Effect Of Heat Treatment Process On Microstructure And Properties Of High Boron Low Chromium Cast Iron Teeth Roll

In order to improve the properties of low chromium cast iron, this paper designs two kinds of low chromium boron cast iron materials. Microstructure and mechanical properties of two kinds of low chromium boron cast iron materials is studied by heat treatment test, hardness test, impact-toughness test, optical microscope (OM) observation, X-ray diffraction (XRD) analysis and scanning electronic microscope(SEM) analysis.The results show that:The cast microstructure of two materials are both composed of pearlite and carbides and residual austenite, the content of carbides in high carbon high boron and low chromium cast iron is about 67.4%, the carbide microstructure is coarse; the content of carbides in low carbon low boron and low chromium cast iron is about 30.3%, The microstructure is relatively small and dense. After the heat treatment of different heating temperature and holding time, the microstructure of two materials are both composed of martensite, carbides and residual austenite. The microstructure of two materials are both composed of tempered martensite,carbides and residual austenite after tempering heat treatment of different temperature and time, the carbide of metallurgical microstructure is mainly eutectic carbides and secondary carbides, eutectic carbide belongs to M3C type net carbide, the secondary carbides is M23C6 type carbides of granular distribution.With the increase of tempering temperature and time, eutectic carbide morphology did not change basically, secondary carbides of the matrix organization has the trend of aggregation group up and granular.With the increase of heating temperature and holding time, the hardness of two materials are both have the trend of increase at first and then decrease. After normalizing treatment at 920℃×2h, hardness of high carbon high boron and low chromium cast iron is 59.5HRC, the impact energy is 5.5J; after normalizing liquid treatment at 920℃×0.5h, the hardness is 67.5HRC, the impact energy is 3J. After normalizing treatment at 960℃×1h, hardness of low carbon low boron and low chromium cast iron is 52.2HRC, the impact energy is 6.1 J; after water quenching treatment at 920℃×0.5h, the hardness is 66.5HRC, the impact energy is 5J. With the increase of tempering temperature, the hardness of two materials both showed a change trend of rapid decrease after slightly change. After normalizing and normalizing liquid treatment, the hardness transition temperature of high carbon high boron and low chromium cast iron are both 450℃; after normalizing and water quenching treatment, the hardness transition temperature of low carbon low boron and low chromium cast iron is 600℃ and 450℃ respectively. After tempering at different times, the hardness of two experimental materials were little changed.After different cooling medium treatment, the property variation range of high carbon high boron and low chromium cast iron is hardness of 59.5-68.5HRC, impact energy of 2-5.5 J, after using 100% normalizing liquid treatment, the material has better comprehensive properties. After different cooling medium treatment, the property variation range of low carbon low boron and low chromium cast iron is hardness of 52.2-66.7HRC, impact energy of 4.2-6.1 J, after using water quenching and oil quenching treatment, the material has better comprehensive properties.