Experimental study on air quenched high chromium grinding balls (1)
There are many kinds of grinding media used in various ball mills at present. Among them is Martensite Ductile Iron Grinding Ball, high carbon low chromium table gold casting ball, P-Cu-ti multi-element, alloy casting ball, cr-v-ti casting ball, Cr-Mo-Cu self-cast iron grinding ball, multi-element table, gold cast steel meal ball, high chromium grinding ball, high chromium cast steel grinding ball, etc. . However, for large-scale water and mud mills, it is generally recognized that high chromium wear-resistant materials contain high hardness (HV > 1800) g-type carbide and relatively wear-resistant Metal Matrix, the cast ball made of high chromium material is the wear-resistant and abrasive medium of the large mud-bearing mill.
The choice of the high chromium grinding ball’s chemical composition determines its casting, heat treatment, metallographic structure, mechanical properties, and wear resistance during final use. Correct selection of chemical composition to find out the best range of alloy elements is the key to producing this grinding ball. Our experiment aims to change the composition of CR13 high chromium grinding ball (as shown in Table 1) to achieve air cooling quenching during the heat treatment process. After the experiment, the high-wind cast balls are determined, as shown in Table 2
- CARBON: the role of carbon is to enable the metal matrix to achieve a higher hardness. Carbon can also form various types of carbides with alloy elements. M7C3 type carbides with high hardness are mainly created with chromium and iron in high chromium grinding balls. Increasing the carbon content can increase the amount of carbide, thus improving the wear resistance of materials. However, with the increase of carbon content, the combination of carbon and alloy elements that can improve the hardenability results in the decrease of alloy elements dissolved in the Metal Matrix and decreased hardenability. We chose between 1.8% and 2.1%.
- Chromium: In high chromium cast balls, chromium forms carbides with carbon and iron. Chromium can also be dissolved in the Matrix to improve the hardenability of the material. The hardenability can be improved by increasing the chromium content or decreasing the carbon content when the carbon content is constant. That is, the hardenability rises with the increase of the Cr/C ratio. But too much chromium affects the cost of the ball. On the premise of material hardenability and ball hardness, we choose chromium content in the range of 14%-16%.
- MANGANESE: Manganese both forms carbide (M3C type) and dissolves into the Metal Matrix. The Manganese dissolved in the metal matrix has a strong effect on the stability of austenite. In high chromium materials, Manganese can replace part of Molybdenum and improve the hardenability of the materials. The impact of MN and Mo on the hardenability is more prominent. As to Manganese’s effect on the heat treatment parameters, the data show that the quenching temperature to obtain the highest hardness decreases with the increase of manganese content. The Ms point decreases strongly with the growth of manganese content, which increases the amount of retained austenite after cooling. So the scope of Manganese is determined to be 1.2% ~ 2.0%
- Silicon: Silicon is an element that reduces hardenability, but a small amount of silicon is added for Deoxidation. Typically in the range of 0.3% to 0.8%.
- MOLYBDENUM: Add Molybdenum in high chromium cast ball, most of the formation of M2C carbide, part into the M2C3 carbide, part of the dissolution of the Metal Matrix. The Molybdenum in the Soluble Metal Matrix can improve the hardenability but has little effect on Ms. Point. Considering the production cost, we add 0.1%-02% molybdenum.
- Nickel: Nickel is a non-carbide-forming element, wholly dissolved in the Metal Matrix, can be fully developed, to improve the role of hardenability. The effect of decreasing the Ms point of nickel is greater than that of Molybdenum, but we add a small amount of nickel and don’t form too much-retained austenite
- Titanium: Titanium is a strong carbide forming element; the addition of titanium in the form of TiC, from refining base the role of body tissue
- Sulfur and phosphorus: Sulfur and phosphorus are harmful elements in high chromium cast balls, which cause various defects during casting and heat treatment, and should be controlled below 0.04%.