Influence of temperature on the electrochemical coloration process and properties of the AISI 304 and 430 colored stainless steel

Abstract

The influence of temperature on the speed of an electrochemical coloration process of AISI 304 and AISI 430 stainless steel was investigated in temperature ranging from 25 °C to 40 °C. The surface properties of the interference colored nanofilms obtained in both types of stainless steel substrates, were also evaluated. A higher coloring speed was observed for AISI 304. The coloring time to obtain a gold color decreased with increasing temperature for both steels. This effect was stronger on the AISI 430 substrate, with a decrease of 36.6% in the coloration time for the samples colored at 40 °C and 25 °C. The Arrhenius model was applied to estimate the equations of colored films growth rate. The films porous fractions evaluated by SEM were in the range of 27–29%, without relevant variation with the coloring temperature. The nanohardness of the conjugated film-substrate obtained in a nanoindenter coupled to an AFM shows lower values than the uncolored substrates, and this reduction is more significant for the films grown on the AISI 430 ferritic specimens. The wettability of the surface to water and oil increased after coloring. The amplification effect of the hydrophilic effect can be associated with the increased AFM nanorugosity values.

Keywords

• Colored stainless steel
• Nanoindentation
• Wettability
• Interference film
• Nanohardness