Influência do ciclo térmico de soldagem na formação de tensões residuais em juntas soldadas de aços API 5L X65 e X70.

Abstract

The present work aimed to evaluate the influence of welding thermal cycle on residual stress levels in API 5L X65 e X70 steels welded joints used in pipeline for oil and gas transportation using different welding processes and consumables. Analysis of microstructure and micro hardness were also investigated. The welding process utilized were: Shielded Metal Arc Welding (SMAW); Flux-Core Arc Welding (FCAW-self protected); and Gas Tungsten Arc Welding (GTAW). The transverse and longitudinal residual stress, were measured in regions of the root pass (bottom) and finishing (top), through the technique of X-ray diffraction by a portable diffractometer. The acquisition of welding thermal cycles was by direct method using a thermocouple Chromel Alumel located in two regions of the heat affected zone (HAZ). The cooling time between 800 and 500°C, (Mm) and the peak temperature (Tp) were measured. The effects of (Mm) values on the welded joint microstructure were evaluated. Compressive residual stresses were found in the weld metal and trative in the HAZ. Lower values of residual stress were found in root passes welded by GTAW process. There were no significant changes in microhardness welded joint values for the welding parameters used.