Cause of the defect:
1. Excessive heating temperature
2. The temperature controller has a problem, or the measured value is inaccurate
3. The workpiece is too close to the Bogie Furnace heating element
4. Furnace Bottom There is too much sediment, which contacts the heating element, causing Furnace Bottom excessive temperature, and the workpiece overheats or overburns due to contact with or being buried in the sediment.
5. Workpiece decarburization or carburization during heating
6. Heat treatment process problems of the workpiece, such as excessive heating time in Bogie Furnace
7. Bogie Furnace The design is unreasonable. The design of the heating element causes uneven temperature inside Furnace Chamber , resulting in local overheating.
8. Heat treatment process control is not strict
Preventive measures for defects
1. Accurately control the three elements of the heat treatment process, Liter heating speed, holding temperature and holding time
2. Tooling Fixture and other designs shall be reasonable
3. Regularly inspect and calibrate temperature control instruments
4. Strictly inspect the metallographic structure after heat treatment
5. Cut off the power after the workpiece is discharged from the furnace
6. Prevent non-process materials or impurities from being mixed together
Handling methods for defects:
1. Severely overburnt workpieces are generally scrapped.
2. General overheating can be re-annealed and Quenching , Tempering .
Causes of defects:
1. In a salt bath, the contents of water, oxygen and impure substances (such as sulfate and carbonate) are too high
2. Scale falls into the furnace
3. Nitrate salt is brought into the furnace
4. Poor deoxidation and incomplete slag skimming
5. Quenching Fixture Excessive surface rust
6. Summer Day air humidity is too high
Preventive measures for defects:
1. Barium chloride must be dried and dehydrated at 300~500oC for 2~4h before use.
2. Quenching Before heating, strictly deoxidize and skim the slag of the salt bath
3. Clean Bogie Furnace electrode oxide scale frequently.
4. Replace nitrate salt on schedule.
5. Clean up Quenching Fixture rust and dry.
Treatment method for defects
1. Severe decarburization, scrapped.
2. The decarburization depth is less than the grinding allowance, and can be used as Qualified Product
3. The decarburization depth is greater than the grinding allowance. After quenching Tempering , the surface hardness Hardness is not lower than 55~60HRC. It can be remedied by annealing and Carburizing methods.
Causes of defects:
1. Quenching Low temperature, short heating time
2. The preheating time is too short, and the preheating temperature is too low.
3. Large furnace loading, too dense arrangement of parts, causes uneven hardening.
4. The raw materials contain serious graphite carbon, or coarse granular carbide
5. Raw material decarburization or Quenching heating decarburization
6. Quenching slow cooling, Isothermal Quenching 's isothermal temperature is too high or the time is too long
7. Tempering High temperature, Tempering insufficient
8. Foreign materials mixed in , the decarburization layer of raw materials is not removed.
9. Poor furnace temperature uniformity and inaccurate instrument measurement.
10. The workpiece is too shallow from the furnace surface or the workpiece contacts the salt slag below, causing uneven temperature.
Preventive measures for defects:
1. Strengthen raw material inspection, grind sparks, check spectrum or test chemical composition
2. Remove the decarburized layer from the raw material. Bogie Furnace Deoxidize and skim slag before heating. Workpieces heated in air furnaces require protective gas for vacuum heating.
3. Accurately grasp parameters such as temperature and time in the Quenching Tempering process.
4. Select the appropriate Quenching Medium
5. Water Quenching , The cooling time of oil cooling cannot be too short
6. Understand the functions of heating furnaces and instruments, grasp the error values
7. Check the Hardness value after Quenching
Treatment method for defects:
1. If there is too much retained austenite, the Hardness value can be increased through cold treatment or the Hardness value can be increased by re- Tempering .
2. Reheat, Quenching , Tempering
3. The tools whose grinding amount does not exceed the decarburized layer shall be treated as defective products or waste products.
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