Method of manufacturing foundry from grey cast iron

FIELD: metallurgy.

SUBSTANCE: there is implemented melting of cast iron, its pouring into non-metallic forms, crystallisation of ingots and heating of ingot located in non-metallic mould in induction-arc furnace up to 1147-1300C with isolation 0.2-0.5 hours.

EFFECT: upgraded hardness of cast iron ingot.

1 ex, 1 tbl

 

The invention relates to ferrous metallurgy.

Widely known method of melting iron in a melting furnace [Grachev, VA Furnace foundry. M., 1994], adopted by the author for the prototype.

This method of smelting iron includes the process of smelting iron in a melting furnace, the process of pouring liquid iron in metallic form, where the process of its crystallization.

The disadvantage of this method of smelting iron is the dependence of the structure of the obtained shaped castings from the cooling rate of liquid iron. The structure is formed in two States of aggregation of liquid iron in the crystallization process. The state diagram of iron-carbon [Knorozov BV and other Technology metals. M.: metallurgy, 1978] shows that the crystallization process starts at temperatures below 1300C, when the molten cast iron is in the austenitic state and ends at a temperature below 1147C when the liquid cast iron is ledeburite condition. The structure formed in the austenitic state, unlike ledeburite state has plasticity, which determines the strength of the resulting shaped castings. However, due to the large temperature gradient in the interval 1147C-1300C, the cooling rate of liquid iron is large, therefore, in the austenitic state of the liquid cast iron is not more than 0.1 hour, and in the main page is the established levels of castings formed in ledeburite condition. And as a result, we have shaped castings have low durability.

The closest analogue is known a method of manufacturing shaped castings from grey cast iron, including the production of pig iron, fill it in non-metallic form, crystallization castings and subsequent heating of castings [SU inventor's certificate No. 1413146 A1, CL 21D 5/04, 30.07.1988].

The technical result of the invention is to increase the strength of the resulting shaped castings by increasing the residence time of liquid iron in the austenitic state.

To achieve a technical result of the claimed method of producing shaped castings from grey cast iron, including the production of pig iron, fill it in non-metallic form, crystallization castings and heat that you are carrying out heating of castings in metallic form in the induction furnace, to 1147C-1300C with a holding time of 0.2-0.5 PM

An example of the method

In cupola furnaces smelted cast iron brand mid 20 GOST 1412-85. Liquid iron is poured into the sand molds, where he carried out his crystallization of obtaining shaped castings.

Cylindrical samples with a diameter of 30 mm, in sand molds were placed in an induction furnace where they were heated up to 1200C with a holding time of 0.1 to 0.6 hours the samples were tested for strength. Data mechanical COI the tests are summarized in table.

Table
The exposure time, h
00,10,20,30,40,50,6
20-2220-2223-2528-3025-2723-2520-22
The tensile strength, kgf/mm2

As can be seen from the table, the optimal exposure time is 0.2-0.5 hours

When the exposure time is less than 0.2 h was not observed an increase in the strength of the samples.

The exposure time of more than 0.5 h does not lead to further increase the strength of the samples.

Thus, the proposed method of smelting iron can increase the tensile strength of cast iron in the gap by 40-50% compared to mid 20 GOST 1412-85.

The method of manufacture of shaped castings from grey cast iron, including the production of pig iron, fill it in non-metallic form, crystallization castings and heat, characterized in that conduct heat castings, located in a non-metallic forms of the induction furnace to 1147-1300C with exposure to 0.2-0.5 hours



 

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