RU2341562C2 - Method of high-duty cast iron receiving - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes charge dissolution in melting facility, reduction of melt temperature till 1420-1460°C, primary modification of it by ligature with containing of rare-earth metals and silicon with receiving in cast iron structure vermicular graphite at fracture of reference template and secondary modification. Ligature at primary modification is uniformly fed to metal jet through dosing tank at metal discharge into bull ladle, and at secondary modification together with secondary ligature into cast iron melt it is additionally introduced primary ligature in amount till 0.5% of liquid cast iron mass with its folding to ladle bottom for receiving of cast iron with globular shape of graphite.

EFFECT: process stability at usage in the capacity of charge scrap iron with different chemistry, reduction of ligature consumption, reduction of founding discard amount by discordance to required cast iron mark.

3 cl

Description

The invention relates to ferrous metallurgy and foundry regarding methods of producing high-strength cast iron from source cast iron with a sulfur content of more than 0.04% and can be used in the mass production of castings from high-strength cast iron with vermicular and spherical graphite.

Existing methods for producing high-strength cast iron with spherical and vermicular graphite involve the use of alloys with different contents of rare-earth metals, silicon, magnesium, aluminum, and other elements in various combinations.

One of the most common methods for producing ductile iron is the method of treating liquid metal with a master alloy with a content of rare-earth metals 30–40%, silicon 40–43%, aluminum 7.5–8% in an amount of 0.8–2.5% of the mass of molten iron (see Shumikhin BC, Kutuzov VP, Khramchenkov AI, etc. High-quality cast iron for castings - M .: Mechanical Engineering, - 1982. - S.157-158) or in the processing with the same ligature in in the amount of 0.8 ÷ 1.5% by weight of the metal with secondary modification by FS75 grade ferrosilicon in the amount of 0.5 ÷ 0.8% by weight of the metal (see Foundry »-. 1987. - №1 - C.5). However, a possible supersaturation of cast iron with rare-earth metals over 0.05 ÷ 0.06% or silicon over 3.0 ÷ 3.5% leads to changes in the metal matrix of castings and causes a sharp decrease in the mechanical properties of cast iron.

Another way to obtain ductile iron is a method of treating liquid metal with a master alloy containing rare earth metals, silicon and magnesium in an amount of 1.5 ÷ 1.8% by weight of cast iron. In this case, the ligature is loaded onto the bottom of the bucket before it is filled with the melt and sprinkled with steel die cutting (see "Foundry". - 1996. - No. 10, - P.19). However, to implement this method, non-sulfur cast irons are required as starting materials. In addition, powdered steel die cutting dramatically reduces the temperature of the processed melt, the ligature does not dissolve and does not react with the metal, floats in the slag and alloying elements burn out in air. Thus, the assimilation of alloying elements is less than 50% (see Shumikhin B.C., Kutuzov V.P., Khramchenkov A.I. et al. High-quality cast iron for castings - M .: Mechanical Engineering. - 1982. - P.150).

The method of intra-molten processing of the melt with a ligature with the content of rare-earth metals, silicon, magnesium in the amount of 1.4 ÷ 1.6% by weight of the metal poured into the mold has found wide application (see "Foundry". - 1996. - No. 10 - P.18 -19 and Chaykin V.A., Ishutin V.V., Chaykina N.V. Comparative analysis of the quality indicators of high-strength cast irons obtained by various methods./ Proceedings of the VII Congress of Foundry Workers of Russia - Novosibirsk: Publishing House "Historical Heritage of Siberia." - 2005 . - S.76-77).

The specified method requires strict sorting of the metal charge by chemical composition in order to be able to calculate the mass of the in-mold ligature bookmark. The source cast iron should have a sulfur content of not more than 0.02%, and the ligature should have a strictly seasoned chemical composition.

Alloys with rare-earth metals produced in the Russian Federation are characterized by a significant range of the percentage of alloying and related elements, which creates additional difficulties in achieving the stability of the process of producing high-strength nodular cast iron by existing methods. In addition, in-mold modification must be carried out at a temperature of cast iron not lower than 1400 ° C, which in some cases is difficult due to the characteristics of the existing smelting equipment, and also causes an additional risk of defective parts for a number of signs (see Cast iron. Reference under Edited by Sherman A.D. and Zhukov A.A. - M.: Metallurgy, 1991. - P.290).

A sufficiently stable process is a method of producing high-strength cast iron with spherical and vermicular graphite, including preliminary modification of the original cast iron with a alloy with a content of rare earth metals 30%, silicon 43%, aluminum 8% and secondary modification with the same ligature (see the description of the patent of the Russian Federation Na 2156809, IPC ⁷ C22 C37 / 04, published on November 20, 2000). However, the manufacturing process according to this patent has positive results with a stable chemical composition of the master alloy with a content of rare earth metals of 30 ÷ 35% and silicon over 40%, which does not correspond to the quality of the master alloys produced in Russia in bulk quantities.

Closest to the proposed method is a method for producing high-strength cast iron from initial cast iron, including melting the charge in the melting unit, adjusting the melt temperature to 1420-1480 ° C, initial modification with a ligature containing rare-earth metals and silicon, and secondary modification, characterized in that the primary the modification is carried out until the effect of overmodification of cast iron with subsequent secondary modification with a ligature containing rare earth metals, magnesium and silicon, and the amount of the ligature of the initial modification is determined by the appearance of vermicular graphite in cast iron during the addition of new batches of liquid metal (see the description of the patent of the Russian Federation No. 2188240, IPC ⁷ C21C 1/10, C22C 37/04, published on 27.08.2002 - prototype) . Moreover, all the methods of introducing the ligature of the primary modification (the most expensive material) indicated in the prototype assume a rather low degree of utilization of the main elements of the ligature by cast iron. At the same time, the achievement of the effect of overmodification during the initial modification obviously implies an overspending of the corresponding ligature.

The problem solved by the proposed method is to increase the stability of the process and minimize the cost of obtaining high-strength nodular cast iron.

The specified technical result is achieved by the fact that in the method for producing high-strength cast iron from initial cast iron with a sulfur content higher than 0.04%, including melting the charge in the melting unit, adjusting the temperature of liquid cast iron to 1420 ÷ 1460 ° C, primary modification with a ligature containing rare-earth metals and silicon by feeding it in an amount of 0.4-1.2% by weight of molten iron with the help of a dispenser for a jet of metal to be drained, holding the metal in a transfer ladle with subsequent removal of slag and secondary modification, primary odifitsirovanie carried out until the samples in vermicular graphite cast structures detectable splitability sample. The required amount of primary ligature is determined depending on the sulfur content in the original molten iron.

Secondary modification is carried out at a temperature of molten iron of 1280 ÷ 1400 ° C with a ligature containing rare earth metals, magnesium, silicon in an amount of 0.3 ÷ 1.0% of the mass of molten iron with laying the ligature on the bottom of the casting ladle immediately before the metal is drained into it. Upon receipt of vermicular graphite at the fracture of the control sample after primary modification, during secondary modification together with the secondary ligature, additional primary ligature is introduced into the molten iron in an amount up to 0.5% by weight of the melt. This allows you to guaranteed to obtain spherical shape of graphite in the final cast iron without necessarily achieving the effect of overmodification at the first stage.

After primary and secondary modification, the metal must be aged for 4 + 6 min and 0.5 + 1.0 min, respectively, for the surfacing of the rod, which is removed from the surface of molten iron.

Due to the high variability of the proposed method, the present invention allows to control the process depending on the initial parameters of the raw materials and materials and thereby eliminate the dependence of the results on the instability of the qualitative and chemical composition of the charge, as well as the chemical composition and properties of the ligature used.

The method is implemented as follows.

The source cast iron is melted in an IChT-6 induction crucible furnace with a crucible capacity of 6 tons for molten cast iron. After melting, the metal is overheated to 1420 ÷ 1460 ° C. The initial cast iron on average contains carbon 3.75 ÷ 3.85%, silicon 1.8 ÷ 2.2%, manganese 0.4 ÷ 0.55%, chromium 0.1 ÷ 0.15%, phosphorus 0.1 ÷ 0.12%, sulfur 0.041 ÷ 0.08%.

Depending on the percentage of sulfur in the source iron, the primary ligature is introduced in an amount of 0.4 ÷ 1.2% by weight of molten iron. The primary alloy contains 30–40% of rare-earth metals, 30–35% of silicon, 2–5% of aluminum. Due to the noticeable instability of the chemical composition and, therefore, the properties of the ligature, even in the volume of the delivered batch, the calculated amount of the introduced ligature is an indicative value. The ligature is introduced during the period of cast iron drain from the furnace and is fed directly to the stream of cast iron being drained. The estimated amount is loaded into the dispenser and fed to the stream of metal, which ensures uniform in volume of metal and complete assimilation of alloying elements.

The metal poured into the dispensing bucket settles for 4 + 6 min to complete the reaction and to ascend the slag. Then, the surfaced slag is removed from the surface of molten iron, and a sample is taken to fill the sample.

Upon receipt of the structure of vermicular graphite at the fracture of the sample, the metal is poured in portions into pouring ladles. The secondary ligature is introduced in an amount of 0.3 ÷ 1.0% by weight of the metal to the bottom of the casting bucket immediately before the metal is drained into it with a temperature of 1280 ÷ 1400 ° C. The secondary ligature contains 0.5 ÷ 1.0% rare earth metals, 5.5 ÷ 6.5% magnesium, 45 ÷ 55% silicon, up to 1.2% aluminum, 0.3 ÷ 0.5% calcium, up to 0, 3% chromium and up to 0.2% titanium. Together with the secondary ligature, an additional primary ligature is added to the bottom of the casting ladle in an amount of up to 0.5% by weight of the molten metal.

After the secondary modification, the metal settles for 0.5 ÷ 1.0 min, slag is re-removed and the bucket is fed to the mold pouring place.

In the process of pouring primary modified metal from the distribution ladle into pouring ladles to control the survivability of the primary ligature and adjusting the amount of secondary ligature introduced, at least three pouring ladles take samples for pouring control samples until a control structure is obtained of high-strength cast iron with spherical graphite.

The mechanical properties and structure of ductile iron in the production process are constantly monitored by the specialists of the plant. Samples for controlling mechanical properties are cast from each transfer bucket, and test results are recorded.

The operational properties of the products manufactured according to the described method correspond to the characteristics of products from high-quality high-strength cast iron.

Using the proposed method allows to achieve practical stability of the process of producing high-strength cast iron with spherical and vermicular graphite while reducing costs due to the use of non-uniform cast iron scrap as a charge, as well as minimizing rejects due to mismatch with the required grade of cast iron.

Claims (3)

1. A method of producing high-strength cast iron from source cast iron with a sulfur content above 0.04%, including melting the charge in the melting unit, raising the melt temperature to 1420-1460 ° C, first modifying it with a ligature containing rare earth metals and silicon to obtain cast iron in the structure vermicular graphite at the fracture of the control sample and secondary modification, characterized in that the ligature during the initial modification is uniformly fed to the metal stream through the dispenser when the metal is drained into the transfer bucket, and during secondary modification together with the secondary ligature, primary ligature is additionally added to the molten iron in an amount of up to 0.5% by weight of molten iron with their laying on the bottom of the ladle to produce cast iron with spherical graphite. 2. The method according to claim 1, characterized in that a preliminary estimated calculation of the amount of primary ligature is based on the sulfur content in the source iron. 3. The method according to claim 1, characterized in that after the primary and secondary modification, the molten iron is maintained for 4–6 min and 0.5–1.0 min, respectively, to float the slag, which is removed from the surface of molten iron.