MECHANICAL AND CORROSION PROPERTIES OF HIGH-STRENGTH 18-PERCENT CR AUSTENITIC STAINLESS-STEEL WELDMENT FOR BOILER

The properties of weld metal of 18Cr heat resistant austenitic steel c ontaining high copper, niobium and nitrogen were investigated to obtai n the matching filler metal for an austentic stainless steel of 18Cr-9 Ni-3Cu-Nb-N steel. This 18Cr-9Ni-SCu-Nb-N steel tube has been register ed as KA-SUS304HJ1TB in the Japanese official standard for fired power plant materials. This steel tube has a high temperature strength 1.4 limes as high as the conventional 18Cr steel ASME TP347H. Welding mate rial applicable to this steel is necessary in the fabrication. However , the weld metal consisting of the same chemistries as the base metal had a lower strength than that of the base metal. In this work, the ef fect of chemistries of molybdenum and nitrogen on the strength of weld metal was investigated. The addition of molybdenum up to 1 mass% was effective for improving the strength without a deterioration of the co rrosion resistance. The nitrogen was also effective for improving the strength, but the nitrogen can be decreased by vaporizing during tungs ten inert gas are welding. For improving the solubility of nitrogen in the molten pool, the addition of manganese was effective. From these findings, the chemistry of welding material was determined as 18Cr-16N i-3Cu-1Mo-3Mn-0.6Nb-0.2N and the tube weldment with that welding mater ial was evaluated in terms of mechanical properties including creep ru pture property. it was confirmed that the weldment had comparable prop erties to the base metal.