Magnetically impelled arc butt (MIAB) welding is a pressure welding process used for joining of pipes and tubes with an external magnetic field affecting arc rotation along the tube circumference. In this work, MIAB welding of low alloy steel (T11) tubes were carried out to study the microstructural changes occurring in thermo-mechanically affected zone (TMAZ). To qualify the process for the welding applications where pressure could be up to 300 bar, the MIAB welds are studied with variations of arc current and arc rotation time. It is found that TMAZ shows higher hardness than that in base metal and displays higher weld tensile strength and ductility due to bainitic transformation. The effect of arc current on the weld interface is also detailed and is found to be defect free at higher values of arc currents. The results reveal that MIAB welded samples exhibits good structural property correlation for high pressure applications with an added benefit of enhanced productivity at lower cost. The study will enable the use of MIAB welding for high pressure applications in power and defence sectors.

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Magnetically Impelled Arc Butt (MIAB) welding is an unique forge welding process in which an arc is drawn in the gap between the two tubes to be welded in order to raise them to a high temperature to allow forging to form a solid state weld. This paper presents the investigations carried out on MIAB welding trials of carbon steel tubes with varying upset current. Upset current is the short pulse of high current applied prior to upset. It plays a significant role in expulsion of molten metal and impurity from weld interface. This study aims at studying the effect of upset current on weld properties. Carbon steel tubes of SA-210 Grade A have been chosen with outside diameter of 44 mm and thickness of 4.5 mm. Mechanical and microstructural characterization of MIAB weldments was carried out. Good correlation exists between the mechanical properties/microstructure and upset current. Lower upset current has detrimental effect on weld tensile strength due to incomplete expulsion of decarburized zone.

High strength low alloy (HSLA) steels are developed to provide better strength, toughness, and improved weldability. These steels are often used as better alternatives for quenched and tempered steels due to the excellent combination of these properties. The beneficial properties in these steels are achieved by careful control of composition and by adopting suitably controlled thermomechanical processing (TMCP). Improved weldability is achieved by maintaining carbon at lower level. To compensate the effect of carbon, small amounts of alloying elements, such as niobium, vanadium, titanium, aluminium, and nitrogen are added. Though these steels have good weldability, they suffer from hydrogen induced cracking especially at high strength levels. In the present study, hydrogen induced cracking susceptibility of a newly developed indigenous vanadium-titanium microalloyed high strength steel was evaluated by means of implant cracking test. Welding was carried out using the GMAW process at different heat input levels. It was found that the coarse-grained heat affected zone (CGHAZ) of the steel is prone for hydrogen induced cracking at lower heat inputs. The implant test results indicated that the critical stress level increases with increasing heat inputs. The results were correlated with the microstructural modifications that occur in the CGHAZ at different welding conditions. The microhardness variations in that region were in good agreement with the observed results.

Magnetically Impelled Arc Butt (MIAB) welding is a pressure welding process that uses the circumferential rotating arc to cause uniform heating of the faying surfaces. In this work, notched tensile testing of MIAB welded Carbon steel was carried out to determine the notch sensitivity of Thermo-Mechanically Affected Zones (TMAZ) and to compare the notch tensile property of these zones with the base metal property. In MIAB welding, after sufficient melting of the faying surface, a short pulse of high current is applied to expel the molten metal and impurities from the interface before welding. Insufficient expulsion and formation of Light Band (LB) zone at weld interface resulted in lower Notch Tensile Strength (NTS). Incomplete expulsion with lower upset current at the weld interface contributes to lower Normalized Notch Strength Ratio. Instead higher upset current contributed to higher NTS due to complete expulsion and stronger acicular ferrite formation. Other TMAZs away from the weld interface showed higher notch tensile strength with Notch Strength Ratio (NSR) and Normalized Notch Tensile Strength Ratio (NTSN) greater than unity.