The difference of ductile iron and gray iron manhole cover of manhole cover
Because of the high strength and good toughness, nodular cast iron covers are about 30% lighter than those of the same type of grey cast iron manhole cover. Nodular cast iron grade by QT500-7, hot metal temperature not lower than 1456 DEG C, with low rare earth ferrosilicon magnesium alloy and the sulfur content in the ball at the disposal of the coke and nodulizing grade more than three grade.
From the smelting method, ductile iron is in the smelting of iron in adding inoculant and spheroidizing agent that graphite by dispersing flocculent into spherical ferrite to reduce the fragmentation, increase strength, performance mentioned to arrive.5, is the gray iron manhole cover does not add any auxiliary materials, pig iron smelting directly into molten iron, then poured into the manhole cover. But ductile iron manhole cover is to add spherical agents, rare earth, magnesium and other metal alloys, so now the market and the relevant departments requested the use of ductile iron manhole cover. That is because ductile iron covers, in the bearing capacity is far beyond the gray iron manhole cover.
From the fracture (not machined surface) can be a simple difference between the appearance of ductile iron and gray iron, with the naked eye, the iron grain fracture compared to thick, gray and white, crystal face with metallic luster. Ductile iron fracture of the grain is very small, black and gray, and if the ball is good, there is no metal luster, if there is white sheen, the general situation is that the white tissue.
1, the iron graphite is flat, flaky, ductile iron graphite is in the shape of a ball. Tapping a ductile iron, such as the sound of an approximately striking carbon steel, illustrates that spheroidal graphite iron is ductile. The percussion sounds very dull gray.2, on the rate of spheroidization, can say so, the same is the product of ductile iron, spheroidization rate is different, that quality is different, the price is also very different. The average factory rate has reached 85% for qualified products. Spheroidization rate below 85% is due to the casting time, without spheroidization, and the formation of molten iron temperature is low, the product produced by the pressure can not meet the request.
