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High Strength Steel Welding Research

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Final rept. 1 Mar 95-28 Feb 98

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By optimizing the contents of microalloying elements and elements that promote dual precipitation, a family of welding consumables with excellent characteristics were developed. These electrodes were insensitive to moderate variations in chemical composition or cooling rate, had acceptable strength and impact toughness, and exhibited more uniform mechanical properties throughout the entire weldment cross-section, including the reheated weld zones. An electrode containing 1.25 wt. pct. Mn, 2 wt pct Ni, 0.5 wt. pct. Mo, and reduced nitrogen met the project mechanical property requirements yield strength 88 to 115 ksi Charpy impact energy 60 ft-lb at 0 deg F and 35 ft-lb at -60 deg F. Adding 1.0 wt. pct. Cu and 0.03 wt. pct. Nb as dual precipitation agents, a consumable with 0.03 wt. pct. C, 1.25 wt. pct. Mn, 0.28 wt. pct. Si, 1.5 wt. pct. Ni, 0.50 wt. pct. Mo, Ti between the 240 and 400 ppm range, and N below 80 ppm, also easily met the Navy requirements. To improve hydrogen management in high strength steel welding, CSM investigated the following three metallurgical practices 1 use of fluoride additives to control hydrogen in arc welding plasmas, 2 adjustment of the martensite start temperature for hydrogen control, and 3 hydrogen trapping in high strength steel weldments. These concepts were incorporated in the design of innovative consumables for experimentation. Welding electrodes containing five percent cryolite, K3AlF6, reduced weld metal diffusible hydrogen content by approximately 25 percent. Results obtained using KF and MnF3 additions were even more encouraging, with over 40 percent reduction of diffusible hydrogen content The addition of 0.1 wt. pct. yttrium as hydrogen trap resulted in a fifty-percent reduction of diffusible hydrogen, from 6.7 ml to 3.1 H2100g. Addition of 0.2 wt. pct. yttrium reduced the diffusible hydrogen content even more significantly, to 1 ml H2100g.

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  • Metallurgy and Metallography

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