Grey cast iron is widely used in the production of automobile brake discs because it combines the main properties required by this part, especially the low production cost and good friction performance. Flake graphite has excellent thermal conductivity, ensuring that the heat generated in the braking process can be quickly spread and released. Flake graphite gray cast iron is preferred to nodular cast iron or vermicular cast iron, mainly because gray cast iron creates continuous mesh graphite sheets, which can better conduct and release heat.
In the actual casting production process, in order to achieve some specific properties, alloy elements need to be added for adjustment, such as Cr, Cu, Mo, Sn and other elements, to meet some specific microstructure requirements of gray cast iron brake discs. Ti is also often used to stabilize the friction coefficient of gray cast iron brake discs and enhance wear resistance [6]. On the other hand, the effect of Ti on the hardness and tensile strength of gray cast iron changes with the amount of W (TI). When the amount of W (TI) is very small, it promotes graphitization, coarsens the structure and reduces the hardness and tensile strength; When the amount of W (TI) is large, refining A-type graphite will promote the production of D-type graphite, and the volume fraction of ferrite in the matrix will also increase.
ZHY casting designed three kinds of gray cast iron brake discs with different w (TI) content, and the composition of other elements is similar, verifying the influence of Ti element on the metallographic structure and mechanical properties of HT200 brake disc.
When the amount of W (TI) is 0.01% – 0.12%, the influence of Ti on gray cast iron is as follows:
(1) With the increase of W (TI), the hardness of gray cast iron brake discs first decreased and then increased, and the tensile strength also showed the same rule;
(2) With the increase of W (TI), the formation of A-type graphite in gray cast iron brake discs was promoted first, and then D-type graphite was promoted;
(3) With the increase of W (TI), the size of eutectic is coarsened to reduce the number of eutectic, and then the size of eutectic is refined to increase the number of eutectic;
(4) With the increase of W (TI), the volume fraction of pearlite is reduced and the formation of ferrite is promoted;
(5) With the increase of W (TI), shrinkage casting defects will occur at the hot spot inside the brake disc;
(6) With the increase of W (TI), the turning / grinding performance of the brake disc decreases and it is difficult to machine.
Therefore, for the production of HT200 gray cast iron brake discs, the amount of W (TI) should be controlled within 0.03%.