RU2315815C1 - Method for producing of vermiculate graphite cast-iron - Google Patents

Abstract

FIELD: metallurgy, in particular, manufacture of cast products from cast-iron with vermiculate shape of graphite.

SUBSTANCE: method involves placing modifying admixtures in layers within pocket provided in ladle bottom, with lower layer of admixtures consisting of vermiculating complex readily cooled modifier, middle layer consisting of graphitizing modifier, and upper layer consisting of refining material such as silicon iron alloys comprising rare-earth metals producing oxides upon reaction with metals; introducing modifying admixtures in an amount, by weight of cast-iron: vermiculating complex readily cooled modifier 0.4-2.0%; graphitizing modifier 0.1-0.8%; refining material 0.2-0.8%.

EFFECT: high physical and mechanical properties, improved stability of modification process, prolonged retention of modifying effect, and absence of pyroelectric effect.

1 dwg, 2 tbl

Description

The invention relates to metallurgy, in particular to methods for producing high-strength cast iron, and can be used in the mass production of castings from cast iron with a vermicular form of graphite.

Closest to the claimed is a method of producing cast iron with vermicular graphite, including heating the melt in an electric furnace, releasing the melt into the ladle, primary modification of cast iron by introducing additives containing rare earth metals to its bottom, secondary modification of the melt with ferrosilicon. The molten iron is heated in an oven to 1500-1550 ° C, maintained for 10-20 minutes. Before the release of the metal, steel trim and ferrotitanium are additionally planted on the bottom of the bucket in an amount that ensures that residual titanium content of 0.07-0.1 wt.% Is obtained in cast iron (patent RU 2188240, С21С 1/10). The disadvantages of this method for the production of cast iron include high overheating of the melt in an electric furnace (up to 1500-1550 ° C) and the necessity of holding the melt at this temperature for 10-20 minutes, which leads to increased carbon fumes. The effect of modification lasts no more than 15-16 minutes. Cast iron obtained by this method has low mechanical characteristics (tensile strength, elongation, etc.).

The present invention is directed to creating a method for producing cast iron with high physicomechanical properties, characterized by increased stability of the modification process, to increase the retention time of the modification effect, to reduce the expendable characteristics of the modifiers and the temperature of the modification.

To solve the tasks, a method for producing cast iron with vermicular graphite is proposed, which includes heating the melt and releasing the melt into the ladle, to the bottom of which modifying additives are introduced. Additives are placed in the pocket of the bottom of the bucket in layers, the lower of which consists of a vermicularizing complex fast-cooled (“chip”) modifier, the middle of the graphitizing modifier, and the upper of refining material, which is used as silicon-iron alloys containing rare-earth metals forming oxides interacting with the metal, and the modifying additives are introduced in an amount: 0.4-2.0% vermicularizing modifier, 0.1-0.8% graphitizing modifier, 0.2-0.8% by weight of refining material talla.

The method for producing cast iron in vermicular graphite is based on the use of a complex rapidly cooled (“chips”) modifier of vermicularizing action together with a graphitizing modifier and refining material. A modification method in the bucket is proposed. Buckets can be used with capacities from 50 kg to 30 tons. A diagram of a method for producing cast iron with vermicular graphite is shown in the drawing. The order of introduction of materials into the bucket: vermicularizing complex modifier, graphitizing modifier, refining material. When filling the bucket with liquid cast iron, initially the interaction occurs with the top layer of the added additives. As the refining material, iron-silicon-based ligatures are used containing rare-earth materials (of the type FSZ0RZM30, FSZ0RZM20, etc.) with a fraction of 0.5-20 mm in an amount of 0.2-0.8% by weight of the metal. As a result of their interaction with the metal, complexes of rare-earth metal oxides are formed in the melt volume, which are deposited on the substrates of the growing graphite phase. Entering refining material below the lower level (less than 0.2%) does not ensure the formation of a sufficient amount of rare earth metal oxides, which are the initiators of the formation of vermicular graphite. Entering refining material above the upper level (more than 0.8%) creates increased melt subcooling, which leads to the formation of complex carbides.

Further dissolution of the graphitizing modifier ensures the creation of the required number of graphitization centers, which reduces the supercooling created by the vermicularizing modifier. The consumption of graphitizing modifier in the range of 0.1-0.8%. Below the lower level (0.1%), with fluctuations in the chemical composition of the original cast iron and increasing additives of a vermicularizing modifier, carbides may form. Above the upper level (0.8%), the effect of graphitizing treatment is not enhanced.

A vermicularizing modifier in an amount of 0.4-2.0%, dissolving in cast iron, forms a vermicular graphite skeleton based on graphitization centers with oxide complexes of rare-earth metals, which ensures the stability of the process. Entering a vermicularizing modifier below the lower level (0.4%) does not ensure the formation of a vermicular graphite skeleton in the entire volume of cast iron, which is unacceptable. The amount of vermicularizing modifier above the upper level (2.0%) promotes the formation of graphite in the form of spherical inclusions and causes a tendency to form carbides.

The sequence of dissolution of the introduced additives ensures the stable formation of vermicular graphite in a wide temperature range of the initial cast iron: from 1170 to 1600 ° C.

The difference of the proposed method for the production of castings from iron ore is to create in the volume of processed liquid iron oxide compounds (oxides and oxysulfides) of rare-earth metals, which, precipitating on graphite inclusions under the action of a vermicularizing modifier, create conditions for the stable formation of vermicular graphite in cast iron.

The proposed method for the production of castings from cast iron with vermicularizing graphite can be used in the melting of the original (base) cast iron in arc, induction furnaces, cupola furnaces (coke oven and gas), as well as in any combination of duplex processes.

The consumable characteristics of the materials used (vermicularizing modifier, refining material, graphitizing modifier) are determined based on the content of impurities (sulfur, oxygen) in the source (base) cast iron. The time to save the effect of vermicularizing modification with this method is provided for 30 minutes from the time of filling the bucket until the end of pouring forms. Table 1 presents the optimal flow characteristics of the modifiers.

Reagents are placed in the “pocket” of the bucket, formed by a transverse partition of refractory material (brick). The release of metal (cast iron) is carried out in such a way that the "pocket" with the reagents is closer to the melting unit, then a stream of metal will fall on the wall of the ladle, and a column of molten iron will smoothly "cover" the modifiers.

The proposed method is characterized by the absence of pyroelectric effect, metal splash, stable results, simplicity and reliability. Table 2 presents the results of experimental swimming trunks of the proposed method and the prototype.

Table 1 No.
p / p Sulfur content in base cast iron,% Vermiculizing modifier Vermicularisation expense. modifier,% Refining Modifier Refining modifier consumption,% Graphitizing modifier Graphitizing modifier consumption,% one Up to 0.02 Chip modifier 0.4-0.6 FS30RZM30 0.2 FS75 0.1-0.3 2 0.02-0.04 Chip modifier 0.7-0.9 FS30RZM30 0.3 FS75 0.2-0.4 3 0.04-0.06 Chip modifier 1.0-1.2 FS30RZM30 0.5 FS75 0.3-0.5 four 0.06-0.08 Chip modifier 1.3-1.7 FS30RZM30 0.6 FS75 0.4-0.6 5 More than 0.08 Chip modifier 1.8-2.0 FS30RZM30 0.8 FS75 0.6-0.8

table 2 Option No. Sulfur content in the outcome. cast iron Vermicularisation expense. modifier, wt.% The required temperature for obtaining chvg, ° C Retention time of the effect of modifications., Min Tensile Strength, MPa Relative extension, % one 0.01 0.4 From 1170 thirty 450 2.0 2 0.02 0.6 From 1170 thirty 450 2.0 3 0,03 0.8 From 1170 thirty 440 2.2 four 0.04 1,0 From 1170 thirty 440 2.2 5 0.05 1,1 From 1170 thirty 430 2,8 6 0.06 1.3 From 1170 thirty 430 2,8 7 (prototype) 0.02 0.7 From 1500 fifteen 425 0.8 8 (prototype) 0,03 1,0 From 1500 fifteen 410 1,0 9 (prototype) 0.04 1,5 From 1500 fifteen 400 1,5

Claims (1)

A method of producing cast iron with vermicular graphite, including heating the cast iron melt, pouring the melt into a ladle, to the bottom of which modifying additives are introduced, characterized in that the modifying additives are placed in layers on the bottom of the bucket, the lower of which consists of a vermicularizing complex, rapidly cooled modifier, the middle of which graphitizing modifier, the upper one is made of refining material, which is used as iron-silicon alloys containing rare-earth metals, which form oxides with a melt, and the modifying additives are introduced in an amount by weight of the melt: vermicularizing complex quick-cooled modifier - 0.4-2.0%, graphitizing modifier - 0.1-0.8%, refining material - 0.2-0, 8%.