Detailed process and precautions for salt bath furnace quenching

Before entering the furnace, it is necessary to check whether the quenching medium has good circulation and fluidity, whether the quenching fixture is complete, and whether the lifting equipment for large quenching is normal and reliable. The operator should take protective measures. When the salt bath furnace heat treatment production line is produced in batches, the quenching principle is to prevent the occurrence of more waste products after the first piece is quenched and qualified before continuing to be discharged from the furnace.
Parts with different shapes should be pre cooled in the air before entering the quenching medium. The pre cooling time should ensure that the temperature is higher than Ar3 or Ar1 before entering the quenching medium. The shaft and rod parts should be vertically fed with cooling medium, the long plate shaped parts should be horizontally and laterally fed with cooling medium, and the sleeve or thin-walled circular ring parts should be axially fed with cooling medium. For parts with large cross-sectional differences, the larger part should be fed with cooling medium first. For parts with concave surfaces, the concave surface should be fed with cooling medium upwards. For parts with long grooves on one side, the groove should be tilted upwards by 45 º to feed cooling medium. For blind hole parts, residual salt should be poured out, and the orifice should be fed with cooling medium upwards. Water quenched oil cooled parts can be taken out and cooled with oil when the cooling time in water is 1s/(3-5 mm), or when the hand vibration is weakened or the noise decreases. The transfer time from the water pool to the oil pool is 1-2 seconds.
Generally, carbon steel is quenched with a NaC1 aqueous solution with a mass fraction of 5% to 10%, with a water temperature of<40 º C. The density of the aqueous solution should comply with the requirements of the process documents, and there should be no dirt in the water. Medium carbon low alloy steel is quenched with quenching oil or tap water, while high alloy steel, cast iron, and powder metallurgy parts are quenched with oil. The oil contains no water, mud, or impurities, and the oil does not age. Parts with complex shapes that are prone to cracking are subjected to graded or isothermal quenching. For cutting tools, shaft components, etc. that are easily broken due to cold straightening It can be cooled to 150-250 º C in the medium before being removed for hot straightening. When pre deformation and pre stress quenching are applied to a tubular electric furnace, it is necessary to grasp the stable deformation law, and reverse deformation can be applied in advance to offset each other after quenching.
When the same piece has two hardness requirements, the high hardness area should be quenched first, and then the low hardness area should be quenched. Alternatively, after quenching together, the low hardness area can be first removed from the cooling medium and air cooled and self tempered. The principle for determining the cooling time of quenched and self tempered parts is that the surface conduction temperature of the parts should be 80~100 º C higher than the normal tempering temperature (equivalent to high temperature rapid tempering), otherwise the surface tempering is not sufficient. After quenching and cooling to room temperature, it is necessary to immediately clean, sandblast, and temper. The quenching and tempering time should generally not exceed 4 hours. High alloy steel parts and complex shaped parts should be tempered immediately after quenching.
The rapid heating quenching temperature is 100-200 º C higher than the normal quenching temperature, and can be put into the furnace at high temperatures. The insulation time is determined based on experiments. The color of the surface of the workpiece must be consistent with the color of the salt bath or furnace wall before it can be quenched.

The above content is organized by Superb heater Company, super heater. Mainly professional production: industrial heating elements, temperature measuring elements, production equipment, accessories, and raw materials such as tubular heaters, tubular heaters, belt heaters, ceramic heaters, silicone rubber heaters, thermocouples, etc.

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