Recently, the Platts iron ore index surged to a near 9-year high of $176.9 per ton, doubling from its lowest point this year. In addition to iron ore prices, many non-ferrous metal prices are also rising. According to data from the China Nonferrous Metals Industry Association, since July, the prices of copper, aluminum, lead, and zinc have remained high, exceeding pre-pandemic levels.

Copper rose by 38%, and aluminum by 37%.

Zinc alloy rose by 48%, and stainless steel surged by 45%.

The scope is wide, and the increase is astonishing!

The rise in ore prices has also led many mining companies to expand their production scale, and the demand for ore grinding is also constantly increasing. However, many mining companies have experienced varying degrees of steel ball breakage when using large semi-autogenous mills. This results in substandard ground materials, delays production progress, and requires the repurchase of new steel balls, significantly increasing production costs. Gangnuo New Materials Co., Ltd. has provided an answer to this problem.

Large-size grinding steel balls, as an indispensable grinding medium for large semi-autogenous mills, their quality directly affects the ore processing capacity and wear and tear of production technical indicators and the stable operation of grinding. Because the diameter of semi-autogenous mills is mostly larger than that of ball mills, the diameter of steel balls used for effective ore crushing is also larger, and the impact they experience is higher. Therefore, this large-size steel ball needs to have good impact resistance to avoid breakage during service. At the same time, in order to reduce the wear of steel balls, the steel ball products must have good wear resistance. This is usually ensured by the high hardness of the effective volume of the steel ball product. For large-size steel balls, the increase in hardness is usually accompanied by a decrease in impact resistance. How to make the steel balls have high hardness while also ensuring the necessary impact resistance is an important technical challenge that steel ball producers need to solve. Gangnuo New Materials Co., Ltd., as a professional manufacturer integrating the research and development, production, and service of high-performance steel balls, has developed a new series of large-size (φ120mm—φ180mm) steel balls for semi-autogenous mills through years of technological innovation, combining iron and steel metallurgy technology, steel ball production process technology, and mining crushing and grinding engineering technology. These have been successfully industrialized and applied in mines such as Rio Tinto, BHP, Russian Copper, Zijin, and China Gold. Gangnuo is willing to apply this new product to more large-scale mines and make new contributions to the development of mines.

1. Chemical Composition Design and Technical Requirements for Large-Size Steel Balls

Grinding steel balls are produced using round steel produced by special steel plants as raw materials. The chemical composition of steel ball steel is an important guarantee for the performance of steel ball products and an important aspect of the economic rationality of steel ball products. Usually, the chemical composition of steel ball steel mainly involves the content of four major elements: C, Si, Mn, and Cr, as well as the limit content of harmful elements. Trace elements may be added appropriately according to the operating conditions of the mine to improve the toughness-hardness ratio of the steel ball.

Since the carbon content in steel determines the hardness after quenching and the composition of different substructures of martensite in the microstructure, it also affects the toughness after quenching. For steel ball steel, too high a carbon content reduces the impact fatigue life of the steel ball. If the carbon content is too low, although the toughness of the steel ball can be guaranteed, the wear resistance decreases. For large-size steel for semi-autogenous mills, how to balance wear resistance and impact resistance to achieve the best use effect, Gangnuo Company, through long-term technical research, has developed the most applicable grinding ball products for semi-autogenous mill mining conditions through optimal chemical composition design and matching heat treatment processes.

First of all, the determination of the carbon content in steel is crucial. It determines the hardness after quenching and the composition of different substructures of martensite in the microstructure, and also affects the toughness after quenching. For grinding ball steel, too high a carbon content reduces the impact fatigue life of the grinding ball. However, a lower carbon content reduces wear resistance. Gangnuo Company has a unique steel ball composition formula.

2. Organizational Performance Characteristics of Steel Balls

Gangnuo Company has advanced production processes and technologies for high-quality steel balls, ensuring the stability and consistency of quality during the production of large-size steel balls for semi-autogenous mills. Based on the reasonable chemical composition and high metallurgical quality of large-size steel ball steel, a matching heat treatment process has been developed to ensure that the large-size steel balls have a refined martensite microstructure from the surface to the core after heat treatment. The new φ140 steel balls have high surface hardness and internal hardness, ensuring that the large-size steel balls maintain high wear resistance during service in the semi-autogenous mill. The microstructure after heat treatment of the φ140 steel ball is shown in Figure 1. The internal hardness distribution is shown in Figure 2. This inherent microstructure and hardness distribution are important guarantees for the good application effect of the φ140 steel ball in actual mine use.

Figure 1 Microstructure of Gangnuo's new φ140 steel ball

Figure 2 Hardness distribution from surface to core of Gangnuo's new φ140 steel ball

3. Conclusion

Gangnuo's large-size steel balls for large semi-autogenous mills have been applied to many large metal mines at home and abroad, and have achieved good results. The wear and tear indicators satisfy customers, and the steel balls maintain a good spherical appearance throughout their service life until they are discharged, with no peeling or chipping. Due to work hardening during the use of steel balls, the surface of the new steel balls maintains high hardness and therefore has good wear resistance. These are all attributed to the purification of steel ball steel, the optimal chemical composition design and matching heat treatment process, the advanced steel ball production process, and the perfect quality management system. Gangnuo is willing to serve various metal mines, provide new and high-quality products, and contribute to increasing mine production efficiency, energy saving, and consumption reduction.