Ductile iron castings have developed rapidly at home and abroad because of its high strength and plasticity. Its output has exceeded that of cast steel and malleable iron, and become the casting alloy material second only to gray iron. Graphite in nodular cast iron is spheroidal mainly because of the addition of spheroidal agent in molten iron. The products produced by nodular cast iron casting technology have the advantages of high strength, high toughness and low price, which meet the requirements of automobile production. Therefore, nodular cast iron casting technology has been widely used in automobile production. Nodular cast iron has shown its superiority through its application in automobile industry. Through the continuous improvement of technical level, I believe that in the future, nodular cast iron will be applied in various fields.

The rules for attention in the production of ductile iron castings are as follows:

1. Ductile iron has poor fluidity and large shrinkage, so higher pouring temperature and larger size of pouring system are needed. Risers and chills should be reasonably applied and sequential solidification principle should be adopted.

2. The heat treatment of ductile iron castings must be standardized, which will directly affect the success or failure of the production of ductile iron castings.

3. Strict chemical composition is required. The content of carbon and silicon required for molten iron is higher than that of gray cast iron. The content of manganese, phosphorus and sulfur in nodular cast iron is reduced.

4. Inoculant was added for inoculation treatment.

5. The tapping temperature of molten iron is higher than that of gray cast iron to compensate for the loss of molten iron temperature during nodularization and inoculation.

6. Spheroidizing treatment, i.e. adding spheroidizing agent to molten iron.

How to test the hardness of ductile iron castings: The properties of the castings themselves directly affect the quality of processing, and the hardness value is an important index to determine the casting processing.

1. Vickers hardness: It can be used to measure the hardness of thin and steel parts, and also can be used to measure the hardness of surface hardened parts such as carburizing, cyaniding and nitriding.

2. Rockwell hardness: HRA is mainly used for high hardness specimens. The material and surface hardness, such as cemented carbide and nitrided steel, whose hardness is higher than HRC67, are measured in the range of HRA > 70. HRC is mainly used to determine the hardness of steel parts (such as carbon steel, tool steel, alloy steel, etc.) after quenching or tempering. The measuring range is HRC20 ~ 67.

3. Brinell hardness: It is mainly used to measure the hardness of castings, forgings, non-ferrous metal parts, hot-rolled billets and annealed parts, and to determine the range of HB450.

Production steps of ductile iron castings:

(1) Strict chemical composition is required. The content of carbon and silicon required for molten iron is higher than that of gray iron, and the content of manganese, phosphorus and sulfur in nodular iron castings is reduced.

(2) The tapping temperature of molten iron is higher than that of ash casting, and the temperature loss of molten iron during inoculation treatment is higher than that of compensating spheroidization.

(3) Spheroidizing treatment, i.e. adding spheroidizing agent to molten iron.

(4) inoculation.

(5) Ductile iron castings have poor fluidity and large shrinkage, so higher pouring temperature and larger size of pouring system are needed. Risers and chills are often used, and sequential solidification principle is adopted.

(6) Heat treatment.

Advantages of Ductile Iron Castings: Polystyrene foam mold is used in full-mold casting production, and gustator resin self-hardening sand is used in moulding. When molten metal is poured into the mold, the foam plastic pattern is gasified rapidly under the action of the high and boundless liquid metal, and burns away. The liquid metal replaces the position occupied by the original foam plastic, and solidifies into a solid casting with the same shape as the model. Resin sand mold has good rigidity. It is conditional to use graphitization expansion during solidification of cast iron to effectively eliminate shrinkage cavity and shrinkage defect, so as to realize less riser and no riser casting for gray iron and nodular iron castings.

Special attention should be paid to the difference between surface pore and surface trachoma in the external inspection of ductile iron castings. Generally speaking, surface pore is smooth and regular, while surface trachoma is irregular and contains more dust or non-metallic impurities such as sand. If the surface concave defect of ductile iron castings is pore, it can be compared and tested according to SCRATA test block, if judged. When breaking into surface sand holes, it is generally necessary to carry out grinding repair, because most of the root of sand holes will extend to the metal interior. When the shot peening effect is not good, the roughness of nodular iron castings will not meet the requirements. When oxygen reaction skin is retained on the surface of nodular iron castings and large area surface defects such as coating agent are difficult to grind, re-shot peening or grinding should be considered. For this kind of defect will affect the appearance inspection, especially easy to produce surface sand and mud missed detection.