SU1361182A1 - Method of modifying cast steel - Google Patents

Abstract

The invention relates to metallurgy and foundry, in particular to after-furnace treatment of steels for the manufacture of castings. The purpose of the invention is to increase the absorption of mods (lactating additives, grinding J. lKliES —r.Tr TWJneSI RGLUZ of nonmetallic inclusions, improving ductility and toughness. The method of modifying casting steel includes preliminary deoxidation of manganese-containing alloy in the steelmaking unit, final finishing. aluminum in the ladle and modification during casting with rare metals. Aluminum is introduced as silumin in the amount of 0.9-1.3 kg / t into the ladle with subsequent silicium in the amount of 1.5-2.5 kg / t and 30-4 0% of rare-earth metals, and modification is carried out by 60-70% of rare-earth metals with a total mass ratio of silumin and rare-earth metals, respectively, 1: (o, 8-1.1). This increases the mechanical and operational characteristics, ensuring an increase in reliability and durability. responsible castings. 2 tab. (O (L

Description

The invention relates to metallurgy and foundry, in particular baking processing of steels for the manufacture of castings.

The purpose of the invention is to increase the absorption of modifying additives, grinding non-metallic inclusions, improving ductility and toughness.

Deoxidation and modification of the steel is carried out in three stages. In the first and second stages, respectively, in the furnace and the tundish, as a result of preliminary and final deoxidation, the oxygen concentration is reduced and non-metallic, mainly oxide, inclusions are removed. This is due to the formation of corundum particles and calcium oxides, which are rapidly removed from the liquid metal. In addition, due to the high vapor pressure of calcium, the latter is removed in a significant amount in a gaseous state, contributing to a good purification of the metal. Also important is the flow of convective mixing processes in the tundish during melt production, when the resulting oxides of aluminum, calcium and in a small amount of rare earth metals (REM) are carried by the flows to the interface with the slag and are assimilated by it. The use of silumin instead of traditional aluminum allows improving refining effects on the metal and enhancing the modulating effect of other additives.

At the third stage, in the pouring ladle in the absence of oxygen, most of the injected rare-earth metals (60–70%) interact with impurities, mainly with sulfur. As a result of the very high chemical affinity of rare-earth metals and sulfur, a large number of small and round sulphides and oxysulfides of these metals are formed, which have a high density

5.5-6.5 g / cm and poorly removed from the metal.

Due to the fact that these particles have a high melting point and are formed in the liquid metal, as the temperature decreases, they play the role of substrates in the crystallization process and contribute to the refinement of the structure. The regulated ratio of the components introduced by the new method.

5 0 5 0 s

Q 5

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five

provides high assimilation of modifiers and obtaining in the metal the optimal residual concentrations of rare-earth metals in the range of 0.04-0.09%. Rounded and fine sulphides of rare-earth metals, particles that are evenly located in the matrix, in contrast to round manganese sulphides of unfavorable elongated shape, are largely concentrated along the grain boundaries and reduce the ductility and toughness of steel.

The introduction of silumin less than 0.9 kg / t does not provide sufficient deoxidation of the metal and can lead to the appearance of gas porosity, and the addition of more than 1.3 kg / t leads to the appearance of a large amount of aluminum nitrides, most characteristic of electric smelting, is ushdhs foci destruction under static and dyna | Mytic loads.

Silicocalcium additive less than 1.5 kg / ton is ineffective, since it slightly affects the reduction of oxide inclusions, resulting in a significant amount of REM works as dissolving agents and decreases the amount of REM sulfides, contributing to the 1X grinding of non-metallic phases. The introduction of silicocalcium more than 2.6 kg / t is impractical, since it leads to strong intoxication and excessive consumption of silicocalcium. In addition, the silicon content in finished steel increases significantly, exceeding the required grade. Therefore, the amount of silicocalcium injected is regulated 1.5-2.5 kg / t. The optimal amount of input rare-earth metals is 0.07–0.14% or 0.7–1.4 kg / ton. With a smaller amount of rare-earth metals, the effect of modification is small, and as a result of the formation of manganese sulphides, the values of ductility and toughness are noticeably reduced. With an increase in the number of reclining REMs, clusters of cerium-containing particles that have an irregular acute-angular shape and are stress concentrators are intensively formed. In addition, an increase in the number of prisazhivaemae REM leads to a significant increase in the cost of steel.

Additive in intermediate. a bucket less than 30% of REM alloy does not provide maximum final deoxidation of steel, while the introduction of more than 70% of the total amount of REM alloy added to the casting bucket does not ensure uniform distribution of REM in a small volume of metal and structure homogeneity. The addition of more than 40% of the REM alloy to the tundish leads to the secondary oxidation of REM at the overflow from the tundish to the casting ladle and reduction of the stem-JQ of the RZM that is squeezed into the intermediate one and, as a result, their modifying effect on the steel.

Example. In an electric arc furnace, low-alloyed Si-Mn-Mo cast steel is melted according to standard technology. After the predetermined carbon content has been reached at the end of the oxidation period, the metal is preliminary deoxidized, after which the smelting is released into the tundish. During the run, silumin in an amount of 0.8-1.4 kg / ton is seated in the intermediate bucket, and then silage buckets. Option 14 specifies the parameters of a known method.

The assimilation of REM in variants 1-7 is significantly higher than in variants 8-13, 15 due to the introduction of optimal amounts of silumin, silicocalcium and the implementation of the ratio of silumin and REM in accordance with the regulated introduction to the REM bucket: between 20 and 30-40 % of the total amount and in the casting ladle 60-70%.

The highest degree of assimilation of rare-earth metals is observed in variants 2.6 and 7, when the amounts of introduced silumin

licocalcium in the amount of 1.4-2.6 kg / t 25 and silicocalcium are on the upper

and 20-50% of the alloy of rare-earth metals, taking into account the introduction of additives in various combinations: in the amount below the lower level, within the limits required by the proposed method, and Bbmie of the upper level .. Accordingly, 50-80% of the alloy of rare-earth metals is used in casting bucket under the stream of metal. The proposed method uses silumin containing 6-8% silicon, the rest is aluminum, and according to the well-known aluminum is secondary, silico-alloys of SKZR, an alloy of rare-earth metals containing 36% of the amount of rare-earth metals 42% silicon, 4% aluminum, the rest is iron. Steel castings are heat-treated according to the accepted mode: quenching from 800-900. C, cooling in water, tempering at 630-640 C, cooling in water. The nature of the inclusions (shape, size) and the contamination of the steel with them emit metallographically, the mechanical properties according to standard methods.

The parameters of the proposed and known methods of modifying and the characteristics of the steel are given in Table. 1 and 2 respectively.

Table 1 shows the parameters of the methods for modifying the cast steel and the chemical composition of the smelted metal. The steel of variants 1-7 is finally crushed and modified with the introduction of silumin in the amount of 0.9-1.3 kg / t, silicocalcium in the amount of 1.5-2.5 kg / t and REM in the amount of 11824

0,7-1,4 kg / t, providing the maximum and average values of the parameters of the proposed method g modification. Variants 8-11 provide for the introduction of exorbitant amounts of silumin, silicocalcium, and ratios of silumin and rare-earth metals, options 12.13 - exorbitant quantities of rare-earth metals,

shower buckets. Option 14 specifies the parameters of a known method.

The assimilation of rare-earth metals in variants 1–7 is significantly higher than in variants 8–13, which is due to the introduction of optimal amounts of silumin, silicocalcium and the implementation of the ratio of silumin and rare-earth metals in accordance with the regulated introduction to the bucket of rare-earth metals: between 30 and 30% of the total amount and in the filling ladle 60-70%.

The highest degree of assimilation of rare-earth metals is observed in variants 2.6 and 7, when the amounts of introduced silumin

five

0

limit or average level and provide maximum metal deoxidation.

As a result, the rare-earth metals most fully interact with sulfur, completely binding it to refractory inclusions, poorly removing the liquid from the molten metal, thereby paralyzing the negative effect of this impurity on the mechanical and technical properties of cast steel.

The formation of a large number of fine rounded sulphides of rare-earth metals is indicated by the calculation of the pollution index. The ratio of globular (REM-containing) sulphides to acute-angular (manganese sulphides) in Stable, modified in options 1-7, is 1.43-3.1. For options 8-11, this ratio is 0.39-1.1, i.e. in this case, the formation of acute-angular manganese sulphides takes place, mainly concentrating along the boundaries of dendritic crystallites and primary grains.

An unfavorable ratio of globular sulphides to acute-angular (0.48-1.06) is also observed in treatment options 5 12 and 13, when the additive of the increased amount of REM (more than 70%) in the casting ladle leads to intensive formation along with small round particles. clusters

five

0

conglomerates of irregular shape, unevenly located in the metal (option 12), or unjustified loss of REM as a result of secondary oxidation, their lack of interaction with sulfur and the formation of favorable non-metallic inclusions (version 13). A significant degree of formation of dispersed particles of REM sulfides is indicated by the calculation of particle sizes: in variants 1-7, the size of globular sulfides is within 2.6–10–3.6 10 m, and in variant quantities and ratios - within 2.6 10 - 4.3-10 m.

large clusters of REM-containing particles (cerium inhomogeneity), which increase the tendency to brittle fracture. The addition of increased amounts of silumin in treatment variants 9 and 11 leads to the formation of aluminum nitrides, which contribute to the reduction of toughness and plastic properties. The negative effect on the metallic inclusions of the above additives of rare-earth metals in the tundish (version 13) was mentioned, therefore the values of the mechanical properties here as well -13 beyond the limit-15 are small.

The known method of deoxidation (option 14) has an unsatisfactory level of properties. This is due to the fact that the introduction of most of the rare-earth metals in the data obtained according to the amount of added additives depends on the carbon content and the degree of legio-2O intermediate bucket leads to the failure of the steel. It is envisaged to introduce this loss at overflow into the additives to ensure an efficient pouring ladle, which, in addition to their general effect on the morphology of a non-small amount (0.25 kg / ton) of detrimental inclusions and mechanical effects education processes

25 favorable in shape, size and

the nature of the location of sulfide rare earth metals. The ratio of the concentration of globular sulfide to acute angle is 0.36, and the size of the prevailing properties of silicon-manganese-molybdenum-containing cast steel with a carbon content of 0.30-0.40%.

Variations 1-7 of the steel modification provide the highest values of ductility and toughness. This is due to the formation of fine and round REM-containing sulfides, which largely bind sulfur, and good metal refining.

Variants 8-13 of steel processing with extreme quantities and parameters have significantly lower values of mechanical properties. This is mainly due to the fact that the large and acute-angled manganese sulphides that are predominantly formed are stress concentrators and sources of metal destruction under static and dynamic loads. The size of these inclusions is 6 W - 5.1-10 mi, which noticeably exceeds the size of globular sulphides. In variants 8 and 10, the formation of manganese sulphides is caused by the unsatisfactory final deoxidation of the metal due to the lack of input silumin and the interaction of rare-earth metals with oxygen.

At the same time, the ratio of silumin to rare earth metals in the beyond (1: 1.25) leads, as in option 12 with the additive of an extreme amount of rare earth metals in the casting ladle (80%), to the formation of 30 manganese coal sulphides equal to 5-10 m. Aluminum used in the known deoxidation process is less effective than silumin.

The economic effect of using the proposed modification method is to increase the mechanical and operational characteristics, which ultimately increase the reliability and durability of the critical castings.

Claims (1)

Invention Formula 45, Method for modifying cast steel, including preliminary deoxidation in a steel-smelting unit with a manganese-containing alloy, final deoxidation with aluminum QQ in the ladle and modification when casting with rare earth metals, characterized in that, in order to improve the absorption of the modifying additives, grinding non-metallic inclusions, improve ductility and toughness, aluminum is introduced as silumin in a quantity of 0.9-1 , 3 kg / ton in the ladle with the subsequent addition of silicocalcium in the amount of .71361182 1.5-2.5 kg / t and 30-40% rare earths with metals, and modifying the actual ones are 60-70% rare earth metals. eight the total mass ratio of the introduction of sulimin and rare-earth metal, respectively 1: (0.8-1.1). Table 1 Editor S.Pekar Compiled by A. Minayev Tehred M. Margental Corrector M. Maksimishinets Order 6198/30 Circulation 550Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4