SU505686A1 - Method of modifying cast iron - Google Patents

Description

(54) METHOD OF MODIFICATION OF A PIG IRON

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The invention relates to ferrous metallurgy, in particular to the centrifugal casting of cast iron pipes and can be used in iron foundries.

Graphitizing modification of cast iron has been used in foundry for a long time. Fundamentally, the use of graphitizing additives in cast iron was known to eide when the advantages of this treatment from the point of view of mechanical properties were not so clearly established. Already in 1890, Yungst recommended introducing ferrosilicon in the production of gray cast iron with enhanced mechanical properties from white blast furnace. For the first time, Berdenheier and Zeyen suggested introducing additives into the ladle. In doing so, they used powdered ferrosilicon or ferromanganese. At present, hundreds of graphitizing modifiers have been patented. However, ferrosilicon was the most widespread in both our country and abroad. The content of silicon in this modifier is in the range from 10 to 90%. Most often ferrosilicon with 75% silicon is used to modify cast iron. Ferrosilicon, like other graphitizing modifiers, is introduced into the cast iron to eliminate chill and improve the quality of castings. In order to obtain stable results, the consumption of the modifier is chosen in accordance with the type of casting and especially with the wall thickness (see E. Pivovarsky. High-quality cast iron, m. 1, Metallurgi, 1965, pp. 213, 218).

When mass production of cast iron castings (e.g., centrifugal casting of pipes), especially under conditions of cupola melting, deviations of the chemical composition of cast iron from the optimal limits are inevitable, leading to bleaching and a decrease in product quality stability. Under these conditions, an additive in front of a given constant amount of modifier, for example, 75% ferrosilicon, which does not take into account the change in the properties of the original cast iron, can not only fail to improve the quality of the castings, but even lead to its decrease. Thus, with an increased tendency of the pig iron to bleach, the additive of ferrosilicon may be insufficient to eliminate surface chill and the fragility of the castings. If the tendency of the original iron to chill is insignificant, then the additives of ferrosilicon can cause a decrease in the strength of the castings.

The purpose of the invention is to stabilize the quality of the castings and increase them mechanically. properties.

This is achieved by the fact that the graphitizing modifier is planted, according to the weight of the liquid metal, for every millimeter of the bleed above the nominal value, according to the gravitating modifier.

When using the developed method, the consumption of additives is selected depending on the change in the properties of the original cast iron. With an increased tendency of the pig iron to chill, the chill depth on the wedge sample increases and, accordingly, increases the amount of the introduced graphitizing modifier, which suppresses the formation of excess cementite in the casting. When reducing the tendency of the original iron to chill, the chill depth on the wedge sample decreases and, accordingly, the modifier consumption decreases. Due to the established relationship between the change in the chipping tendency of the pig iron and the consumption of the modifier with variations in the properties of the initial cast iron, the quality of the castings is stabilized.

Claims (1)

Invention Formula The method of modifying the cast iron during casting into metal molds by adding graphitizing modifiers, characterized in that, in order to stabilize the quality of the castings and increase their mechanical properties with variations in the properties of the original cast iron, the modifier is squared in proportion to the depth of chill to the wedge sample in a quantity of 0.03-0 , 07% of the weight of the molten metal for every millimeter of chill off more than nominal.