High-strength-and-toughness cast iron heavy-duty automobile brake drum and making technology thereof

Abstract

The invention discloses a high-strength-and-toughness cast iron heavy-duty automobile brake drum. The brake drum is characterized in that brake drum comprises 3.55-3.85wt% of C, 2.35-2.75wt% of Si, 0.45-0.85wt% of Mn, 0.02-0.06wt% of P, 0.01-0.04wt% of S, 0.06-0.12wt% of Ti, 0.02-0.08wt% of Sn, 0.01-0.04wt% of Sb, 0.008-0.05wt% of Mg, 0.015-0.035wt% of RE, and the balance Fe. The making technology of the brake drum sequentially comprises the following steps: weighing raw materials in proportion, carrying out alloy melting, carrying out creeping and inoculation, carrying out cast molding, cleaning, and machining. Compared with the prior art, the technology has the advantages of best thermal fatigue resistance, good deformation resistance, good cooperation of strength, ductility, hardness and wear resistance, and good casting and machining properties.

Description

technical field [0001] The invention relates to a high-strength and tough cast iron material, in particular to a high-strength and tough cast iron heavy-duty automobile brake drum and a manufacturing process thereof. Background technique [0002] Brake drums of heavy-duty vehicles are subjected to large braking force and centrifugal force during their service. They are key components working under complex working conditions such as strong friction, high thermal load, and alternating cold and heat effects. The reliability of the system directly affects the driving safety of heavy-duty vehicles. Therefore, the brake drum used is required to have high strength, plasticity, good thermal fatigue resistance and wear resistance, high friction coefficient, and low friction coefficient attenuation rate, so as to ensure that it does not run under heavy load. The breakage and wear of the brake shoes are small, the braking is smooth and effective, and it has a long service life and hig...

AI Technical Summary

Problems solved by technology

HT250, HT300, vanadium-titanium cast iron and low-alloy cast iron are often used (the amount of pearlite in the matrix is ​​greater than 90%, A-type plus a small amount of D-type flake graphite); And thermal fatigue resistance is poor, while low-alloy cast iron is usually added with precious alloying elements such as Cr, Mo, Cu, Ni, etc. Although the strength and wear resistance have been improved to a certain extent, the thermal fatigue resistance has not improved much, and the production cost higher

(2) Ferritic ductile iron (ferrite content greater than 80%, spheroidization rate 1-3), which is characterized by good strength, plasticity, wear resistance and thermal fatigue resistance, but thermal conductivity and deformation resistance Poor capacity, low coefficient of friction and instability

[0004] The main problems of the above three types of cast iron brake drums: (1) The strength, plasticity and wear resistance of pearlitic gray cast iron are relatively low, especially the flake graphite with sharp angles in the microstructure, which splits the matrix and causes stress concentration , to promote the initiation and expansion of thermal fatigue cracks, resulting in early cracks and even fractures of the brake drum, low service life, and poor safety and reliability

(2) Ductile iron has low thermal conductivity, small friction coefficient, and low yield strength ratio. The brake drum produced by it is seriously deformed when it is used under heavy load and large braking force, and the cracks on the brake surface protrude inward and are severely torn and worn. Brake shoes, poor braking stability and reliability, used for heavy-duty vehicles with a load capacity of more than 70 tons, and their service life is equivalent to that of brake drums produced by ordinary HT250

(3) Due to the pursuit of high creep rate and high content of single matrix (creep rate greater than 80%, ferrite or pearlite content greater than 85%), vermicular cast iron has a narrow range of creep and difficult stable control

Ferritic vermicular iron has insufficient strength and wear resistance when used under heavy load conditions, is easy to deform, sticks to the knife during machining, and has poor surface finish; pearlitic vermicular iron generally needs to be added with Cr, Mo, Cu and other alloying elements or Heat treatment, high production cost, and its thermal conductivity is lower than that of ferritic vermicular iron

[0005] The existence of the above problems often causes the brake drum to fail due to the expansion of thermal cracks, fatigue spalling, cracking and bottoming, deformation and out of round, etc., which threatens the driving safety of heavy-duty vehicles and also brings greater economic benefits to vehicle maintenance. burden