The material grade of 16L vermicular cast iron cylinder block is RuT450, element C is detected by thermal analyzer, element S is detected by carbon and sulfur analyzer, and other elements are detected by spectrometer.
Compared with gray cast iron, the shrinkage tendency of vermicular graphite cast iron is relatively large. In order to prevent the shrinkage defect of vermicular graphite cast iron cylinder block, the carbon equivalent should be increased as much as possible without graphite floating, and the w (C) content should be controlled at 3.7%~3.9%. If the amount of w (Si) is too low, the vermicular graphite cast iron cylinder block is easy to produce white spots, which is difficult to process. If the amount of w (Si) is too high, the vermicular graphite cast iron cylinder block is easy to increase the number of graphite spheres, and the amount of w (Si) is controlled at 1.9%~2.1%. When the amount of w (S) in molten iron is too high, the consumption of vermicularizing agent will increase, forming inclusions, and the process is not easy to control. In order to stabilize the process control, the w (S) quantity is controlled at 0.01%~0.02%. Due to the high content of w (P) will increase the shrinkage tendency and brittleness of compacted graphite cast iron [4], the content of w (P) will be controlled below 0.03%.
RuT450 cylinder block needs alloying treatment. When w (Mn) > 1%, the hardness and pearlite of vermicular graphite cast iron cylinder block will increase significantly. When w (Mn) content is too high, it is easy to segregate, the white tendency is large, and the toughness of cast iron decreases, which is generally controlled at 0.2%~0.4%. Cr can increase and refine pearlite, improve the strength, hardness, wear resistance and heat resistance of vermicular graphite cast iron cylinder block, but it can obviously increase the white tendency of vermicular graphite cast iron cylinder block and promote the generation of carbides. The content of w (Cr) in vermicular graphite cast iron is generally not more than 0.08%. Cu can obviously increase and refine pearlite, strengthen ferrite, improve the uniformity, hardness and wear resistance of vermicular graphite cast iron cylinder structure, and control the content of w (Cu) in 1.2%~1.3%. Sn strongly promotes the formation of pearlite and controls the amount of w (Sn) at 0.09%~0.11%. When w (Ti) is less than 0.1%, graphitization is promoted. After that, with the increase of w (Ti) content, the volume fraction of pearlite increases, the white tendency of vermicular graphite cast iron increases, and the fluidity of molten iron becomes poor. Considering the processing performance, the amount of w (Ti) is generally controlled below 0.04%.
ZHY Casting adopts the wire with Mg as the main element for vermicularization treatment, and the content of w (Mg) and w (RE) in molten iron is controlled within 0.015%~0.02%. Finally, the chemical composition of molten iron is determined as shown in Table 1. It is difficult to control the production of vermicular graphite cast iron. In order to obtain a stable quality vermicular graphite cast iron cylinder block, the chemical composition of molten iron must be stable during the production process and controlled in a relatively narrow process range.