Microstructural Evolution during Gas Tungsten Arc, Laser and Resistance Spot Welding of Al-Containing Transformation Induced Plasticity (TRIP) Steel

In this work, the microstructural evolution of aluminum containing commercial grade TRIP steels during gas tungsten arc (GTA), Laser beam (LB) and resistance spot (RS) welding have been studied. Microstructural analysis was carried out using optical and scanning electron microscopy. Results show that fusion zones of welded TRIP steels contain complex inclusions with similar size distribution. The energy dispersive spectroscopy analysis of inclusions indicated that these inclusions are primarily oxides of aluminum with epitaxial enrichment of manganese and phosphorous. The fusion lines of GTA and LB welded aluminum containing TRIP steel contain a zone of polygonal ferrite with a size of about 200 m and 50 m respectively. It is found that aluminum partitioned from the liquid weld to the solidified delta ferrite in the fusion line causing enrichment and resulting in ferrite stabilisation. This ferrite zone was not found in the case of resistance spot welded samples due to faster cooling rates.