RU2640368C1 - Master alloy for refining and modifying chromium cast irons - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: master alloy contains, wt %: titanium 8-12; silicon 8-12; aluminium 4.5-5.5; boron 2.8-3.5; carbon 1.0-1.2; vanadium 8-12; cerium 1.8-2.2; manganese 10-12; samarium 10-12; nickel 28-32; calcium 0.5-1.5; the rest is iron.

EFFECT: invention makes it possible to create master alloy for chromium cast irons with increased radiation resistance and stability of strength characteristics under exposure to radioactive hydroabrasive mixtures.

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Description

The invention relates to metallurgy and foundry, in particular to compositions of ligatures for refining and modifying chrome cast iron, used for the manufacture of wear-resistant working parts of hydraulic pumps, which are used in the mining and metallurgical industries for pumping waterjet mixtures in the form of pulp, including radioactive.

Known ligature, which contains carbon, copper, silicon, aluminum, chromium, manganese, titanium, nickel and iron in the following ratio, wt. %: carbon 2.0-4.0; copper 5.0-40.0; silicon 2.0-5.0; aluminum 0.05-1.5; chrome 0.15-2.0; manganese 0.20-0.5; titanium 0.5-1.0; nickel 0.25-1.0; iron - the rest (RU 2017853, C22C 35/00, published August 15, 1994).

The closest in technical essence, the achieved technical result and selected as a prototype is a ligature for chromium cast iron containing titanium, silicon, aluminum, boron, carbon and iron in the following ratio of components, wt. %: titanium 43.5; silicon 13.5; aluminum 20.0; boron 3.0; carbon 1,2; iron - the rest (Kolokoltsev V.M., Shevchenko A.V., Shatokhin I.M., Goltsov A.S. Improving the service life of iron castings IChKh28N2 by modifying its melt with a complex ligature based on titanium and boron, Russian Foundry, 15.08 .2010, No. 8, pp. 9-12).

A disadvantage of the known ligatures is the impossibility of using them to obtain radiation-resistant chromium cast irons used for the manufacture of castings of products (pumps) for pumping hydroabrasive mixtures, including radioactive ones, since there are no elements in the ligature that ensure radiation resistance and stability of the mechanical characteristics of cast iron.

The objective and technical result of the invention is to create a composition of the ligature, which allows to obtain chromium cast irons with high radiation resistance and stability of strength characteristics when exposed to radioactive hydroabrasive mixtures.

The technical result is achieved in that the ligature for refining and modifying chromium cast irons contains titanium, silicon, aluminum, boron, carbon, vanadium, cerium, manganese, samarium, nickel, calcium and iron in the following ratio of components, wt. %: titanium 8-12; silicon 8-12; aluminum 4.5-5.5; boron 2.8-3.5; carbon 1.0-1.2; vanadium 8-12; cerium 1.8-2.2; manganese 10-12; samarium 10-12; nickel 28-32; calcium 0.5-1.5; iron is the rest.

Vanadium is introduced into the composition of the ligature in an amount of 8-12% to increase the hardness and wear resistance of cast iron due to the formation of stable and solid VC carbides and additional crystallization centers that contribute to the refinement of the structure. When the content of vanadium in the ligature is less than 8%, it does not affect the structure and properties of cast iron. When the content of vanadium in the ligature is more than 12%, its content in chromium carbides increases, and the chromium content, on the contrary, decreases. As a result, the carbide hardness decreases and, accordingly, the wear resistance of cast iron under radiation exposure.

Cerium is introduced into the composition of the ligature in an amount of 1.8-2.2% for the modification of chromium cast irons in order to purify the melt of gases and sulfur, which reduce the radiation resistance of cast iron after modification. When the cerium content in the ligature is less than 1.8%, it does not clear the melt of gases and non-metallic inclusions. The cerium content in the ligature of more than 2.2% leads to the formation of complex eutectic-type inclusions that degrade the properties of cast iron.

Manganese is introduced into the ligature in an amount of 10-12% to stabilize austenite in all temperature zones of transformation. When the manganese content in the ligature is less than 10%, conditions are created for the formation of perlite, which has a low hardness. When the manganese content in the ligature is more than 12%, the carbon content in austenite increases, as a result of which the amount of carbides decreases and the proportion of residual austenite increases. This helps to reduce the hardness of chrome cast iron.

Calcium is introduced into the composition of the ligature in an amount of 0.5-1.5% for the refinement of cast iron in order to reduce the number of non-metallic inclusions in it and eliminate dendritic crystallization of austenite. When the calcium content in the ligature is less than 0.5%, it does not clean the melt from non-metallic inclusions. When the content in the ligature of calcium is more than 1.5%, it reduces wear resistance due to coarsening of the structure and the formation of slag.

Samarium is introduced into the composition of the ligature in an amount of 10-12% to increase the stability of chromium cast iron to radiation due to the absorption of radiation. When the samarium content in the ligature is less than 10%, it has little effect on increasing the radiation resistance of chrome cast iron. When the samarium content in the ligature is more than 12%, a further increase in the capture of thermal neutrons does not occur and its use in such an amount becomes economically inexpedient.

Nickel is introduced into the composition of the ligature in an amount of 28-32% to increase the hardness of chromium cast iron. When the nickel content in the ligature is less than 28%), conditions are created for the formation of perlite with low hardness. When the nickel content in the ligature is more than 32%, the proportion of residual austenite increases, which also has low hardness.

The ligature was smelted in an induction furnace. The ligature components were introduced into the furnace in the following sequence: metallic nickel and aluminum are melted in the crucible of the furnace. Silicocalcium, carbon ferromanganese, ferrosilicon, ferrotitanium, ferroboron, ferrovanadium, ferrocerium, and samarium were introduced into the liquid bath at 1500 ° C. The bath is kept for 3-5 minutes and after mixing and the final dissolution of all components, the molten ligature is poured into the molds.

The master alloy according to the invention was used for smelting high-chromium white cast iron containing carbon, silicon, manganese, chromium, nickel, tungsten, molybdenum, titanium, vanadium, aluminum, boron, niobium, samarium, cerium, calcium and iron.

The table shows the compositions of the known (prototype) and the proposed ligatures, as well as the radiation resistance of high-chromium cast iron obtained using the known ligature and ligature according to the invention, expressed by the value of the thermal neutron capture cross section. Comparative studies of cast irons showed that the use of the ligature according to the invention increases the strength characteristics of cast iron by 1.2-1.3 times, the radiation resistance by 5.7 times and ensures the stability of the service characteristics of chrome cast iron during waterjet wear.

Claims (2)

Ligature for the refinement and modification of chromium cast irons, containing titanium, silicon, aluminum, boron, carbon and iron, characterized in that it additionally contains vanadium, cerium, manganese, samarium, nickel and calcium in the following ratio of components, wt. %: titanium 8-12 silicon 8-12 aluminum 4,5-5,5 boron 2.8-3.5 carbon 1.0-1.2 vanadium 8-12 cerium 1.8-2.2 manganese 10-12 samarium 10-12 nickel 28-32 calcium 0.5-1.5 iron rest