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Submerged arc welding of many high strength low alloy steels requires close control of welding procedures. An important consideration in welding procedure selection is control of the welding thermal cycle. In order to investigate the effect of welding technique on weld metal cooling rates, bead on plate weld cooling curves were measured for a wide range of submerged arc welding techniques. Temperature-time curves were obtained by plunging a platinum vs. platinum/13% rhodium thermocouple into the molten weld pool behind the arc.Cooling rates determined by computerized analysis of the cooling curves were related to welding technique. Weld metal cooling rates at 1000°F (538°C) and at 1300°F (704°C) were seen to correlate to welding heat input, weld nugget area, and welding preheat temperature. Regression analysis of the data resulted in empirical equations that described these correlations. Low alloy and mild steel base plate and welding wire compositions were found to have no measurable effect on weld metal cooling rates.A study of the effect of welding technique on weld nugget area resulted in an empirical equation that can be used to predict the effect of welding voltage on weld nugget area.In mechanical property tests of HY 130 weld metal, weld nugget area was shown to provide the best correlation between welding technique and resulting mechanical properties. Measured cooling rates for multi-pass welds were found to be lower than those for bead on plate welds. |
