Abstract

Title:         Improvement of Abrasion Wear Resistance of MgO-C Brick for BOF Scrap Impact Area

Authors:   Ryoma Fujiyoshi, Masakazu Iida, Atsuhisa Iida, Atsushi Torigoe and Hiroki Yoshioka

As generally accepted, reduction of green house gas emission is one of the most important tasks for all industrial sectors. For integrated steel mills, increase in steel scrap as raw material is an effective measure since it decreases use of hot metal from the blast furnace which emits large amount of CO2 gas. Therefore, amount of scrap charged to the BOF has been increasing. The increase in steel scrap charging accelerates the wear of the scrap impact area. Particularly, heavy scrap charging seriously damages MgO-C bricks installed on the scrap impact area. Thus, it is considered that mechanical abrasion is the dominant factor of refractory wear there.

In order to investigate the wear in detail, the scrap drop impact test, of which 12kg cubic steel mass was dropped onto the brick-assembled structure from 2m height, was carried out. According to the observation of the brick after the test, it was verified that the abrasion wear of scrap impact area is a result of linking of cracks, which were initiated and propagated by mechanical shock induced by scrap collision. Therefore, two ways for brick improvement were suggested. One was suppression of crack initiation and the other was suppression of crack propagation.

Therefore, three materials were developed as; high strength material, matrix reinforced material and carbon bond enhanced material. Purpose of high strength materials was improving crack initiation resistance. The other two materials were designed to improve the crack propagation resistance. High strength material was obtained by optimizing metallic additive distribution status. Matrix reinforcement was achieved by suitably engineered matrix graphite arrangement. Carbon bond was enhanced by adequate utilization of pitch. HMOR and Fracture energies were measured by three point bending test at 800℃ in an Ar atmosphere, the test sample were heat treatments at 1200℃ for 3h in cokes breeze. HMOR of these materials are 17, 13 and 12 MPa, respectively. Fracture energies of these materials were evaluated by three point bending test and evaluated values were 0.26, 0.40 and 0.49J, respectively.

By practical application, the wear rate index of these materials were evaluated as 100, 75 and 50, respectively. Remarkable reduction in wear rate was obtained for high fracture energy material. Proportional relation between wear rate index and fracture energy was clearly confirmed while poor relation was recognized for relation between wear rate index and HMOR.

Hence, it is concluded that suppression of crack propagation by improving fracture energy of MgO-C brick is essential for reducing abrasion wear of BOF scrap impact area.