Certain aspects of cooling in a water-air mixture during induction hardening

Conclusions

• 1. The use of a water-air mixture makes it possible to control the cooling rate at the pearlite and martensitic transformation points.

• 2. An increase in the water content of the mixture to a “limit” value increases the cooling rate, reduces the cooling time and increases the temperature gradient through the section. When the humidity is increased beyond the “limiting” compositions, the cooling rate, overall cooling time and temperature gradient are either stabilized or changed only slightly.

• 3. Stabilization of the cooling rate, the overall cooling time and the maximum temperature gradient through the section is attained by reducing the heat-transfer coefficient when the mixture is humidified beyond the “limiting” values.

• 4. The high degree of dispersion of the water drops in the mixtures with compositions below the “limit” means that they are cooled by the primary “explosive” vapor formation. Here there is an improvement in the heat-transfer conditions from the surface and it then becomes possible to obtain coolrates above critical at some depth. Cooling by means of water-air mixtures improves hardenability.