Effect of inoculation treatment process on graphitization

Inculation treatment is a key part of gray cast iron production, with the aim of promoting graphitization and refining the graphite structure.Insufficient inoculant addition (e.g., 75SiFe <0.4%) or a long residence time (>8 minutes) after incubation can lead to coarse and uneven distribution of graphite, as well as reduced strength and wear resistance of the casting.

Typical defects: Poor inoculation is prone to "recession defects", which are manifested by the appearance of D-type (interdendrite punctate) or E-type (directionally arranged) graphite in localized areas, accompanied by loosening of the matrix structure, especially at the thin-walled edges of castings or in the cold iron quenching area.

Control points: The "instantaneous inoculation" process (such as the flow inoculation method) is used to directly add the inoculant to the pouring stream to ensure that the contact time between the inoculant and the molten iron is < 3 seconds to avoid inoculation decline;For large-tonnage castings, it can be combined with in-mold inoculation (built-in inoculation block in the sprue cup or sprue) to control the graphite size at ISO 945 level 4~5, and the distribution uniformity can be increased by more than 30%.