Because the brake drum works in the harsh environment with strong friction and complex alternation of cold and heat. Therefore, the brake drum material should have good thermal conductivity. The following table compares the thermal diffusivity and thermal conductivity of vanadium titanium gray cast iron brake drums with different components.The graphite state in ordinary gray iron is the most favorable form of carbon in iron for heat conduction. The thermal conductivity of gray iron is higher than that of all iron-based alloys, with a value of 44 ~ 67 w / m · K.
The thermal conductivity of different types of flake graphite is also different. Because the bending technology of type a graphite flakes is connected with each other and evenly distributed, its thermal conductivity is better than that of other types of graphite.
In vanadium titanium gray cast iron, carbon exists in the form of flake graphite and carbide. Among them, flake graphite is conducive to the increase of its thermal conductivity, while the carbides in cast iron are mainly Fe3C and alloy carbides. Their structure is complex and their thermal conductivity is far lower than that of graphite and metal matrix, which sharply reduces the thermal conductivity of cast iron and decreases rapidly with the increase of the amount of carbides.
In 1# and 2# samples, the graphite morphology is mainly A-type graphite, and its vanadium titanium content is relatively low, so its carbide content is relatively low, and its thermal conductivity is relatively better than that of 3# and 4# samples. The 3# samples with higher content of carbon, vanadium and titanium changed into D-type graphite, and the content of carbide was higher than that of 1# and 6# samples, and the thermal conductivity decreased. Compared with 1# and 2# samples, the thermal conductivity of 4# samples is significantly increased because the carbon content and titanium content are significantly increased. After the addition of vanadium and titanium, vanadium can promote the formation and refinement of pearlite, but a small amount of titanium hinders the formation of pearlite. At the same time, the supercooling tendency of molten iron increases during solidification, resulting in the decrease of pearlite content and the increase of graphite content, Thus, its thermal conductivity is improved.