Study On Wear Resistance And Thermal Fatigue Resistance Of Compacted Graphite Iron

Current reform already entered deep water area, the downward pressure on the economy has increased, excessing production capacity has became the red alert of manufacturing industry. C hanging ideas and yielding more reliable products which consumes low energy has became the only choice for the survival and development of enterprises. Heavy truck as an important mean of transportation, safety and reliability restricted by brake drum. In the service process, brake drum is under strong friction, heat load and great temperature gradient, which makes the wear resistance and thermal fatigue become the key of the material. In this paper, a new type of engineering material-compacted graphite iron is selected as the research object, through the composition design and performance study, A compacted graphite cast iron brake drum material with better comprehensive performance was obtained.Combined with production actual choice of raw materials and production methods, vermicularizing treatment using commercially available ball of agent RE-Mg-Si and self interference agent composed of Vermicular Agent, 75 ferrosilicon ladle bottom flushing method for a pregnant and silicon barium alloy reladling flushing method secondary inoculation treatment method for preparation of compacted graphite cast iron. By adjusting the C u and Sn content, the pearlite content of the compacted graphite cast iron was varied between 5%, 10%, 20%, 30%, and adjust the Mg, Ti and Re contents obtained the compacted graphite cast iron which creep rate vary between 60%, 70%, 80%, 90%. The tensile strength of the specimens obtained above 387 MPa, the elongation rate above 1.9%, the hardness above 160 HB, has a good mechanical properties, meeting the requirements of brake drum materials.We studied the friction and wear properties of the compacted graphite cast iron specimen which has different creep rate or different pearlite content, by MG-2000 high temperature and high speed friction and wear testing machine, pin on disk wear form, compacted graphite cast iron for disk specimen, commercial truck brake pads for pin. Compared with HT250, the wear resistance of compacted graphite cast iron is obviously enhanced, and the wear amount of the same condition is about 1.4~4.5 times of HT250, and the gap between HT250 and compacted graphite cast iron increases with the increase of load and wear rate. The wear resistance of compacted graphite cast iron decreases with the increasing of the creep rate, and is proportional to the content of pearlite. Among them, the wear resistance of Ru60 is increased by 69%~76% than that of Ru90, and the wear resistance of P30 is increased by 51%~104% than that of P5. Vermicular cast iron friction coefficient is more stable and at low speed and load, friction coefficient of HT250 is greater than that of vermicular graphite cast iron, with increasing speed and load, both the friction coefficient decreased gradually, but HT250 fell even more sharply, leading to final vermicular cast iron friction coefficient and HT250, even more than HT250.The Jilin University of homemade self constraint thermal fatigue testing machines of different percentage of vermicular graphite and pearlite content of vermicular graphite cast iron at 350 ℃, 550 ℃ and 800 ℃, thermal fatigue crack initiation and propagation of thermal fatigue test. Co mpared with HT250, the thermal fatigue crack initiation of the compacted graphite cast iron is relatively late, and the final crack length is small. The creep rate of compacted graphite cast iron is high, the early crack initiation is early, but the final crack length is not good because of the thermal conductivity. The pearlite content increases and the thermal fatigue crack length decreases firstly and then increases. This is due to the strength of the P5 resulted in lower crack initiation early and expansion period is long; P30 low thermal conductivity, thermal relaxation should be ability difference, the final crack the longest; P20 mechanical properties and thermal conductivity can realize optimal matching, thermal fatigue performance best, crack length shortest.The failure mode of the brake drum of the compacted graphite cast iron is analyzed, and the main failure mode is thermal fatigue fracture. Working face of the brake drum and the distance from the 400 μm deep microstructure of martensite transformation occurred, and coarse graphite, oxidation. The distance from working face 400 m to 1mm between hardness decreased slightly had the lowest value, and the resulting stress relaxation of crack. During the normal braking, the number of cracks in the compacted graphite cast iron material is small, and the main crack is much larger than that of the small crack. Braking load greater or higher speed conditions, most cracks have the opportunity to expand, showing obvious characteristics of cracking. The oxidation degree of graphite was increased obviously under the condition of long time and frequent brake.