Reasons for low hardness, soft bands or soft points when shaft parts are quenched at high frequency:

① The power of the equipment is improperly selected, the heating is less than the power, and the heating time is short;

② The design of the inductor and the cooler is unreasonable, the inner diameter of the inductor is not consistent with the workpiece, resulting in uneven heating and cooling;

③ The heating and cooling processes are unreasonable, or there is water in the sensor, which causes a soft spot after quenching attached to the workpiece, or the pressure of the cooling medium is small, the flow rate of the medium is small, and the water spray holes are blocked, resulting in insufficient cooling;

④ Excessive heating power and heating time, overheating or coarse grains;

⑤ There are coarse massive ferrite in the original structure, the carbon content of the material is too high or the hardenability of the material is too high or too poor;

⑥ Uneven tempering temperature or insufficient tempering;

⑦ The quenching temperature is low or the moving speed is too fast;

The measures to be taken are:

① Reasonably select the power of equipment, determine reasonable heating process parameters, and perform process verification;

② Improve the design of the inductor and cooler, make the size of the induction ring consistent with the requirements of the shaft, and ensure that the surface of the part is fully and uniformly heated and cooled;

③ Check the set heating and cooling parameters, re-harden after normalizing, adjust the heating temperature, time, pressure and flow of the cooling medium as required, and clean the water spray holes;

④ Adjust the heating process parameters and carry out the necessary metallographic examination;

⑤ Change the material (select materials that meet the requirements) or select a suitable cooling medium and use pre-heating such as normalizing or quenching and tempering to obtain a uniform and fine structure;

⑥ Strengthen the control of tempering temperature and spot check of hardness;

⑦ Strictly control and adjust the movement speed of the shafts for the heating temperature and hardness of the gold fork to ensure that the quality is qualified;

⑧ Strictly control the composition of the raw materials and the requirements of the organization, remove the surface decarburization layer or replace the steel, improve the control of the atmosphere in the pre-heat treatment furnace, perform carbon supplementation, and normalize the structural defects.