Effect of Post Heating on Toughness of Bond Region for Super Duplex Stainless Steel Weldment
Yoshihiko KITAGAWA and Toshio KURODA
Abstract:Post weld heating was applied to the simulated samples of the bond region of super duplex stainless steel in order to improve the toughness of weld bond region. The heating temperatures used were 1173 K, 1273 K and 1373 K. The morphology of the secondary austenite changed from small intragranular type to massive austenite type as the heating temperature increased. The rate of austenite formation was fastest when the heating temperature was 1273 K due to the C-curve kinetics. When the heating time exceeded 120 s, the austenite content reached 50% in any heating temperatures. Charpy impact tests were performed using the specimens in which austenite content reached 50%. In the case of the heating temperature of 1173 K, the toughness was hardly improved probably because of the precipitation of chromium nitrides or small amount of sigma phase. When the heating temperature was 1273 K, good toughness comparable to the base metal could be obtained. It was found that the massive intragranular austenite arrested the cleavage crack and formed small steps and tear ridges among the cleavage facets from the fractographic observation based on three-dimensional morphology and observation of the cross sectional microstructure of cleavage fracture surface. Key Words:Super duplex stainless steel, Toughness, Bond region, Post weld heating, Secondary austenite