1Department of Marine Engineering, Amirkabir University of Technology, Iran
2Department of Marine Engineering, Bauhaus University Weimar, Iran
*Corresponding author: Mir Mostafa Hosseinioun, Department of Marine Engineering, Amirkabir University of Technology, Tehran, Iran
Submission: October 10, 2017; Published: February 20, 2018
ISSN: 2576-8840Volume3 Issue4
In this investigation, high strength low alloy (HSLA) steel plates, welded by Manual Metal Arc (MMA) process. The microstructure was studied accompanied with its effect on the mechanical properties. Microstructural features in each weld run as well as inter run region of the multi run weld metal were studied and the essential cause of deteriorated weld metal toughness were explained. The micro structural studies revealed:
1. Inter granular acicular and pro-eutectoid ferrite in the as cast last run
2. Refined grains in previous runs
3. Some heterogeneous ferrite grains as well as internal defects, porosities, and precipitated micro alloying elements in the inter-layer region with previous runs.
In the last run fusion and heat affected zones interface the solidification is phenomenon of epitaxial growth structure. However, in previous weld run there was neither epitaxial growth nor typical refined grains structure which is defined by Dube classification and IIW modification. The weld metal mechanical properties were varied in different parts of the welded plate due to the weld dilution with parent plate and inherited weld metallurgical characteristics in comparison with those from HSLA steel plate.
Therefore; there is a need for re-evaluate the codes and standards for definition and tolerance acceptance of the weld metal microstructural defects with comprehensive one in the as-cast structure, inter-run region and previous runs as well as their welding procedure specification.
Keywords: HSLA steel; Weld metal mechanical properties; Microstructural defects