Analysis of ways to prevent corrosion of high-strength fasteners

Some black stripes are often seen on 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.

The presence of calcium and sulfur in the rust spots indicates that this substance is a quenching oil that has dried out, and it is also the evolution of vapor phases during the quenching process. Because the quenching oil is excessively aging, it is recommended to pour out the old oil, add new oil, and implement process supervision and quenching oil maintenance during the entire process cycle.