Avaliação do efeito da utilização de processos manuais e automatizados sobre a microestrutura e as propriedades mecânicas de aço API 5L X80.

Abstract

The objective of this study was to evaluate the influence of robotic and mechanized welding processes on the microstructure and mechanical properties of welded joint of API 5LX80 steel used in pipelines to transport oil and gas. For this plates of this steel were welded by manual Shielded Metal Arc Welding (SMAW) process with interpasses temperatures of 473 e 673 K, and using AWS E8010-G electrode as filler metals ; robotized Flux Cored Arc Welding (FCAW) process, using AWS E71T-1C wire with a diameter of 1.2 mm and Ar25%C02 as consumable and mechanized Gas Tungsten Arc Welding (GTAW) process, for the root pass using AWS ER70S-3 with a diameter of 3mm and Ar as consumable . The weld metals microconstituent and columnar and equiaxials grains percentual and the granulometry and extension of the Heat Affected Zone (HAZ) and a qualitative analysis of microconstituents present in this region using optical and scanning electronic microscopy were performed. The microstructural analysis was related with the weld metals Charpy impact test results and with the welded joint Vickers microhardness profiles The results indicated that the weld metals obtained by automatized welding process presented the greatest Acicular Ferrite percentuais and a shorter and more refined HZA which promoted the best results of the impact test.