1. Contamination during rinsing
After quenching, the fasteners are cleaned with silicate cleaning agent, and then rinsed. XX solid substance appears on the surface. This substance is analyzed by infrared spectrometer, which is confirmed to be inorganic silicate and iron oxide. This is caused by incomplete rinsing and residual silicate on the surface of fasteners.
2. Unreasonable stacking of fasteners
After tempering, the fasteners show signs of discoloration. Soak them in ether. After volatilizing the ether, it is found that there are oily residues left. These substances are high contents of lipids. It indicates that the fastener is polluted by cleaning agent and quenching oil during rinsing, and melts at heat treatment temperature, leaving chemical burn scars. Such substances prove that the fastener surface is not clean. It is a mixture of base oil and ether in quenching oil. The ether may come from the additive of quenching oil. The analysis results of quenching oil in mesh belt furnace confirm that the fasteners are slightly oxidized in quenching oil due to unreasonable stacking during heating, but it is almost negligible. This phenomenon is related to the cleaning process, not the problem of quenching oil.
3. Surface residue
There was white residue on the high-strength screw, which was analyzed by infrared spectrometer and confirmed to be phosphide. The rinsing tank was not cleaned with acid detergent, and it was found that the tank solution had high carbon solubility through inspection. The tank solution should be poured out regularly, and the concentration level of alkali solution in the rinsing tank should be detected frequently.