Effects of Alloying Elements on the Toughness and Microstructure of HIGH CURRENT DENSITY GAS SHIELDED ARC PROCESS Weld Metals

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The effects of major alloying elements (Mn, Ni, Mo, etc.) and microalloying elements (Nb, V, B, etc.) on microstructure, hardness and toughness of single run HIGH CURRENT DENSITY GAS SHIELDED ARC WELDS made at 8.64KJ/mm (plate thickness 25 mm) have been studied. Microstructures of the weld metals were classified quantitatively. Toughness was assessed with respect to Charpy fracture transition temperature (vTs). An increase in acicular ferrite raised hardness. The fact that the increase in acicular ferrite was beneficial to improvement in toughness was valid within certain range of hardnesses (175-225Hv). However, the increase in acicular ferrite, i.e. the increase in hardness lowered toughness at a hardness level up to 175Hv due to the formation of much proeutectoid ferrite or over 225Hv due to the formation of martensite. Niobium and Vanadium increased ferrite side-plate regarded as undesirable microstructure, and raised hardness by precipitation of Nb carbides and V carbides during stress relief heat treatment, which resulted in lower toughness. The effect of Niobium was more influential than that of Vanadium. Boron increased acicular ferrite and inhibited the formation of ferrite side-plate, consequently improving remarkably toughness.
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1980-04-01