SILICONIZATION OF HIGH ALLOYED STEEL FROM SOLID PHASE

Abstract

The studies outlined in the article are devoted to the problem of siliconizing the surface of high-alloyed austenitic steels, which are used to make high-temperature heating furnace coils for oil refining. The presence of coke-like hydrocarbons and non-hydrocarbon impurities, which are deposited on the inner surface of the pipes and coke, complicate the operation of the furnace units and significantly reduce the durability of the coils. One of the possible effective methods to combat coke deposition and diffusion of carbon from deposits deep into the metal is the saturation of the surface layers with silicon. Experiments have shown that silicon from the solid phase saturates the surface of tube steel 10X23H18. At the same time, the highest silicon adsorption on the surface is observed when the furnace is held for 5 h. When silicon diffuses deep into the material, no carbon is pushed aside before the diffusion front of silicon, as it was observed for ferritic-pearlite steels. Judging by the distribution of silicon, the diffusion front propagates along the grain boundaries and structure defects. At the same time, carbon is evenly distributed in the steel structure. It is shown that to achieve the desired effect, due to the obstacle of coke deposition on the inner surface of the furnace tubes and the diffusion of carbon into the chimney material, there is no need for long exposure at high temperatures, since the penetration depth of silicon does not increase significantly. Experiments have shown that more intensive interaction with silicon is observed on curved surfaces of steel. A similar result was obtained in experiments with a fragment of a welded joint. In further experiments it is necessary to test other compounds as a source of silicon.