How to deal with the hardened layer problem when gouging high alloy steel?

How to deal with the hardened layer problem when gouging high alloy steel?

The hardened layer produced during gouging of high alloy steel is mainly due to the high temperature and rapid cooling during the gouging process, which causes changes in the metal structure. The following are some methods to deal with the hardened layer problem during gouging of high alloy steel:

Preheating

Preheat the high alloy steel workpiece before gouging, and heat the workpiece as a whole or the part to be gouged to a certain temperature. Preheating can slow down the cooling rate during the gouging process and reduce the intensity of the metal structure transformation, thereby reducing the depth and hardness of the hardened layer. Generally speaking, the preheating temperature varies depending on the specific composition and thickness of the high alloy steel, usually between 150-300℃.

Control gouging parameters

Choose the right current: The current directly affects the heat input of gouging. For high alloy steel, the appropriate current should be selected according to its material and thickness to avoid overheating and over-hardening caused by excessive current. The general principle is to use a smaller current as much as possible while ensuring the gouging efficiency. For example, for high alloy steel with a thickness of 10-20mm, the gouging current can be controlled between 100-200A.

Adjust the gouging speed: The gouging speed also affects the heat distribution and cooling rate. Properly increasing the gouging speed can reduce the accumulation of heat on the workpiece and reduce the depth of the hardened layer. However, too fast a speed may lead to a decline in gouging quality, such as carbon inclusion, slag sticking and other problems. Usually, the gouging speed can be adjusted within the range of 0.5-1.2m/min.

Optimize compressed air parameters: The pressure and flow rate of compressed air should be moderate. If the pressure is too high, the cooling speed will be too fast and the hardness of the hardened layer will increase; if the pressure is too low, the molten metal cannot be effectively blown away, affecting the gouging quality. Generally, the compressed air pressure can be controlled between 0.4-0.6MPa, and the flow rate is adjusted according to the specifications of the gouging gun and the actual situation.

Post-heating and slow cooling

After gouging, the workpiece should be post-heated in time, that is, the workpiece is heated to a certain temperature and maintained for a period of time, and then slowly cooled. Post-heating can release the internal stress generated during the gouging process, reduce the hardness of the metal structure, and reduce the impact of the hardened layer. The post-heating temperature is generally between 300-600℃, and the holding time is determined according to the size and thickness of the workpiece, usually 0.5-2 hours. Slow cooling can be done by covering with asbestos cloth or placing in a slow cooling pit, so that the workpiece can be slowly cooled to room temperature.

Mechanical processing removal

If the hardened layer is thin, it can be removed by mechanical processing. For example, grinding, milling and other processing methods are used to cut off the hardened layer on the surface of the gouging so that the workpiece reaches the required size and surface quality requirements. During the mechanical processing, it is important to select the appropriate tool and processing parameters to avoid new work hardening.

Selecting the right carbon rod

Selecting the right carbon rod can also help reduce the hardened layer. For example, the carbon content, diameter, and end shape of the carbon rod will affect the gouging effect. Carbon rods with moderate carbon content, appropriate diameter, and good end shape can stabilize the arc, evenly distribute heat, and reduce local overheating and the generation of hardened layers. For high-alloy steel gouging, copper-plated carbon rods with a diameter of 6-10mm can be used, and the ends can be ground to a suitable angle to improve gouging efficiency and quality.