Heat treatment of steel parts, esp races for rolling bearings - using brief immersion in liq. nitrogen to reduce residual austenite in surface

摘要

The part is heated to form austenite, and is then quenched, followed by tempering is required to reduce brittleness. The surface region only of the part is next cooled in a liq. gas, esp. in N2, which is pref. applied as a sprayed mist. The invention is designed to eliminate residual tensile stresses in the surface zones of the parts. By selective sub-zero cooling of the surface zones, some of the residual austenite in these zones is converted to martensite, which creates an increase in vol., producing desirable compressive stresses working in opposition to the stress applied when the part is in use.