Heat treatment process for high chromium grinding ball

Ball mill is widely used in building materials, mineral processing, cement, thermal power generation and fertilizer production of the main grinding equipment, grinding ball is the largest consumption of wear-resistant parts. Therefore, with the continuous development of key industries such as building materials, the demand for grinding balls will increase greatly. At present, ordinary forged steel balls are mainly used, with an average consumption of one kilogram of steel balls per ton of cement, and about two kilograms of steel balls per ton of metal ore ground This was nearly ten times more relevant than at the time. Especially as the third generation of anti-wear Alloy High Chromium White cast iron developed successfully, so that more than 4.5 m of large-scale cement mill ball consumption to 30 ~ 50 G / T, medium and small-scale cement mill ball consumption also reduced to only 100 G / T or so The new material revolution has greatly improved productivity and economic returns. It was only in the mid-1970s that I began my research on the development of cr-based white cast iron. The Xi’an Jiaotong University of Mn-Cr-Cu-Mo series and high-cr-based wear-resistant white cast iron were selected and developed. Since the 1980s, a variety of new wear-resistant materials developed in China have been gradually applied to the actual abrasive wear operations, some of which have reached the level of similar products abroad.

The good wear resistance of high chromium cast iron mainly depends on its matrix structure and the type and distribution of carbides. High Chromium cast iron is a kind of chromium white cast iron with chromium content between 12% -28%. This alloy of carbon and hard compounds gives high chromium cast iron good wear resistance. On the other hand, during solidification, M7C3 type carbides distribute in a rod-like shape, which can improve the toughness of high chromium cast iron to some extent. The production of high chromium cast ball is mainly composed of casting and heat treatment. Casting is mainly composition design, the casting method, carbide, and matrix structure directly, affect the wear resistance and toughness. Carbides and Metal Matrix Organization is first, by its chemical composition, so must be the reasonable design of its chemical element, content, followed by the heat treatment process

As mentioned before, high chromium grinding ball has excellent wear resistance in abrasive wear and has been widely used in many industries of national economy This is mainly because the high-chromium cast ball can obtain strong and tough matrix structure and high hardness M7C3 carbide by proper heat treatment and alloy modification. Many units at home and abroad began to choose high-chromium cast ball as a cement, mining, electricity and other industries as Abrasives, so high-chromium cast ball production technology has been the main topic of study at home and abroad.

Heat treatment of high chromium grinding ball is the main method to obtain good wear resistance. The research on high chromium cast iron ball mainly focuses on chemical composition selection, heat treatment process determination, modifier selection, good carbide type and wear mechanism. Foreign foundry researchers are more committed to the high-chromium cast iron microstructure, wear-resistant mechanism, and new preparation process development. Here are the specifications for the High Chromium Grinding Ball:

Composition: C: 1.8-3.2 ; Si 0.3-1.2; Mn 0.3-1.0; Cr 10-10.5; P ≤0.1; S ≤0.1; Mo,Al: little
HRC:≥58; Impact value: J/cm2:≥4; Micro-structure:M+C; Falling Times:≥10000

From the above indexes, it can be seen that the hardness of the grinding ball before and after quenching is quite different. The heat treatment process of high chromium cast iron grinding ball includes wind quenching, oil quenching, and special quenching solution treatment. After repeated test and mining, the oil quenching can fully meet all its technical specifications The consumption of iron ore is twice that of iron ore. The heat treatment process is the use of two-stage heat quenching and low-temperature tempering. At the rate of less than 70 °C / h, the temperature is increased to 650-680 °C for 2 hours, at the temperature increasing to 950 °C for 4 hours, forced air-cooling, oil-cooling, and special quenching liquid cooling respectively, and tempering is carried out at 200 °C or 420 °C According to the ball diameter was 4 hours, 6 hours, 7 hours, out of slow cooling.

From the above indexes, it can be seen that the hardness of the grinding ball before and after quenching is quite different. The heat treatment process of high chromium cast iron grinding ball includes wind quenching, oil quenching, and special quenching solution treatment. After repeated test and mining, the oil quenching can fully meet all its technical specifications The consumption of iron ore is twice that of iron ore. The heat treatment process is the use of two-stage heat quenching and low-temperature tempering. At the rate of less than 70 °C / h, the temperature is increased to 650-680 °C for 2 hours, at the temperature increasing to 950 °C for 4 hours, forced air-cooling, oil-cooling, and special quenching liquid cooling respectively, and tempering is carried out at 200 °C or 420 °C According to the ball diameter was 4 hours, 6 hours, 7 hours, out of slow cooling.

The results are as follows:

  • MICROSTRUCTURE: The microstructure of high chromium cast iron ball after heat treatment was observed by an optical microscope. The microstructure was mainly composed of martensite and Eutectic carbides with a little-retained austenite.
  • After heat treatment, the surface hardness and the core hardness of the high chromium cast iron are all above HRC58. The hardness is stable and fluctuated little, and the wear resistance is very good. The impact energy is 4.7-5j / CM2, the impact toughness is very good, the breakage rate of the grinding ball is less than 1% 3. The ore consumption is 0.23 kg / ton compared with 0.6 kg / ton of forging ball.

The results are as follows:

  • MICROSTRUCTURE: The microstructure of high chromium cast iron ball after heat treatment was observed by an optical microscope. The microstructure was mainly composed of martensite and Eutectic carbides with a little-retained austenite.
  • After heat treatment, the surface hardness and the core hardness of the high chromium cast iron are all above HRC58. The hardness is stable and fluctuated little, and the wear resistance is very good. The impact energy is 4.7-5j / CM2, the impact toughness is very good, the breakage rate of the grinding ball is less than 1% 3. The ore consumption is 0.23 kg / ton compared with 0.6 kg / ton of forging ball.

After reasonable matching of all elements, ratio casting qualified grinding ball blank, adopt continuous heat treatment furnace to ensure the uniformity of furnace temperature, select the appropriate quenching medium and tooling, the equipment to ensure the consistency of the process, to ensure the stability of product quality. Problems such as low wear resistance of high chromium grinding balls, high rate of breakage and large roundness loss were solved.

  1. Continuous gas-fired pusher heat treatment furnace and industrial computer control are adopted to realize automatic production. Ensure the accuracy of process parameters, reduce human interference, interference factors, to ensure product quality stability and consistency.
  2. The problems of high hardness and toughness of the grinding ball were solved, and the loss of roundness and broken rate of the ball were reduced.
  3. The ore consumption is greatly reduced, the production cost of ore dressing is reduced, and the production efficiency is improved.
  4. In the experiment of casting ball containing CR27 %, the high effective corrosion solution configuration is also an innovation. After the innovation, the original corrosion solution has no obvious corrosion effect, and the time to hit is more than 20 minutes. After the innovation configuration, the corrosion solution only takes 10 seconds The effect of corrosion is obvious.