SeAH Besteel Holdings Corp.

Absorption kinetics and mechanisms of CO in liquid Nb were studied at 2700-3000 K in samples levitated in CO/Ar stream.The C and O dissolution in liquid Nb from CO gas is an exothermic process, and the solubilities of C and O (Ce, Oe in at. pct) are related to temperature (T in Kelvin) and partial pressure of CO (P_co in atm) as follows: ln Ce + ln Oe - P_co = 2.32.10⁴/T - 2.35.The reaction CO → [C] + [O], which occurs along with the evaporation of Nb oxide during the absorption of C and O, is a 2nd-order process with a 1st-order dependence on C and O concentrations, resp.The absorption mechanism implies that the overall reaction rate is controlled by the substep of dissociation of surface-adsorbed CO mols.The rate equations for C and O absorption are given as follows:(dC/dt) = (1/0.76)(dO/dt) = 12.1(A/V) exp (-26,700/T)(Ce Oe - CO) where C and O are C and O concentrations in at. percent, resp., A is the surface area of the sample in cm², and V is the volume in cm³.

It was confirmed that main process variables for surface defects such as depression, bleeding, and vertical cracking of continuous casting bloom of low-C alloy steel are operation condition of main electromagnetic stirrer (M-EMS), quantity of mold cooling water, and mold powder.The surface defects were not improved much when those variables were individually improved, but simultaneous improvement of those variables eliminated the surface defects.

The development of direct quenching (DQ) steel bars by direct quenching and self tempering process was discussed.The authors investigated the production feasibility of DQ steel bars by submerged simulation test and then put into practice online DQ rolling by CRCT.The steels from submerged simulation and DQ rolling exhibited the microstructures and hardness equivalent to reheat quenching (RQ) steel bars.Also, mech. properties of direct quenched and tempered (DQ&T) bars were equivalent to those of RQ&T bars.The strength-toughness balance of DQ&T bars was superior to that of RQ&T bars.