Influence of External Magnetic Field on Mechanical and Metallurgical Properties of Pressure Vessel Steel (SA 516 Grade 70) Welds Using Gas Tungsten Arc Welding

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Abstract
The mechanical and metallurgical properties of the weld play the most important role in the performance of welds which needs to be enhanced. The superimposing external magnetic field to the welding arc provided wonderful and favorable results for improving the shape and properties of the weld. In this research, different configurations of specially designed electromagnets were used to investigate their effects on the weld characteristics of SA 516 grade 70 welds. It was observed that 0–0–S–N configuration yielded maximum penetration (3.92 mm) compared with other configurations as well as the conventional gas tungsten arc welding (GTAW) process. Tensile test, Charpy impact test and microhardness were performed to investigate the mechanical properties and microstructure analysis was used to determine the metallurgical properties of the weld joints. The results show that the tensile strength, impact strength, and microhardness of magnetically controlled GTAW (MC-GTAW) weld was 620 MPa, 275 J and 198 HV respectively which is 3.16%, 22.76%, and 1.51% higher than the weld produced by GTAW process. It has also been observed that electromagnetic stirring refined the microstructure of the weld pool. The average grain size of MC-GTAW weld was 31.035 μm whereas 42.558 μm average grain was obtained in conventional GTAW weld. The electromagnetic stirring enhanced the weld cooling rate resulting in the formation of more acicular ferrite which is desirable.

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