The strength of gray cast iron mainly depends on graphite and matrix structure. With the increase of carbon equivalent, the strength of gray cast iron decreases. Low carbon equivalent cast iron generally refers to a kind of cast iron with less than carbon equivalent. This kind of cast iron generally has high strength, but its casting performance will deteriorate, the tendency of shrinkage porosity, stress and crack of casting defects will increase, and the tendency of white cast iron will be large, which will affect its performance. Therefore, the traditional low carbon equivalent gray cast iron is basically inoculated cast iron, such as HT250, HT300 and HT350. They are widely used in mechanical manufacturing, such as automobile, pressure vessel, machine tool and other fields.
For example, Li Wei of Chengdu University of science and technology and Sichuan Institute of Geology and mineral research carried out experimental research with barium ferrosilicon and found that the gray cast iron treated with barium ferrosilicon is more suitable for making gray cast iron with high grade, thin wall and large change of wall thickness; Zhang Feng of the new factory branch of Shanghai Tobacco Machinery Co., Ltd. studied high-strength gray cast iron. He added a small amount of alloy and inoculated it with inoculant to make the eutectoid transformation of molten iron more and more stable, refine some pearlite and promote the formation of carbides. The graphite of cast iron is like a spiral, The cutting effect of graphite on the matrix is reduced. At the same time, the number of eutectic clusters and tensile strength of cast iron are increased. Due to the addition of a small amount of alloy in the melting process, the amount of scrap steel is greatly reduced, which is of great significance to the poor quality of raw materials and scrap steel currently provided in China The Tonghai resin sand foundry of Yunnan CY Group has realized the continuous production of the above machine tool gray cast iron. Shijiazhuang sprocket general factory has optimized the gear production process, improved the molding process and melting process, and adopted low alloying treatment to make the castings in the as cast state meet the standard requirements in terms of hardness and strength, At the same time, the normalizing process is saved, the yield is improved, and the cost is reduced.
The application of rare earth in cast iron began in the s of last century. The British and first announced the application of clock to make nodular cast iron, which successfully realized the industrial production of nodular cast iron, while the wide application of rare earth in gray cast iron began in the s of last century.