Studies On The Effect Of Heat Treatment On Microstructure And Properties Of White Cast Iron For Mill Guide Roller

Guide roller of mill was in high temperature and high speed rolling conditions, when the mill worked. Higher requirements for guide roller of mill’s high-temperature oxidation resistance, hot hardness, wear resistance and thermal fatigue resistance were put forward. As the excellent performance of anti-wear material, the chromium white cast iron was applied to guide roller of mill. During the preparation of guide roller of mill, reasonable annealing heat treatment was applied to improve its machinability. Reasonable quenching and tempering heat treatment were applied to improve its microstructure and properties, which can satisfy the actual working performance of guide roller of mill.In this paper, Cr13% white cast iron was used as the research material. First of all, based on the research work on microstructure and properties of the as-cast material, effects of different kinds of annealing processes on microstructure and properties of the material were explored, and then the best annealing process was determined. In order to obtain a higher hardness and better toughness guide roller of mill, influences of quenching and tempering on microstructure and properties of the material were explored. Finally, the high-temperature oxidation resistance of chromium white cast iron was studied. The main conclusions were summarized as follows:1. The as-cast Cr13% white cast iron’s matrix organization was austenitic and its hardness was 52.56HRC. In order to improve the machinability of material, effects of three kinds of annealing heat treatment processes on microstructure and properties were studied in detail. The results showed that the microstructure of Cr13% white cast iron after annealing process C (850℃×2h+600℃×15h) was pearlite and carbides(eutectic carbides and secondary carbides). Meanwhile, the hardness of material was markedly reduced to 39.54HRC. In this case, the machinability of Cr13% white cast iron was very good.2. In order to satisfy the actual working performance of guide roller of mill, quenching and tempering heat treatment were applied to improve the microstructure and properties of as-annealed Cr13% white cast iron. The results showed that the best quenching and tempering heat treatment process was 980℃×1h air quenching and 300 ×3h air tempering. The microstructure of material was tempered martensite, eutectic carbides, and a small amount of secondary carbides. The hardness of material was higher than 60HRC and the impact toughness was not lower than 4J·cm-2.The material was the best microstructure and mechanical properties.3. Researches on the high-temperature oxidation resistance of chromium white cast iron showed that as the temperature increased, the weight of oxidation increased, the oxidation reaction enhanced, and the high-temperature oxidation resistance declined. Nevertheless, as the content of chromium increased, the weight of oxidation declined, the oxidation reaction declined, and the high-temperature oxidation resistance significantly enhanced.From the above, the method of heat treatment process can obviously improve the microstructure and properties of Cr13% white cast iron for guide roller of mill. Reasonable annealing heat treatment can improve the machinability of Cr13% white cast iron. And, reasonable quenching and tempering heat treatment can obtain a higher hardness and better toughness of material to satisfy the actual working performance of guide roller of mill. The temperature and the content of chromium were closely related to the high-temperature oxidation resistance of chromium white cast iron. And, the temperature was the most important factor. So this paper may be a guide not only to produce but also to use chromium white cast iron for guide roller of mill.