Dongguan Precision CastingThe graphite flakes in medium gray iron castings have the effect of cutting non-metallic matrix, destroying its continuity and increasing its strength. From the perspective of strength, it is necessary to prevent the production of long and thin graphite flakes and small graphite flakes, especially graphite flakes with obvious positional properties. Mastering the distribution of graphite flakes is the key to ensuring the functions of gray iron castings.

Type A graphite is formed in an environment where the carbon stoichiometry is low and the freezing rate is also low. Because there are more primary austenite dendrites, the degree of supercooling is not large when the eutectic changes occur, the graphite center is not too much, the eutectic cluster is larger, and the graphite flakes formed are larger than D-type graphite. Because the icing is more turbulent, the Austrian When the eutectic changes occur, the liquid phase is mainly between the primary austenite dendrites, and the graphite flakes formed grow along the position of the dendrites. There is a certain positional property, which is important for the mechanical function of pig iron. The reaction is large, and we must try to prevent it from happening.

Type B graphite is yellow flower-like under the optical goggles. The graphite flakes at the core of the eutectic cluster are relatively thicker, and the core graphite flakes are smaller. In practice, the core position is D-type graphite, and the core is A-type graphite. The nucleation environment of type B graphite is worse than that of type A graphite, and the degree of supercooling when the eutectic is changed is also greater than that of the formation of type A graphite. When crystallization, supercooled graphite (type D) occurs at the core of the eutectic group first, and it is released. The latent heat of crystallization increases the degree of supercooling in the surrounding area, forming type A graphite. If the amount of B-type graphite is not large, the functional response to pig iron is not large, and it can be promised under normal conditions.

C-type graphite is a pig iron with a low carbon chemistry equivalent, a high freezing rate, and a high degree of undercooling. The primary austenite dendrites are formed between the austenite dendrites in an environment where the graphite flakes are thick and thick. There is directionality. Type D graphite is rare in thin-walled gray iron castings with low carbon chemical equivalent, and is also called supercooled graphite or interdendritic graphite. When no alloying elements are added, D-type graphite is often accompanied by a lasso body. If the base body is pearlite, the wear resistance of pig iron is better, and the finer nominal roughness can be lost after machining.

D-type graphite mainly emerges when the carbon stoichiometry is very high (hypereutectic),Dongguan Precision CastingIn the fast-freezing pig iron, there are small flakes of primary graphite, and there are also small flakes of graphite. Sometimes there are lumps with sharp corners on the whole graphite flakes. When the hypereutectic molten iron freezes, after passing through the liquidus, primary graphite is precipitated at a certain degree of supercooling, and it is gradually growing in the liquid phase. Because of the high degree of crystallinity, the formation time is short and the time is longer, forming small flakes with fewer branches. When the measurement is raised to the eutectic measurement, a deformed eutectic change occurs. The graphite that occurs at that time is deformed eutectic graphite (type A graphite), and the final result is that deformed eutectic is scattered between the fine graphite sheets. graphite. Therefore, C-type graphite is formed by fine, massive graphite and A-type graphite. Type C graphite can improve the thermal conductivity of pig iron and improve its resistance to taxation. However, it has a greater response to the mechanical function of pig iron. Normal structural castings do not have this kind of graphite.

E-type graphite is formed when the graphite in pig iron has a strong nucleation power, a low freezing rate, and a eutectic change occurs in an environment with a small degree of subcooling. When inspected under optical goggles, the graphite is uniformly distributed and meandering The serpentine shape is directional, and its length is not the same due to the nucleation environment and icing rate of pig iron. High-quality structural castings are expected to exist in intermediate-length A-type graphite.

Dongguan Precision CastingFor the production of high-quality gray-mouth precision casting, the base mechanism should be made of pearlite, the graphite should be type A, and the graphite flakes should be evenly distributed in the non-metal matrix, and the pearlite should also be thick and well-proportioned. It is necessary to reduce the B-type graphite and D-type graphite in the organization to the minimum, and there should be no C-type graphite and E-type graphite. For this reason, it is necessary to stop the invalid incubation solution and master the icing rate of castings. The pig iron that can emerge E-type graphite, if the freezing rate is higher, will also constitute D-type graphite. Therefore, D-type graphite and E-type graphite are often seen simultaneously in high-strength thin-walled pig iron parts.