Recent Improvement of Continuous Casting Practice for High Quality Free Surface Defect Slab Product of Gas Cylinders Application

摘要

Due to high crack sensitivity of slab product of gas cylinders application, its continuous casting process and alloy composition were continuously evaluated and then improved to overcome its critical solidification process. The study was conducted at CC No.3 Slab Steel Plant Krakatau Steel. The purpose was to improve slab surface quality by reducing surface defects such as longitudinal, transverse and star crack so that the slab surface doesn't need to be totally scarfed. The method applied was by performing plant trial process, which the casting parameters such as casting powder selection, metallurgical cooling, mould level control, superheat and casting speed were continuously monitored and then adjusted to the surface quality of the product. The casting powder selected has lower viscosity and melting point than the previous one. The water quantity was reduced from 0.67 l/kg to 0.58. l/kg at casting speed of 1.1 m/minute. The mould level was controlled in the range of +- 5%. The casting speed was dynamically adjusted to the temperature condition. In addition the chemical composition such as carbon was designed to achieve optimum casting parameters by setting the carbon content less than 0.09% in order to avoid the peritectic grade. The results of the study are decreased surface defect quantity, free intercolumnar crack and smooth casting process. The quantity of the transverse and longitudinal crack decreased by almost 90%. The star crack was reduced from 62.21 % to 28.87 %. The slab surface scarfed was significantly reduced from 85.54 % to less than 25%. The yield loss per slab of the steel decreased from 3.4 % to 0.05 %. These new casting parameters and developed alloy composition are then used and standardized for the mass production of the steel.