Application of medium frequency induction heating equipment to heat treatment of T8 steel bar cutting clamps

Steel bar cutting pliers are widely used tools in the construction and electrical industries. The hardness of the entrance is required to be 55-60HRC and the remaining part is 33-40HRC. In the past, GCR15 steel was used as the material of the pliers in China. The forgings were rough processed after spheroidizing annealing. Quenching and tempering treatment (quenching at 840℃, tempering at 620℃, hardness 33HRC), the cutting edge is tempered by medium frequency induction quenching for 180-200x2h, which can meet the technical requirements. The final process is grinding and sharpening. The austenite grain size of the cutting edge after induction quenching is 13.5, and the service life of shearing steel is more than 1500 times. Later, some manufacturers used T8 steel instead of Gcr15 steel and adjusted some process parameters. The technical requirements were also met, and the shearing life reached more than 1,500 times (the material to be sheared was cold-drawn 45 steel with a diameter of 10mm). Moreover, another advantage of using T8 steel is that it is not as prone to grinding cracks as GCR15 steel, which simplifies the production process and reduces costs. The relevant experimental conditions are now introduced as follows.

1) Experimental methods. Randomly select 16 pieces from the T8 steel pliers forging blank with a specification of 609.6mm and a full length for testing. The process flow is: cutting - die forging - spheroidizing annealing - rough machining - 800x30min heating oil quenching (hardness is 33-40HRC) - oil removal - medium frequency induction quenching - 180-200℃x2h nitrate salt tempering - grinding blade. The model of the medium frequency induction heating equipment is WH-VI-200. The approximate size of the sensor and the position of the blade sensor during heating. The distance between the sensor and the blade during heating is 3mm. A larger gap will help reduce the surface area of the workpiece. of overheating. The end of the sensor is designed into an arc shape with a radius of 8mm. This is because the R5mm semicircular hole of the clamp head does not need to be hardened.

2) Test results and the influence of process parameters on the depth and structure of the hardened layer. The depth of the hardened layer is roughly expressed by the macroscopic quenching depth of the tool tip after etching with 4% alcohol. Generally speaking, the hardened layer is required to be as deep as possible to increase its load-bearing capacity. In this way, extending the heating time of the four walls will cause overheating of the surface. To solve this contradiction, the only way is to adjust the electrical parameters to reduce the specific power of the heated surface. The data in the table shows that when the output voltage of the multi-frequency generator is greater than 700V and the corresponding output current is greater than 30A, the heating speed is too fast and the process is difficult to control, causing the austenite grain size to increase to above 11.5; at the appropriate voltage By selecting the pinch-off heating time under the parameters, the austenite grain size of T8 steel can also reach grade 13, but at this time the quenching layer is too shallow and the hardness is low.

3) Conclusion

① Because the austenite manager of T8 steel has a greater tendency to coarsen, when the medium-frequency induction heating is performed with the original structure of the solid body, the output voltage of the equipment should not be higher than 700V, and the output current of this device should not exceed 30A. Select an appropriate heating time. , an austenite grain size of about 11.5 and sufficient hardened layer depth can be obtained.

② Using T8 steel instead of GCR steel to make steel bar cutting pliers can achieve a similar connection and unloading life as bearing steel, and can reduce processes and costs.