Journal of Sol-Gel Science and Technology (2018) 86:568–579
https://doi.org/10.1007/s10971-018-4664-4
ORIGINAL PAPER: FUNCTIONAL COATINGS, THIN FILMS AND MEMBRANES
(INCLUDING DEPOSITION TECHNIQUES)
The effect of sol–gel boehmite coatings on the corrosion and
decarburization of C45 steel
Aleš Nagode
1
●
Kaja Jerina
1
●
Ivan Jerman
2
●
Daniel Vella
3
●
Milan Bizjak
1
●
Borut Kosec
1
●
Blaž Karpe
1
●
Borut Zorc
1
Received: 7 November 2017 / Accepted: 16 April 2018 / Published online: 3 May 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Sol–gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon steel by dip coating. After
the deposition the coatings were heat treated by drying at RT, 150 and 200 °C. It was found that for crack-free coatings, the
drying temperature needs to be ≥150 °C. Properly heat-treated boehmite coatings then improve the corrosion resistance of
steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the
decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and
thermomechanical process of C45 steel, i.e., <A
C1
(tempering, sphereoidization) and >A
C3
(austenitization, thermo-
mechanical process). The sol–gel alumina coating decreased the decarburization rate of the quenched steel during the
tempering (≤600 °C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a
smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings
can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the
decarburization. Under annealing conditions (T = 950 °C, t = 0.5–2 h) at which the oxidation rate is higher than the
decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface
together with the scale. No visual decarburization is then observed.
Graphical Abstract
* Aleš Nagode
ales.nagode@omm.ntf.uni-lj.si
1
Faculty of Natural Science and Engineering, University of
Ljubljana, Aškerčeva cesta 12, SI – 1000 Ljubljana, Slovenia
2
National Institute of Chemistry, Hajdrihova 19, SI – 1000
Ljubljana, Slovenia
3
Faculty of Engineering, University of Malta, Msida MSD, 2080,
Malta
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