1、in the typical part of the austenitic isothermal transition diagram, i.e., about 500-600℃, the water is in the steam film stage, and the cooling speed is not fast enough, which often leads to the "soft point" formed by uneven cooling and insufficient cooling speed of forging.In the martensitic transformation system, that is, about 300-100℃, the water is in the boiling stage, the cooling speed is too fast, easy to make the martensitic transformation speed is too fast and produce a large amount of internal stress, resulting in the forging deformation or even cracking.

2、the water temperature has a great influence on the cooling capacity, so it is sensitive to the change of the ambient temperature. As the water temperature increases, the cooling capacity decreases sharply, and the temperature range of the maximum cooling rate moves to low temperature.When the water temperature exceeds 30℃, the cooling speed in the range of 500-600℃ decreases obviously, which often leads to the forging not to be hardened, but has little influence on the cooling speed in the range of martensite transformation.When the water temperature is raised to 60℃, the cooling rate will decrease by about 50%.

3、when the water contains more gas (such as new water), or water mixed with insoluble impurities, such as oil, soap, mud, etc., will significantly reduce its cooling capacity, so the use and management should be special attention.
According to the cooling characteristics of water, water H can be used for quenching and cooling of carbon steel forgings with small section size and simple shape.Quenching, must also note: keep the water temperature below 40 ℃, the best between 15 to 30 ℃, and keep the water or liquid circulation, to destroy the forging surface steam membrane, also can use swing workpiece during quenching (or make the workpiece moves up and down) method to subvert the steam membrane, increase the degree of cooling between 500-650 ℃, the cooling conditions, avoid to produce soft point.

 From:168 forgings net