Effect of Heat Treatment Process on Microstructure and Properties of NM450 Wear-resistant Steel
This article will discuss the effects of various heat treatments on the microstructure and mechanical properties of NM450 wear-resistant steel.
The microstructure of NM450 steel exhibits a ferrite and pearlitic matrix. The pearlite is composed of alternating bands of ferrite and cementite, a form of iron carbide. During the quenching process, the martensite, a hard and brittle phase, is formed. The martensite can also have bainitic, a more ductile and fracture resistant form, which is formed during the tempering process.
The quenching process involves rapidly cooling the steel in a quench medium, which is an oil, saltwater or water bath, or a combination thereof. This hardens the steel and increases the strength. The isothermal process involves a slower cooling rate and therefore, results in a softer, more ductile material. It also increases the toughness.
The continuous heat treatment process is used to alter the microstructure and mechanical properties of the NM450 wear-resistant steel. This process involves heating the steel to above the austenitizing temperature, which is approximately 900°C, and holding it at this temperature for a predetermined time to convert it to austenite. The steel is then cooled continuously to an intermediate temperature known as the martensite start temperature, and held there for a period of time, before being further cooled to the quench temperature. This results in a much finer microstructure, with an evenly distributed dispersion of smaller grains and complex carbides.
The pearlite and cementite are also transformed into a softer form of iron carbide, known as upper bainite, which is tougher and more ductile than other forms of carbide. This improves the wear resistance and abrasion resistance of the material.
The mechanical properties of NM450 wear-resistant steel are also greatly improved by heat treatment processes. The tensile strength and yield strength are significantly improved after prolonged heat treatment. Similarly, the toughness, impact strength and fatigue strength, can also be improved with the appropriate heat treatment process.
In summary, a range of heat treatment processes are available to significantly alter the microstructure and mechanical properties of NM450 wear-resistant steel. Through hardening or tempering, the steel can be hardened and strengthened. Isothermal and continuous processes can be used to alter the microstructure and improve its toughness and wear resistance.
Overall, heat treatment can effectively improve the performance of NM450 wear-resistant steel and make it more suitable for its intended use in applications such as mining and construction.
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