High quality non-oriented electrical steels: ladle metallurgy aspects

Background/purpose: Stringent specification in respect of magnetic properti es and core loss values are required to be met for efficient and powerful d evices in electrical industries. Lowering of carbon, sulphur and nitrogen t o very low levels is essential to minimise the core losses. In addition, in clusion distribution, content and shape are also of significance. Methods: Extensive process modification especially during ladle refining, h ave been carried out at Rourkela Steel Plant (RSP) of the Steel Authority o f India Limited to develop high-grade nonoriented electrical steels with lo w core loss and high cleanliness rating. Measures include the development o f a decarburisation, deoxidation and alloying model for desired chemistry. High sulphide capacity CaO-Al2O3-SiO2 slag was used for deep desulphurisati on, and modification of the shape of inclusion was done by CaSi wire inject ion to improve the electrical properties. Similarly a scheme for denitrogen ation was worked out. Results: Measures developed resulted in achieving carbon <0.02%, sulphur 30 -60 ppm, nitrogen <40 ppm consistently. Conclusion: Close control of carbon, aluminium, silicon, sulphur, nitrogen and inclusion shape modification helped in achieving the excellent electric al properties.