Hot cracking susceptibility of weld metals by angle expanding type cracking test (gas mixture ratio; 0, 20, 40%), chemical compositions of weld metals by bead welding (0, 10, 20, 30, 40, 50%) and mechanical properties, chemical compositions of weld metals by narrow gap butt welding (gap; 10 mm, 0, 20%) in the flat position and vertical position have been investigated for CO
2-O
2, Ar-CO
2, Ar-O
2 gas shielded arc welding of high carbon steel (0.65%C, 0.O26%S). The results obtained are as follows:
(1) Appropriate shielding gas composition concerning hot cracking susceptibility is CO
2+20%O
2. In case of Ar-CO
2, Ar-O
2 shielding gases, hot cracking susceptibility increase as increasing gas mixture ratio.
(2) In case of bead welding, carbon contents of weld metals increase 0.24%, to 0.34% as increasing gas mixture ratio. Contents of Si, Mn, Ti decrease as increasing gas mixture ratio. Decreasing tendency of these elements are in order of Ar-O2, CO2-O2 and Ar-CO2. Hot cracking are not recognized in the weld .metals:
(3) In case of narrow gap welding, weld metals with sound mechanical properties (tensile test, impact test) are obtained by CO2+20%O2. Carbon contents of weld metals for butt welding in the flat position are about 0.14-0.15% and for vertical welding are about 0.18% and hot cracking are not recognized in the weld metals.
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