SU1734928A1 - Synthetic slag for protection of steel surface against oxidation - Google Patents

Abstract

Purpose: The invention relates to metallurgical technology associated with surface protection, predominantly steel ingots from oxidation at a crystallization temperature, for example, in the production of iron-based bimetals using linear methods or in the preparation of blanks in combined casting-rolling units. Essence: the slag contains, wt%: borax 6-13; iron oxide 0.5-10; sodium carbonate 215%, boron fused concentrate 25-85; silicon oxide the rest. Melted boron concentrate is a product of thermochemical processing of borate ores. It contains, wt%: BaOZ 8-35, CaO 40-60, MgO 10-20, SI02 6-15, AlaOs + Fe203 + KAO 5-8. The sintering temperature is 800 ° C, the spreading temperature is 1050 ° C, and the viscosity at 1450 ° C is 20 MPa. The presence of melted boron concentrate in the slag accelerates the slagging process and improves the protective properties, which makes it possible to increase the effectiveness of protecting the steel surface from oxidation at 1450 ° C, to increase the service life of the slag by 3-3.5 times, as well as the yield. 3 tabl (L s

Description

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The invention relates to a foundry industry, in particular, to compositions of synthetic coatings used to protect the surface of parts or ingots, mainly from iron-carbon alloys, from oxidation during heating.

Synthetic slag is known to protect the steel surface from oxidation when heated, containing borax, boric anhydride, potassium fluorocirconate, silica, expanded perlite, and silicate lump.

The closest in composition and use is synthetic slag to protect the steel surface from oxidation, containing, in wt.%: Borax 39-45; potassium fluorozirconate 2-6; iron oxide 2-10; sodium carbonate 11-20; silicon oxide the rest.

The disadvantages of this slag are insufficient high protective properties against oxidation and service life at temperatures of steel crystallization interval. This leads to a deterioration in the quality of the protected

surfaces and, consequently, deviations from the design, technological parameters of the products obtained using the blanks processed by this slag.

The purpose of the invention is to improve the protective properties of slag from the oxidation of the surface of parts or ingots, mainly from iron-carbon alloys, at a surface temperature corresponding to the crystallization interval of steel.

The goal is achieved by the fact that the composition of the slag additionally introduces fused boron concentrate in the following ratio, wt.%: Borax 6-13; iron oxide 0.5-10; sodium carbonate 2-15; fused boron concentrate 25-85; silicon oxide the rest. The presence of melted boron concentrate in the mixture accelerates the slagging process and enhances the protective properties of the slag. Melted boron concentrate is a product of thermochemical processing of borate ores, has the composition, (wt.%) В20з 8-35; CaO 40-60; MDO 10-20; Si02 6-15; Re20z + K20 5-8. The sintering temperature is 800 ° C, the flow temperature is 1050 ° C, and the viscosity is at a temperature of 1450 ° C 20 MPa.

Synthetic slag is produced by fusing oxide components. After melting, it is crushed, the necessary amount of sodium carbonate is set, granulated and packaged in portions, in this form the slag is ready for use.

The properties of the proposed slags were studied in detail in the laboratory.

The compositions of the slags studied are given in Table 1, and their properties in Table 2.

From tab. 1 and 2, it follows that melts 4-8 are characterized by optimal properties. Increasing the content of borax above 13% and a decrease of less than 6% is impractical because the surface quality of the protected workpiece is reduced.

When the content of iron oxide in the slag is more than 10%, the protective properties against oxidation sharply deteriorate and the service life of the slag at a temperature of 1450 ° C decreases. Reducing the content of iron oxide to 0.5% and its complete absence in the slag does not significantly affect the studied properties of the slag and is permissible.

An increase in the sodium carbonate content of over 15% leads to an increase in the rate of slag evaporation and its loss. A decrease in the sodium carbonate content of less than 2% leads to a decrease in the fluidity of the slag.

Oxidation of the ingot surface when using the proposed slag in comparison with the known one is prevented due to higher protective properties, the latter, in turn, are determined by a complex of characteristics — viscosity, adhesion work and oxides of variable valence. To ensure these properties at a temperature of 1450 ° C, the proposed amount of fused boron concentrate is introduced into the slag.

The content of melted boron concentrate in the slag less than 25% and more than 85% reduces the protective properties of the slag at T 1450 ° C, leads to an increase in the oxidation rate of the metal, a decrease in the service life and a decrease in the quality of the billet being protected.

Example. Slags (1 and 7) were tested in industrial conditions for the preparation of bimetallic billets. Billets are produced by continuous casting on a vertical caster. A bag consisting of two stainless steel 08X18H10T sheets with a cross section of 20,540 mm with a separating mixture located between them is poured into the mold with a cross section of 210–740 mm and the steel of Steel 3 is poured at T 1600 ° C. In this case, the steel is crystallized on the surface of the package and the walls of the mold. On the metal mirror in the mold serves the proposed (7) and known (1) slag-forming mixtures (consumption of the mixture is established in preliminary experiments in the amount of 4-5 kg / t). Upon melting of the mixture, a slag bath is formed on the metal mirror, in which non-oxidative heating of the sheets of the bag introduced into the mold is carried out. Casting lead with a speed of 0.25 m / min

After the slab is drawn out of the crystallizer, it is cut into pieces of 1.5 m and transverse temples are taken from each piece to analyze the macrostructure and evaluate the welding of metals.

According to the results of the control, the defectiveness of slabs (cracks) obtained using the proposed and known slags is equivalent.

According to the results of metallographic analysis, the number of nonmetallic inclusions in the body of the ingots cast under the proposed slag and the prototype is comparable: 80% of the detected inclusions are 20–40 µm in size.

The yield of slabs for these parameters is 100%. After preparing the slabs for rolling (gouging of wide faces to a depth of 3 mm), no cracks were found.

The ingots are subjected to hot rolling and subsequent culling of the layer. The quality of welding is assessed by the number of macrodefects in the transition zone. The results of calculations of macrodefects and rejection are given in table. 3

From tab. 1-3, the use of the proposed slag makes it possible to increase the effectiveness of protecting the steel surface from oxidation at a temperature of 1450 ° C by 3.5-4 times, to increase the service life of the slag by 3-3.5 times and to increase the yield of suitable products from 70 to 90%.

Note. VOK is the oxidation rate of steel samples coated with a slag film; t-life slag; K.P. - quality of the sample surface,%, (for 100%, a profilograph signal is applied on the sample surface prior to the test); Vncn. - slag evaporation rate; rj is the viscosity of the slag; (e) slag surface tension; ftfe-adhesion work. The temperature of the experiments 1450 ° C.

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Claims (1)

Invention Synthetic slag to protect the steel surface from oxidation, including borax, iron oxide, sodium carbonate and silicon oxide, characterized in that, in order to improve its protective properties against oxidation in the temperature range of the crystallization interval, it further contains fused boron concentrate at the following the ratio of components, wt.%: Bura6-13 Ferric oxide 0.5-10.0 Sodium carbonate 2-15 Melted boric concentrate 25-85 silica Oxide Else Table 1 table 2 Editor A. Kozoriz Tehred M. Morgenthal Order 1771 Circulation: Subscription VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, 4/5 Raushsk nab. Production and Publishing Combine Patent, Uzhgorod, Gagarin st., 101 Table 3 Proofreader M. Demchik