Estudo da influência da concentração de cloreto e da temperatura na resistência à corrosão de aços utilizados em rolos do processo de lingotamento contínuo.

Abstract

The continuous casting process is one of the possible solidification routes of steel, commonly used in the production of slabs, sheets, billets or preforms. In this process, the liquid metal is poured and cooled through two main systems, one inside of the mold and another one outside of it with water showers positioned between the several types of rollers along the shaft of the equipment. These rollers also have an internal cooling system in order to make them able to withstand the high temperatures and tensions of the process, providing the maximum protection to the material. Therefore, the present work aims to study the influence of the chloride concentration in the water used on the secondary cooling and the temperature of the process on the corrosion resistance of three rolls, which one with different thicknesses. These materials were identified as the AISI 4140 steel for the body and as the AISI 414 steel for the coating. From each material sample, an electrode with dimensions of approximately 1 cm² was prepared. Solutions containing the following concentration of chloride ions in parts per million (ppm) were used: 150 ppm, 250 ppm, 350 ppm and 450 ppm. For each solution, the electrodes were submitted to the temperatures of 25 ºC, 35 ºC, 45 ºC and 55 ºC. The tests conducted to analyse the samples were electrochemical tests, such as Open Circuit Potential and Potentiodynamic Polarization, as well as the surface analysis by using an optical microscopy to acquire images with 100x magnification before and after the experiments. As a result, the tests shows that the corrosion resistance of the metals tend to decrease the more the temperatures gets higher and the more the chloride concentrations increases, thus the deterioration of the samples is more significant as the chloride content increases in the environment.