Showing papers on "Shielded metal arc welding published in 2017"

Effect of A-TIG Welding Process on the Weld Attributes of Type 304LN and 316LN Stainless Steels

Abstract: The specific activated flux has been developed for enhancing the penetration performance of TIG welding process for autogenous welding of type 304LN and 316LN stainless steels through systematic study. Initially single-component fluxes were used to study their effect on depth of penetration and tensile properties. Then multi-component activated flux was developed which was found to produce a significant increase in penetration of 10-12 mm in single-pass TIG welding of type 304LN and 316LN stainless steels. The significant improvement in penetration achieved using the activated flux developed in the present work has been attributed to the constriction of the arc and as well as reversal of Marangoni flow in the molten weld pool. The use of activated flux has been found to overcome the variable weld penetration observed in 316LN stainless steel with <50 ppm of sulfur. There was no degradation in the microstructure and mechanical properties of the A-TIG welds compared to that of the welds produced by conventional TIG welding on the contrary the transverse strength properties of the 304LN and 316LN stainless steel welds produced by A-TIG welding exceeded the minimum specified strength values of the base metals. Improvement in toughness values were observed in 316LN stainless steel produced by A-TIG welding due to refinement in the weld microstructure in the region close to the weld center. Thus, activated flux developed in the present work has greater potential for use during the TIG welding of structural components made of type 304LN and 316LN stainless steels.

Review on magnetically controlled arc welding process

Abstract: External magnetic field (EMF) has a strong effect on the welding arc shape, droplet transfer, weld forming, microstructure, and properties of joint metal. This paper defines the types of external magnetic field and reviews the development of magnetically controlled arc welding process, particularly, the effect of external magnetic field parameters on the welding process. It is found that the welding productivity, the weld formation, the ductility, and toughness of welded metal can be improved; and the welding residual stresses, the chemical inhomogeneity, and the welding defects can be reduced. Finally, the development trend is discussed in the later sections of the paper.

Microstructure, Mechanical and Intergranular Corrosion Behavior of Dissimilar DSS 2205 and ASS 316L Shielded Metal Arc Welds

Abstract: There are many industrial situations particularly in petro-chemical, marine, power plant and other such industries where the use of dissimilar metal weldments is necessary, mainly due to economic benefits and also sometimes to improve the performance of the component. Both austenitic stainless steels and duplex stainless steels have received much attention in recent days due to their superior anti-corrosive and mechanical properties. Further, the use of shielded metal arc welding (SMAW) process is inevitable in engineering industries. In the present work, microstructure, mechanical and intergranular corrosion behavior of dissimilar 2205 duplex stainless steel and 316L austenitic stainless steel fabricated by SMAW process using E2209 electrode by taking two different heat input (0.45–0.60 kJ/mm) was investigated. The microstructures were characterized by using optical microscopy and scanning electron microscopy (SEM), while the localized chemical information was obtained by an energy dispersive spectrometer attached to the SEM. Double loop electrochemical potentiokinetic reactivation test was performed to quantitatively assessing the intergranular corrosion based on degree of sensitization. The effect of weld dilution on mechanical properties (i.e. tensile/hardness properties) was also studied. The ferrite content was experimentally measured by using ferritoscope and it was observed that the weld joint achieved the required ferrite content for both the heat inputs. Higher ferrite content (results of faster cooling rate) increased the hardness and tensile strength of low heat input as compared to high heat input. While, high heat input improved the corrosion resistance due to formation of higher austenitic phases. Higher impact energy was observed in E2209 weld metal than that of the base metals. No welding defects were observed and recommended for industrial use.

Effect of Continuous and Pulsed Current Gas Tungsten Arc Welding on Dissimilar Weldments Between Hastelloy C-276/AISI 321 Austenitic Stainless Steel

Abstract: In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

Evaluation of strength property variations across 9Cr-1Mo steel weld joints using automated ball indentation (ABI) technique

Abstract: The variations of strength properties across 9Cr-1Mo steel weld joints fabricated by different arc welding processes such as shielded metal arc welding (SMAW), tungsten inert gas (TIG) and activated tungsten inert gas (A-TIG) have been evaluated employing automatic ball indentation (ABI) technique. ABI tests were conducted at 298 K across various zones of the weld joints comprising of base metal, weld metal, heat affected zone (HAZ) and intercritical HAZ (ICHAZ) regions. The flow curves obtained from ABI tests were correlated with corresponding conventional tensile test results. In general, the tensile strength decreased systematically across the weld joint from weld metal to base metal. Inter critical HAZ exhibited the least strength implying that it is the weakest zone. The incomplete phase transformation in the ICHAZ during weld thermal cycle caused the softening. The A-TIG weld metal exhibited higher UTS and strain hardening values due to higher carbon in the martensite. The strain hardening exponent exhibited only slight variation across the various regions of the weld joints. A-TIG weld joint exhibited higher weld metal and HAZ strength, marginally higher UTS to YS ratio in the weld metal and HAZ compared to that of the other two processes. Hence, among the three welding processes chosen, A-TIG welding process is found to be superior in producing a 9Cr-1Mo steel weld joint with better strength properties.

Erratum to: Mechanisms of weld pool flow and slag formation location in cold metal transfer (CMT) gas metal arc welding (GMAW)

Abstract: This work investigates the weld pool flow behavior by observing the flow pattern of floating slag particles for cold metal transfer (CMT) gas metal arc welding (GMAW) using three different welding wires. These wires contain different amount of deoxidizers in the form of silicon and manganese. In situ high-speed videography shows that for the wire containing a high amount of deoxidizer, the weld pool flows from the center towards the toe. With the presence of a lower amount of deoxidizers, it flows from the toe towards the center. Besides, a higher amount of CO2 in the shielding gas changes the amount and location of slag formation. Chemical composition analysis of weld metals relates the weld pool flow behavior with the amount of dissolved oxygen (surface active element). The presence of adequate amount of oxygen in the weld pool can alter the weld pool flow pattern, which changes with the amount of deoxidizers present in the materials and the amount of oxygen supplied through the shielding gas. Based on this concept, the mechanisms involved in weld pool flow pattern and slag formation location for different composition of the consumables are disclosed to improve weld quality and productivity through the selection of the proper welding consumables in CMT-GMAW.

Residual stresses in cold-wire gas metal arc welding

Abstract: This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5- mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.

Microstructure and Mechanical Properties of Cryogenic High-manganese Steel Weld Metal

Abstract: Extant studies have focused on the development of high-manganese austenitic steel, which is a potential cost-effective alternative to commercial cryogenic materials such as 9% Ni steels, 304 stainless steels, and Al5083 alloys. The development of suitable welding consumables is of significant importance in the commercial application of this new material for cryogenic applications. Specifically, flux-cored arc welding consumables that allow all-positional welding for high-Mn steel are required to fabricate liquefied natural gas (LNG) tanks. Hence, a welding wire alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) was developed for cryogenic toughness. The microstructure and mechanical properties were evaluated as a function of the alloy composition. This unique combination of strength and toughness demonstrated the potential of this newly developed high-Mn steel for cryogenic services.

GTA pulsed current welding of thin sheets of SS304 producing superior quality of joint at high welding speed

Abstract: Thin sheets of austenitic stainless steel (SS304) are assembled using various pulse parameters of pulsed current gas tungsten arc welding The sheets are joined with high welding speed for higher production rate, but the mean current is enhanced with higher welding speed for maintaining required heat input to get a sound joint Application of pulsed current gas tungsten inert gas welding for joining of SS304 has been found advantageous in the form of production of weld joints with better mechanical and metallurgical characteristics It has been observed that there can be elimination or lesser humping in weld joints Undercut or dipped weld faces are also not found due to application of pulsed current There is improvement of tensile strength and hardness by 125 and 12%, respectively The enhanced tensile strength and hardness is justified through TEM micrograph showing presence of dislocation

Optimization of vibratory welding process parameters using response surface methodology

Abstract: The current investigation was carried out to study the effect of vibratory welding technique on mechanical properties of 6 mm thick butt welded mild steel plates A new concept of vibratory welding technique has been designed and developed which is capable to transfer vibrations, having resonance frequency of 300 Hz, into the molten weld pool before it solidifies during the Shielded metal arc welding (SMAW) process The important process parameters of vibratory welding technique namely welding current, welding speed and frequency of the vibrations induced in molten weld pool were optimized using Taguchi’s analysis and Response surface methodology (RSM) The effect of process parameters on tensile strength and hardness were evaluated using optimization techniques Applying RSM, the effect of vibratory welding parameters on tensile strength and hardness were obtained through two separate regression equations Results showed that, the most influencing factor for the desired tensile strength and hardness is frequency at its resonance value, ie 300 Hz The micro-hardness and microstructures of the vibratory welded joints were studied in detail and compared with those of conventional SMAW joints Comparatively, uniform and fine grain structure has been found in vibratory welded joints

Single pass full penetration joining for heavy plate steel using high current GMA process

Abstract: As an arc voltage decreases, an arc length shortens and a surface of molten pool right under the arc becomes dented at a high current range in gas metal arc welding (GMAW) using 100% CO2 as a shielding gas and a carbon steel solid wire. And the arc is finally generated at a lower position under the surface of the molten pool and in a space formed by a wall of molten pool. A spatter generation level is extremely low even at a high current range in this metal transfer mode. This arc phenomenon is referred to as “buried arc,” and the arc stabilization technique at the high current buried arc more than 450A is described in this report. The arc phenomenon taken by an X-ray observation system and a high-speed video camera were observed using a low-carbon steel as a base metal, a carbon steel solid wire of 1.2 mm, 100% CO2 as the shielding gas, and travel speed of 30 cm/min. The high current buried arc stabilized by an external characteristic control of welding power source (maximum current 1000 A, maximum wire feed rate 100 m/min) showed three kinds of metal transfer mode including rotating transfer mode at the current range more than 450 A. Consequently, a new current waveform control combined an adequate gradient of the external characteristic and a low-frequency voltage oscillation, which realizes more stable high current buried arc, has been developed in order to improve a weld bead formation using these particular metal transfer modes.