Contamination during rinsing
After the fasteners were quenched, they were cleaned with silicate cleaning agent and then rinsed. XX solid matter appeared on the surface. The infrared spectrometer was used to analyze this matter and it was confirmed that it was inorganic silicate and iron oxide. This is caused by incomplete rinsing and residual silicate on the surface of the fastener.
2. Unreasonable stacking of fasteners
Fasteners show signs of discoloration after tempering, and oily residues are found after volatilization, which are high-content lipids. It shows that the fastener is contaminated by cleaning agent and quenching oil during the rinsing period, and it melts at the heat treatment temperature, leaving chemical burn scars. Such substances confirm that the surface of the fastener is not clean. Analyzed by infrared spectrometer, it is a mixture of base oil and ether in quenching oil. The ether may come from the addition of quenching oil. The analysis results of the quenching oil in the mesh belt furnace confirm that the fasteners are slightly oxidized in the quenching oil due to unreasonable stacking during heating, but it is almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.
3. Surface residues
There is a white residue on the high-strength screw, which was analyzed by infrared spectrometer and confirmed to be phosphide. No cleaning with acidic cleaning agent was performed, and inspection of the rinsing tank found that the tank liquid had a higher carbon solubility. The tank liquid should be poured out regularly, and the rinsing tank should be checked frequently. 4. Alkaline burns
High-strength screws are blackened by quenching heat and have a uniform and smooth oil-black outer surface. However, there is an area visible to the naked eye with orange XX in the outer circle. In addition, there are visible slightly light blue or light red areas. The original bar and wire rod are coated with phosphating film to facilitate cold heading and tapping. They are directly heat treated without rinsing, cooled in quenching oil, cleaned with alkaline cleaning agent, blow-dried (not rinsed), tempered at 550°C, hot After removing the anti-rust oil from the tempering furnace, red spots were found on the screw threads.
It has been tested that the red area on the screw is caused by alkali burn. Alkaline cleaning agents containing chlorides and calcium compounds will burn the steel fasteners during heat treatment, leaving scars on the surface of the fasteners.
Iron and steel fasteners cannot remove surface alkalis in the quenching oil, so that the surface burns in the high-temperature austenite state and aggravates the damage during the next step of tempering. The recommendation is to thoroughly clean and rinse the fasteners before heat treatment to completely remove the alkaline residues that cause the fasteners to burn.
5. Improper rinsing
For large-size fasteners, polymer aqueous solution quenching is often used, and alkaline cleaning agent is used to clean and rinse before quenching. After quenching, the fasteners have rusted on the inside. Analysis with an infrared spectrometer confirmed 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 rust. Rinse the fasteners to check whether there is excessive contamination. It is also recommended to change the rinse water frequently. In addition, adding rust inhibitors to the water is also a good way.
6. Excessive corrosion
Some black stripes are often seen in high-strength fasteners. We have also seen in experiments that we have used inorganic and organic cleaning agents to rinse the fasteners before heat treatment. After quenching, there are still black stripes and even careful cleaning before heat treatment. , Will also leave streaks after heat treatment. An infrared spectrometer was used to analyze the contaminants remaining on the surface, and it was found that there were higher concentrations of sulfur and calcium. Using a small amount of acetic acid and isopropanol, fold a small piece of test filter paper firmly on the dark spot, leaving the dark spot on the filter paper. Analysis of the filter paper with an infrared spectrometer confirmed that calcium, sulfur, iron, manganese and chromium are the main elements.
