Abstract:

The microhardness measurement, the ferrite content measurement and the metallographic microscopic observation of SAW (submerged arc welding) welding joint of  S30408 + Q245R composite board were carried out. Through these studies, the influence of welding line energy and the cooling rate on the microstructure of welding in the composite board base layer and the precipitation of the σ phase in the parent metal coating was discussed.Results showed that when using SAW welding in the base layer, the weld hardness was slightly lower than that of welding with SMAW (shielded metal arc welding) and the ferrite content in the base metal coating and that in the weld transition layer/coating were both slightly lower than those measured by SMAW in the base layer. The metallurgical structures of the weld layer of the two welding methods were basically the same. But the microstructure of weld coating/transition layer were different when using SMAW and GTAW (gas tungsten arc welding）. when using SAW in weld base layer, the weld microstructure has no obvious coarse grain characteristics, and neither parent metal coating nor the weld transition layer/coating would make the precipitation of σ phase happen.

Key words: submerged arc welding, welding process, composite plate,  austenite