Effect Of Manganese On Microstructure And Properties Of Carbidic Austempered Ductile Iron

Carbidic austempered ductile iron (CADI) is a new ductile iron materials, which was developed from Austempered Ductile Iron in recent years. The components of CADI based on austempered ductile iron, adding a certain amount of carbide forming elements, there was a10%to20%of the carbide substrate after austempering heat treatment. CADI not only had the variety of excellent mechanical properties, also shows a more superior wear resistance than ADI. CADI has become one of the fa-mous materials of the21st century, and has good application prospects.In this paper, microstructure observasion, X-ray diffraction,Scanning electron microscopy, rockwell hardness test, impact toughness test, wear test, impact fracture observation and wear morphology analysis were conducted to study the effects of manganese and austempering temperature on microstructure and properties of CADI.The microstructure of as-cast CADI consists of spheroidal graphite, pearlite, carbide, and a very small amount of ferrite. The increasing manganese content not only promotes the formation of pearlite and carbide, it also leads to the decline of fer-rite, but the content of spheroidal graphite was decreased.The microstructure of CADI consists of spheroidal graphite, needle-like bainite, retained austenite and carbide. When the component contains manganese, Mn tend to dissolve out to form (Fe, Mn)3C. The increasing manganese content lead to austenite and carbide increased, while CADI Rockwell hardness increased, but lead to the de-cline of impact toughness. The wear rate of the sample decreased, wear resistance in-creased, materials became smooth, the furrows reduced, cutting marks faded gradu-ally.When the austempering temperature rose, the content of residual austenite in matrix increased, the stability improved, the morphology of bainite transforms from needle to feather, the content of martensite reduces gradually; CADI Rockwell hard-ness decreases, Impact toughness increases, the wear rate of the sample increased, wear resistance gradually decreased. Fracture morphology by SEM showed that, when the austempering temperature was220℃, impact fracture morphology was cleavage fracture characteristics, crystal sugar like pattern was presented in eutectic grain boundaries; When the austempering temperature was250℃, the fracture mechanism was mainly brittle fracture, therewere a lot of leavage steps and river-like patterns, but a little of flat cleavage facets and short curved tear ridges appeared in the fracture; When the austempering temperature was280℃, impact fracture morphology was quasi cleavage fracture characteristics.The wear resistance rusults showed that when the austempering temperature was220℃, the wear surface was smooth and flat, there was no adhesive surface and me-tallic transfer, its wear mechanism was micro-ploughing; When the austempering temperature was250℃, there was a little furrows, but its wear mechanism was still micro-ploughing; When the austempering temperature was280℃, cutting marks of wear surface were deeper, there was a little micro-spalling, its wear mechanism was furrow action and there was a little micro-cutting.The research on effect of manganese and austempering temperature on micro-structure and mechanical properties of carbidic austempered ductile iron was shown that, when the content of manganese was1.80wt.%, while after austeniting at900℃for90min and250℃salt bath furnace insulating for90min, the microstructure of CADI consisted of graphite spheres, bainite, retained austenite and carbide, the mor-phology of bainite was needle, the hardness was55HRC, impact toughness was9.2J/cm2and the wear rate was0.198mg/m.