M. Nageswara Rao

Bio: M. Nageswara Rao is an academic researcher from VIT University. The author has contributed to research in topics: Welding & Acicular ferrite. The author has an hindex of 1, co-authored 2 publications receiving 1 citations.

Studies on Microstructure and Mechanical Properties of Weldments Produced in 12 mm Thick Naval Grade High Strength Low Alloy Steel for Sub-Zero Application by Single and Double Pass Hybrid Laser Arc Welding

Abstract: The present study deals with studies on HLAW joints produced in a naval grade HSLA steel using both single-pass (HLAW-1) and two-pass (HLAW-2) approach. The weld joints were subjected to different methods of characterization—optical microscopy, EBSD analysis, residual stress analysis, and mechanical testing. Microhardness testing, tensile testing and impact testing constituted the mechanical testing. Impact testing was carried out at both room temperature and − 60 °C. For both HLAW-1 and HLAW-2, the fusion zone and heat-affected zone (HAZ) showed higher hardness than the base metal and tensile fracture location was in the base metal. The HLAW-2 joint was characterized by a higher volume fraction of acicular ferrite, a higher fraction of high angle grain boundaries, and a finer grain size compared to the HLAW-1 joint. It is believed that these factors contributed to the observed higher impact toughness of the HLAW-2 joint at − 60 °C.

Effect of inclusions on microstructure and mechanical behavior of multi-pass welded naval grade steel:

Abstract: This paper assesses the metallurgical characteristics and mechanical properties of multi-pass gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of micro-alloyed steel DMR 249-A. The ...

Characterization of weld joints produced by continuous wave and double pulse gas metal arc welding in naval grade high-strength low-alloy steel

Abstract: The current research examines gas metal arc welding (GMAW) joints generated in naval grade high-strength low-alloy (HSLA) steel using both continuous wave GMAW (CW-GMAW) and double pulse GMAW (DP-GMAW). The joint was created in four passes with DP-GMAW, whereas CW-GMAW required eight passes. Weld joints were characterized using various techniques, including optical microscopy (OM), scanning electron microscopy (SEM), residual stress analysis, and mechanical evaluation. The mechanical evaluation consisted of microhardness, impact, and tensile tests. The Charpy V-notch (CVN) impact test was performed at room temperature and −60°C. For both CW-GMAW and DP-GMAW, the heat-affected zone and the fusion zone were harder than the base metal. The fracture occurred in the base metal region in all the tensile test specimens containing the weld joints. The DP-GMAW joints showed higher impact toughness at both room temperature and −60°C. In comparison to the fusion zone of the CW-GMAW joint, the fusion zone of the DP-GMAW joint had a greater volume fraction of acicular ferrite, a finer grain size, and a higher percentage of high-angle grain boundaries. These factors have contributed, it is believed, to the higher impact toughness of the DP-GMAW joint.

Characterization of steel weld metal in multi-pass submerged arc welds after post-weld heat treatment using electron backscatter diffraction

Abstract: Light optical microscopy (LOM) has previously been used to characterize and quantify steels microstructures; however, bainitic microstructures are complex and difficult to characterize accurately by LOM, particularly in multi-pass high-strength steel submerged arc weldments, which possess complicated thermal histories. More advanced techniques, such as electron backscatter diffraction (EBSD), can eliminate some of the ambiguity present in LOM characterization. EBSD allows for the utilization of features such as image quality (IQ) and inverse pole figures. This paper characterizes the microstructure of multi-pass high-strength low-alloy steel submerged arc weld metal after a stress-relief heat treatment using LOM and EBSD. Unlike LOM, EBSD was able to distinguish the various bainitic morphologies. Specifically, bainite, ferrite, and martensite were able to be distinguished by examining EBSD IQ, misorientation, and kernel average local misorientation.