possible defects and causes of gray cast iron
In the production of gray iron castings, common casting defects are：pores, unqualified composition and performance, hot and cold cracks, shrinkage and porosity, slag holes and iron beans, insufficient cold insulation and pouring, trachoma and sand inclusion, fleshy and cross-spoke, deformation, etc. Usually, the reason for these defects is not only the core making problem, but sometimes there are many production process problems such as smelting and pouring, sand mixing quality, falling sand cleaning, etc. Therefore, specific analysis is necessary in order to take corresponding reasonable measures to solve them.
The main factors affecting the mechanical properties of gray cast iron: cooling rate, overheating of molten iron, inoculation treatment, charge characteristics, etc.
1.The effect of cooling rate
There are many factors that affect the cooling rate of castings: casting wall thickness and weight, type of casting material, pouring riser and weight, and so on. Since the wall thickness, weight and structure of castings depend on the working conditions and cannot be changed at will, their influence on the organization should be considered when choosing chemical compositions.
2.The influence of molten iron overheating
Increasing the overheating temperature of molten iron can:
(1)Increase the content of combined carbon and correspondingly reduce the content of graphite carbon.
(2)Refine the graphite, and make the formation of dendritic graphite.
(3)Eliminate the "heredity" of cast iron.
(4)Improve the uniformity of the structure of the casting section .
(5)Conducive to the feeding of castings. Similarly, the heat preservation of molten iron also has a similar effect on the overheating of molten iron.
3.The influence of molten iron inoculation treatment
The inoculation treatment is to add the inoculant to the molten iron to change the metallurgical state of the molten iron before the molten iron enters the casting cavity, thereby improving the microstructure and performance of the cast iron. For gray cast iron, the inoculation treatment is to obtain the structure of A-type graphite, pearlite matrix, and fine eutectic clusters, and to reduce the tendency of whitening at the thin walls or corners of the casting and the sensitivity to the wall thickness of the casting; For malleable cast iron, it is to shorten the short annealing cycle, increase the allowable wall thickness of the casting and improve the structure; for nodular cast iron, it is to reduce the tendency of castings to whiten, increase the spheroidization rate and improve the roundness of graphite.
4.The influence of charge characteristics
In the actual production, it is often found that under the situation of that change the metal charge and keep the chemical composition does not to change, the cast iron will have different structures and properties, which shows that the nature of raw material directly affects the characteristics of smelting cast iron. This properties of cast iron is called “hereditary”, for this season, increasing the temperature of molten iron and using a variety of iron ingredients can eliminate this “hereditary” and improve the structure and performance of cast iron.
Anyang Huatuo Metallurgy Co., Ltd in the materials for gray and ductile cast iron for more than 10 years, own rich experience in the casting production, so if any problem or requirement just contact us.