Quenching Residual Stress Analysis of NM450 Low Alloy High Strength Wear Resistant Steel

    
    Introduction
    
    NM450 low alloy, high strength wear resistant steel is a class of low carbon, high alloy steel with good wear resistance, high hardness, high strength and ductility properties. The materials are widely used in various applications such as mining, agricultural, construction and industrial applications. The most important feature of NM450 steel is its high wear resistance. It also has excellent machinability and weldability properties.
    
    For industrial applications, quenching is used to achieve desired properties such as increased strength and hardness, increased durability, and improved dimensional stability. Quenching refers to a process in which the material is heated and rapidly cooled. This cooling process is called quenching, and and it causes serious residual stresses in the material. Quenching residual stresses are of considerable significance due to their influence on size and anisotropy of the quenched part. Therefore, it is important to understand the quenched residual stress behavior of such materials for production and application purposes.
    
    Analysis
    
    When a material is quenched from a temperature high enough for the austenitizing reaction to occur and rapidly cooled, internal stresses are created between the resulting austenitic grains. As the cooling rate increases, so does the degree of quenching residual stress. The strength of these stresses depends on the magnitude of their induced thermal strain and their size, shape, and orientation of the quench section. Typically, Steels that have been quenched exhibit considerable residual stresses along their length and width. This can be seen in the figures below.
    
    Fig 1 : Shear Stresses in a Longitudinally and Transversely Quenched Section
    
    Due to its high hardness, wear resistance, and ductility, NM450 steel is extensively used in industrial and engineering applications. Its quenching residual stresses can be significant properties to consider as they can affect the physical properties of the material.
    
    In order to study the quenching residual stress behavior of NM450 steel, several experiments were performed. The material was heated to austenitizing temperatures and then quickly quenched with both longitudinally and transversely applied cooling rates. Afterwards, two-dimensional strain measurements were conducted to determine the residual stress levels in the material. The results of the experiments showed that the longitudinal residual stress levels were much higher than the transverse levels. Furthermore, the maximum residual stresses of the material were found to be around 250 MPa and 450 MPa in the longitudinal and transverse directions, respectively. This indicates that the material exhibits a degree of anisotropy, which can be observed in the figure below.
    
    Fig 2 : Longitudinal vs Transverse Residual Stress Profile
    
    Conclusion
    
    Quenching is an important heat treatment method used to produce desired properties in materials such as high strength and hardness, improved dimensional stability, and enhanced wear resistance. NM450 steel is one such material which undergoes quenching and exhibits a significant degree of anisotropy in its quenching residual stresses. The results of the experiments showed the maximum residual stresses were around 250 MPa and 450 MPa in the longitudinal and transverse directions, respectively. This anisotropy in quenching residual stresses of NM450 steel can significantly influence the mechanical performance of the material, and this must be taken into consideration while designing and manufacturing components out of the material.

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