Defect 1: Decarbonization
Impact on spring performance: low fatigue life
Causes of defects:
1. Air furnace heating and quenching without protective gas
2. Incomplete deoxidation in salt bath
Preventive measures:
1. Air furnace heating and quenching should be protected by protective gas or drops of organic solution
When the salt bath furnace is heated, the salt bath should be deoxidized, and the mass fraction of impurity BAO is less than 0.2%
2. Strengthen the inspection of the surface quality of raw materials
Defect 2: Insufficient hardness after quenching
Impact on spring performance: residual deformation and reduced service life
Causes of defects:
1. Many non-martensitic structures
2. Ferrite appears in the heart
3. Low quenching heating temperature
4. Poor cooling capacity of quenching medium
Preventive measures:
1. Use steel with good hardenability
2. Improve the cooling capacity of the quenching medium
3. The temperature of the spring entering the quenching medium should be above AR3
4. Appropriately increase the quenching heating temperature
5. Strengthen the metallographic inspection after quenching
Defect three: overheating
Impact on spring performance: coarse grains and increased brittleness
Causes of defects:
1. The quenching heating temperature is too high
2. The hot forming temperature is too high
Preventive measures:
1. Heat and quench according to the correct temperature of the process test
2. Appropriately reduce the hot forming temperature
3. Strengthen the calibration of the instrument to ensure accurate temperature measurement
Defect 4: Cracking
Impact on spring performance: increased brittleness and severely reduced service life
Causes of defects:
1. The heating temperature is high or the cooling capacity of the quenching medium is too large
2. Surface decarburization
3. Tempering is not timely
Preventive measures:
Quenching heating temperature
1. Strict control
2. Use austempering or martensite graded quenching
3. Cool to 250～300ºC in the quenching medium and take out air cooling
4. Tempering immediately after quenching