Ductile cast iron for brake disc of heavy-duty truck

Abstract

The invention discloses ductile cast iron for a brake disc of a heavy-duty truck, which consists of the following components in percentage by weight: 0.5 to 0.6 percent of molybdenum, 0.008 to 0.02 percent of antimony, 3.6 to 3.8 percent of carbon, 2.0 to 2.5 percent of silicon, 0 to 0.4 percent of manganese, 0 to 0.02 percent of sulfur, 0 to 0.04 percent of phosphorus, 0.03 to 0.06 percent of magnesium, 0.02 to 0.05 percent of rare earth, and the balance of iron. The ductile cast iron has the characteristics of having high thermal fatigue property and wear-resisting property under the use condition of cold and heat circulation, prolonging the service life of the brake disc of the heavy-duty truck, having high strength, low carbide content, good toughness and small heat stress, and greatly improving thermal fatigue strength.

Description

technical field [0001] The invention belongs to the technical field of nodular cast iron for brake discs, in particular to a nodular cast iron containing molybdenum-antimony alloy used for brake discs of heavy trucks. Background technique [0002] The automobile brake disc is the main component of the automobile disc brake. It and the brake lining act as a pair of friction pairs, relying on the clamping and friction of the friction lining on the brake disc to slow down or stop the car. The brake disc must bear the axial clamping force of the friction lining on it and the friction force of the two. The greater the self-weight and load of the vehicle, and the faster the speed, the greater the force on the brake disc during deceleration and braking. Every time the car brakes, the driving kinetic energy is converted into heat energy, and 90% of the heat is absorbed by the brake disc body. Frequent braking, the temperature at the friction surface of the brake disc that rubs aga...

AI Technical Summary

Problems solved by technology

Once these combined forces exceed the strength limit of the material, the brake disc will inevitably break from the weakest part of the disc surface.

[0003] Whether it is a light vehicle or a heavy-duty vehicle, the fracture and failure of the brake disc is caused by the thermal fatigue of the material. The heavy-duty truck has a large load, a long continuous driving distance, relatively poor driving road conditions, and a long continuous working time of the brake disc. The use of disc brakes is more prone to fracture and failure of the brake disc, which not only shortens the service life of the brake disc, but also affects driving safety, which restricts the promotion of disc brakes on heavy trucks. At present, the brake discs of heavy trucks all over the world use higher Carbon content and low-alloyed high-carbon gray cast iron with copper, chromium, molybdenum, and other alloying elements as materials. High-carbon gray cast iron has high thermal conductivity, low linear expansion coefficient and elastic modulus. High thermal conductivity is conducive to Reduce the temperature difference between the disc surface and other low-temperature parts when the brake disc is working, accelerate the transfer of heat to the air duct, reduce the temperature of the disc surface, and avoid local overheating. The low linear expansion coefficient and elastic modulus can reduce the temperature change of the material. expansion and contraction, thereby reducing the residual tensile stress in the brake disc. Copper, chromium, molybdenum, and other alloying elements promote the formation of pearlite, improve the tensile strength of high-carbon materials, and improve the wear resistance of the brake disc. But Gray cast iron is a brittle material, and the graphite in it is flaky and splits the matrix, so its tensile strength is low. The tip or edge of the flake graphite is prone to stress concentration, causing brittle cleavage or interface fracture, which becomes the root of the crack. The physical characteristics of gray cast iron determine that even this high-carbon and low-alloyed material is difficult to meet the requirements of heavy-duty truck brake discs. The graphite of ductile iron is spherical, which reduces the splitting effect of stress concentration on the matrix, and the strength of the matrix The utilization rate can reach 70%-90%, so its mechanical properties at room temperature and high temperature are significantly better than gray cast iron, and its fatigue strength is also much better than that of gray cast iron. However, due to the thermal conductivity of ductile iron is worse than that of gray cast iron, the coefficient of linear expansion and The modulus of elasticity is higher than that of gray cast iron, so the creep resistance at high temperature is poor, and the deformation tendency is large. In the case of binding force, it will lead to large internal stress, which will promote the generation and expansion of cracks. Therefore, it is made of nodular cast iron. Compared with gray cast iron, the heat resistance of heavy-duty truck brake discs has no obvious advantages under the conditions of cold and hot cycles, especially in the case of rapid cooling and rapid heating.