Microstructure and mechanical properties of lost foam casting gray cast iron

Lost foam casting is based on foam model, using non binder dry sand vibration modeling, negative pressure pouring, high temperature metal liquid to dissolve the foam pattern and occupy the space, and finally obtain the casting process. Compared with traditional sand casting, lost foam casting is widely used because of its high dimensional accuracy, low surface roughness, no need to lower the core and take the mold. However, for molten iron with the same chemical composition, there are few reports on the difference of graphite morphology, matrix structure and mechanical properties of gray cast iron under lost foam casting compared with sand casting under the same pouring conditions. Therefore, the graphite morphology, matrix structure and mechanical properties of ordinary gray cast iron (HT200) and inoculated cast iron (HT250) under the conditions of lost foam casting and clay sand casting were discussed in order to provide reference for improving the quality of lost foam casting iron castings.

(1) During lost foam casting, due to the use of dry sand molding, the sand consumption is large and the cooling speed is relatively slow; on the other hand, due to the use of high temperature and negative pressure pouring, high temperature pouring promotes graphitization, which will cause some nucleation and mass points in molten iron to move to the surface of the casting. Therefore, the A-shaped flake graphite formed during lost foam casting is thicker and the graphite length is longer.

(2) Under the same chemical composition of molten iron and the same pouring conditions, the ferrite in the matrix of EPC gray iron is more and the pearlite is less than that in clay sand casting.

(3) In lost foam casting, the chemical composition and pouring conditions are the same Φ The mechanical properties of 30mm test bar are lower than those of clay sand casting, and even the tensile strength can not meet the requirements of the corresponding brand. Therefore, in order to ensure the mechanical properties of the casting body, corresponding strengthening measures should be taken according to the requirements of casting brand and production conditions, such as appropriately adjusting the control range of chemical composition, alloying, strengthening inoculation treatment, etc.