Experimental study on Cr12 high chromium grinding balls (1)
With the development of wear resistance, materials, and related technologies, cr-series white cast iron has been used more and more widely in the grinding industry, especially in high-chromium cast iron, which is a kind of wear-resistant material, it has been fully utilized in the major industrialized countries of the world. We can find that its organizational characteristics determine high chromium cast iron well, wear-resistant, performance through a large number of analysis and research. Here this article is mainly talking about the experimental of the Cr12 high chromium grinding balls.
At present, the matrix structure of high chromium cast iron used in the market is mostly quenched martensite. This kind of cast iron has higher hardness and certain toughness. However, in order to improve the hardenability, the addition of alloy is more and more, which is especially needed, a certain amount of expensive metal elements, such as copper and molybdenum, should be added to the high-chromium cast ball, which contains 12% CR without the addition of these metal elements, wear resistance after modification and heat treatment.
1.Test conditions and methods
1.1 The selection of the composition of the high chromium grinding balls
High chromium alloy, white cast iron, the chemical composition, composition, and alloy element selection has a very significant impact on its performance, specific analysis as follows:
1) Carbon and Chrome
Carbon and chromium are two of the most important elements in high chromium white cast iron. Increasing carbon content can increase the number of carbon compounds in the microstructure and thus improve the wear resistance of high chromium white cast iron, the coarse eutectic carbide will be formed, and the toughness of the eutectic carbide will be significantly reduced.
Chromium is a strong-forming, carbide-forming element, in addition to carbon-forming carbide; in addition, there is some part dissolved in austenite, so the amount of chromium is also related to the cast iron quenching, permeability.
The content of carbon and chromium (or the ratio of chromium to carbon) determines the type of carbides. According to the test results, when the content of carbon is 3.0%, and the content of chromium is 11.6%, most carbides are M7C3 type.
Silicon is an element that strongly promotes graphitization. Almost all silicon is distributed in the matrix, which reduces the hardenability. Only a small amount of silicon is available for solid solution and strengthening. In other alloys, with a certain element content, with the increase of silicon content, the amount of pearlite formed in the cooling process increases. Thus the decrease of hardness and the increase in wear. Therefore, high chromium, white cast, iron silicon content should be below 1.0%.
Manganese is a very effective element to stabilize austenite, but it strongly lowers the MS point and leads to a large amount of residual austenite.
4) Variable mass agent
Modification is the condition of changing the eutectic transformation, temperature, and concentration field of white cast iron. It can change the growth process of the two-phase eutectic. Modification can improve the structure and morphology of white cast iron, especially carbon and carbide, so it is an effective process to improve high chromium white cast iron’s toughness.
1.2 Chemical composition of the test grinding balls
C:2.7 ~ 3.0%, Si:0.6 ~ 1.0%, Mn:0.40.8%, Cr:11 ~ L3%, variable mass agent: 0.5% for the first time, 1.0% for the second time, 1.5% for the third time.
1.3 Producing process
The casting technology of metal mold and the insulating riser was adopted, and the pouring sample was a 90mm casting ball.
Metal burden using gw-7800kw power frequency coreless induction, electric furnace melting, lining, for stone, quartz sand. When the burden is melted and heated to about 1400 °C, ferrosilicon and Ferromanganese are added. A modifier is added into the ladle of molten iron, and when the molten iron is heated to 1550 °C, the molten iron is drawn out. The molten iron is covered with carbonized rice husk insulation material; the casting temperature is about 1400 °C.
1.4 Heat treatment
High-temperature quenching + low-temperature tempering technology (as shown in Figure 1) was adopted for the sample, and the quenching medium was No. 30 machine oil.