RU2110582C1 - Method for producing spherulitic iron from cupola iron with melt temperature below 1300 c - Google Patents

Abstract

FIELD: metallurgy; treatment of industrial low-temperature (below 1300 C) cupola iron melts by PPM process, in particular, in mass casting of medium ingot molds. SUBSTANCE: spheroidizing treatment of melt is carried out by two-stage procedure. At the first stage, introduced onto cupola runner is calculated amount of magnesium-calcium-containing powder wire inoculant in the form of dimension ends, and at the second stage, inoculant is introduced into riser of gating system of casting mold in the course of its assembly. EFFECT: simplified and low-cost process of spherulitic iron production. 1 tbl

Description

The invention relates to methods for processing industrial low-temperature (below 1300 ^o C) melts of cast iron cupola melts spheroidizing magnesium-calcium-containing flux-cored wire modifiers.

 In the production of nodular cast iron castings, a large number of spheroidizing graphite processing methods are used. All of them provide for the introduction of magnesium into the cast iron melt in the form of metal, alloys with elements carriers of chemical compounds. The method of smelting cast iron is a determining factor in the choice of the method of spheroidizing graphite treatment, however, in all methods of production of spheroidal graphite iron, there are distinguished: pre-spheroidizing inoculation, spheroidization, post-spheroidizing inoculation, as independent components of the modification process.

A known method of producing cast iron with spherical graphite and a device for its implementation [1]. The method involves introducing iron-silicon-magnesium-containing alloys into the molten iron of cupola melting, passing the melt through a confuser mixer, and then pouring the melt into the ladle. The pre-spheroidizing treatment is carried out together with spheroidization when passing the melt through a confuser mixer, where calcium carbide powder is introduced, and screening of silicon-magnesium-containing ligatures. The use of a magnesium-containing ligature as a spheroidizing agent allows for a more relaxed introduction of magnesium into the molten iron, and reduction of dust and gas emission during modification. The disadvantages of the method include:
passing the melt through a confuser mixer, additional overheating of the melt to 1450-1500 ^o C, blowing it with oxygen leads to the extinction of the effect of spheroidization and inoculation, which reduces the degree of absorption of magnesium by molten cast iron and reduces the content of spherical graphite in castings;
the need to use additional equipment for the preparation and introduction of spheroidizing additives.

 A known method of producing high-strength cast iron, including the processing of molten cast iron in the reaction chamber of the casting mold with a magnesium alloy and ferrosilicon [2]. The method is a special case of the Inmold process, an intra-mold processing process, and involves the combined spheroidizing and post-spheroidizing and post-spheroidizing treatment of cast iron melt in the process of pouring metal into a mold. The method has the following advantages: the absence of smoke and glow, a high (up to 80%) degree of absorption of magnesium, the absence of the disappearance of the effect of spheroidization and inoculation.

The disadvantages of the method include:
the method is effective only for low-sulfur cast iron and requires a uniform dissolution rate of the granular spheroidizer and inoculator, which is fraught with unstable absorption of magnesium by the molten iron;
the use of the reaction chamber requires thorough preparation (accuracy, etc.);
getting into the casting in the form of slag inclusions of insoluble particles of a spheroidizer and inoculator, as well as products of chemical modification reactions;
2-3% reduction in removal of castings from the mold due to the installation of the reaction chamber of the gate system.

Being close in technical essence to the proposed solution, there is a method for introducing easily evaporating modifiers into liquid Alazene cast iron [3]. The method is a special case of the Sandwich Process — placing a magnesium-containing spheroidizer in the bottom of the lined bucket and applying a coating material to the entire open surface of the spheroidizer and provides for the combination of the pre-spheroidizing, spheroidizing and post-spheroidizing processing of a low-temperature (below 1300 ^o C) melting melter the bucket. The essence of the method is to apply a lightweight coating material in the form of a dry heat-insulating mixture of crushed coke or graphite and expanded perlite to the surface of the crushed magnesium-containing ligature, previously loaded onto the bottom of an open casting ladle before pouring melt into it and onto a mirror of processed cast iron after the formation of a continuous layer of metal over a metal modulator. In this case, crushed coke or graphite plays the role of a pre-spherodizing additive, and when applied with a mixture of perlite swelling onto a mirror of a cast iron melt treated with a magnesium alloy, it provides a heat-insulating and post-spheroidizing effect.

 Using this method allows you to process spheroidizers melt cast iron cupola melting without additional overheating of the metal. The method is characterized by relative simplicity and technological flexibility.

The main disadvantages of the method include:
significant smoke emission, luminescence and metal emissions;
unstable absorption of magnesium cast iron by a melt;
limiting the effect of spheroidization and inoculation due to the length of the period between the release of metal from the cupola and pouring it into the mold;
the need to use additional equipment for the preparation and input of the modifier;
the need for thorough cleaning of the casting ladles from slag to prevent it from falling into the castings.

The objective of the proposed solution is to develop a method for producing spheroidal graphite iron for mass production of medium molds during the processing of industrial low-temperature (below 1300 ^o C) melts of cupola iron castings with spheroidizing magnesium-calcium-containing flux-cored wire modifiers, which allows to significantly simplify and reduce the cost of modifying to create safe and environmentally friendly working conditions.

This problem is solved by the fact that a technology for processing low-temperature melts of cupola iron with spheroidizing and inoculating magnesium-calcium-containing flux-cored flux-cored wire modifiers according to a two-stage scheme is proposed. The essence of the proposed method is as follows: the operation of spheroidization of graphite of the treated cast iron is carried out together with pre-spheroidization inoculation on the cupola of the cupola (the first stage) and with post-spheroidization inoculation in the riser of the gating system of the casting mold (second stage), using flux-cored wire as a spheroidizing and inoculating additive from a metal shell and magnesium-calcium-containing filler, which allows to completely exclude ladle processing of metal, thereby minimize the time between the release of the metal and its pouring into molds at a minimum temperature difference of the melt: 1260-1300 ^o C at release, 1190-1220 ^o C during pouring.

 The first stage of metal processing, given that the low-temperature molten iron is kept in the cupola for a short time, is produced on the cupola of the cupola when it is discharged into an open rotary casting ladle. For this, the estimated amount of additives in the form of measured ends of magnesium-calcium containing wire is placed in a special recess in the lining of the gutter (before the metal is released), which is then closed with a protective screen. The gradual dissolution of the protective steel shell in contact with the molten iron prevents intense burning of the filler and ensures a smooth entry with the subsequent absorption of metal when filling the bucket. The design of the screen protects the working area from the glow and ejection of metal, removes the resulting smoke "under the umbrella."

The second stage of melt processing involves the introduction of the calculated amount of magnesium-calcium-containing wire in the form of measuring ends in the risers of the gating systems of casting molds at the stage of their assembly. The molten cast iron processed at the trough with a temperature of 1200 ^o C, dissolving the protective shell, is in contact with the filler in the risers of the gate systems with the gradual assimilation of magnesium by the metal when filling the casting molds.

 The main practical effect of exposure to magnesium-containing spheroidizers is a sharp increase in the strength and plastic forms of cast iron due to the transition of the form of inclusions from lamellar to spherical. The spherical form of graphite is associated with a high and stable concentration of magnesium in it. With a decrease in the concentration of magnesium in graphite, its compactness decreases. The concentration of magnesium required for spheroidization is ensured by its two-stage introduction into the cast iron stream with sufficiently developed turbulence, which ensures dissolution and uniform mixing throughout the melt volume.

 The introduction of calcium into the melt allows you to adjust the intensity of the interaction of magnesium with molten iron. The reaction rate in this case slows down while increasing the absorption of magnesium. The presence of calcium improves nucleation (inoculation), improves the shape of graphite, and increases the number of inclusions of spherical graphite per unit volume of cast iron.

High (95%) magnesium content in the wire allows to reduce the consumption of a spheroidizer per ton of melt from 150-180 kg (prototype) to 20-22 kg (in terms of 100% magnesium). The processing of the melt on the trough and in the mold does not inhibit the casting process, which allows the treatment of cupola cast irons with a melt temperature below 1300 ^o C with a significant reduction in the dust and metal emission.

 The implementation of the method is simple and cheap. The higher price of the flux-cored wire modifier compared to the cost of the ligatures is compensated by its low consumption, there is no need for preparation equipment and, in view of the spheroidizer, the service life of casting ladles is increased.

 Execution example. The method was tested in the conditions of the iron foundry of the Vyksa Metallurgical Plant when casting molds weighing 4.5 tons in accordance with TU-14-12-14-71, TI 153-L-88-96 "Smelting cast iron in a cupola" and STP 153-03 -84. 10 swimming trunks were proposed. As a cupola mixture, limiting cast iron was used according to GOST 805-80 with a content, wt.%: Silicon 0.5-1.2, manganese 0.3-1.0, chromium less than 0.1. As a spheroidizing agent, a flux-cored wire modifier was used with a content, wt.%: Magnesium 95, calcium 2.0. The input of the modifier was carried out on the cupola of the cupola with the release of cast iron and the risers of the gate systems of casting molds. For this, the calculated amount of the modifier in the form of measuring ends was placed before the metal was released into special grooves made in the lining of the gutter and covered with a protective screen, and the other part of the modifier, also in the form of measuring ends of the wire, was introduced into the risers of the gating systems of the casting molds at the stage of their assembly .

The produced cast iron with a melt temperature of 1260–1300 ^o C, flowing down the cupola chute to an open casting ladle with a capacity of 5 tons, was treated with a modifier on the chute with the assimilation of spheroidizing elements when filling the bucket. Processed at the stage of production, the melt with a temperature of 1190-1200 ^o C was poured into casting molds, where it was processed a second time. The contact of liquid metal with the modifier occurred in the risers of the gate systems with the assimilation of spheroidizing elements when filling the mold.

 At the same time, the treatment of cast iron by cupola melting was carried out according to the prototype with the FS50Mr5 modifier with a magnesium content of 4.5%.

 Data on the conditions of modification and durability of the molds are given in the table. The results obtained indicate the effectiveness of the method, which allows to obtain almost 100% spherical graphite content over the entire volume of castings, which significantly affects the strength and operational characteristics of the molds. Reducing the consumption of modifier while increasing the degree of assimilation by the molten magnesium reduces the cost of cast iron processing technology and makes it safer and more environmentally friendly.

Claims (1)

A method of producing spheroidal graphite cast iron from cupola melting cast iron with a melt temperature below 1300 ^° C, including cast iron melting, discharge into an open casting ladle, spheroidizing a melt with magnesium-calcium-containing flux-cored wire modifier, and pouring metal into molds, characterized in that the spheroidizing treatment lead according to a two-stage scheme, introducing the estimated amount of magnesium-calcium-containing flux-cored wire modifier in the form of measuring ends on the cupola of the cupola in the first stage and in riser of the gating system of the mold during its assembly on the second.

Images