RU2156809C1 - Method for making high strength cast iron - Google Patents

Abstract

FIELD: foundry, namely processes for making high strength cast iron, possibly in wholesale manufacture of castings. SUBSTANCE: method for making high strength cast iron from initial iron with sulfur content more than 0.4% comprises steps of melting burden in melting aggregate; providing temperature of melt in range (1420-1450)C, realizing its initial treatment by means of master alloy containing (30-33)% of rare earth metals, (43-44)% of silicium, (8-9)% of aluminium in quantity consisting (1.4-1.8)% of melt mass; seasoning metal; performing secondary modification with use of the same master alloy in quantity equal to (0.1-0.5)% of metal mass in melting ladle at temperature of melt (1400-1300)C. EFFECT: possibility of controlling structure formation of matrix and mechanical properties of cast iron at casting. 3 cl, 2 tbl

Description

 The invention relates to the field of foundry and metallurgy, and in particular to methods for producing high-strength cast iron with graphite of vermicular and spherical shape, and can be used in mass production of castings.

 The existing method of producing cast iron with spherical and vermicular graphite based on the source iron with high sulfur content using alloys based on rare-earth metals and silicon consists in introducing the ligature into the transfer ladle with obligatory secondary modification to eliminate bleached 75% ferrosilicon in an amount of 0.5-0 , 8% of the mass of liquid metal.

The disadvantage of this process is the supersaturation of the matrix ferrite with silicon and the formation of a star-shaped graphite part of the graphite, which does not allow to obtain cast iron with high mechanical properties (see the book "High-quality cast iron for castings" edited by NN Aleksandrov. - M .: Engineering, 1982, p. 193)
The problem solved by the present invention is to control the process of structure formation of ductile iron in the process of melting and casting.

 The technical result achieved by using the invention is the stability and uniformity of the structure and strength properties of cast iron in castings weighing from 0.5 to 30 kg with a wall thickness of 5 to 40 mm and reducing the number of defects due to the possibility of correcting errors made during the introduction of the ligature into a large capacity transfer bucket. A scatter in the content of the chemical elements of the ligature in the transfer bucket is inevitable, since it depends on many factors, for example, the temperature of the metal being poured, the level of metal poured, which is a purely subjective factor, etc.

The specified technical result is achieved by the fact that in the method for producing high-strength cast iron from initial cast iron with a sulfur content of more than 0.4%, including melting the charge in the melting unit, adjusting the melt temperature to 1420-1450 ^o C, treating it with a ligature containing 30-33% rare earth metals, 43-44% silicon and 8-9% aluminum, in the amount of 1.4-1.8% by weight of the melt, secondary modification in the casting ladle is carried out with the same ligature as the preliminary one, in the amount of 0.1-0 , 5% by weight of the metal at a melt temperature of from 1400 to 1300 ^o C.

 In addition, the initial processing of the melt by the ligature is carried out in the transfer bucket.

 In addition, an induction or arc furnace is used as the melting unit.

The method is implemented as follows. Cast iron was melted in a six-ton induction furnace and overheated to a temperature of 1440 ^o C. The chemical composition of the source cast iron is given in table. 1. A ligature containing 30-33% of rare-earth metals, 43-44% of silicon, 8-9% of aluminum, the rest is iron, in the amount of 1.7% of the capacity of the bucket, was covered with a ligature and poured onto the bottom of a heated dispensing bucket melt from the furnace. The liquid metal was kept for 5 min until the abundance of slag ceased. Periodically, the slag was removed. Molded parts such as earrings weighing 700 g with a wall thickness of up to 40 mm and standard tensile specimens with a diameter of 20 mm. Pouring made in earthen forms. Secondary modification was carried out in a casting ladle with a capacity of 30 kg, adding a ligature in the following quantities from the ladle capacity: ladle N 1 - 0.10%; bucket N 2 - 0.25%; bucket N 3 - 0.50%
Metallographic studies and chemical analysis were carried out on the details, mechanical tests on samples. The chemical composition is given in table. 1, structure and mechanical properties in table. 2.

 As can be seen from the results of the experiment, the use of double modification of rare-earth metals with a ligature of the same composition allows you to control the process of structure formation of ductile iron in the process of melting and casting.

Claims (3)

1. A method of producing high-strength cast iron from source cast iron with a sulfur content above 0.4%, including melting the charge in the melting unit, adjusting the melt temperature to 1420 - 1450 ^o C, initial modification with a ligature containing 30 - 33% rare-earth metals, 43 - 44% silicon, 8 - 9% aluminum, in an amount of 1.4 - 1.8% by weight of the melt, metal aging and secondary modification, characterized in that the secondary modification is carried out with the same ligature in the casting ladle in an amount of 0.1 - 0 , 5% by weight of the metal at a melt temperature of 140 0 - 1300 ^o C.  2. The method according to claim 1, characterized in that the initial processing of the melt by the ligature is carried out in the transfer bucket.  3. The method according to p. 1 or 2, characterized in that as the melting unit using an induction or arc furnace.

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