Study On The Preparation And Properties Of A New Compacted Graphite Iron Used In Brake Drum

Brake drum is one of the most important parts of the automobile braking system, which plays an important role in the safety of the vehicle. Brake drum is generally working in a harsh environment of a very strong friction and alternating hot and cold. Therefore, the brake drum materials should have adequate mechanical properties, wear-resisting property and a good thermal fatigue property as well.At present, high strength gray cast iron is a major material used in the production of heavy truck brake drum, recently developed metal matrix composites and compacted graphite iron (CGI) to produce brake drum. CGI is an ideal material applied to brake drum for its performance between ductile iron and gray iron. But traditional CGI has low hardness and poor wear resistance because its ferrite contents is too high. In addition, the stability of the pearlite is very poor, in the long term heating cooling process, the pearlite contents and strength will decrease, eventually leading to the crack failure. This topic through optimize the material composition of CGI currently used in company, by adding Mo and Cu in the smelting process, to explore influences on the micro structure and properties of the specimen. Finally developed a new type of brake drum material with high performance.The result shows that:Molybdenum urges the graphite to refine, and the pearlite contents has been obviously increased. When adding 0.25% Mo, the specimen has a best property. With more and more Cu adding in the alloy, the contents of pearlite can be as high as 90%, and the pearlite inter-lamellar spacing is gradually being shorter., the phenomenon of Cu enriched in the graphite matrix interface was found.With the increase of additive of Mo, the tensile strength of the alloy is elevated firstly and then decreased. When the contents of Mo is 0.25%, arrived the maximum tensile strength (439 MPa), increased by 15.2%. The effect of Cu on the enhancement of strength is specially significant, with Cu contents of 0.83%, the strength increased to 542 MPa, compared with the sample containing 0.33% Cu increased by 55%.Mo and Cu can ameliorate the thermal fatigue property of CGI. When the contents of Mo is 0.29%, CGI has a best thermal fatigue property, the crack length is 15.84 mm when the cool-heat cycle is 600 times. Cu has certain influence on thermal fatigue property, but it has a limitation. When the contents of Cu is 0.83%, the crack length is 5.46 mm after 400 circle times, decreased by 4.01 mm when compared with the sample crack length of 0.33% Cu.The strength, wear resistance and thermal fatigue property of the new material are greatly improved when compacted with existing material. When operation 85000 km, inner surface of the new material brake drum is still intact, no any cracking and spalling phenomenon; At this time unimproved brake drum is seriously cracked. Therefore, the new brake drum material has a good comprehensive performance, it is bound to bring huge economic and social benefits.