QUENCH & TEMPER
It is the quenching and Tempering (Blueing) process performed in order to obtain the desired hardness and mechanical properties. It is especially used for situations where the entire cross-section of the part is desired to be rigid. The process of hardening methods can be described in the simplest way as heating the material to the hardening temperature and hardening it by sudden cooling. Regarding the subject, the interrelationship of factors such as the selection of the curing temperature, the heating rate, the selection of the cooling medium and the cooling rate, and the determination of the correct values are subjects that require expertise. The hardening temperature ranges are values determined by a series of experiments to ensure that the maximum hardness is achieved with the smallest grain structure. Heating below or above these values will result in a low hardness value and the final internal structure not being as desired. In addition, the holding time at the hardening temperature is also important, it is related to the alloy, low alloying of the material and the suitability of the grain sizes.
The selection of the quenching medium is related to the alloy content of the material. While water and salt baths are preferred for low alloy steels, soft environments such as oil are preferred for high alloy steels considering the risk of warping. Intensively used cooling media can be specified as water, oil, salt bath and air.
Water: One of the most important characteristics associated with water quenching is the temperature of the water used to cool the hot part. Cooling water temperature between 20-40 ˚C is the most efficient temperature. At temperatures above 60 ˚C, the cooling rate drops drastically.
Oil: The cooling rate of oil in oil quenching is slower than the cooling rate of water. The oil temperature at which the cooling rate is most efficient is between 50-80 ˚C. In addition, the continuous rapid mixing of the oil greatly increases the yield.
Salt Water Solution: Sodium hydroxide or kitchen salt can be added to the water to increase the water quenching efficiency. Kitchen salt is less preferred because it causes corrosion on the part. NaOH to be added at the rate of 10% will increase the cooling rate too much. This type of use also provides low internal stresses by increasing the high hardening depth.
Air: Air quenching is the least efficient rate compared to other methods. The biggest reason for this is that the cooling rate of the air is very low. In fact, the cooling rate of calm air is less than 1% of water. For this reason, this method can only be preferred for high speed steels.
- Fasteners (bolt, nut, washer, pin)
- Engine and gear parts, axles, shafts
- Cold work tool steels
- Various molds and machine parts
- Tool parts