Slow-speed cutting: Another way to avoid cutting cracks is to reduce the cutting speed. If it is not possible to preheat the entire plate, local preheating can be used instead. The use of low-speed cutting method to prevent cutting cracks is not as reliable as preheating. We recommend that the cutting strip be preheated with a flame gun several times before cutting, and the preheating temperature should be around 100°C. Its maximum cutting speed depends on the grade and thickness of the steel plate.

Special note: Combining the two flame cutting methods of preheating and low speed can further reduce the probability of cutting cracks.

Post-cutting slow cooling requirements: Regardless of whether the cutting plate is preheated or not, slow cooling after steel plate cutting will effectively reduce the risk of cutting cracks. If the warm plate is stacked after cutting and covered with an insulation blanket, slow cooling can also be achieved. Slow cooling requires cooling to room temperature.

Post-cutting heating requirements: For the cutting of wear-resistant steel plates, heating (low-temperature tempering) immediately after cutting is also an effective method and measure to prevent cutting cracks. The steel plate can be effectively eliminated by low-temperature tempering treatment (low-temperature tempering process; insulation time is 5min/mm)

For the heating method after cutting, the heating method of combustion gun, electronic heating blanket and mourning furnace is also used for heating after cutting.

Measures to reduce the softening of steel plates The softening resistance of steel mainly depends on its chemical composition, microstructure and processing method. For hot-cut parts, the smaller the part, the greater the risk of softening of the entire part. If the temperature of the steel plate exceeds 200-250°C, the hardness of the steel plate will decrease.

Cutting method: When cutting small parts of steel plates, the heat supplied by the welding gun and preheating will accumulate in the workpiece. The smaller the cutting size, the cutting workpiece size must not be less than 200mm, otherwise the workpiece will be at risk of softening. The best way to eliminate the risk of softening is cold cutting, such as water jet cutting. If hot cutting must be used, plasma or laser cutting should be selected. This is because flame cutting provides more heat to the workpiece, thereby increasing the temperature of the workpiece.

Underwater cutting method: An effective method to limit and reduce the softening zone range, using water to cool the steel plate and the cutting surface during the cutting process. Therefore, the steel plate can be cut in water or by spraying water on the cutting surface. Plasma or flame cutting can be selected when using the underwater cutting method. Underwater cutting has the following characteristics:

Small cutting heat affected zone;

Prevents the hardness of the entire workpiece from decreasing;

Reduces deformation of the cut workpiece;

The workpiece can be cooled directly after cutting.