STUDY OF THE INFLUENCE OF THE HEAT INPUT ON MECHANICAL PROPERTIES OF C-Mn STEEL WELD METALS OBTAINED BY SUBMERGED ARC PROCESS

The present work is part of a research program that aims to evaluate the technical feasibility of increasing productivity in the manufacturing of tubular components for offshore oil industry, which are fully welded by automatic submerged arc welding process, with high heat input, but with no impairment on the impact toughness of the weld metal. Multipass welds were produced by the submerged arc welding process, with a combination of F7A4-EM12K (wire/flux), by using a 3.2 mm-diameter wire, preheating at 80 degree C, with direct current, in flat position, with heat input varying from 3.5 kJ/mm to 12 kJ/mm. After welding, tensile tests and Charpy-V impact tests at -60 degree C, -40 degree C, -20 degree C, 0 degree C and 20 degree C were carried out, as well as metallographic examination by both optical (OM) and scanning electron microscopy (SEM), of specimens obtained entirely from the weld metal, allowing the discussion over the toughness X microstructure relationship. The weld metals have shown higher toughness levels in relation to the minimum required for use with low-alloy C-Mn steels welding with requirements of impact toughness of 27 J at 0 degree C for heat input up to 12 kJ/mm allowing an increase in productivity of 58% on the effective manufacturing time.