As shown in the figure, the phase diagram of gjv450 vermicular graphite cast iron seen under the laser microscope after polishing and corrosion of the materials used by ZHY casting is shown. It can be seen from the figure that most graphite particles are surrounded by ferrite, and there are a large number of lamellar pearlite, which is also the most abundant phase in gjv450, reaching more than 90%.
The tensile strength of vermicular graphite cast iron is higher than that of gray cast iron, resulting in higher cutting force and faster tool wear in the cutting process. At present, processing vermicular cast iron faces the following four challenges. First, compared with gray cast iron, vermicular cast iron sacrifices some heat transfer performance. During the cutting process, the heat dissipation conditions become worse and the tool life is reduced. Second, there is soft ferrite in vermicular graphite cast iron, which will bond to the tool surface during cutting. Third, in the process of cutting flat graphite cast iron, MNS with lubricating effect will not be generated at the tool tip, and abrasive wear is easy to occur on the rake face. Fourth, the addition of titanium in vermicular graphite cast iron will produce a casting skin with high strength, which has a great impact on the service life of tools.
Graphite particles have the lowest strength in vermicular graphite cast iron, followed by ferrite and finally pearlite. Starting from the microstructure of vermicular graphite cast iron, Walid M. Mohammed et al., using tensile test and ABAQUS analysis software, found that the fracture originated from graphite particles or graphite matrix interface without special sequence selection, and propagated to the metal matrix in the form of microcrack network, which finally coalesced, Resulting in complete failure of the material. In the cutting process of vermicular graphite cast iron, the generation process of cutting shoulder is that the crack first occurs on the free surface, then propagates to the crack tip along the graphite or graphite matrix interface, and finally forms a long crack.
Walid M. Mohammed proposed to simulate the three-phase structure of spiral cast iron in ABAQUS, which verified the above conclusions. After that, Surui also verified this conclusion in the study of vermicular cast iron chips at various cutting speeds.