Reasons and Preventive Measures of Hardness Insufficiency in Quenching Medium
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1. The low quenching temperature is mainly caused by improper process setting temperature, error of temperature control system, improper method of loading furnace or entering cooling tank, etc. The process temperature should be corrected, the temperature control system should be checked and checked. When loading furnace, the workpiece interval should be reasonably arranged evenly, dispersed into the tank, and no accumulation or bundling into the tank for cooling should be prohibited.
2. The quenching temperature is too high, which is caused by improper process setting temperature or temperature control system error. The process temperature should be corrected, and the temperature control system should be checked and checked.
3. Overtempering, which is caused by over-tempering temperature setting, fault error of temperature control system or when the furnace temperature is too high, should correct the process temperature, check and check the temperature control system, not higher than the furnace temperature loading.
4. The reason for improper cooling is that the pre-cooling time is too long, the choice of cooling medium is inappropriate, the temperature of quenching medium increases gradually and the cooling performance decreases, the stirring is not good or the temperature of outlet tank is too high. Measures should be taken: quicker outlet and outlet tank; master the cooling characteristics of quenching medium; oil temperature 60-80 C, water temperature below 30 C; when quenching amount is large and the cooling medium is heated, cooling quenching medium should be added or changed. Cooling in other cooling tanks, strengthening the agitation of coolant, and removing at MS+50 C.
5. Decarbonization is caused by the residual decarbonization layer of raw materials or quenching heating. The preventive measures are controlled atmosphere heating, salt bath heating, vacuum furnace and box furnace using packing protection or anti-oxidation coating, and the machining allowance is increased by 2-3 mm.