GG20-GCI Brake Drum: The Effect of Mn/S on Machinability and Tensile Behavior

This study aims to assess the influence of the Mn to S ratios on the machinability and tensile behavior of GG20-gray cast iron brake drums. The effect of various Mn and S contents on microstructural characteristics such as type, size, and aspect ratio of graphite particles, interlamellar spacing of pearlite, and the distribution factor, size, and volume fraction of MnS were investigated. The microstructural results showed that a decrease in the Mn/S ratio to 5.1 and a decrease in the Ti/S ratio to under 0.11 promote the lengthy A-type graphite formation. Meanwhile, with the %Mn × %S value of about 0.08, the best uniform distribution of MnS inclusions has been obtained (about 55% of MnS inclusions are near A-type graphite flakes in the P1 specimen with %Mn × %S about 0.08 and Mn/S value of 5.1). Good machining in terms of less wear of the cutting tool and easier fragmentation of the chip in the sample with Mn/S value of 1.5 (0.65% Mn and 0.128% Sulfur) due to having more MnS inclusions, as well as a larger grain size graphite and its high aspect ratio have been obtained. The minimum tensile strength has been calculated to be 193MPa in the specimen with Mn/S value of 3.5 (0.55% manganese and 0.156% sulfur) due to the effects of higher sulfur content on changing the morphology of graphite to a higher aspect ratio. Meanwhile, at the same content of Mn (almost 0.55 wt%), further reduction of sulfur results in promoting E and D types of graphite in the microstructure.

Graphic Abstract