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Prediction of fatigue performance of large structures and components is generally done through the use of a fatigue analysis software, FEA stress/strain analysis, load spectra, and materials properties generated from laboratory tests with small specimens. Prior experience and test data has shown that a specimen size effect exists, i.e. the fatigue strength or endurance limit of large members is lower than that of small specimens made of same material. Obviously, the size effect is an important issue in fatigue design of large components. However a precise experimental study of the size effect is very difficult for several reasons. It is difficult to prepare geometrically similar specimens with increased volume which have the same microstructures and residual stress distributions throughout the entire material volume to be tested. Fatigue testing of large samples can also be a problem due to the limitation of load capacity of the test systems available.

A nano-composite high strength (NCHS) steel was tested and evaluated in this work. Monotonic tension, strain controlled fatigue and fracture toughness tests were conducted at ambient temperature. Chemical composition, microstructure and fractography analysis were also performed. The NCHS steel showed excellent combination of high strength, high ductility and high fracture toughness with relatively low alloy content, compared with a S7 tool steel. Fatigue performance of the NCHS steel was also better than that of S7 tool steel. With the exceptional combination of high strength and high fracture toughness, the nano-composite high strength steel may have potential applications in gears, shafts, tools and dies where high fatigue performance, shock load resistance, wear and corrosion resistance is required.