1. Pollution generated during rinsing
After the fasteners were quenched, they were washed with a silicate cleaning agent, then rinsed, and XX solid matter appeared on the surface, and the material was analyzed by an infrared spectrometer to confirm that it was an inorganic silicate and iron oxide. This is due to the fact that the rinsing is not completely caused by the residual silicate on the surface of the fastener.
2. Unreasonable stacking of fasteners
After the fasteners are tempered, there are signs of discoloration. Soaking with ether, and evaporating the ether, the remaining oily residue is found. These substances are high-content lipids. It is indicated that the fastener is contaminated by the cleaning agent and the quenching oil during the rinsing period, and melts at the heat treatment temperature, leaving a chemical burn scar, which proves that the surface of the fastener is not clean. Analysis by infrared spectrometer is a mixture of base oil and ether in the quenching oil. The ether may be derived from the addition of quenching oil. The quenching oil analysis results in the mesh belt furnace confirmed that the fasteners were unreasonably stacked due to the improper heating, and the fasteners were slightly oxidized in the quenching oil, but they were almost negligible. This phenomenon is related to the cleaning process, not the quenching oil. The problem.
3, surface residue
A white residue on the high-strength screw was analyzed by an infrared spectrometer and confirmed to be a phosphide. There is no acid cleaning agent cleaning, and the rinsing tank inspection shows that the bath has a high carbon solubility. The bath should be periodically drained, and the concentration of the lye in the rinsing tank is often detected.
4, alkali burns
High-strength screw quenching residual heat blackening has a uniform, flat oil black outer surface. However, there is an area visible to the naked eye in the outer ring. In addition, there is a slightly light blue or light red area visible. The original bar and wire rod are coated with a phosphate film to facilitate cold heading and tapping. Direct heat treatment without rinsing, cooling in quenching oil, alkaline cleaning agent cleaning, drying (no rinsing), tempering at 550 °C, heat The state was taken out of the tempering furnace and the rust-preventing oil was removed, and as a result, red spots were found at the screw threads.
The red area on the tested screw is caused by alkali burn. The alkaline cleaning agent containing chloride substance and calcium-containing compound will burn the steel fastener during heat treatment and leave marks on the surface of the fastener.
Steel fasteners do not remove surface alkalines in quenching oil, causing surface burns in high temperature austenite and aggravating damage in the next tempering.