Fracture toughness test for flux cored wire welded joint

Abstract

Test techniques using unloading compliance single specimens to determine crack opening displacement (COD) resistance curves for flux cored arc welded joints were investigated in detail. Computer based methods for data acquisition and processing were incorporated in the test procedure. The causes of the shorter calculated crack length in comparison with the length measured according to unloading compliance single specimen techniques were studied, and the counter measures used to correct the crack length were analysed. The COD resistance curves for YJ657 basic flux cored wire (FCW) weld metal and joint line regions were then obtained using these techniques. The correlation coefficient using the least squares method to fit the curves was greater than 0.99. The results showed that the present test system and computer based data acquisition and processing techniques offered advantages such as flexibility of operation, stability of performance, and high accuracy when they were used to measure the COD resistance curves for FCW welded joints. The test results also indicated that the characteristic value of fracture toughness (extrapolated COD at zero crack length) for the YJ657 basic FCW weld metal and joint lines at 253 K was greater than 0.1 mm, indicating high toughness. This was because the weld metal microstructure consisted of a large proportion of acicular ferrite plates which were in different orientations and therefore able to deflect propagating cleavage cracks.