Carbide Precipitation in Low Alloy Wear Resistant Steel During Tempering

    
    Carbide precipitation during tempering is a common phenomenon observed in low alloy wear-resistant steels. This phenomenon is due to the alloying elements present in the steel, and can cause a range of issues, such as impairing the steel’s workability, increasing its brittleness, and decreasing its ductility.
    
    When heat treating low alloy wear resistant steels, certain alloying elements, such as chromium and molybdenum form carbides. These carbides form due to a number of reasons including the presence of oxygen and other impurities in the steel. The presence of these carbides significantly affects the mechanical properties of the steel, as they reduce its strength and ductility. Additionally, they can make the steel more brittle, causing it to be easier to crack and creating a greater risk of equipment failure.
    
    Carbides in low alloy wear resistant steels can form during tempering at temperatures around 600-700°C, which is usually within the range of tempers used in this type of steel. During tempering, some of the alloying elements, such as chromium and molybdenum, form carbides, as shown in the figure below.
    
    Figure 1. Temperatures and times used for carbide precipitation in low alloy wear resistant steels
    
    At this stage, the carbide particles become finely dispersed, forming a dispersed carbide layer on the surface of the steel, which is known as carbide precipitation. This can lead to reduced toughness and strength at the surface of the steel, as the carbides increase the microhardness, causing premature wear or fracture of the steel. Furthermore, the presence of carbides on the surface of the steel can reduce its corrosion and abrasion resistance, leading to further problems down the line.
    
    Therefore, it is important to understand the different mechanisms of carbide precipitation and the effects it can have on the properties of low alloy wear resistant steels. The rate of carbide precipitation will vary depending on the alloying elements present in the steel, the temperature and time of tempering, and the steel’s composition.
    
    For example, in low alloy wear resistant steels, the rate of carbide precipitation increases with the contents of chromium and molybdenum, and decreases with increasing tempering times. In addition, the rate of carbide precipitation decreases as the temperature of tempering increases. As such, it is important to understand the rate at which carbides form in order to provide the optimal tempering conditions for the steel.
    
    Moreover, carbide precipitation can be minimized by adding an appropriate amount of deoxidation agents during the steel making process. This helps to reduce the amount of oxygen present in the steel, which in turn helps reduce the rate of carbide precipitation. In addition, the steel’s chemical composition can also be optimized to lessen the precipitation of carbides by adjusting the contents of chromium, molybdenum and other alloying elements.
    
    Ultimately, carbides in low alloy wear resistant steels can significantly affect the properties of the steel. To minimize the effects of carbide precipitation, it is important to understand the factors that cause it, and to adjust the steel’s composition and temperature and time of tempering appropriately. By doing so, it is possible to achieve the desired properties without compromising the integrity of the steel.

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