Mechanism of Black Strips Generated on Surface of CSP Hot-Rolled Silicon Steel

Because of the effect of silicon on the formation of oxide scale, black strip defect is common on the surface of compact strip production (CSP) hot-rolled silicon steel, which leads to difficulty in pickling process compared with plain carbon steels. Although high-temperature oxidation of Fe-Si alloy has been discussed a lot, few studies have explained the mechanism of black strip defect generated on the surface of hot-rolled silicon steel and proposed means to prevent it effectively. Thermogravimetric analyzer (TGA) is used to simulate oxidation of Fe-2. 2Si alloy for 30 min under air condition, and temperature range is from 1000 to 1150°C. Effect of rolling deformation on scale morphology is also discussed. Electron probe microanalysis (EPMA) is used to analyze cross-sectional morphology and elemental distribution of the oxide scale. Schematic diagram of formation of black strip defect is obtained, which helps to provide theoretic basis for proposing of solutions for the problem. It is proposed that lowering furnace temperature and shortening time to stay at high temperature condition after rolling will be helpful to relieve the black strip problem.