HT 후판강재의 용접 열영향부(HAZ)에서 발생하는 용접균열의 민감도에 관한 고찰

A Study on the Weld Cracking Sensitivity Around of Heat Affect Zone in Welded Thick(High Tensile Steel) Joint

The welding crack susceptibility around of heat affected zone in welded thick(HT80 steel) joint is very important, and especially the welded structure for industrial structure such as plant, shipping, bulding, car parts welding is needed various welding method. In joining method of welding structure, welding residual stresses inevitably occur welded joints after welding, the evaluation of welding cracking susceptibility in HT80 steel was performed using thermally simulated heat affected zones. So, this paper deals with investigations into the testing of electric shield metal arc welding(SMAW) process that is frequently in welding HT80 steel that are quenched and tempered after welding. It has been carried out to study the weldability using test of welded specimen in welding cracking of HT80 steel that frequently occur after reheating. Also, are selected for examining the mechanism of welding crack-occurrence and way to reliability in cracking of the welded metal. This examinations were carried out in terms of micro-structural characterization, micro-hardness measurement and welded bend test. It was found that welding cracking susceptibility increased as hardness increased and cooling speed of weld heat cycle, Cooling curve Diagram HT80 steel shows what can be prevented in the weld metal and heat-affected zone when be controlled by hardness value in heat treatment from 800℃ to 500℃, and welding crack susceptibility of HT80 is not occur when bead pass below about multi 10 pass. It evident that welding cracking susceptibility can be eliminated or reduced by controlling the welding parameters such as the realation of cooling cycly, max. hardness value in HAZ, affect of residual stress according to reheating cycle or In view of the results, welding crack is not occur below about 490MPa(50kgf/mm2) in reinforcement and welding pass is below about 10 pass. For the improving of Welding crack can be controlled of various parameters(decrease of HAZ hardness, stress-relief in HAZ, micro-structural characterization, cooling cycle, etc.) in welding.