Si-based coatings were formed on iron surfaces by low pressure chemical vapor deposition of pure SiH4 and He-diluted SiH4 under the following conditions: temperature of 350 to 850°C, gas flow rate of 0.1 to 100 sccm, gas composition of pure or He-diluted SiH4, pressure of 0.01 to 600 Torr and deposition time of 2 to 20 min. Coatings are essentially overlay type, with more than 30 at.% Si, for temperatures between 350 to 650°C regardless of other conditions. When the temperature exceeds 650°C, low gas flow rates (<10 sccm) produce diffusion type coatings with 26-29 at.% Si, whereas high gas flow rates form overlay coatings with underlying diffusion layers containing 2-5 at.% Si. Adjustment of conditions, mainly temperature and gas flow rates, allows the control of overlay or diffusion characteristics and composition gradient of coatings.