Abstract
The changes of α-and β-Si3N4 on heating the liquid nitrided Fe-Si alloys (Si1∼3%) were studied by X-ray diffraction, electron microscopy and hardness test. In Fe-1 % Si alloy, α-Si3N4 was only obtained by nitriding. The amount of Si3N4 decreased by heating at 800°C∼1,000°C owing to Si3N4 dissolving in γ solid solution. The Fe-Si-N martensite structure was obtained in the sample quenched at 1,000°C. In Fe-2%Si alloy, α-and β-Si3N4 were obtained by nitriding. Those Si3N4 decreased by heating at 800°C∼1,000°C because it dissolved in the γ solid solution. In Fe-3%Si alloy, α-and β-Si3N4 were also obtained and Si3N4 decreased by heating at 900°C∼1,000°C. As there is no A3 transformation in the Fe-Si binary alloy, α solid solution (silico-ferrite) remains up to high temperature. Decrease of two nitrides is not due to dissolution in γ solid solution but to dissolution in α solid solution. The amount of α-and β-Si3N4 by the nitriding changed with the ability to form iron and silicon nitrides and diffusion rate of nitrogen in Fe-Si alloys. A large amount of Si3N4 was found in Fe-2%Si alloy up to 800°C.
