The graphite of gray cast iron is flat and flat, while the graphite of nodular cast iron is round and spherical. However, the spheroidization of nodular cast iron is very good. If it produces a sound similar to hitting carbon steel, and the sound of gray iron knocking is very dull, what is the difference between nodular cast iron manhole cover and ordinary gray cast iron manhole cover?
In the smelting method, the spheroidizing agent and inoculant are added to the gray cast iron in the smelting process, so that the graphite can form a ball from the scattered floccules, so as to reduce the cut-off of ferrite, improve the strength and enhance the strength.
2. For spheroidizing rate, it can be said that the quality and price of ductile iron products with different spheroidizing rate are different. The spheroidizing rate of ordinary factory has reached 85% of the qualified products. The spheroidizing rate is 85% because of the casting time, there is no good spheroidizing and low-temperature iron formation, and the pressure on the finished products can not meet the requirements.
3。 From the fracture appearance, it can be simply divided into nodular iron and gray iron。 With the naked eye, the fracture particles of gray iron are relatively thick, gray white, with metallic luster on the crystal surface。 The fracture particles of nodular iron are very thin and black gray, such as the words with good nodules have no metallic luster, and if there is white luster, the common state is the appearance of white tissue。
4. Nodular cast iron has high strength and good toughness. Therefore, the cover of nodular cast iron well is about 30% lighter than that of the same type of gray cast iron well. QT500-7 is the trademark of nodular cast iron. The melt temperature of molten iron is not lower than 1456 ℃. Rare earth magnesium silicon iron is made and coke is selected in the nodularization treatment. The content of sulfur is low and the level of nodularization can reach above grade 3.
5. The gray cast iron manhole cover is directly melted into molten iron without any auxiliary materials, and then poured into the manhole cover. However, the nodular cast iron manhole cover is made by adding spheroidizing agent, rare earth magnesium and other metal alloys. Therefore, the market and relevant departments now require the use of the nodular cast iron manhole cover, because the bearing capacity of the nodular cast iron manhole cover is far greater than that of the gray iron manhole cover.