During the heat treatment process, workpieces often suffer from defects such as distortion, brittleness and cracking, insufficient hardness, oxidation and decarburization. These issues not only increase the scrap rate but may also affect subsequent assembly and operational safety. In fact, most defects stem from improper process parameters, inadequate equipment precision, or operational errors. This article compiles the causes and solutions for 5 common defects to help you enhance production stability.
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Causes: Excessively fast heating rate, uneven cooling, improper loading method (overstacking of workpieces), incorrect selection of quenching medium.
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Solutions:
a. Adopt "stepwise heating" (low-temperature preheating → high-temperature holding) to reduce thermal stress;
b. Optimize cooling methods: Use marquenching for thick and large workpieces, and isothermal quenching for thin-walled workpieces;
c. Improve furnace loading: Secure workpieces with special fixtures to avoid stacking and ensure uniform air flow inside the furnace;
d. Select appropriate quenching medium: Adjust cooling rate when switching from oil quenching to water quenching, or use water-soluble quenching agents.
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Causes: Excessively high quenching temperature, excessively fast cooling rate, delayed tempering, excessive impurities in materials.
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Solutions:
e. Reduce quenching temperature (adjust according to material composition, e.g., lower the quenching temperature of high-carbon steel from 860℃ to 820℃);
f. Slow down the cooling rate: Oil quenching is milder than water quenching, or add cooling modifiers to the quenching medium;
g. Perform tempering within 2 hours after quenching to eliminate internal stress;
h. Use high-purity raw materials to avoid excessive sulfur, phosphorus and other impurities.
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Causes: Insufficient heating temperature, inadequate holding time, slow quenching cooling rate, low carbon content in materials.
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Solutions:
i. Increase heating temperature (within the allowable range of the material, e.g., raise the temperature of medium-carbon steel from 830℃ to 850℃);
j. Extend holding time (adjust according to workpiece thickness: extend holding time by 30 minutes for every additional 10mm thickness);
k. Replace with a medium with faster cooling rate (e.g., switch from water quenching to brine quenching, or check if the quenching medium is aged);
l. Test the carbon content of raw materials in advance to ensure compliance with process requirements.
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Causes: Improper control of furnace atmosphere (excessive oxygen), excessively long heating time, poor equipment airtightness.
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Solutions:
m. Use atmosphere-controlled furnaces (e.g., nitrogen or methanol cracked gas protection) to isolate oxygen;
n. Shorten heating time to avoid excessive oxidation;
o. Inspect furnace door gaskets and repair air leakage points;
p. For decarburized workpieces, repair them through carburizing/nitriding replenishment processes.
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Causes: Uneven flow of furnace atmosphere, improper workpiece loading position, unstable carburizer/nitriding agent concentration.
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Solutions:
q. Optimize the internal air flow design of the furnace and install deflectors;
r. Distribute workpieces evenly to avoid blocking the contact between the carburizer/nitriding agent and the workpiece surface;
s. Monitor the concentration of the carburizer/nitriding agent in real time and maintain stability through an automatic feeding system.
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