The metal matrix structure of the casting is pearlite, the uniformly distributed ferrite is not more than 5%, and the graphite is a uniformly distributed spiral sheet of A type, and its content is 3%-11%, and the length is 60-240 microns. The width ratio is greater than 25, and the graphite spacing is a large interval, and free cementite and any foreign inclusions are not allowed. The finely dispersed phosphorus eutectic content is <2%. Hardness inspection, hardness Brinell hardness 187-241 (3.9-4.4d), X-ray inspection is also required, and no defects are allowed. Metallographic examination should be carried out before and after the hardness test of castings. Therefore, the conditions are more demanding. We have summarized some experiences through practice.
Cast iron structure
The various compositional phases of cast iron have different effects on the wear of cast iron, and the effective change of cast iron structure can enhance the performance of castings.
The wear resistant castings is required to have a matrix of a multi-phase structure comprising a flexible substrate with a hard component embedded in the substrate. The flexible substrate wears to form a groove for the lubricant, while the hard component is stressed. Pearlite can satisfy this principle, and it is better to use platy pearlite.
Ferrite is one of the least wearable tissues. Generally wear resistant castings should limit its content.
Graphite has both positive and negative effects. On the one hand, since it does not have strength itself, the slit is present in the matrix, which reduces the effective area of the metal matrix and weakens the resistance of the cast iron to the damage caused by the frictional force, thereby reducing the wear resistance. On the other hand, graphite can be used as a "self-generated lubricant" (in the case of semi-dry friction), and can adsorb and store lubricating oil to maintain the continuity of the oil film (when the liquid is rubbed), thereby improving the wear resistance. In wear resistant castings, if there is too much graphite, the matrix is loosened; if the graphite is too small, the lubrication is insufficient.
4. Phosgene eutectic
Phosphorus eutectic is a kind of hard phase inclusion, which is firmly distributed on the pearlite in the anti-wear cast iron with the binary phosphide eutectic single inclusion, which is beneficial to improve the wear resistance. The ternary phosphorus eutectic or network-like phosphorus eutectic distributed along the grain boundary deteriorates the mechanical properties of the cast iron and affects the wear resistance.
5. Free cementite
Free cementite is a hard and brittle component that sharply reduces the impact toughness and wear resistance of cast iron and therefore requires strict control.