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 carbon equivalent less than 3.9%. This kind of cast iron generally has high strength（ δb> 250Mpa), but the casting performance will deteriorate, the tendency of shrinkage porosity, stress and crack of casting defects will increase, and the tendency of white mouth 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 conducted experimental research with barium ferrosilicon HT250 and found that the gray cast iron treated with barium ferrosilicon is more suitable for gray cast iron with high grade, thin wall and large change in wall thickness; Zhang Feng of the new factory branch of Shanghai Tobacco Machinery Co., Ltd. studied the high-strength gray cast iron (HT300). He added a small amount of alloy and inoculated it with inoculant, which made the eutectoid transformation of molten iron more and more stable and refined part of pearlite, promoted the formation of carbides, and the graphite of cast iron was like worm, which reduced the cutting effect of graphite on the matrix, At the same time, the number of eutectic clusters and tensile strength of gray cast iron have increased, and due to the addition of a small amount of alloy in the melting process, the amount of scrap steel has been 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, so that the hardness and strength of the castings in the as cast state meet the standard requirements, while eliminating the normalizing process, The yield is improved and the cost is reduced.
The applThe application of rare earth in cast iron began in the 1940s. The British morrogh H and Williams WJ first announced the successful industrial production of nodular cast iron by using clock, while the wide application of rare earth in gray cast iron began in the 1940s.