Technical Aspects of Pulsed CVD Siliconizing of Steel Surfaces

摘要

Thick siliconized diffusion zones provide enhanced protection against corrosion. A realisation of pulsed siliconizing via CVD (PSC) of steel surfaces is presented. Totally integrated automation applications are used for the development and for exact control of the process run, for transferability and to ease the integration into industrial processes. This PSC process is combined with advanced heat treatment of the surface. The silicon is from the reduction of SiC14 with hydrogen at high temperature. At high temperature the silicon diffuses into the steel surface while cleaning with hydrogen flow. The reduction of SiC14 precursor takes place at the specific austenizing temperature of the steel during the first high temperature cycle of the typical heat treatment. The pause time between the Si-pulses is needed for dechlorination and other effects. The pulses and pauses are automatically generated with a combination of valves for volume and time control. The siliconized surfaces show increased resistance against oxidation and corrosion. This is used, for example, to protect tubes for boilers in new conventional power plants with increased steam parameters that show waterside oxidation.