The Effect of Rock Properties on the High Stress Abrasive Wear Behavior of Steels, Hardmetals and White Cast Irons

Mining and mineral processing is a challenging field of industry for many reasons, including technological, economical, as well as political aspects. The market prices are constantly changing, many of the mines are located in politically unstable areas, environmental issues are becoming more and more topical, and, of course, technological requirements for the machinery used in various applications are constantly increasing. There are many ways to answer the technological challenges, and materials science is evidently one of the key areas where technological development can and must be expected. As wear of materials is a technological problem that causes huge expenses to the mining and mineral processing industry, it is only natural that this area is being under intense scientific and technological research, a part of which also this doctoral thesis is.The correct material selection for a certain wear environment will provide not only longer service intervals but also higher productivity, reduced use of energy and lower operating costs, as well as better environmental balance and lower climate impact. Despite the many changes that have taken place in mineral handling over the years, still today the significantly highest fraction of mine products constitutes mineral fuels, ferro-alloys, and other industrial minerals. All these product lines are very different from each other, and therefore the material selection suitable for one type of production may not be applicable to the other ones. Also the location of the production plays a huge role, for example whether it is in subtropic or in arctic regions of the globe.In this work, high stress abrasive wear of several different types of materials was studied using four different natural abrasives, i.e., rocks, and several different test methods. The main aim was to identify such characteristics of the abrasives that affect the most the wear behavior of the studied materials. In the best case, with that kind of knowledge prediction of the material’s performance at various mineral handling sites could be done just by knowing the composition of the soil or the bedrock in the area. Although this ultimate goal was not yet reached, some useful features were identified, which together with increased scientific understanding will help to better understand and control the practical wear processes. For example, one of the important findings was related to the embedment of quartzite particles on the surfaces of wearing materials, leading to the formation of mechanically mixed layers and affecting the further wear behavior of the studied materials.In addition to looking at the wear problems from the abrasive point of view, also the influence of the microstructure of the wearing materials was widely studied in this work. Different features in the microstructures of the studied steels, WC-Co hardmetals, and white cast irons were found to affect the high stress abrasion processes significantly, including the overall (bulk) hardness of the materials, hardness of the different constituents of the microstructure, and the size of the abrasives relative to the microstructural features of the materials.The producers of engineering materials usually provide the customers with data sheets containing the basic material properties, such as the strength, ductility and hardness values. However, when used in circumstances where wear is the main mechanism of material deterioration, these values should be considered with caution. This is because the behavior of materials in wear related applications is strongly dependent on the entire tribosystem. In addition, when the materials become into contact for example with rocks, especially under high stresses, these properties may also be changed even quite drastically. These effects were studied in this work with tribometer measurement of differently worn and polished surfaces to see and quantify the differences in their tribological behavior