1. Pollution during rinsing
After the fasteners are quenched, they are cleaned with a silicate cleaning agent, and then rinsed, and XX solid substances appear on the surface, which are analyzed by an infrared spectrometer, which proves to be inorganic silicate and iron oxide. This is caused by silicate remaining on the surface of the fastener due to incomplete rinsing.
2. Unreasonable accumulation of fasteners
After the fasteners are tempered, there are signs of discoloration. After soaking in water, it is found that there is an oily residue after evaporation. 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 melt 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. The ether may come from an additive to the quench oil. The analysis results of the quenching oil in the mesh belt furnace prove that the fasteners are slightly oxidized in the quenching oil due to unreasonable accumulation when they are heated, but it is almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.
3. Surface residue
There is a white residue on the high-strength screw, which is analyzed by infrared spectrometer and proved to be phosphide. No acid cleaning agent was used for cleaning, and the rinsing tank was checked to find that the tank solution had a high carbon solubility, the tank solution should be poured out regularly, and the concentration level of the lye in the rinsing tank should be checked frequently.
4. Alkali burn
High-strength screws are blackened by residual heat after quenching 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 light blue or light red 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 taken out from the tempering furnace in the state, 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.
Iron and steel fasteners cannot remove the 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. The recommendation is to thoroughly clean and rinse fasteners prior to heat treatment to completely remove alkaline residues that cause fastener burns.
5. Improper rinsing
For large-scale fasteners, polymer aqueous solution quenching is often used. Before quenching, it is cleaned and rinsed with alkaline cleaning agent. After quenching, the fasteners have rusted on the inside. Analysis with an infrared spectrometer shows that in addition to iron oxide, there are sodium, potassium and sulfur, indicating that there is an alkaline cleaning agent on the inside of the fastener, which is likely to be potassium hydroxide, sodium carbonate or similar substances, which promotes its rusting. Fastener rinses are inspected for excessive contamination, and frequent rinse water changes are also recommended. In addition, it is also a good way to add antirust agent to the water.
6. Excessive corrosion
Some black stripes are often seen on high-strength fasteners. It is also seen in the test. The fasteners before heat treatment have been rinsed with inorganic and organic cleaning agents. After quenching, black stripes are still found, and even carefully before heat treatment. Washing, also leaves streaks after heat treatment. Using an infrared spectrometer to analyze the residual pollutants on the surface, it was found that there were higher concentrations of sulfur and calcium. Use a small amount of isopropanol of acetic acid to rub a small piece of test filter paper on the black spot and leave the black spot on the filter paper. The filter paper was analyzed by infrared spectrometer, and it was proved that calcium, sulfur, iron, manganese and chromium were the main elements.
