Deformation and fracture behavior of surface oxide scale on Fe-13Cr alloy in hot-rolling process

The behavior of the surface oxide scale on steel products during hot rolling process influences the surface properties of final products. To investigate the deformation and the fracture behavior of surface oxide scale of Fe-13Cr alloy, a hot rolling test was carried out. The oxide scale rolled out was observed in detail by using TEM. The specimen was hot-rolled after oxidation at 1100 degrees C for 90 minutes in air. The hot rolling tests with two conditions (I. The hot rolling test of the outer scale {=whole layer scale}, II. The hot rolling test of the inner scale that removed the outer scale) were carried out. The rolling reduction rate was 25, 44, 58, and 68%. The outer scale was composed of Fe2O3 and F3O4, and the inner scale was composed of Fe3O4, FeCr2O4, and a small amount of Fe2SiO4. Fe2SiO4 formed along the grain boundaries of the other oxides (Fe3O4, FeCr2O4) was observed by TEM. In the test I, Fe2O3 of the outer scale was pulverized to fine particle that looks like red powder, and Fe3O4 of the outer scale was cracked by hot rolling. A ductility-like behavior was observed in the inner scale (Test II). That is, it was found by the SEM observation that porosity and micro cracks of the surface oxide disappeared gradually. according to the increase in the rolling reduction. It was thought that the porosity and the micro cracks eased the compression stress caused by hot rolling. In the case of high reduction rate, FeSi2O4 which is a low melting point oxide, formed on grain boundary caused grain boundary slipping. When the rolling reduction is very high, plastic deformation by dislocation occurred in Fe3O4 and FeCr2O4. However, these oxides were broken, when their plasticity would not be able to accept considerably high rolling reduction.