Effect of heat treatment process on wear resistance of low alloy wear-resistant steel for TBM cutter head

    
    Technological progress has enabled modern tunnel boring machines (TBMs) to work faster, more efficiently, and at ever increasing depths and diameters, with increases in both labor and material costs. Wear resistance is an important factor in the economic and productive life of a TBM cutter head as abrasive material passing through the opening is capable of wearing away the cutting edges of the dulling teeth.
    
    Wear resistance of a TBM cutter head can be increased through the use of low alloy wear-resistant steel (LAWRS). LAWRS is a high-strength steel alloy, formulated to provide high wear resistance to the TBM cutter head. However, even with the use of this alloy, the wear resistance of a cutter head can be increased through a heat treatment process.
    
    1. Heat Treatment Process
    
    The heat treatment process typically involves multiple steps, which include preheating, austenitizing, hardening, and tempering. Preheating consists of heating the steel up to a specific temperature for a specific period of time before subjecting it to further heat treatment. This preheating step softens the steel, making it more malleable, and increases its workability.
    
    The austenitizing phase consists of heating the steel to a temperature above its critical point and then quenching it in either oil or water. This phase leads to the formation of austenite crystals in the steel, which are harder and more wear-resistant than the unheated steel. The hardening phase follows where the steel is further heated and quenched to increase the hardness of the steel.
    
    Finally, tempering takes place, where the steel is exposed to temperatures below its critical point to reduce the hardness and brittleness of the steel, while still retaining its wear-resistance properties.
    
    2. Effect on Wear Resistance
    
    The heat treatment process can effectively increase the hardness and wear-resistance of the LAWRS used in TBM cutter heads. This increased wear resistance leads to increased life expectancy of the cutter head and improved cutting efficiency. As the cutter head is heavily exposed to abrasion during its working life, increased wear resistance can significantly reduce the amount of material and labor required to manufacture replacements for worn out cutter heads, as well as reduce the frequency of replacements needed.
    
    Additionally, the increased wear-resistance of the TBM cutter head can lead to improved cutting performance, as the teeth of the cutter head have an increased capability to penetrate deeper into the material, reducing the resistance from material build-up and providing a more efficient cutting process.
    
    Overall, the heat treatment process can provide significant benefits by increasing the wear resistance of a TBM cutter head, ultimately resulting in cost savings and improved performance.
    
    3. Summary
    
    The heat treatment process can be used to increase the wear resistance of low alloy wear-resistant steel (LAWRS) used in TBM cutter heads. This process involves multiple steps, beginning with preheating and concluding with tempering. The heat treatment process results in increased hardness and wear-resistance of the LAWRS, enabling the TBM cutter head to remain sharper for longer periods of time and leading to cost savings and improved performance. The use of a heat treatment process is an effective and economical way to improve the wear-resistance of a TBM cutter head.

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