Influence of hydrogen content on weldability of api 5L X80 steel
This paper reflects on the weldability of steel API 5L X80. The steel was delivered in a plate form, and was produced by the TMCP (Thermo Mechanical Controlled Process). FCAW (Flux Cored Arc Welding) was applied as a welding technology using three different filled wires. The flux in the wires was of rutile and basic character and the wires were delivered by two different manufacturers (A and B). According to the DOE (Design of Experiments) there were 14 different experimental states, by which 6 of them were in the center. Heat input (E, kJ/cm) and preheat temperature (Tp, 0C) were chosen as independent variables. The goal was to determine how each of the chosen variables affects the content of the diffusible hydrogen in the material after welding and the critical Implant stress through all experimental states. The experimental work was carried out at the Faculty of Mechanical Engineering and Naval Architecture in Zagreb, in the Laboratory of Welded Structures. Test pieces were made for experimental purposes to investigate the content of diffusible hydrogen and Implant test. Of all test pieces used for Implant tests, the ones that were declared as critical Implant stresses were used for macro and microanalysis, for hardness measurements (HV 10), and for SEM (Scanning Electron Microscope) and EDS (Energy Dispersive Spectrometer) analysis. Results were analyzed and statistically processed. According to the results and the design of experiment model it was possible to determine a mathematical model for prediction of the diffusible hydrogen content and critical Implant stress. Based on all collected results it was possible to determine the critical hydrogen concentration in ml H2/100g weld metal, and the optimal welding parameters for which the risk of HIC (Hydrogen Induced cracking) is minimized.
Tanja Tomić Kovačević
SVEUČILIŠTE U ZAGREBU, FAKULTET STROJARSTVA I BRODOGRADNJE