B. Tigges, S. Benfer, A. Tenié, M. Yekethaz, W. Bleck, W. Fürbeth
In "Proc.Hot Sheet Metal Forming of High Performance Steel" (eds. K. Steinhoff, M. Oldenburg, B. Prakash), Verlag Wissenschaftliche Skripten, Auerbach 2015, 699-705
Press-hardening is an established process in automotive industry to produce high strength steel components and thereby reduce fuel consumption and increase passenger's safety.[[i]] The heat treatment at 950 °C prior to quenching leads to the formation of an oxide layer which causes problems in further manufacturing and surface treatment processes.
Oxidation at high temperatures can be hindered by application of protective layers[[ii]] such as Zn based coatings, AlSi and Nano-X. However, all systems in industrial use show significant disadvantages, i.e. burn-off of organic components at high temperatures, requested very low heating rates and confined weldability. Therefore, new routes for oxidation protection have to be found.
A novel way of oxidation protection is the coating of ethanolic sol-gel solutions on steel substrates resulting in thin films that can resist high temperatures of up to 1000 °C. However, measuring the oxidation rate of coated samples revealed that these films are only able to provide good protection up to 800 °C. At higher temperatures their ability to provide reasonable protection is decreasing due to the porous nature of the sol-gel film.
To overcome these problems, a new strategy using commercially available SiO2-dispersions with discrete nanoparticles and high solid contents was developed. By this, the oxidation could be significantly reduced even at temperatures of up to 950 °C.
[i] Hein, P.; Wilsius, J.: Status and innovation trends in hot stamping of Usibor 1500P. In: Steel Research Int. 79 (2008), pp. 85 – 91.
[ii] Fan, D.W.; Kim, H.S.; De Cooman, B.C.: A Review of the Physical Metallurgy related to the Hot Press Forming of Advanced High Strength Steel. In: Steel Res. Int. 80 (2009), pp. 241 – 248.