Microscopic arrangement of gray iron castings in precision casting processing plants

- Apr 10, 2019-

Graphite sheets in gray iron castings in precision casting processing plants have the effect of cutting non-metallic substrates, damaging their continuity and increasing their strength. From the strength of thinking, it should avoid the growth of thin graphite sheets and slender graphite sheets, and the graphite sheets with significant orientation are particularly reactive. Grasping the dispersion of graphite sheets is the key to ensuring the function of gray iron castings.

Type A graphite is formed in an environment where the carbon chemical equivalent is low and the freezing rate is low. Because the primary body has more dendritic crystals, the supercooling degree is not large when eutectic transformation occurs, there is not much graphite center, and the eutectic group is larger, and the graphite sheet is larger than D-type graphite. Because the icing is more urgent, the body branches Jing Xinglong, when the eutectic transformation occurs, the liquid phase is not necessary between the dendrites of the primary body, and the graphite sheet formed in the direction of the dendrite crystal grows in a certain orientation. The reaction on the mechanical function of the pig iron is large. Strive to avoid it.

B-type graphite is yellow-flowered under optical goggles. The center of the eutectic graphite sheet is relatively coarse, and the graphite sheet at the center is slender. In practice, the center orientation is D-type graphite and the center is A-type graphite. The nucleation environment of B-type graphite is inferior to that of A-type graphite, and the degree of sub-cooling during eutectic transformation is also larger than that of A-type graphite. When crystallization occurs, cold-cooled graphite (D-type) occurs in the center of the eutectic group. The latent heat of crystallization increases the degree of subcooling in the periphery to form A-type graphite. For example, the amount of B-type graphite is not much, and the functional response to pig iron is not large, and it can be allowed under normal conditions.

C-type graphite is a pig with a lower carbon chemical equivalent, a higher icing rate, and a greater degree of subcooling. It is formed between the dendrites in the environment where the primary dendrites are prosperous, and the graphite sheets are coarse and directional. D-type graphite is rare in thin-walled gray iron castings with low carbon chemical equivalents, also known as supercooled graphite or interdendritic graphite. D-type graphite is often accompanied by a lasso body when no alloying elements are being added. If the matrix is arranged as pearlite, the wear resistance of the pig iron is good, and the finer nominal roughness can be lost after machining.

D-type graphite is not necessarily present in the high carbon chemical equivalent (hypereutectic), in the icy pig iron, there are fine flake-like virgin graphite, also small flake graphite, and sometimes the whole graphite sheet has a block with sharp corners. . When the hypereutectic iron is frozen, after passing through the liquidus, nascent graphite is separated under a predetermined degree of subcooling, and gradually grows in the liquid phase. Because of the high crystallization measurement, it takes a short time to form a slender sheet with fewer branches. When the measurement is increased to the eutectic measurement, the eutectic deformation occurs, and the graphite that occurred at that time is the deformed eutectic graphite (type A graphite). After all, the result is that the deformed eutectic is interspersed between the fine graphite sheets. graphite. Thus, C-type graphite is composed of fine, massive graphite and A-type graphite. C-type graphite can make the thermal conductivity of pig iron trek, and improve the power of its anti-tax charge. However, the mechanical function of pig iron reacts greatly. Normal graphite castings do not have such graphite.