Relationship of the structure of slide valve periclase plates to their metal resistance

Abstract

It is known that the degree of wear of the refractory plates in the slide valves of sLeel teeming ladles is determined primarily by their service conditions.Plates of the same mroducing plant provide normal teeming in some steel plants but in others may not be used and require replacement by stronger ones.The structure of refractory plates may also influence their life.For example, a comparison of the character of the structure and high temperature strength characteristics of corundum plates with their service results showed the possibility of evaluating plate quality from these indices [i].It has also been established that depending on the form of the periclase grains, which is the basic index of their purity, plates differ significantly in high temperature strength and thermal resistance, which correlates well with the service results of periclase plates. An increase in impurity content, primarily silicates, leads to the formation of an unsatisfactory microstructure, with the formation of fine layers between the periclase grains, and to a reduction in the life of the periclase plates.Petrographic investigation of magnesia plates after service showed that a substantial role in their wear is played by the formation of lamination cracks as the result of a reduction in the high temperature strength of the material [3].The relationship of the high temperature strength and wear of periclase refractories in teeming of steel to the content and composition of impurities, which determine the degree of development of direct bonds in the structure, has been described in [4]. Obviously, a generalized investigation of the relationship between the metal resistance of refractories for slide valve plates and their structure has great significance in the search for means of increasing their life and reliability in service.The investigations were made on samples cut from pieces for an MSP-95 periclase plate and produced at refractory plants (samples No. 1-4) and in the institute (sample No. 5). The pieces (standard) for samples No. i, 2, and 4 were made from fused periclase with 96-98 wt.% MgO and the piece for sample No. 2 was taken during the period of introduction of a method, including addition to the charge of 0.5% B~O3.The piece (experimental) for sample No. 3 was prepared from burnedpericlase clinker.The refractory from uhich sample No. 5 was cut was a biceramic insert.Its working portion was made from special purity periclase with a weight percentage of MgO of more than 99% with a sintering addition.The characteristics of the investigated samples are presented in Table I.The microstructure of the samples* is shown in Fig. i. Samples No. 1 and 4 have a similar structure characterized by the presence of sharp-angled and single-crystalline aggregates of 0.2-1.5 mm periclase grains and fine rounded grains.The silicates (monticellite, dicalcium silicate) form 0.01-0.05-mm filaments between the periclase grains.The voids are quite uniform in shape (elongated) and size (width 0.03-0.06 mm). At the interface of the filler and the...