Influence of welding current on microstructure and properties of welded joint of wear-resistant steel NM500 steel plate

    
    Introduction
    
    Wear-resistant steel NM500 is a kind of low-alloy steel with high strength and good wear resistance. It is commonly used on railway vehicles, land transportation and construction machinery, etc. The welding process ofNM500 steel plate plays a critical role in ensuring the physical integrity and service life of railway works. The welding current is one of the most important process parameters that can have an influence on microstructure, properties and service life of welded joint of NM500 steel plate.
    
    Influence of Welding Current on Microstructure
    
    When NM500 steel plate is welded, the welding current provides the necessary energy required by the welding process. Increasing the welding current can accelerate the completion of the whole welding process, while too high welding current can cause deep fusion and insufficient weld penetration, resulting in poor welding quality.
    
    When the welding current is too low, the heat input in the welding is not sufficient, so that insufficient energy for welding process is generated, which can cause the temperature in the welding area to be insufficient to melt the base metal, leading to incomplete alloy elements in the molten pool and the weld metal, affecting the grain size and mechanical properties of the welded joint. The weld metal usually has higher hardness, coarse grains, poor cross-sectional shape and lower impact toughness. The weld metal is also prone to welding cracks, which accordingly limits its service life.
    
    When the welding current is appropriate, the heat input generated by the welding process is sufficient to meet the welding process requirements and form ideal weld metal. With appropriate welding current, the microstructure of the weld metal is fine and even, and the alloy elements are fully dissolved and evenly distributed in the weld metal, making the mutual bonding of the organizations more firm, thereby enhancing the comprehensive properties of the welded joint. The weld metal also has good crack resistance, high impact toughness and good weld appearance, which all can effectively extend the service life of the welded joint of NM500 steel plate.
    
    Influence of Welding Current on Properties
    
    The welding current is an important parameter for welding of NM500 steel plate. The welding current has a significant influence on the welding penetration, the welding imprint and the mechanical properties of the weld metal.
    
    When the welding current is inappropriate, the heat input generated by the welding process is insufficient and the welding penetration is shallow, resulting in poor welding imprint and poor mechanical properties of the weld metal, especially the welded joint strength, crack resistance and impact toughness are seriously affected.
    
    When the welding current is optimal, the heat input is sufficient, the welding penetration is deep, the heat of welding zone is uniform, the melting depth of base metal and welding rod is moderate, and the fusion of the two layers is smooth, so that the weld metal has higher strength, better toughness, better cracking resistance and better corrosion resistance, thereby extending the service life of the welded joint of NM500 steel plate.
    
    Conclusion
    
    The welding current plays an important role in determining the microstructure and mechanical properties of the welded joint of NM500 steel plate for special carriage body. Proper control of the welding current can obtain ideal weldmetal, which can extend the service life of the welded joint.

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