Based on the above description of graphite distribution shape, the following conclusions can be drawn:
(1) F-type graphite is only found in specific iron castings, but not in general iron castings.
(2) C-type graphite weakens the matrix greatly, and there is no primary austenite dendrite in hypereutectic cast iron, so the tensile strength of gray cast iron is very low. C-type graphite is taboo. Of course, in order to increase the comfort of braking, hypereutectic gray cast iron is used as the brake disc of high-end cars, otherwise. However, the tensile strength of the cast iron is low, and it can only reach HT200 level after alloying.
(3) the distribution of A-type graphite is uniform and directionless. The cast iron with A-type graphite has good homogeneity and stability, and high strength utilization rate of cast iron. Therefore, A-type graphite is the goal of high-strength gray cast iron.
The distribution shape of graphite in gray cast iron can be concluded as follows:
(1) the microstructure of high strength gray iron is fine pearlite matrix and fine A-type graphite.
(2) the method of reducing CE to obtain high strength gray cast iron has some disadvantages, such as deterioration of casting performance, high scrap rate of casting, difficulty in accurate control of graphite shape and poor machining performance.
(3) taking high CE and low alloying as the core, optimizing furnace burden, purifying molten iron and strengthening inoculation treatment are the right methods to produce high strength gray cast iron.