The output data of castings of various materials in China in 2010, including 29.5 million tons of cast iron, 9.9 million tons of nodular cast iron and 19 million tons of gray cast iron, accounting for 74.5% of the total output of castings in China, indicating that gray cast iron still plays a major role in casting production. Automobile industry is one of the main application fields of cast iron industry. Benefiting from the long-term and rapid economic development, China’s automobile industry has entered a period of rapid development. In 2009, China’s annual sales of automobiles were 13.7910 million and 13.6448 million respectively. In 2010, the annual sales rose to 18.267 million and 18.0619 million respectively, becoming the largest automobile production and marketing country. The output of automobile castings in 2010 increased by 2.3 million tons compared with that in 2009, accounting for 53.5% of the increase in the total output of castings.
The development of automobile, machinery, construction and other industries also provides good opportunities for the development of gray cast iron industry, but it is still faced with problems such as low casting quality, poor basic conditions of casting production technology and equipment, high energy consumption, poor technical and economic benefits, environmental pollution and so on. The dimensional accuracy of castings in China is generally 1-3 levels lower than that in developed countries, and the surface roughness is 1-2 levels lower. Under the same carbon equivalent condition, the grade of gray cast iron is 1-2 levels lower than that in foreign countries.
Although there is still a certain gap with foreign countries, the research on gray cast iron in China has been in-depth research. For example, for the research work of thin-walled high-strength gray cast iron, the strength of gray cast iron has been greatly improved and the processability has been significantly improved by improving the melting process, optimizing the alloy composition and carrying out inoculation modification. Of course, the improvement of gray cast iron strength also makes gray cast iron materials better used. At present, China mostly uses high-strength gray cast iron to produce high-power diesel engine cylinder block. The brands of high-strength gray cast iron are HT250 and HT300. The cylinder block of high-power diesel engine is a complex casting, and its wall thickness varies greatly. The thickness at the thin wall is only 5-6mm, while the thickness at the thick wall is more than 24mm, which leads to the differences in the performance of various parts of the cylinder block. Therefore, it is also necessary to study the machinability and section sensitivity of gray cast iron.
In recent years, the number of enterprises melting synthetic cast iron in induction furnace to produce high-strength and high horsepower engine cylinder head has also increased significantly. The furnace charge contains more scrap, and the nitrogen brought in by scrap has a significant effect on the strength of cast iron. Compared with the general gray cast iron with the same basic composition, the synthetic cast iron prepared with scrap steel and carburizing agent has a significant increase in the number of eutectic clusters, pearlite content and tensile strength of about 30-50mpa. At the same time, it also has good casting process properties. Therefore, the production of synthetic cast iron should be encouraged in qualified factories.