The influence of the vanadium content on the toughness and hardness of wear resistant high-alloyed Cr-Mo steel

    
    Introduction
    
    Cr-Mo steel is a high-alloyed steel consisting of primarily chromium (Cr) and molybdenum (Mo). This steel alloy is becoming increasingly popular in manufacturing applications due to its wear-resistant properties and high strength-toughness combination. The addition of a variety of alloying elements, such as vanadium (V), can further improve the wear resistance of this Cr-Mo steel. The use of vanadium in Cr-Mo steel has been found to result in increased hardness and toughness, which are key properties in ensuring the longevity of components subjected to wear.
    
    The Role of Vanadium in Cr-Mo Steel
    
    Vanadium is a strong carbide-forming element, forming vanadium carbides during the tempering process at high temperatures and imparting significantly improved wear resistance to the steel. These vanadium carbides are characterized by their extremely hard and abrasion-resistant properties, allowing for improved protection against wear. As a secondary hardening element, vanadium further provides an increase in toughness, which is the property that enables the steel to absorb more energy before it fractures.
    
    Vanadium has a positive effect on the hardness and toughness of steel due to its ability to form beneficial secondary phase microstructures that act as a partitioning agent between austenite and ferrite grains. This partitioning action helps to minimize the size of ferrite grains, which reduces their susceptibility to tearing when the steel is subjected to tensile forces. Additionally, vanadium significantly increases the retention of retained austenite, which is beneficial in high-alloyed steels since the retained austenite increases the steel's strength while simultaneously aiding in preventing grain boundary fragmentation.
    
    Figure 1: Effect of vanadium content on the microstructure of Cr-Mo steel
    
    Effect of Vanadium Content on Toughness and Hardness
    
    The addition of vanadium to a Cr-Mo steel alloy has a positive effect on its hardness and toughness, increasing both of these properties. This improvement is due to the higher levels of retained austenite, smaller grain size, and improved manganese sulfide inclusion count found in the higher-vanadium alloys. The hardness of the steel is substantially improved from the presence of the vanadium carbides, which increase the hardness and abrasion-resistance of the steel.
    
    The increase in toughness is due to the stabilization of austenite, which helps reduce and prevent grain-boundary tears. Additionally, the partitioning of vanadium between austenite and ferrite acts as a buffer between these phases to minimize the effects of the rotational forces caused by tensile stresses on the grain boundaries. Finally, the higher manganese sulfide inclusion count and the improved fine-grain size promote an accelerated austenite-to-martensite transformation upon cooling, increasing the toughness and strength of the steel.
    
    Figure 2: Effect of vanadium content on hardness and toughness of Cr-Mo steel
    
    Conclusion
    
    High-alloyed Cr-Mo steel containing vanadium is increasingly popular in manufacturing applications due to its wear-resistant properties and high strength-toughness combination. The addition of vanadium in modest amounts has been found to result in a significant increase in the hardness, wear-resistance, and toughness of the steel alloys, making them more suitable for use in harsh operating conditions. The improvement in effectiveness is due to the formation of fine-grained microstructures and the secondary hardening action of the vanadium carbides, both of which lend improved properties to the steel.

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