According to the ball mill manufacturing process, steel ball manufacturing can be divided into two types: Casting and forging, but their wear resistance is different. Due to the crushing of materials, steel balls need good wear resistance and enough toughness. Generally, alloy steel, high manganese steel, cast iron with ferrochrome and other materials are used for one-time forming by forging or casting method. It is more economical to match the corresponding heat treatment process. According to the process and material, steel balls of ball mill can be divided into:

　　1. Forged steel ball: low carbon alloy steel ball, medium carbon alloy steel ball, high manganese steel ball, rare earth chromium molybdenum alloy steel ball;

　　2. Cast steel ball: low chromium cast ball, medium chromium cast ball, high chromium cast ball.

　　Which kind of steel ball is the best in the market? Now let's analyze it:

　　1、 Forged steel ball:

　　Good surface quality, impact resistance, toughness, wear resistance, not easy to break and out of round. That is to say, when the metal is heated to 700-1300 ℃, the forging machine is used to apply pressure on the metal blank to produce plastic deformation so as to obtain the processing method of forging with certain mechanical properties, certain shape and size. One of the two main parts of forging (forging and stamping). Through forging, the defects of loose as cast metal produced in smelting process can be eliminated, and the microstructure can be optimized. At the same time, the mechanical properties of forgings are generally better than those of castings of the same material because of the intact metal streamline. For the important parts with high load and severe working conditions in the related machinery, except for the simple shape of rolled plates, profiles or weldments, forgings are often used. In addition, the most wear-resistant materials, such as 60Mn and 65Mn of national standard, or high-efficiency wear-resistant alloy steel independently researched and developed by some companies, must be selected for wear-resistant forging steel balls, and it is recommended to use the steel produced by the national super large steel plant, which is also a kind of material, and the quality produced in different steel plants is also different, and 80% of the quality of forgings depends on the quality of the material Such as using high manganese steel, good impact resistance, strong toughness, good wear resistance, not easy to break. Forged steel balls are favored by the majority of users because of their low price and durable economy. For example, international mining giants Rio Tinto, BHP Billiton and AngloGold all use forged steel balls.

　　Features of forging production:

　　(1) Forging is the forging of heated metal materials into tools, mechanical parts or blanks of various shapes. Forging can change the internal structure, refine the crystal and improve the mechanical properties of metal materials.

　　(2) Heating equipment, forging equipment and many auxiliary tools must be used in forging production.

　　(3) Forging equipment mainly includes steam hammer, air hammer, die forging hammer, mechanical hammer, splint hammer, spring hammer, belt hammer, crank press, friction press, press, reamer, roll forging machine, etc.

　　2、 Cast steel ball:

　　Low and medium chromium cast ball has poor wear resistance and high crushing rate, although it is cheap, but its comprehensive cost performance is not high, so it is not recommended here. High chromium cast ball is a kind of high-quality wear-resistant material with excellent hardness, which has been widely used in the dry ball mill of cement industry. However, the toughness of high chromium cast ball is poor, and it is easy to break in the ball mill with a diameter of more than 3 meters, and the price is high.

　　Influence of cast steel ball material: Generally speaking, the harder the steel ball is, the greater its wear resistance is. In order to improve the wear resistance of steel ball, it is necessary to increase its hardness, but with the increase of hardness, the impact toughness of steel ball will be reduced. At the same time, the hardness of steel ball should take into account the material and hardness of lining plate, not too high (smashing lining plate), not too low (not wearing). Therefore, the key to improve the wear resistance of steel ball is how to consider the suitable hardness and good impact toughness of steel ball.

　　The commonly used materials of steel balls are:

　　Low carbon alloy, high manganese steel, high chromium cast iron, high carbon and high manganese alloy steel. Low carbon alloy steel ball has good toughness and low price. Under the same working condition, its service life is more than 1 times longer than that of low chromium cast ball;

　　High manganese steel has good toughness, good processability and low price. Its main feature is that under the action of large impact or contact stress, the surface layer will produce work hardening rapidly, its work hardening index is 5-7 times higher than other materials, and its wear resistance is greatly improved;

　　High chromium cast iron is a kind of wear-resistant material with excellent wear resistance, but its toughness is low, brittle fracture is easy to occur and its price is expensive.

　　High carbon and high manganese alloy steel is mainly alloy structural steel containing chromium, molybdenum and other elements, with high hardness and good toughness. Its matrix structure is composed of martensite, bainite or bainite martensite composite structure. The hardness of steel ball is about HRC60, the impact toughness is ≥ 15J / cm2. Under the same working conditions, the service life of steel ball is at least one time longer than that of high manganese steel ball.

　　The tempering heat treatment of steel ball is the key. After the tempering heat treatment, not only the overall toughness is required to reach 12 joules / cm2, but also the plasticity and wear resistance are required. However, the general casting process can only reach 3-5 joules, resulting in a high crushing rate, even if it is a high chromium casting ball, so it is recommended to use forgings when the working condition strength is large.

　　The manufacturing process of steel ball is also the key factor to determine its service life. If there are defects on the surface or inside of the steel ball, such as shrinkage cavity, crack, transgranular, etc., it will not only reduce the performance of the steel ball, but also cause the steel ball to be broken. Therefore, a reasonable forging, casting and heat treatment process must be established in the production of steel balls. For example, for the high chromium cast iron ball, measures such as vertical casting and reasonable use of external cold iron, and strict control of casting temperature should be taken, so that the steel ball has good solidification sequence and feeding conditions in casting, and then the dense internal structure can be obtained, and the phenomenon of coarse grain can be weakened. The heat treatment process of steel ball determines the realization of its mechanical properties and the distribution of carbides. Because there are a certain amount of chromium and other alloy elements in the composition of steel ball, how to make these alloy elements form hard point carbides to play a full role is also a factor to be considered in the formulation of heat treatment process. In a word, it is a prerequisite to make a reasonable production process and strict quality inspection means to ensure that the steel ball can reach the service performance.

　　To sum up, forgings are better than castings, and the specific steel ball to be used is more appropriate according to their working conditions and economic strength. As the saying goes, there is no best, only better, do not buy expensive, only buy the right.