1. Pollution during rinsing

After the fasteners are quenched, they are cleaned with a silicate cleaning agent, and then rinsed. XX solid substances appear on the surface. This substance is analyzed by an infrared spectrometer, and it is confirmed that it is an inorganic silicate and iron oxide. This is due to silicate residues left on the surface of the fastener without rinsing.

2. Unreasonable stacking of fasteners

Fasteners show signs of discoloration after tempering. Soak them in ether and let the ether volatilize to find an oily residue. This kind of substance is a high content of lipids. It shows that the fasteners are contaminated by cleaning agents and quenching oils during the rinsing period, and melted at the heat treatment temperature, leaving chemical burn scars. Such substances prove that the surface of the fasteners is not clean. Analyzed by infrared spectrometer, it is a mixture of base oil and ether in quenching oil. Ether may come from quench oil additives. The analysis results of the quenching oil in the mesh belt furnace confirmed that the fasteners were slightly oxidized in the quenching oil due to unreasonable stacking when they were heated, but it was almost negligible. This phenomenon was related to the cleaning process, not the quenching oil The problem.

3. Surface residue

There was a white residue on the high-strength screw, which was analyzed by an infrared spectrometer and confirmed to be phosphide. No acid cleaning agent was used to clean the rinsing tank, and it was found that the rinsing tank had a high carbon solubility. The tank should be poured out regularly, and the concentration of lye in the rinsing tank should be checked frequently.

4. Alkali burn

High-strength screws are blackened by quenching waste heat and have a uniform and smooth oil-black outer surface. But there is an orange XX visible area on the outer ring. In addition, there are slightly bluish or reddish areas visible. The original bar and wire rod are coated with phosphating film to facilitate cold heading and tapping, direct heat treatment without rinsing, cooling in quenching oil, cleaning with alkaline cleaning agent, drying (without rinsing), tempering at 550°C, heat treatment The anti-rust oil was removed from the tempering furnace, and red spots were found on the screw threads.

It has been detected that the red area on the screw is caused by alkali burns. Alkaline cleaning agents containing chloride substances and calcium-containing compounds will burn the steel fasteners during heat treatment and leave spots on the surface of the fasteners.

Steel fasteners cannot remove surface alkalinity in quenching oil, so that the surface will be burned in the high temperature austenite state, and the damage will be aggravated in the next step of tempering.