When cutting the thick NM500 steel plate, we need to pay attention. With the increase of NM500 steel plate thickness and hardness, cracks tend to increase at the edge of cutting. In order to prevent cracks in NM500 steel plate cutting, the following suggestions should be followed:
Cutting Cracks: Cutting cracks in NM500 steel plates are similar to hydrogen-induced cracks in welding. If a crack occurs at the edge of NM500 steel plate, it will occur within 48 hours to weeks after cutting. Therefore, the cutting crack belongs to delayed crack. The bigger the thickness and hardness of NM500 steel plate, the bigger the cutting crack will appear.
Preheating cutting: the most effective way to prevent cracks in NM500 steel plate cutting is to preheat before cutting. Before flame cutting, the NM500 steel plate is usually preheated. The preheating temperature mainly depends on the quality grade and thickness of the NM500 steel plate. The preheating method can be carried out by flame burner, electronic heating pad or heating furnace. In order to determine the preheating effect of NM500 steel plate, the temperature required for hot spot test should be added.
Attention: Preheating should make the interface heating of NM500 steel plate uniform, so as to avoid contact with the heat source of the local overheating phenomenon.
Low speed cutting: another way to avoid cutting cracks is to reduce the cutting speed. If the whole NM500 steel plate is not preheated, the local preheating method can be used instead. Using low speed cutting method to prevent cutting cracks is not as reliable as preheating. We suggest that the flame gun should be used to preheat the air cavity several times before cutting, and the preheating temperature should reach about 100 DEG C. The maximum cutting speed depends on the grade and thickness of the NM500 steel plate. In particular, the combination of preheating and low-speed flame cutting methods can further reduce the incidence of cutting cracks.
Slow cooling requirements after cutting: Regardless of whether the cutting is not preheated or not, slow cooling after cutting NM500 steel plate will effectively reduce the risk of cutting cracks. If it is cut and stacked without heat, it can also be cooled slowly by covering it with an insulating blanket. Slow cooling requires cooling to room temperature.
Heating requirements after cutting: for the cutting of NM500 steel plate, immediately take heating (low temperature tempering) after cutting, is also an effective method and measures to prevent cutting cracks.
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