Development of gray cast iron alloy modified by Niobium for brake disc production

Disc brake systems are used on a large scale in the global automotive industry, due to their efficiency, system simplicity and easy maintenance. In this work, niobium-modified gray cast iron brake discs were developed. Niobium additions of 0.11%, 0.17% and 0.26% to the chemical composition of a commercial gray cast iron were studied. The brake discs were cast and machined to final dimensions and finish for application. The microstructure was evaluated using an optical mi-croscope and digital image analysis software. Braking performance and wear test were performed on an inertia dyna-mometer. Non-destructive testing was conducted using penetrating liquids to reveal cracks after the braking test. In addi-tion, the generation of cracks due to cyclical mechanical and thermal stresses suffered by the discs during use was ex-plained. With increasing the Nb addition, there was a tendency to increase the friction stability and settlement speed, a decrease in the braking temperature and a reduction of wear loss. The addition of niobium improved the behavior of the brake discs, mainly in reducing the wear of the friction pair, 31% for the disc and 15.5% for the pads. The best results were found with disc 4 containing 0.26% Nb.