Expansion Off The Rod With A New Non-quenched And Tempered Steel Of Carbon

The traditional processing of connecting rod is complicated, it is high to machining precision. It is a conventional problem that engine reliability is affected by machining error. This problem was solved commendably by fracture splitting technology. The material should have the following properties which suitable for fracture splitting technology:strength of connecting rod is kept constantly, and toughness is restricted. So feature of fracture is happened brittle failure. SAE1070 or C70S6 is the most widely applications steel that made connecting rod of fracture splitting now. It was developed based on high-carbon steel's chemical composition of the C content is 0.70% C70S6 is fractured easily, but fatigue property is low and machining property is poor. It is necessary which study how improve fatigue properties of steel that made connecting rod of fracture splitting.C70S6 that come from different place is select in this paper. Them are tested by fatigue test of rotating bar bending. High-cycle fatigue property are studyed comparatively. These experiment results compared with 38MnVS that is conventional connecting rod' steel. R8 is a conventional high-carbon microalloyed steel that made connecting rod of fracture splitting. R9 and R10 are new type microalloyed mediun-carbon steel, and the use range is the same as R8. These steels'microstructure, fracture morphology, conventional mechanical property, property of fracture splitting and fatigue property are studied comparatively. The following conclusions can be gain:High-cycle fatigue property of C70S6 steels used for connecting rod of fracture splitting which were manufactured in two different factories were studied using rotating-bending fatigue test. The experimental results indicate that all fatigue cracks initiated from matrix surface and therefore microstructure especially pearlite interlamellar spacing is the main factor which controls C70S6 steels'high-cycle fatigue property. For each C70S6 steel used, its fatigue property and strength in the as-forged condition are almost the same as these in the as-normalized condition. The high-cycle fatigue property of high-carbon pearlite type C70S6 steel is rather lower than that of medium-carbon microalloyed steel 38MnVS which has a ferrite-pearlite type microstructure in the as-forged condition.R8, R9 and R10 are tested in simulation experiment of fracture splitting. R9 and R10'property of fracture splitting are superior to R8 obviously. Compare with R8, R9and R10 involve higher content about P, Si and V. Original austenite grain boundary is embrittled properly. Ferrite is strengthened and embrittled. When the fracture splitting happended by R9 and R10, Brittle cleavage fracture and intergranular fracture are occurred preferentially. Ductile fracture is inhibited. The tested steels' property of fracture splitting are improvedThe experimental results indicate that all fatigue cracks initiated from matrix surface and therefore microstructure is the main factor which controls steels' high-cycle fatigue property. Pearlite interlamellar spacing of R8 is very thickly, it is a principle cause of lower fatigue property. R9 and R10's ferrite are strengthened and pearlite interlamellar spacing are reduced. These are principle cause of higher fatigue property. It is reached level of 38MnVS that a microalloyed medium-carbon steel made conventional connecting rod.