Low temperature fracture toughness of thick duplex and superduplex stainless steel weldments

摘要

Low temperature fracture toughness behaviour of 40 mm duplex stainless steel (UNS S31803 -- DIN Werskstoff No.1. 4462) and of 35 mm thick superduplex stainless steel (UNS S32760 -- ZERON 100) weldments has been investigated. Welds were made usingSMA and submerged arc welding. The lowest notch impact test results of duplex and superduplex stainless steels weldments have been found at mid-thickness in the weld metal and at the fusion line for both shielded metal arc weldments. The shielded metalarc weld in the duplex stainless steel was clearly demonstrated to possess the lowest CTOD fracture toughness. All other weldments have provided minimum CTOD values beyond generally applied requirements. Thorough calculations of acceptable defect sizesbased on a Engineering Critical Assessment method have shown that well detectable surface breaking defects could be tolerated for all investigated weldments for service temperatures down to - 40℃. Performing wide plate tensile tests has proven that therisk for premature brittle fracture is extremely low and in all cases plastic straining was obtained prior to failure. Because of the overconservatism inherent in existing Engineering Critical Assessment, demonstrated by available wide plate test data, anew proposal for toughness requirements has been formulated which was suitable for most practical applications and for subzero temperatures based on experimental data.