Influence of cast iron vacuuming on the level of mechanical characteristics of the material of the working layer of double-layer chromium-nickel rolls

The object of research is chromium-nickel cast iron of the working layer of two-layer sheet-rolling rolls of the LPKhNd design. At present, chromium-nickel cast iron is widely used for the manufacture of rolls for sheet and section rolling mills. One of the ways to improve the operational properties of products made of chromium-nickel cast iron is the refining of molten metal by vacuum. The existing problem is that information on the effect of vacuuming on the performance of chromium-nickel iron is very limited. Rolls with the most characteristic concentration of alloying elements for LPKhNd performance were selected for the study. When evaluating the properties of vacuumed cast iron and cast iron by traditional technology, the level of strength, hardness, as well as special properties were determined, the study of which is caused by the peculiarities of the operation of rolling rolls (thermal wear resistance and crack resistance). It has been established that there is no significant difference in the structures of rolls made of vacuumed and non-vacuumed cast iron. The structure of the rolls consists of martensite, bainite and carbides. With an increase in the content of graphite-forming elements (C, Si, Ni), graphite inclusions appear in the structure, and with their decrease, individual troostite colonies appear. The physical and mechanical properties of vacuumed and non-vacuumed cast iron are on the same level. The crack resistance of the chilled zone of vacuum cast iron is 12.35 % higher than that of cast iron of the traditional production method, and the transition zone is 11.96 %. The thermal endurance of the chilled zone of the roll material increased by 14.95 % as a result of vacuuming of the molten metal, and the transition zone – by 14.56 %. An increase in crack resistance and heat resistance can help reduce the chipping of the working layer of chromium-nickel rolls of sheet mills during operation and increase their resource indicators. The obtained results of research indicate a positive effect of vacuuming on individual indicators (crack resistance and heat resistance) of the working layer of the forming tools of sheet rolling mills.