Toughness assessments of laser arc-hybrid welds of ultra high strength steel

Abstract

This paper investigates the toughness properties of laser arc hybrid welds of HT980 (980 N/mm2 class) and HT780 (780 N/mm2 class) steels. In the Charpy tests, a side groove specimen, along with the standard V-notch specimen, is employed to try prevention of fracture path deviation. A three-point bending test, a double-edge notch tensile (DENT) test, and a deep notch (DN) test are performed to measure the critical crack tip opening displacement (CTOD) at brittle fracture initiation. It is demonstrated that the critical CTOD is affected by the loading mode; critical CTOD by tension test is apparently higher than that by bending test. Nevertheless, three-point bend critical CTOD has exceeded the CTOD required value evaluated by WES2805 (“Method of Assessment for Flaws in Fusion Welded Joints with Respect to Brittle Fracture and Fatigue Crack Growth”) design curve with the allowable stress designed for an assumed crack. It has been observed that even though fracture pass deviation (FPD) occurred in a Charpy impact test, a straight brittle crack propagated throughout welded metal in a notched wide plate tensile test that was conducted at the same testing temperature as that of the Charpy impact test.