Abstract: The hardenability of ‚10CrNi3MoV30C type bulb flats was studied by the measurements of hardenability and middle frequency as quenched transverse section hardness and the observation of microstructure. The results indicate that ‚10CrNi3MoV30C type bulb flats has good hardenability and it is feasible to study the middle frequency hardenability of 30C type bulb flats by Jominy test.