Surface quality of mirror pure Fe at high temperature

This paper studied the effect of different annealing temperature on surface roughness, surface morphology and grain orientation of the mirror surface pure iron insulated for 60 min in vacuum. The results showed that the root mean square surface roughness increased slowly with increasing annealing temperature below the polymorphic transition temperature, and that root mean square surface roughness of mirror surface mutated from 4-5 nm to 700 nm in the polymorphic transformation temperature and above. Recrystallized fine grains were observed on the sample surface at 810 ℃ by scanning electron microscope (SEM). Research of XRD {200} crystal plane pole figures on the raw material and samples with several temperature points between 860-960 ℃ showed that preferential crystalline orientation had occurred at 860 ℃, and that the crystalline orientation is more and more obvious with the temperature increasing. The study found that the recrystallization has little effect on the surface roughness. Preferential crystalline orientation made different coefficient expansion in different directions, and the polymorphic transformation leads to volume changes causing uneven surface by the extrusion between crystal grains and the deeper grain boundaries, which is the main reason causing surface roughness mutation.