SU1731423A1 - Compound for surface alloying of castings - Google Patents

Abstract

Use: the composition is intended for alloying the surface of castings operating in aggressive media. Composition contains, May. %: antimony 5-35; ferrosilicon (FS 75) 2-8; fireclay 3-20; cryolite 1.5-2.5; hydrolyzed ethyl silicate else. New is the introduction of antimony, ferrosilicon and chamotte. The positive effect of the introduction of these components manifests itself in a multiple increase in the corrosion resistance of cast iron.

Description

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The invention relates to a foundry, namely, compositions for alloying the surface of cast iron.

A composition for surface doping is known, consisting of the following components, May. %: boron carbide 22-24; aluminum fluoride 4-6; carbonyl nickel 8 - 10; phenol formaldehyde resin 4 - 8; hydrolyzed ethyl silicate - the rest.

This composition is intended to increase the depth of the doped layer, corrosion and wear resistance, reduce the drying temperature of the composition. The main component of the composition - boron carbide improves wear resistance. Nickel also improves wear resistance, forming borides, and only partly contributes to an increase in corrosion resistance. The stability of castings doped with this composition in solutions of acids and salts is insufficient.

Also known is a composition for surface alloying of castings and rolled products, containing, in May.%: Chromium 60-77; bor0.002-0.03; calcium 0.003 - 0.04; Nickel 20 - 35; niobium 0.05 - 2.0; iron - the rest.

This mixture in terms of composition and ratio of the main components resembles the composition of alloying additives of stainless steel. All elements are included in the mixture in its pure form, which is expensive and technologically inconsistent. The composition is used only for alloying carbon steel. The stability of castings doped with this composition in alkalis, especially during electrolysis, is insufficient.

The closest to the proposed composition according to the technical essence is a composition for alloying the surface of castings in a mold, containing, in wt.%: Boron carbide 12-20; ferrosiliconadium 13-20; tellurium 0.08 - 0.15; barium 0.2 - 0.6; cryolite 1.5 - 2.5; hydrolyzed ethyl silicate - the rest.

This composition provides high surface quality castings, mechanical properties and wear resistance. At the same

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It does not provide sufficient corrosion resistance of castings from cast iron in solutions of alkalis, salts and acids.

The aim of the invention is to increase the corrosion resistance of cast iron in corrosive environments.

This goal is achieved by the fact that the known composition for surface alloying of castings, containing cryolite and hydrolyzed ethyl silicate, additionally contains antimony, FS 75 ferrosilicon, and chamotte in the following ratio, wt.%: Antimony 5 - 35; ferrosilicon Ф С 75 2 - 8; chamotte 3 - 20; cryolite 1.5 - 2.5; hydrolyzed ethyl silicate - the rest.

The limits of the content of components are established, based on the favorable combination of the corrosion resistance of the castings, the properties and manufacturability of the alloying composition itself. The content of the main component is antimony, which provides an increase in corrosion resistance, taken from 5 to 35%. With an antimony content of less than 5%, there is no appreciable increase in the corrosion resistance of the casting. When the content of antimony in the coating is more than 35%, the concentration in the iron increases, however, an increase in the corrosion resistance is not observed, and the mechanical properties of the metal also decrease.

FS 75 ferrosilicon is introduced to compensate for the antihygraphic effect of antimony in the surface layer of the iron casting. A chill-free structure with a lamellar graphite is formed on the surface of the casting. The limits of the content of FS 75 are determined by the optimal structure of the surface casting. Less than 2% of ferrosilicon does not ensure elimination of the department. With a content of more than 8%, no further increase in the degree of graphitization is observed.

Cryolite in the amount of 1.5-2.5% plays the role of a flux and contributes to the production of castings with a clean, uniformly alloyed surface. Fluorine, which is formed during the decomposition of cryolite, impedes the delivery of oxygen to the surface of the doped layer and serves as a protective medium. When the content is less than 1.5% cryolite does not provide the required amount of surface castings. A content of more than 2.5% of cryolite does not further improve the quality of the surface.

Chamotte is a refractory filler of the alloying composition and is added at the top level (20%) with a low content of antimony (5%) to ensure sufficient viscosity and covering ability of the composition. Fireclay at the lower level (3%) is injected at the maximum content of antimony and other ingredients in order for the composition to contain no more than 50% of solid ingredients. Otherwise, the composition is thick, viscous and there are difficulties when applying it to the surface of the mold. Hydrolyzed ethyl silicate is a binder and solvent of this composition.

Example. The dry components in the powder state with antimony particle sizes of not more than 0.16 mm and not more than 0.1 mm for the remaining components are mixed until a homogeneous mass is obtained, then hydrolyzed ethyl silicate is added with a density of 1.05-1.05 g / cm and a suspension with a density of 1.38 - 2.03 g / cm3 is obtained. It is applied to the surface of a mold or rod with a layer thickness of 0.5-1.5 mm. To obtain a thicker layer, the coating is applied twice. Coloring can be made both a brush, and an airbrush. After dyeing, the mold or core is dried at a temperature of 220–280 ° C for 0.5–1 h. The assembled forms are cast with cast iron of composition 3.5 C; 2.2; 0.5 Mp

Variants of the compositions are given in table 1, and the properties of the castings in table 2.

Properties were determined by the following methods.

The depth of the doped layer was determined by the metallographic method on a casting with a wall thickness of 40 mm at a casting temperature of 1350 °. Brinel hardness (HB) according to GOST 27208-87. The corrosion rate was determined by the gravimetric method in a 5% H2SO4 solution at room temperature. Tests in 4% NaOH media and 4% Na OH + 1% NIS04 media were carried out during electrolysis with a current density of 20 A / dm2 at a temperature of 60 ° C. Prototypes were anodes.

As can be seen from Table 2, the corrosion resistance of cast iron superficially doped with antimony at an average level is seven or more times higher than the resistance of cast iron doped with the composition of the prototype.

The implementation of the proposed technical solution allows to increase the corrosion resistance of castings, reduce the consumption of alloying elements, simplify the technology of smelting iron. Higher durability of the obtained castings allows a seven or more times longer service life of castings in aggressive media and lower costs for the manufacture of castings.

Claims (1)

Claims for surface alloying of castings containing cryolite, hydrolyzed ethyl silicate and ferroalloy, characterized in that, in order to increase the corrosion resistance of castings, it additionally contains antimony and chamotte, ferrosilicon is taken as ferroalloy. 0 FS 75 in the following ratio, wt.%: Antimony5-35 FS 752-8 ferrosilicon Cryolite1.5-2.5 Shamot3-20 Hydrol ethyl silicate Else Table 1 table 2