No abstract

The effect of chemical composition on microstructure and mechanical properties was investigated. Optimum contents of Al and N for appropriate prior austenite grain size were determined to avoid the formation of microcracks during oil quenching after a carbonitriding heat treatment. The microhardness and fatigue life of microalloyed steels based on SAE 5140H were compared with those of conventional steels. The surface hardness was increased due to finely distributed V-carbonitrides precipitated during double reheat process at the range of intercritical temperatures. The fatigue life was increased due to a large amount of retained austenite in the steel obtained by a carbonitriding heat treatment.