Abstract

IF (interstitial free) steels are defined by the ultra-low carbon content, which ensures good ductility and plasticity, important properties for a good mechanical shaping and energy releasing during impact. Those properties are essential needs for automotive applications. Currently refractory solutions for steel ladle in Brazil are based on magnesia-carbon system, applied for slag lines, and alumina-magnesia-carbon, applied for metal lines. Both systems, which includes carbon levels generally above five percent weight, assure good performance, but are questionable considering carbon pick-up levels. Based on customer needs to produce low carbon IF steel, new families of free and low carbon alumina-magnesia bricks were developed. Wall and bottom metal line solutions were based on carbon-free alumina-magnesia system, with high corrosion resistance, high penetration resistance, adjusted in situ expansion and low thermal conductivity, which also assure no carbon pick-up into the steel. For the specific case of impact pad, a low carbon alumina-magnesia brick, with high hot mechanical strength, was developed to improve local erosion resistance and to reduce carbon pick up possibilities. Both solutions allowed the costumer the possibility to increase steel ladle life to 130 heats, safely working to avoid carbon pick-up in ultra-low carbon steel production.