INFLUENCE OF THE HEAT TREATMENTS ON THE WEAR-RESISTANT STEELS PROPERTIES
Through heat treatments, physical properties of wear-resistant steels such as mechanical resistance, hardness, tensile strength and fatigue limit, ultimate tensile strength, modulus of elasticity, etc., can be adjusted to the needed characteristics in order to enhance their wear-resistance. Hardening, tempering, and annealing are usually used to improve the wear-resistant properties of steels by changing their microstructures and grain size and by decreasing the presence of grain boundaries in the material.
Hardening is a heat treatment involving heating, quenching and tempering which helps in increasing the wear-resistance of steels by inducing higher hardness. During quenching, the steel is rapidly cooled after it has been heated to the austenitizing or transformation temperature, resulting in the formation of a brittle martensitic microstructure. The quenched part is then tempered to further enhance the mechanical properties such as strength, toughness and ductility. Tempering is an important process which relieves the stresses introduced in the hardening process and creates a finer, more homogeneous microstructure which reduces deformation and wear rates.
Annealing, on the other hand, is an opposite heat treatment process which involves slow cooling or heating of the material to reduce hardness, improve ductility and toughness and enhance fatigue strength. It is usually performed on steel which has been previously processed by other heat-treatment procedures, such as quenching and tempering, in order to increase the wear-resistance of the steel by decreasing its fracture toughness. An annealed steel will have a fine-grained, homogenous microstructure, resulting in improved energy-absorbing strength and fracture resistance.
Certain wear-resistant steels are hardened with a plasma or electric-arc process, which is a coating procedure which increases the hardness of the steel without introducing any additional hard microconstituents. This is typically used with carbide-strengthened materials which contain elements such as tungsten, molybdenum and chromium as alloying elements. These materials are typically used for heavy industrial applications such as mining machinery and construction equipment, where higher strength and wear-resistance is needed.
In addition to the changes brought about by hardening, tempering, and annealing, the surface wear-resistant properties of wear-resistant steels can also be changed through plating, shot peening, abrasive blasting, and other similar processes which add a superficial wear-resistant layer to the surface of the steel. These processes are specifically designed to increase wear-resistance in parts which are primarily expected to operate without forming deformation products, such as gears and bearing surfaces.
In summary, heat treatments are essential in controlling and improving the wear-resistance of wear-resistant steels. Depending on the application and the operating conditions, the mechanical and tribological properties of these steels can be carefully adjusted through hardening, tempering, annealing, and further surface treatments to suit the needs of various applications.
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