The effect of cryogenic treatment on 4X40 series steel was studied. The study included chemistry, microstructure, microhardness, tensile, fracture toughness, fatigue crack propagation, load-controlled tensile fatigue, x-ray diffraction for retained austenite and wear tests. Credible, independent test data about the effects of cryogenic treatment on 4X40 series steels is lacking. The test results show that cryogenic treatment offers no significant benefit on the properties of 4X40 steels. A smaller test regimen was conducted on carbo-nitrided 1018 and 8620 steels with and without cryogenic treatment. Those results will also be presented.