Use of the implant test and acoustic emission technique to investigate hydrogen‐assisted cracking in the fusion zone of welded HSLA‐80 steel

Abstract

Summary Hydrogen‐assisted cracking in the fusion zone (FZ) was studied, using flux‐cored wire (AWS E 70T5 and AWS E 120 T5‐K4) and a CO2 + 5% H2 gas mixture to induce high values of diffusible hydrogen in high strength, low alloy steel (HSLA‐80) welds. An acoustic emission measurement system (AEMS) based on a root mean square (RMS) voltmeter was coupled to the implant test apparatus (NF 89–100) to determine energy, amplitude and number of signals. Using optical microscopy and scanning electron microscopy (SEM), it was observed that, in all tests, cracks were initiated in the partially molten zone and propagated in the coarse‐grained region of the heat affected zone (HAZ) when E 70 T5 wire was used and quasi‐cleavage (QC) fracture mode was predominant. When E 120 T5 K.4 wire was used, the cracks were propagated vertically across the FZ and the mixed fracture mode was predominant. A significant relationship between acoustic emission (AE) parameters and fracture modes was found in the cracking mechanism.