Horizontal continuous casting machine nozzles

Abstract

The determining role of the refractory part located in the mold of a horizontal continuous casting machine in formation of a high quality continuously cast billet has been discussed in detail in the domestic [i] and foreign [2,3] literature.Preliminary stoppage of teeming Of steel in a horizontal continuous casting machine and low quality of the billets cast are caused by wear (failure) of the refractory nozzle. The reasons for wear may be insufficient heat resistance and mechanical strength, low resistance to molten steel, excess wettability of the refractory material by the molten steel, and high thermal conductivity. Necessary conditions determining the life of the nozzle in a horizontal continuous casting machine are the absence of a gap at the joint of the refractory nozzle with the mold and the presence in the composition of the refractory material of components not wetted by the molten metal (C, BN, SiaN~, etc.) [i, 4, 5].As established experimentally, under the action of ferrostatic pressure of the molten metal in the metal reservoir (level of the metal 0.4-0.6 m) the metal flows into the gap between the refractory and the water-cooled surface of the mold with a gap thickness of 0.08-0.05 mm, forming a single whole with the solidifying shell of the ingot (Fig. la). In this case either the shell separates from the refractory with a gradual increase in the gap and accordingly poorer quality of the case billet and failure of the refractory (Fig. ib) or the shell does not separate from the refractory in each step of withdrawal and rupture of it occurs at the junction of the fronts or at the junction of the steps (Fig. Ic).The theory of nonwetting by molten metal of a refractory containing carbon and metal nitrides and carbides was presented in a preceding article [5].During experimental use of refractory nozzles of different compositions it was established that the zone of greatest wear in the absence of flow of metal into the joint of the refractory with the mold is the face portion of the nozzle at a distance of 4-6 mm from the mold (Fig. 2). This zone corresponds to the region of the ingot shell and to the region of the two-phase composition (liquid-solid) of the phase diagram, which was also confirmed by calculation [i]. The high surface activity of oxygen and sulfur at the refractory-metal interface of the phases (in the two-phase zone) leads to formation of intermediate products of interaction with the elements of the refractories being oxidized all the way to formation of solid or gaseous oxides (sulfides). This phenomenon is also confirmed by'analysis of the microstructure of disks from the zone of the junctions of the steps, where gas bubbles and sulfide inclusions are recorded. This process also leads to local wear of the refractory (Fig. 3).Several designs of the refractory nozzle-mold joint and also different refractory materials containing carbon and oxygen-free compounds have been tested on a horizontal continuous casting machine.Three plans of the nozzle-mold joint were tested: a) attached re...