Research On Preparation Process, Microstructure And Property Of Composite Cast Iron Used By Cylinder Head

With the improvement of the power density of the diesel engine, the thermal load and mechanical loaded on the diesel engine cylinder head have been increased significantly, which leads to the larger difference of the service environment during the different parts of the cylinder head. The primary reasons are that the service temperature of fire surface of cylinder head is very high, which requires the good thermal conductivity and oxidation resistance performance of the material. In addition, the high strength and tenacity performance of the other parts are also required. However, the traditional cylinder head is made by the homogeneous cast iron, which is unable to combine obdurability, thermal conductivity and high temperature oxidation resistance properties. Those disadvantage often leads to occur ing cracking problems of the high power diesel engine cylinder head induced by thermal stress. Therefore, the investigation of preparation and organization performance is very important to further study the theoretical and Engineering practical significance of the new composite cast iron material.This paper proposed three preparation of composite cast iron:1)Metamorphic daub coating method on sand mold; 2)The method of increase local solidification rate appropriately; 3)Double metal casting method. Comprehensive utilizating OM, SEM, EPMA, thermal conductivity test detection analyzed and tensile strength tested different preparation’s process effect on the composite cast iron’s microstructure and properties.Using the coating method for produced the composite cast iron a layer of gray cast iron on the surface of vermicular graphite cast iron was successfully prepared by changing the FeS metamorphic agent content in the coating, which formed the Gray/vermicular composite cast iron. with FeS content increasing, gray cast iron’s thickness of the casting’s surface layer gradually startly increased and then reached equilibrium, The maximum thickness was about 5.3 mm; from the internal to the outer layer of casting, the graphite morphology gradually changed from A-type to D-type, and finally to the vermicular graphite. Gray/vermicular composite cast iron from the gray cast iron to vermicular cast iron, the residual S content decreased, the residual Mg gradually increased; the formation of Mg and S compounds decreased, which leaded to the decrease of the residual Mg content in the surface of the casting and the vermicularizing recession. In the preparation of spheroidal/vermicular composite cast iron, With the increasing of magnesium content in nodularizer coating, spheroidal iron of surface layer’s thickness was increased gradually. the 25% magnesium-rare earth and 15% magnesium mixed alterant coating’s had a optimal effect, which obtained around 34 mm nodular layer on the casting’s surface.In the study of cooling rate on morphology of graphite cast iron tests, when the cooling rate increased, graphite gray cast iron’s surface would change from A to D-type graphite graphite, D-type graphite surface layer thickness increased with cooling rate increasing; and the surface layer of compacted graphite iron would transfer to spheroidal graphite, and with the surface’s solidification rate increased, the surface spheroidal graphite layer’s thickness and spheroidization rate were significantly increased.In the process of bimetallic composite cast iron pouring, The flow field and temperature field of double liquid-liquid composite metal were simulated by using casting simulation software. The optimal processing parameters were determined. the lower of molten metal was poured using the bottom gating system, while the upper molten metal was poured by the slit sector system. The casting velocity of upper molten metal was 5 cm/s, and the interval of the casting time between the double metal was 20 s. The pouring height of the lower molten metal was higher 15 mm than theoretical binding boundry. The perturbation near the binding layer was not obvious. Through the actual gray cast iron/compacted graphite iron casting bimetallic composite fluid tests, the results showed that casting’s graphite morphology from bottom to up distributed respectively from the flake graphite to vermicular graphite, and the graphite morphology transition was relatively stable, longitudinal section of the casting graphite morphology had no significant confounding. The gray/compacted graphite composite cast iron’s tensile strength was higher than that of gray cast iron, and its thermal conductivity was higher than the compacted graphite iron.