GB1585253A - Cast iron modifier - Google Patents

Description

(54) CAST IRON MODIFIER (71) We, TULSKY PROEKTNO-KONSTRUKTORSKY TEKHNOLOGICHESKY INSTITUT MASHINOSTROENIA, of ulitsa 9, Mava 66, Tula, Union of Soviet Socialist Republics, a corporation organised and existing under the Laws of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described, in and by the following statement: The invention relates to cast iron modifiers and methods of their use in cast iron production, in particular for foundry.

Widely known in the art are cast iron modifiers used to reduce the formation cementite on the surface of thin-walled cast iron castings. What is desired is a cast iron modifier which enables the manufacture of cast iron castings with a wall thickness from 5 to 10 mm in metal moulds without formation of cementite on the surface of the castings. Another desideratum is an improvement in the quality of cast iron castings. It would also be desirable to reduce production cost in the manufacture of cast iron castings by eliminating high-temperature annealing, expensive equipment, and costly materials, and by reducing the operating staff.

The present invention provides a cast iron modifier containing silicon, rare-earth elements, calcium, aluminium and iron, wherein, according to the invention, there are additionally contained carbon and sulphur, said components being used in the following proportions, in % by weight.

silicon from 30 to 40 rare-earth elements from 2 to 8 calcium from 10 to 20 aluminium from 15 to 30 carbon from 10 to 30 sulphur from 0.1 to 0.3 iron the balance.

If the content of silicon, calcium, or aluminium were below the specified minimum, the process of graphitization of modified cast iron would become unstable. If the content of silicon, calcium, or aluminium were above the specified minimum, the physical properties of modified cast iron would be imPaired.

A content of rare-earth elements(s) such as cerium, below the specified range would not enable the process of graphitization of cast iron to occur. If the content of rare-earth element(s) were increased above the specified range, the content of free cementite in the cast iron structure would increase undesirably.

With lower contents of carbon and sulphur than those specified, the provision of required graphite crystallization centres during solidification of cast iron could not be ensured. With greater contents of carbon and sulphur, the physical and mechanical properties of the cast iron would be impaired.

The above-mentioned components of the cast iron modifier are preferably added to molten cast iron in the form of a mixture of alloys and cupola coke in the following proportions, in % by weight.

silicocalcium 30 to 55 silicomischmetal 5 to 25 silumin 15 to 30 cupola coke 10 to 30 If the content of silicocalcium in the modifier below the specified range, the required silicon-to-calcium ratio might not be ensured in the cast iron. An increase in the content of silicocalcium above the specified range might result in impaired physical and mechanical properties of modified cast iron.

If the content of silicomischmetal were below the specified range, the required ratio of silicon to rare-earth elements might not be ensured. If the content of silicomischmetal were above the specified range, there might be a material increase in formation of cementite on the surface of castings.

With a lower content of silumin than the specified minimum, the graphitization process might become unstable. With an increase in the content of silumin above the specified maximum the physical and mechanical properties, as well as the casting properties of the cast iron, might be impaired.

With a lower content of cupola coke than the specified minimum, the required graphite crystallization centres might not form during solidification of cast iron. With a greater content of cupola coke than the specified maximum, the physical and mechanical properties of the modified cast iron might be impaired.

The modifier is preferably added to molten cast iron in an amount of 0.4 to 0.8% by weight. If the modifier were used in an amount below the specified range, it would not ensure the production of thin-walled and chill castings without formation of cementite on the surface of castings. Adding the modifier to cast iron in an amount above the specified range might impair the physical and mechanical properties of the modified cast iron and results in increased production cost.

The invention will be described further with reference to examples of chemical composition of the modifier, in comparison with a prior-art modifier, as shown in Table 1.

TABLE 1 Example: I II III Prior Art silicon 30 34 40 rest cerium 8 5 2 20 calcium 10 14 20 15 aluminium 15 25 30 7 carbon 30 20 10 sulphur 0.3 0.2 0.1 iron rest rest rest A modifier according to the invention exhibits high graphitization capacity. This is due to the fact that carbon added to cast iron has no time to be completely dissolved, and the remaining solid particles initiate the formation of graphite inclusions. In addition, sulphur added to the modifier reacts with chemical active components thereof (rare-earth elements and calcium) to form refractory compounds, the particles of these compounds also initiating graphite crystallization.

For experimental preparation of the three examples (I to III) of the modifier, three mixtures of components, each containing, in % by weight, respectively: silicocalcium 30, 40, and 55, silicomischmetal 25, 15 and 5; silumin 15, 25, and 30; and coke 30, 20 and 10.

Cast iron was modified with each mixture. For control, similar cast iron was modified using a prior art modifier. The rate of formation of cementite on the surface of castings was determined from wedge shaped production samples as compared with non-modified cast iron.

In the production samples, the cast iron had the amount of cementite formation shown in Table 2.

TABLE 2 Amount of modifier (wt.%) 0.2 0.4 0.6 0.8 zero Amount of cementite formation, mm Prior art modifier 5.4 4.3 3.2 2.6 16 Example I 1.5 0.2 0.0 0.5 16 Example II 1.8 0.8 0.0 0.0 16 Example III 2.5 1.4 0.0 0.0 16 This chemical composition of the modifier according to the invention and method of its application provide graphitization activity higher than with the use of a prior-art modifier for the manufacture of cast iron castings as can be seen from the above table.

With lower contents of the modifier in the cast iron, the desired reduction of cementite formation on the surface of castings cannot be obtained, while with an increase in the content of modifier, the amount of cementite formation on the surface of castings decreases only slightly.

The higher graphitization capacity of the modifier according to the invention permits thin-walled cast iron castings to be manufactured without formation of cementite on the surface thereof, thus improving their machining, eliminating the need for graphitization annealing, and lowering their production cost.

WHAT WE CLAIM IS: 1. A cast iron modifier containing the following components in % by weight: silicon 30 to 40 one of more rare-earth elements (total) 2 to 8 calcium 10 to 20 aluminium 15 to 30 carbon 10 to 30 sulphur 0.1 to 0.3 iron the balance.

2. A method of using the cast iron modifier claimed in Claim 1, wherein the said components are added to molten cast iron in the form of a mixture of alloys and cupola coke, in the following proportions, in % by weight: silicocalcium 30 to 55 silicomischmetal 5 to 25 silumin 15 to 30 cupola coke 10 to 30.

3. A method as claimed in Claim 2, wherein the modifier is added to molten cast iron in an amount of 0.4 to 0.8% by weight.

4. A cast iron modifier substantially as described herein with reference to Examples I to III.

5. A method of modifying cast iron substantially as described herein with reference to Examples I to III.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. In the production samples, the cast iron had the amount of cementite formation shown in Table 2. TABLE 2 Amount of modifier (wt.%) 0.2 0.4 0.6 0.8 zero Amount of cementite formation, mm Prior art modifier 5.4 4.3 3.2 2.6 16 Example I 1.5 0.2 0.0 0.5 16 Example II 1.8 0.8 0.0 0.0 16 Example III 2.5 1.4 0.0 0.0 16 This chemical composition of the modifier according to the invention and method of its application provide graphitization activity higher than with the use of a prior-art modifier for the manufacture of cast iron castings as can be seen from the above table. With lower contents of the modifier in the cast iron, the desired reduction of cementite formation on the surface of castings cannot be obtained, while with an increase in the content of modifier, the amount of cementite formation on the surface of castings decreases only slightly. The higher graphitization capacity of the modifier according to the invention permits thin-walled cast iron castings to be manufactured without formation of cementite on the surface thereof, thus improving their machining, eliminating the need for graphitization annealing, and lowering their production cost. WHAT WE CLAIM IS:

1. A cast iron modifier containing the following components in % by weight: silicon 30 to 40 one of more rare-earth elements (total) 2 to 8 calcium 10 to 20 aluminium 15 to 30 carbon 10 to 30 sulphur 0.1 to 0.3 iron the balance.

2. A method of using the cast iron modifier claimed in Claim 1, wherein the said components are added to molten cast iron in the form of a mixture of alloys and cupola coke, in the following proportions, in % by weight: silicocalcium 30 to 55 silicomischmetal 5 to 25 silumin 15 to 30 cupola coke 10 to 30.

3. A method as claimed in Claim 2, wherein the modifier is added to molten cast iron in an amount of 0.4 to 0.8% by weight.

4. A cast iron modifier substantially as described herein with reference to Examples I to III.

5. A method of modifying cast iron substantially as described herein with reference to Examples I to III.