Historical metallurgy is one of the most interesting fields of archaeometry. However, traditional analytical methods are often too invasive to be applied to the most interesting artefacts. Here we propose to use neutron diffraction to determine the average carbon content and derive some information on the working technique through the possible presence of martensite, in two helmets (kabuto) pertaining to the Japanese Section of the Stibbert Museum in Florence. Also the determination of the presence of mineralization products and slag inclusion will be of great importance for understanding the smelting procedure used to produce the metal.