In terms of the selection and development of automobile engine cylinder block materials, cast iron, aluminum alloy and vermicular iron have become traditional materials. In most of today’s automobile engines, HT250 gray cast iron has become the main material. For example, in Cummins B series, the hardness on the top surface of the engine can reach 197 ± 7hb, in which the content of type a graphite is more than 80% and the content of type B graphite is less than 10%. The graphite body belongs to fine flake pearlite, and its grade length is about grade 4-6.
In the specific material selection, it is first necessary to control the composition of cast iron. In the melting process of power frequency furnace, the content of sulfur and manganese must be scientifically adjusted. The content of type a graphite obtained by inoculation should reach 95%, and the silicon content should be well controlled. The second is to control the carbon content to prevent the reduction of mechanical properties caused by too high carbon content or shrinkage and leakage caused by too low carbon content. Thirdly, in order to effectively improve the casting hardness and strength of the cylinder block, an appropriate amount of alloy should be added, but the amount of alloy should be determined according to the actual situation to avoid the influence of free carbide produced by excessive addition on the hardness and strength of the cylinder block; In order to effectively prevent the formation of carbides and provide sufficient convenience for the acquisition of pearlite matrix, an appropriate amount of tin can be added. Finally, in the specific casting process, we must control the pouring time and pouring temperature of HT250 gray cast iron to ensure the casting quality of the cylinder block.