1、 球墨铸铁强度高、韧性好,因此球墨铸井盖比同类型灰口铸铁井盖轻30％左右。球墨铸铁牌号采用QT500-7,铁水出炉温度不低于1456℃,在球化处理时增配稀土硅铁镁合金和选用含硫量低的焦碳,球化级别达三级以上。球墨铸铁试件的力学性能如下： 抗拉强度：500N/MM 2 延伸率：7％
1. Nodular cast iron has high strength and good toughness, so it is about 30% lighter than the same type of gray cast iron. QT500-7 is adopted for nodular cast iron, and the temperature of molten iron is not lower than 1456 ℃. Rare earth ferrosilicon magnesium alloy and coke with low sulfur content are added during nodularization treatment, and the level of nodularization is above grade III. The mechanical properties of ductile iron are as follows: tensile strength: 500N / mm2, elongation: 7%
2. Graphite of gray iron is flat and flat, graphite of nodular iron is round and spherical. If the percussion of nodular cast iron makes a sound similar to that of carbon steel, it indicates that nodularization of nodular cast iron is good. And the sound of gray iron knocking is very dull.
3d捕鱼3。 As for the spheroidization rate, it can be said that the products of nodular cast iron with different spheroidization rate will have different quality and different prices。 Generally, the qualified products are those with the spheroidization rate of 85%。 The spheroidization rate is less than 85% because of the low temperature of molten iron caused by the lack of spheroidization during casting, and the bearing pressure of the products can not meet the requirements。
4. From the appearance of fracture (not machined surface), ductile iron and gray iron can be simply distinguished. Through visual inspection, the grains of fracture of gray iron are relatively coarse, gray white, and the crystal surface has metallic luster. The fracture grain of nodular iron is very small, which is black gray. If it is spheroidized well, it has almost no metallic luster. If it has white luster, it usually has white mouth structure.
5。 In terms of smelting method, nodular iron is achieved by adding inoculant and nodulizer to gray iron to make graphite change from dispersed flocculent to globular, so as to reduce the cleavage of ferrite, increase strength and improve performance
6。 The gray iron well cover is to smelt pig iron directly into molten iron without adding any auxiliary materials, and then pour it into the well cover。 But nodular cast iron manhole cover is made by adding nodular agent, rare earth magnesium and other metal alloys。 Before pouring, a certain amount of nodular agent is added to the molten iron for nodular treatment, and a small amount of inoculant is added to promote graphitization。 After pouring, the cast iron with nodular graphite crystals is directly obtained。 Therefore, the market and relevant departments require the use of nodular cast iron manhole cover。 That's because ductile iron manhole covers far exceed gray iron manhole covers in bearing capacity。
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