Causes of defects in spring post treatment and preventive measures

Defect 1: decarburization
Influence on spring performance: low fatigue life
The causes of the defects are as follows: 1. The air furnace is heated and quenched without protective gas; 2. The deoxidization in salt bath is not complete
Preventive measures: 1. Air furnace heating and quenching should be protected by protective gas or drop of organic solution: when heating in salt bath furnace, the salt bath should be deoxidized, and the mass fraction of impurity Bao should be less than 0.2%. 2. Strengthen the surface quality inspection of raw materials
Defect 2: insufficient hardness after quenching
Impact on spring performance: residual deformation, reduce service life
The causes of the defects are as follows: 1. More non martensitic structure; 2. Ferrite in the core; 3. Low quenching temperature; 4. Poor cooling capacity of quenching medium
Preventive measures: 1. Select steel with good hardenability; 2. Improve the cooling capacity of quenching medium; 3. The temperature of spring entering into quenching medium should be above Ar3; 4. Properly raise the quenching heating temperature; 5. Strengthen metallographic examination after quenching
Defect 3: overheating
Effect on spring performance: coarse grains and increased brittleness
The causes of the defects are: 1. The quenching heating temperature is too high; 2. The hot forming temperature is too high
Preventive measures: 1. Heating and quenching according to the correct temperature of process test; 2. Reducing the hot forming temperature properly; 3. Strengthening the calibration of instruments to ensure the accuracy of temperature measurement
Defect 4: cracking
Influence on spring performance: brittleness increases and service life is seriously reduced
Causes of defects: 1. High heating temperature or cooling capacity of quenching medium; 2. Surface decarburization; 3. Delayed tempering
Preventive measures: quenching heating temperature. 1. Strictly control 2. Austempering or martensite step quenching; 3. Cooling to 250-300? C in quenching medium; 4. Tempering immediately after quenching.