Title: Variation in magnetic properties of CRNO AISI M-43 grade electrical steel post laser and TIG welding

Abstract

A cold rolled non-oriented (CRNO) electrical steel of M-43 grade is widely used in medium capacity rotating electrical systems and domestic appliances are investigated for observing the variation in magnetic property and losses, post TIG and laser welding. The investigation is made on the toroidal core samples welded on 6 sides around the outer periphery using TIG and laser welding. The welded toroidal core samples are observed for estimating the variation in magnetic properties and power loss density at different ranges of magnetic flux density. Additionally, the grain size analysis and micro-hardness testing of the weld samples is performed. Significant increase in losses is observed for TIG welded M-43 grade samples. The microstructural investigation also revealed the existence of relatively coarse grains in the weld region of TIG welded samples as compared to the laser welded samples. The maximum increase in hardness of around 62.3 HV as compared to the base metal is observed for the TIG welded samples. The B-H curve obtained for M-43 grade TIG welded, laser welded and non-welded samples. The hysteresis losses are found to be increasing as a result of internal stresses generated due to the welding process. It is evident that the laser welded samples revealed much controlled grain size variation as compared to TIG welded.The etched samples are observed under Scanning electron microscope (SEM), the laser welded sample with polygonal shaped ferritic grains. The maximum grain size of 52.1 µm is at the base metal (BM) region. However, coarse sized grains of maximum size 120.8 µm is at Heat Affected Zone (HAZ) region and 187.5 µm in the Fusion Zone (FZ) for TIG. The grain size measurements are performed using the Image J software.