Characterization OF HAZ Simulated Microstructures OF Three HAZ’S in an API 5L X80 Pipe

API 5L X80 steel is a HSLA steel with several strengthening mechanisms. During welding, microstructural changes occur especially in the fusion zone (FZ) and in the heat affected zone (HAZ) caused by melting and by thermal cycles maximum temperatures and cooling rates. These changes involve new microstructures which can decrease steel strength and toughness by reducing the effect of the strength mechanisms produced during controlled rolling of the steel plate. In this work three simulated HAZ with same thermal cycles were made with Gleeble^® machine. Sample positions were in L-T and in T-L directions of base metal rolling direction and in the weld metal of the longitudinal pipe seam weld bead, which has a different chemical composition of base metal. The main idea of this paper was to simulate HAZ of longitudinal weld, girth weld and the HAZ created by the girth weld in the longitudinal seam weld. The thermal cycle maximum temperatures used in this paper were: 1300, 950, 800 and 650^oC. Microstructure was characterized by optical microscopy using Nital and Klemm 1 colored etching. The volumetric fractions of MA and eutectoid constituents were measured using an image analysis software. To evaluate toughness of simulated samples, Charpy V impact test were made at 0^oC. Optical microscopy and SEM analysis of impact test surface fracture were also made. The results showed a difference in the amount and morphology of MA in all simulated samples compared to as-received samples. Comparing the results, the higher amount of MA microconstituent was observed in 1300^oC thermal cycle maximum temperature, followed by as-received condition, 800, 950 and 650^oC with T-L impact test orientation presenting a higher amount than L-T. The longitudinal seam weld bead simulated samples presented a higher amount of MA, depending upon the thermal cycle maximum temperature. The toughness followed the same trend.