Estudo da alteração em taxa de corrosão da liga DOMEX 700 MC devido a soldagem a laser

Abstract

The DOMEX 700 DC is a high strength, low alloy steel that is used in mechanical design of agricultural machinery and cranes, for example. Comparing its mechanical properties to AISI 1020 carbon steel, the DOMEX 700 MC has fourfold higher tensile strength limit (777 MPa) and twofold higher tensile strength limit (826 MPa). It is well established that welding metal alloys generates microstructural changes and, consequently, changes in the materials properties. Laser welding is an industry-leading technology process that allows metal joining with less distortion due to the reduction of the area exposed to heat during processing. Given these assumptions, this work aimed to analyze the microstructural changes, corrosion resistance, hardness, weld bead and thermally affected zone dimensions, due to laser welding of DOMEX 700 MC steel, as a function of scanning speed and laser beam power. For the studied parameters, it was verified that there was a dimensional reduction of the weld beads up to 64% inversely proportional to laser power and directly proportional to the sweep speed. The laser welding reduces the corrosion resistance of the steel when it has a zinc coating, due to partial evaporation of the zinc caused by the laser heating, exposing the base metal with lower corrosion resistance. If the zinc coating is absent, the presence of the weld beads improves the corrosion resistance by up to 30% due to microstructural changes such as grain size refining and phase shifting.