Research And Manufacture Of Alloyed High Carbon Gray Cast Iron For Brake Disc

Gray cast iron has always been the primary material for automotive brakediscs because of excellent thermal transport ability, fine wear resistance, good castability, shock-absorbing properties and the low price. During the braking process,the brake discs are subjected to the big load. The temperature of the brake discsraises with the friction and wear occuring. In the course of vehicle driving,sometimes road condition becomes also very complicated (such as traffic jam andthe rain and snow and foggy conditions), the alternately heating and coolingcaused by frequently braking may lead to the initiation and propagation of thermalcracks. So this puts forward higher request to brake disc–better strength,betterthermal conductivity and better wear resistance and so on.In the gray cast iron, if the carbon equivalent is increased, the graphite contentwill get increased too. If the graphite content in the gray cast iron is higher, its heatconducting properties is good, but its strength and hardness will decrease. Thispaper concerns the analysises and researches about the organization and performance of thethe high carbon alloy cast iron which contains a variety of alloy elements. Based on theanalysis above, main research content and conclusions of this paper are as follows:1. Explore Mn/S and cooling speed how to influent the organization andperformance of high carbon alloy cast iron and inspect the solidificationcharacteristics of hypereutectic alloy cast iron, and how Mn make the impacts onthe organization and performance of hypereutectic alloy cast iron. The results ofthe study showed that in high carbon equivalent alloy gray cast iron, Mn/S had abigger influence on graphite morphology. It was found that when Mn/S for15, theeffect was very good, graphite morphologies were all type A and the graphitedistribution was more even. However, when Mn/S was more than15, some finegraphites would appear no matter how to chang the content of Mn and S. Themicrostructure were100%pearlite and trace amounts of carbide.In the case of containing alloy elements which promote the pearlite to appearsuch as Cr, Cu, Sn and high-sulfur, the content of silicon strongly affected theorganization and performance of the gray cast iron. When w%(Si) was1.3,Strength and hardness decreased with the increase of the section thickness, but when w%(Si) was2.17, strength and hardness increased instead with the increaseof section thickness. In the eutectic gray cast iron, by selecting proper chemicalcomposition, we could acquire good mechanical properties and could meet therequirements of the brake disc.2. Explore fatigue characteristics of the high carbon alloy cast iron, it turnedout that in the process of thermal fatigue test, gray cast iron whose strength andhardness were high and the carbon equivalent was low, crack first appeared andcrack growth was the fastest, the fatigue performance resistance is poor.Priorstudies had shown that the thermal fatigue performance of cast iron containing theD-type graphite was poorer. But in our experiment process, when the matrix of castiron was pearlite and carbon equivalent was very high, we found that even if graycast iron contained a lot of type D graphite, the fatigue performance of gray castiron was also good. The speed of crack propagation was slow.3. Use the ML-10type pin on disk friction-wear tester to explore theinfluencing factors of wear performance of high carbon alloy gray cast iron. Studyshowed that mechanical property and graphite morphology and oxide film weremain factors influencing the wear performance of high carbon alloy gray cast iron.Wear morphology was furrow and exfoliation wear, so mechanism was abrasivewear. With the improvement of strength and hardness of the sample, thecorresponding wear loss would be reduced. In the friction process, the crack firstemerged in the subsurface, then the crack scaled out, most of the crackinterconnected and caused the matrix fall off. Graphite flake quantity was less andthe length was shorter, heat that sample generated in the process of friction andwear dissipated slowly, as a result, the surface temperature rose, matrix becamesoft, the wear was intensified. During the wear process, the oxidation film producedon sample surface would reduce wear loss.