Analysis and control measures of cutting cracks in NM500 wear-resistant steel

    
    Introduction
    
    As an important wear-resistant steel, NM500 wear-resistant steel has a good performance, strong fatigue life and wear resistance performance, but when producing and welding, it is very prone to cutting cracks due to its deep hardening property.It is therefore necessary to carry out a comprehensive analysis of the failure form and refer to the corresponding processing technology to reduce or eliminate its appearance.
    
    Causes of Cutting Cracks in NM500 Wear-resistant Steel
    
    1. Structural defects
    
    1.1 Porosity Structural defects such as porosity formed during smelting process can weaken the structural strength of steel and reduce its ability to resist external forces, and porosity defects may easily attract quenching media such as oil and water. These quenching media accumulate in the porosity and cause the internal structure of the steel to be extremely uneven, leading to the formation of cutting cracks.
    
    1.2 Inclusion of non-metallic materials Non-metallic materials in the raw material are easily brought into the steel during smelting process and form inclusions in the internal structure of steel. During quenching, these inclusions can also easily induce non-uniform temperature distribution, temperature changes too fast, resulting in high stress concentration and cutting cracks.
    
    2. Influence of Quenching Media
    
    The choice of quenching medium has a great influence on the formation of cracks. The quenching medium used for NM500 wear-resistant steel should not be too strong, and the selection of quenching medium should be moderate.
    
    3. Improper Adjustment of Quenching Parameters
    
    NM500 wear-resistant steel has a deep hardening property, so it is very sensitive to changes in quenching parameters. Therefore, adjustment of parameters such as quenching speed, furnace temperature and soaking time during quenching should be very careful, otherwise it will cause the internal structure of steel to be unequally quenched, resulting in high stress concentration and cutting cracks.
    
    4. Wrong Cooling Method
    
    The cooling method used for NM500 wear-resistant steel should be uniform, and cooling too slowly or too quickly can lead to uneven cooling and temperature difference, resulting in too much stress concentration and cutting cracks.
    
    Control Measures for Cutting Cracks of NM500 Wear-resistant Steel
    
    1. Enhance the quality of raw material
    
    The quality of raw material has a great influence on cutting cracks. Therefore, the choice of raw material should be strictly controlled, and test pieces should be rolled out for inspection when selecting raw material.
    
    2. Select reasonable quenching media
    
    The quenching medium is an important factor affecting cutting cracks in NM500 wear-resistant steel. The quenching medium should be moderate, not too strong or too weak, and the quenching medium used in the forming process and the quenching medium used after welding should be insulated.
    
    3. Reasonable adjustment of quenching parameters
    
    When quenching NM500 wear-resistant steel, it is necessary to strictly control the parameters including furnace temperature, soaking time, quenching speed and cooling method, so as to ensure the uniform quenching temperature of the steel and avoid the formation of cutting cracks.
    
    4. Reduce stress concentration
    
    NM500 wear-resistant steel has a deep hardening property. At the time of production and welding, attention should be paid to preventing stress concentration, such as unreasonable design of shape, uniform distribution of hole-side billet and reasonable welding technology.
    
    Conclusion
    
    Cutting cracks in NM500 wear-resistant steel mainly occur due to structural defects, influence of quenching medium, improper adjustment of quenching parameters and wrong cooling method. To reduce or avoid the occurrence of cutting cracks in NM500 wear-resistant steel, it is necessary to enhance the quality of raw material, select a reasonable quenching medium, adjust the quenching parameters reasonably and reduce stress concentration.

---