Ductile iron precision machining as one of the common processing technology, with high strength, high toughness, wear and other characteristics, is widely used in various fields. However, the defects of ductile iron precision machined parts are similar to those of other castings. And ductile iron precision machining will also appear some unique casting defects, such as black slag, graphite morphological variation, graphite distribution of state variation, subcutaneous stomata and anti-white and other shortcomings. The variation of the distribution of graphite in nodular cast iron is also very common. Our company has analyzed this kind of problem. Most of the hypereutectic or near-eutectic nodular cast iron is often present in the graphite-rich area at the top or hot section of the pouring position. Area graphite is spherical or burst, the fracture was dark black. The carbon content in this area is significantly higher than the average carbon content of castings, this phenomenon is often referred to as "graphite floating."

The main reason for the floatation of graphite is that the pre-treatment temperature and pouring temperature are too low, and the molten iron is held for too long. When the eutectic composition of the original hot metal at 1480 ℃ for furnace treatment, 1400 ℃ cast 50 ~ 80mm castings, to avoid graphite floating. Carbon equivalent of molten iron, the residual magnesium is high, the amount of graphite floating, reduce the thick part of the cold measures to speed up the casting cooling rate, but also help to avoid floating graphite.

Another situation graphite spheres anomaly profile is arranged linearly. Near the ball often appear some magnesium silicate and magnesium sulfide inclusions. The fine austenite dendrites in this tissue. Graphite balls may be formed at higher levels of subcooling. The heterogeneous organization sometimes appears at the junction of the riser neck and the casting. There are some white, non - directional facets on the fracture. The fracture surface occurs on a line that is perpendicular to the facet and has a linearly arranged graphite ball. Eutectic is too low, alloying elements and casting conditions conducive to improving the primary austenite undercooling can promote this heterogeneous organization. Ningbo Yinzhou Leisheng Machinery Co., Ltd. is a company specializing in precision casting processing, ductile iron precision machining, CNC die-casting processing and other products manufacturing, product quality is reliable, the price is qualified, please contact us.