1. Exterior residue: White residue on high-strength DIN 603, which was analyzed by instrument and proved to be phosphide. This reaction occurred because the acid cleaner was not cleaned and the rinsing tank was not thoroughly inspected.
2. Pollution during rinsing: DIN 603 needs to be cleaned with silicate cleaner after quenching and then rinsed, so care should be taken during rinsing to avoid residue.
3. Improper rinsing: DIN 603 is often quenched with polymer aqueous solution. Before quenching, it is cleaned and rinsed with alkaline cleaner. After quenching, self-tapping screws and DIN 603 fasteners have rusted on the inside. Therefore, rinse water should be exchanged frequently to ensure DIN 603 will not rust during rinsing.
4. Unreasonable accumulation of square bolts: after tempering, the square bolts will show signs of discoloration, which indicates that the appearance of the square bolts is not clean. The analysis shows that the accumulation of square bolts during heating is unreasonable, resulting in slight oxidation of cylindrical head square bolts in quenching oil.
5. Excessive corrosion: Some black stripes are often seen on high-strength square bolts. The black stripes are pollutants of external residues, which are dried quenching oil and are the evolution of gaseous substances during quenching. Because quenching oil is over-aged, it is recommended to participate in new oil.
6. Alkali burn: The quenching residual heat blackening of high-strength square bolts has a uniform and flat oil-black outer appearance. Through detection, it is caused by alkali burn. Therefore, the steel square bolt cannot be removed from the outer surface alkaline substance in quenching oil, thus causing the outer surface to burn at high temperature and aggravating the damage during tempering. It is suggested that the cylindrical head Square Bolt should be thoroughly cleaned and rinsed before heat treatment, so as to completely remove the alkaline residue causing burns to the square bolt.