Carbon steel is widely employed in the production of parts and machinery which supply the most diverse industrial sectors, such as the production of domestic appliances and cars. However, it presents low chemical resistance, being necessary the superficial treatment with anti-corrosion substances. Most conventional surface treatments present harmful components to the environment and to life in general, as for instance, nickel, which is used in the phosphatization processes. More recently, researchers have been pointing to surface treatments which employ nanoceramics as potential substitutes to phosphatization. This study aims to develop a nanoceramic treatment to the carbon steel 1008, based on self-assembling molecule (SAM) and titanium dioxide. Carbon steel samples were SAM treated and then immersed in a solution containing TiO2. A chemometric study was developed to evaluate the best treatment conditions, using the software Designer Expert. For the electrochemical characterization, electrochemical impedance spectroscopy (EIS) tests were carried out. Results revealed that the SAM + TiO2 coating presents higher resistance to polarization than the samples treated with zinc phosphate, in a 0.01 mol L-1 sulphur acid medium.
Corrosion rate behavior of laser welded dual-phase galvanized steel, DP 600, has been assessed in comparison with the material without the laser weld, in 3.5% NaCl solution. Three combinations of both scanning speed and laser power parameters were selected, maintaining the thermal input of 30 J mm-1, calculated as the ratio between the laser beam power [W] and the scanning speed [mm s-1]. The corrosion studies included measurements of open circuit potential, micro and macro polarization, showing higher corrosion rates as scanning speed decreased. Optical microscopy showed the formation of a grain size refined morphology in the heat affected zone and fusion zone. A mechanism has been proposed to explain the corrosion behavior as a function of the laser parameters, which dictated the galvanized coating vaporization.
Roll bonding is a solid-state welding process widely used to manufacture layered metal composites. Particular properties may thus be obtained using the physical features of each material of the composite. Bimetal plates consisting of two different Fe-Ni alloys were made by roll bonding followed by heat treatment for 90 minutes at various annealing temperatures. The effects of post-rolling heat treatments on the bonding strength of a bimetal strip were investigated in relation to the interface microstructure evolution. Both recrystallization and grain growth took place at the interface during annealing. In particular, nucleation of new grains as well as growing grains crossing the interface may have contributed to the improvement of the bonding strength. Moreover, diffusion through the interface was found to drastically enhance the bonding strength from 850°C up to 1050°C. However, excessive grain growth associated to porosity occurrence probably caused the saturation of the bonding strength beyond 1050°C.
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