1. Pollution caused by rinsing
After hardening, the fasteners were cleaned with silicate cleaning agent, and then rinsed. XX solid substance appeared on the surface, which was analyzed by infrared spectrometer and confirmed to be inorganic silicate and iron oxide. This is due to the residue of silicate on the surface of the fastener due to incomplete rinsing.

2. The stacking of fasteners is unreasonable
Fasteners after tempering signs of discoloration, soak with ether, let ether volatilize found that the remaining oily residue, such substances are high content of lipids. The fasteners are contaminated by cleaning agents and quenching oils during the rinsing period, which melt at the heat treatment temperature and leave chemical burn scars. Such substances confirm that the fastener surface is not clean. Analyzed by infrared spectrometer, it is a mixture of base oil and ether in quenching oil. The ethers may come from the addition of quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirm that the fastener has a slight oxidation in the quenching oil due to unreasonable stacking when heating, but it is almost negligible. This phenomenon is related to the cleaning process, rather than the problem of the 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. There is no acid cleaning agent cleaning, and the inspection of the rinsing tank found that the tank has a high carbon solubility, the tank should be poured out regularly, and the concentration level of lye in the rinsing tank is often tested.

4. Alkali burn
High strength screw quenching residual heat blackening has a uniform, smooth oil black outer surface. But in the outer ring there is an area of orange XX visible to the naked eye. In addition, slightly light blue or light red areas are also visible. The raw bar material and rod are coated with phosphating film to facilitate cold heading and tapping, heat treated without rinsing, cooled in quenching oil, cleaned with alkaline cleaning agent, blown dry (without rinsing), tempered at 550℃, and dipped in anti-rust oil from tempering furnace in hot state. Red spots were found on screw threads.

After detection, the red area on the screw is caused by alkali burn, alkaline cleaning agent containing chloride substances, calcium compounds will burn steel fasteners during heat treatment, leaving marks on the surface of fasteners.
Steel fasteners cannot remove surface alkalinity in quenching oil, which burns the surface at high temperature austenite and aggravates the damage when tempering in the next step.