Primary analyses of cast microstructure design of high chrome white cast iron grinding media (1)

Abstract: Under the actual production condition of the traditional technique, it is easy that high chrome white cast iron grinding media forms more internal stress, which is lead to disabled main reason in production and employ condition. The importance of grinding ball cast microstructure is known by analysis hot working whole process, that is, required cast the microstructure can meet the need of structure and property, only uses inter critical heat treatment. Decrease Not only the internal stress of casting, but also reduce energy consumption, cost, reform work environment, and short production cycle.

Key Words: high chrome cast iron grinding media; casting microstructure; design method

Author: WANG Zhong-jue

(Anhui University of Technology and Science 241000, China)

Cast iron grinding media is widely used in mineral processing, cement, power, metallurgy, chemical, and other industrial fields. Since the 1980s, the abrasive media available for users to choose from on the market has been dazzling. Such as copper, phosphorus, and titanium multi-metal wear-resisting cast iron ball produced by Yunnan Lufeng Iron and steel factory; TQ cast iron ball produced by Hebei Funding ball factory; martensite ductile iron ball produced by Xi’an Jiaotong University and Shaanxi Cement Group; chromium, vanadium, and titanium cast iron ball produced by the Hebei University of Technology; Martensite ductile iron balls developed by East China Jiaotong University. Foreign cast iron grinding media is often imported with imported equipment as a matching grinding ball medium to ensure the overall performance of equipment, efficiency as the introduction. Based on the abrasive wear mechanism, it has been realized that the quality of the abrasive medium depends on its system environment and service condition. The traditional manufacturing process of high chromium white cast iron grinding ball is to select the quenching temperature from 920 °C to 1080 °C to obtain the maximum hardness martensite, but due to the poor thermal conductivity of matrix and carbide, even heating at the allowable heating rate under production conditions will produce a large temperature gradient in the grinding ball, thus increasing the internal stress of the grinding ball more strongly, the higher the hardness and the greater the internal stress of the grinding ball have become the main problems which the traditional manufacturing technology can not solve. This problem also often causes the grinding ball in the production process, the use of the process of cracking, fragmentation. In order to solve this problem, it is proposed in this paper that (1) the concept of as-cast microstructure design must be updated to avoid the formation of large internal stress under the condition of obtaining high hardness, the as-cast microstructure can reach the expected level of microstructure and properties only by sub-temperature treatment (2) on the premise of obtaining high hardness, the toughness can be further improved by grain boundary purification, grain refinement, carbide quantity control, carbide shape and size control, and non-metallic inclusion shape and size control.

1. Organization and performance expectations

As-cast structure: martensite + proper amount of retained Austenite + M7C3 + MC The microstructure after sub-temperature treatment: martensite + a small amount of retained austenite + M7C3 + MC This is mainly based on the following considerations:

1) The wear resistance and toughness of cast iron were obviously improved with the change of carbide type. The order of M3C, M7C3, and MC type, high chromium white cast iron with plate carbide has the best thermal conductivity and heat dissipation. The percentage of carbide should be controlled at 20% ~ 30%.

2) The addition of V, TI, W, and NB not only resulted in VC, TiC, WC, and NBC carbide with higher hardness than (Cr. Fe)7C3chromium carbide but also refined the eutectic structure.

3) As-cast matrix structure: fine lamellar martensite (depending mainly on austenite grain size) + proper amount of retained austenite after sub-temperature treatment, fine lamellar martensite + secondary carbides with uniform distribution in the Matrix + a small amount of retained austenite.

4) The heat conductivity of austenite is low, the specific volume change of austenite to martensite is large, the volume solidification property of high chromium cast iron is strong, and the corrosion resistance of martensite and austenite is obviously higher than that of pearlite.

5) Hardness HRC60-65; impact value (no notch) AK> 6.0J/cm2; H = 3.5 m drop test times < dia80(mm) , over 18000; dia80(mm) , over 13000. [/av_textblock][av_textblock size='' font_color='' color='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' av_uid='av-ks9zhy23' admin_preview_bg=''] Next: Primary analyses of cast microstructure design of high chrome white cast iron grinding media (2)

white cast iron grinding balls