High Strength Structural Steel Welding Report

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WELDABILITY STUDIES OF HIGH STRENGTH STRUCTURAL STEEL FOR MARINE APPLICATION BY GMAW PROCESS

OmprakasamS Dr.B.Basu

ABSTRACT
The ship building industry is one of the pre dominant industries that utilizes welding for construction. The recent developments of weld consumables for the construction of ships has helped to improve durabilty. The development of a high strength high toughness structural steel (DMR249B) for construction of naval ships and Submarines is considered as a stepping-stone in this field. In this research work, we have investigated the weladbility of high strength structural steel (DMR 249B) using controlled thermal severity testing (CTS) test for GMAW welded compound. Cold crack test was carried out on the plate
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INTRODUCTION
DMR249B steel is a high strength high toughness structural steel used for ship building applications. These steels provide a desirable combination of high strength, superior toughness, fatigue resistance and excellent weldability. DMR 249B steel is quenched and tempered to achieve minimum yield strength of 390 and 580 MPa respectively. The various welding process used for welding of these steels are Flux Core Arc Welding, Manual Metal Arc Welding, Submerged Arc Welding, and Gas Metal Arc Welding. Out of these welding processes, GMAW is the most widely used for ship building and ship structural applications.

Recently, Indian electrode manufacturers are producing different types of welds consumables like welding electrodes and wires for SMAW, GMAW, SAW, FCAW processes to the DMR 249B steel for naval
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The top plate has the dimension 76x76 mm, thickness being same as the bottom plate. Both the plates are bolted together securely. Two fillet welds, called anchor welds, are laid between the top plate and the bottom plate. The bolt is again tightened. The test plate is allowed to cool to the room temperature.

Procedure Specifications

Fig-5 sectioning of CTS specimen

Using the selected electrode test welds on the remaining sides of the assembly was laid taking care to see that test specimen is not over heated. The welded assembly is stored for 72 hour for any cracks to develop. After 72 hours the test welds are cross sectioned and polished to see if there any cracks in the heat affected zone.Finally the specimen is polished, etched and examined under microscope at 200x magnification to detect any microcracks in the heat affected zone. During testing we had recorded the heat input for which we had developed a gadget. We conducted several tests with various heat inputs.
RESULT AND DISCUSSION
Microstructure of the base metal, HAZ and the weld metal was revealed by optical microscope as per the three different heat input variations and different conditions are shown in fig.6 &

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