were divided into strips. The residual stresses were then computed by multiplying the strains relieved during sectioning by the measured Young׳s moduli determined from tensile and compressive coupon tests. Residual stress distributions were obtained for 10 I-sections, four square hollow sections (SHS) and four rectangular hollow sections (RHS). Peak tensile residual stresses reached around 80% and 60% of the material 0.2% proof stress for grades EN 1.4301 and EN 1.4462, respectively. Based upon the test data, simplified predictive models for residual stress distributions in stainless steel built-up I-sections and box sections were developed. Following comparisons with other available residual stress test data, the applicability of the proposed models was also extended to other stainless steel alloys. The proposed residual stress patterns are suitable for inclusion in future analytical models and numerical simulations of stainless steel built-up sections.

Effect of welding variables on mechanical properties of low carbon steel welded joint

Abstract: A B S T R A C T� A R T I C L E I N F O� Thispaperdiscussedtheeffectofweldingvariablesonthemechanicalprop- ertiesofwelded�10�mmthicklowcarbonsteelplate,�weldedusingtheShield- edMetalArcWelding�(SMAW)�method.�Weldingcurrent,�arcvoltage,�welding� speedandelectrodediameterweretheinvestigatedweldingparameters.�The� weldedsampleswerecutandmachinedtostandardconfigurationsfortensile,� impacttoughness,�andhardnesstests.�Theresultsshowedthattheselected� weldingparametershadsignificanteffectsonthemechanicalpropertiesof� theweldedsamples.�Increasesinthearcvoltageandweldingcurrentresulted� inincreasedhardnessanddecreaseinyieldstrength,� tensilestrengthand� impacttoughness.� Increasingtheweldingspeedfrom� 40-66.67� mm/min� causedanincreaseinthehardnesscharacteristicoftheweldeds amples.� Initialdecreaseintensileandyieldstrengthswereobservedwhichthereafter� increasedastheweldingspeedincreased.�Anelectrodediameterof�2.5�mm� providedthebestcombinationofmechanicalpropertieswhencomparedto� theasreceivedsamples.�Thisbehaviourwasattributedtothefactthatin- creasedcurrentandvoltagemeantincreasedheatinputwhichcouldcreate� roomfordefectformation,�thustheobservedreducedmechanicalproperties.�

Stub column tests on stainless steel built-up sections

Abstract: This paper presents twenty-eight stub columns tests on stainless steel built-up sections. The test specimens, including I-sections, square hollow sections (SHS) and rectangular hollow sections (RHS), were fabricated by shielded metal arc welding (SMAW) from hot-rolled plates of nominal thicknesses 6 mm and 10 mm. The twenty-eight stub columns, of two stainless steel alloys (austenitic EN 1.4301 and duplex EN 1.4462), were tested in pure axial compression. Both tensile and compressive material properties were obtained by means of coupon tests in three directions – longitudinal, diagonal and transverse to the rolling direction. Geometric imperfection measurements for each specimen were conducted by means of a calibrated electric guideway, and residual stress distributions in the built-up sections were determined by means of the sectioning method. The test strengths were used to evaluate the design strengths predicted by EN 1993-1-4, the Continuous Strength Method (CSM) and the direct strength method (DSM). It was demonstrated that the predicted strengths from EN 1993-1-4 provisions were generally conservative, while both the CSM and the DSM predicted values were closer to the test strengths.

Experimental and numerical investigations of hybrid laser arc welding of aluminum alloys in the thick T-joint configuration

Abstract: In the present investigation, a numerical finite element model was developed to simulate the hybrid laser arc welding of different aluminum alloys, namely 5××× to 6××× series. The numerical simulation has been considered two double-ellipsoidal heat sources for the gas metal arc welding and laser welding. The offset distance of the metal arc welding and laser showed a significant effect on the molten pool geometry, the heat distribution and penetration depth during the welding process. It was confirmed that when the offset distance is within the critical distance the laser and arc share the molten pool and specific amount of penetration and dilution can be achieved. The models and experiments show that the off-distance between the two heat sources and shoulder width have considerable influence on the penetration depth and appearance of the weld beads. The experiments also indicate that the laser power, arc voltage and type of the filler metal can effectively determine the final properties of the bonds, specifically the bead appearance and microhardness of the joints. The experiments verified the numerical simulation as the thermocouples assist to comprehend the amount of heat distribution on the T-joint coupons. The role of the welding parameters on the mechanism of the hybrid laser welding of the aluminum alloys was also discussed.

Fume and gas emission during arc welding: Hazards and recommendation

Abstract: Welding is the principal industrial process used for joining metals, but at the same time, it’s the significant source of toxic fumes and gases emission. With the advent of new types of welding procedures and consumables, the number of welders exposed to welding fumes is growing constantly in spite of the mechanisation and automation of the process. Having in mind that, in some cases, toxic fumes and gases can be over the respective limits for toxic substances, one of the most important requirements for chosen welding procedure is its harmlessness to the environment. The health aspects associated with welding are complex and the industry is continuing its research to evaluate the effects of the welder’s exposure to typical constituents of welding fumes and gases, as well as its impact on what concerns climatic changes. The aim of this paper is to estimate the influence of the type of filler material on the emission of toxic substances, and to show the potential hazards. In order to determine that effect, microalloyed steel has been welded using two different filler materials (metal cored wire and self-shielded wire). The concentrations of emitted total dust, CO 2 , CO, SO, Mn, Ni, Al, Cr, Cr(VI), Ca and P were measured. By comparing results for both filler materials, it was established that the special attention must be paid to the high concentration of manganese and CO in metal cored wire, as well as high concentrations of phosphorus and aluminum in self-shielded wire. Also, conducted experimental measurements of emission of certain elements did not show higher toxicity of self-shielded wire compare to metal cored wire, what is in the contrast with previous studies.

Influence of welding process on Type IV cracking behavior of P91 steel

Abstract: Influence of laser welding (LW) and shielded metal arc welding (SMAW) processes on Type IV cracking behavior of modified 9Cr–1Mo (P91) steel has been investigated in this paper. The study involved comparison of stress rupture lives of modified 9Cr–1Mo steel weldments prepared by SMAW and continuous wave CO2 laser welding processes. Width of the heat affected zone (HAZ) in laser weldment was found to be 1.0 mm, whereas it was ~2.5 mm in SMAW weldment. The rupture lives of laser weldment were found to be higher than SMAW weldment at higher stress level and comparable at lower stress level. Under similar stress levels, the creep rupture lives of 875 °C heat treated specimens were found to be lower than that of the base metal and cross weld specimen. These results clearly suggest that the instability of microstructure in the intercritical heat affected zone (ICHAZ) is responsible for lower creep rupture lives of P91 steel weldment than the base metal. The experimentally observed variations in creep cavitation have been corroborated with the results of finite element (FE) analysis.

Effects of wire feed conditions on in situ alloying and additive layer manufacturing of titanium aluminides using gas tungsten arc welding

Abstract: An additive layer manufacturing (ALM) process based on gas tungsten arc welding (GTAW) was used to produce simple 3-dimensional titanium aluminide components, which were successfully in situ alloyed by separately delivering elemental Al and Ti wires to the weld pool. The difference in microstructure, chemical composition, and microhardness of four wall components built with four different wire-feeding conditions has been evaluated. There was no significant change in the microstructure of the four walls. The composition and microhardness values were comparatively homogeneous throughout each wall except the near-substrate zone. However, with increasing the ratio of Al to Ti wire feed rates from 0.80 to 1.30, an increase of Al concentration and γ phases were observed. The situation was reversed for the effect of the Al:Ti ratio on microhardness. Additionally, an unexpected increase in the α2 phase was produced when the ratio was increased to 1.30.

Microstructure and joining mechanism of Ti/Al dissimilar joint by pulsed gas metal arc welding

Abstract: Butt joining of titanium alloy Ti–2Al–Mn to aluminum 1060 using AlSi5 filler wire was conducted using pulsed gas metal arc welding. Joining mechanism of Ti–2Al–Mn/Al 1060 dissimilar joint with different welding heat input was investigated. Formations of precipitation and Ti/Al interface were discussed in detail. Fusion zone near aluminum is composed of α-Al dendrites and Al–Si hypoeutectic structures. A few TiAl3 precipitations appear in the weld metal owing to metallurgical reactions of Al with dissolved Ti. When the welding heat input was in the range of 1.87–2.10 kJ/cm, titanium alloy Ti–2Al–Mn and Al 1060 were joined together by the formation of a complex Ti/Al interface. With a low welding heat input, a serrate TiAl3 interfacial reaction layer was formed near Ti/Al interface. With the increasing of the welding heat input, α-Ti, Ti7Al5Si12, and TiAl3 layers were formed orderly from Ti–2Al–Mn to weld metal.

Evaluation on microstructure and mechanical properties of high-strength low-alloy steel joints with oscillating arc narrow gap GMA welding

Abstract: with the purpose of improving weld joint quality and productivity, the oscillating arc narrow gap gas metal arc (GMA) welding was employed in welding quenched and tempered high-strength low-alloy thick steel. The microstructure and mechanical properties of weld joints were evaluated, namely micro-hardness, tensile strength, and low-temperature impact toughness. The test results indicated that mechanical properties of weld joints with oscillating arc narrow gap GMA welding were excellent and found to meet stipulated requirements. Oscillating arc narrow gap GMA welding is a promising process for welding quenched and tempered HSLA thick steels due to the low energy input and narrow square-butt groove.

Characterization of Microstructure and Mechanical Properties of Inconel 625 and AISI 304 Dissimilar Weldments

Abstract: This investigation has been performed to characterize the microstructure and mechanical properties of the GTA and PCGTA welded dissimilar combinations of Inconel 625 superalloy and AISI 304 austenitic stainless steel. These welds were obtained by employing ERNiCrMo-3 filler metal. The weldments were characterized by the combined techniques of optical microscopy and SEM/EDAX analysis. Hardness and tensile studies were conducted to assess the mechanical properties of the weldments. Tensile studies showed that the fracture had occurred at the parent metal of AISI 304 side in both the cases.

Microstructural evolution during creep of 316LN stainless steel multi-pass weld joints

Abstract: Creep rupture behaviour of 316LN austenitic stainless steel weld joint fabricated by multi-pass shielded metal arc welding process has been studied at 923 K over a stress range of 120–225 MPa. The weld joint exhibited inferior creep rupture strength than the base metal and extensive creep cavitation in weld metal led to the premature failure. Weld metal microstructure was found highly inhomogeneous having different morphologies of delta (δ)-ferrite. The δ-ferrite transformed into intermetallic phases on creep exposure and the creep cavitation was associated with the intermetallic phases. Extensive creep cavitation in weld metal was confined to regions containing δ-ferrite with vermicular morphology. The region near the weld pass interface having globular δ-ferrite was less susceptible to creep cavitation. The globular δ-ferrite region possessed higher hardness than the vermicular δ-ferrite region. High dislocation density was observed in the globular δ-ferrite region which is a consequence of the microstructural modification by the heat input from the successive weld passes. The strength inhomogeneity between the globular and vermicular δ-ferrite regions together with the transformation of δ-ferrite into intermetallic phases produced pronounced creep cavitation in the vermicular δ-ferrite region which led to premature failure of the stainless steel weld joint.

Material characterizations of mild steels, stainless steels, and both steel mixed joints under resistance spot welding (2-mm sheets)

Abstract: Resistance spot welding is an essential welding mechanism for joining two or more metal sheets together in automotive industries. The mechanical assemblies are easily joined at discrete spots using high current flow through the area of concentration. It is easily achieved by compressing the base metals together to a certain pressure using copper electrode caps and allow the high current to flow through the concerned areas. The heat generation due to the current flow causes the metal sheets to be fused and consequently form bonds between base metals. The molten areas of base metals undergo solidification process by itself when the current flow is utterly stopped. Basically, the weld growth in any joint is determined by its process-controlling parameters, particularly the welding current, weld time, electrode force, and electrode tip. In these experiments, the welding current and weld time variations were carried out to characterize the weld growth for three types of joints mainly for stainless steel, mild steel, and both steel mixed joint. A pneumatically driven 75-kVA spot welder was used to accomplish the entire welding processes, and the welded samples were later subjected to tensile, hardness, and metallurgical tests to relate the diameter growth, loading force during tensile test, failure crack initiation, post-failure crack propagation direction, macro and microstructural changes, and also the hardness changes due to solidification process. Assessing the experimental results of 2-mm thickness of materials revealed that the welded areas’ characteristics have been varied from its original states to enriched states, in terms of shearing strength and hardness distribution as well as the microstructural orientation.