The main disadvantages of water as a quenching cooling medium for forgings?

The main disadvantages of water as a quenching cooling medium for forgings?

1) In the code area of the austenite isothermal transformation diagram, that is, about 500-600 ℃, the water is in the vapor film stage, and the cooling rate is not fast enough, which often results in "soft spots" formed by uneven cooling of the forgings and insufficient cooling rate. . In the martensite transformation system, that is, about 300-100 ° C, the water is in the boiling stage, the cooling rate is too fast, and it is easy to make the martensite transformation speed too fast and generate great internal stress, which causes severe deformation and even cracking of the forging.

2) Water temperature has a large effect on cooling capacity, so it is sensitive to changes in ambient temperature. When the water temperature increases, the cooling capacity drops sharply, and the temperature range of the maximum cooling rate moves to low temperatures. When the water temperature exceeds 30 ° C, the cooling rate decreases significantly in the range of 500-600 ° C, which often results in hardening of the forging, but has a small effect on the cooling rate in the martensitic transformation range. When the water temperature increases to 60 ° C, the cooling rate will drop by about 50%.