Generally, the carbon content is less than 0.2% is called wrought iron or pure iron, the content is 0.2-1.7% is called steel, and the content is more than 1.7% is called pig iron. Wrought iron is soft, good in plasticity, easy to deform, low in strength and hardness, and not widely used; pig iron contains a lot of carbon, is hard and brittle, and has almost no plasticity.
Ductile iron is a type of cast iron that undergoes spheroidizing treatment during the melting process to make graphite into a spheroid. It has high mechanical properties and good casting properties. Ductile iron has lower production costs than cast steel and better mechanical properties than ordinary cast iron, so it has been widely used.
(1) Nodular cast iron structure Nodular cast iron is composed of spheroidal graphite and metal matrix. In production practice, common metal substrates for castings are pearlite and ferrite.
"QT" in the grade is the first letter of the Chinese word "qiutie". The first number after the letter represents the lowest tensile strength, and the second number represents the lowest elongation.
It can be seen from the table that the ductile iron has a high yield strength, which is about 0.7-0.8 in tensile strength. The ratio of yield strength to tensile strength of general cast steel is lower than this value. This is an extremely valuable property of ductile iron.
Practice has also proved that ductile iron is a good wear-resistant material, and its wear resistance is better than gray cast iron and carbon structural steel. Therefore, it is used at home and abroad to make cylinder blocks, pistons, crankshafts, gears, and machine tools such as wearable parts.
In recent years, China has made rapid progress in the research, production and application of ductile iron, especially high-toughness rare-earth ductile iron and high-strength rare-earth magnesium ductile iron made of rare-earth magnesium as a nodulizing agent. Performance indicators have greatly exceeded the data listed in Table 2.
(3) Castability The ductility of cast iron is generally better than that of gray cast iron because of its higher equivalent weight, which is closer to the eutectic point. However, the temperature of the molten iron is often lowered due to the spheroidizing treatment, and the fluidity is deteriorated. The solidification process of ductile iron is not layer-by-layer solidification like gray cast iron, but it is performed simultaneously in the entire volume. Its shell is not solid. Therefore, the expansion of graphitization expands the shell, which increases the occurrence of shrinkage and The possibility of shrinking.
Nanjing Kirin Scientific Instrument Group Co., Ltd.