RU2074786C1 - Method to produce high-strength pig-iron with ball-shaped form of graphite - Google Patents

Abstract

FIELD: metallurgy, production of mainly high-strength pig-irons with ball-shaped form of graphite. SUBSTANCE: pig-iron spray running in discharge canal of brick-lined chute during discharge from smelting aggregate or during moulds casting is treated with vapors of magnesium, that is formed during contact with surface of longitudinal rib of stripe insert of magnesium bearing modifier located in body of chute discharge canal. As a version, metal magnesium or magnesium-silicon alloy is used as magnesium-bearing modifier. EFFECT: improved process. 3 cl, 1 dwg

Description

 The invention relates to the field of metallurgy, mainly for the production of high-strength grades of cast iron with spherical shape of graphite, as well as during the desulfurization of any alloys in the process of draining them from smelting units or pouring molds. In both cases, the issues remain relevant and require their correct solution.

 As far back as 1947, it was found that even if a small amount of metallic magnesium is introduced into liquid cast iron, it immediately turns from ordinary gray with lamellar graphite to high-strength cast iron with spherical graphite, not inferior in quality to the quality of structural steels in its mechanical and plastic properties, and in antifriction non-ferrous alloys intended for use in friction units. It would seem that the eternal dream has come true for people of science and practice: using a convenient and cheap melting unit, such as a cupola, for smelting, to obtain material from it with the strength properties of steel, and with technological qualities for casting, like gray cast iron. From the newly discovered material there was a real opportunity with large technical and economic effect to produce blanks previously made only from steel, malleable cast iron, bronze and from antifriction alloys. The use of magnesium cast iron can reduce the weight of cast iron castings and increase their performance by increasing their strength and ductility.

For almost 50 years, it has been proven that high-strength cast iron is a full-fledged substitute for not only steel casting and rolling, but even expensive forgings in various engineering industries. All this taken together caused industry a great interest in the new material, bearing in mind the presence in nature of a sufficient amount of raw materials for the production of magnesium itself. But from the very beginning of the work, great difficulties were revealed related to the introduction of magnesium into molten iron. Having a melting point of only 621 ^o С and a boiling point of 1102 ^o С when cast iron is introduced into the melt, magnesium instantly turns into steam, accompanied by rapid boiling of the metal with catastrophic emissions of it from the ladle. The free ejection of vapors and metal particles outside does not give the desired effect of saturation of cast iron with magnesium, and it is not uncommon for the mechanical and plastic properties of cast iron to become unstable, even with the same amount of introduced magnesium and with the same charge. This disadvantage is further enhanced by the fact that, with intensive vaporization, in all cases, channels are created in liquid cast iron through which magnesium vapor rises to the surface at a high speed and is very poorly absorbed by the metal due to insufficient volume contact. Magnesium vapors, when combined with atmospheric oxygen, form a blindingly bright flame and a large amount of white smoke (magnesium oxide), which is an inconvenience and even a considerable danger to maintenance personnel. To keep these and other shortcomings to a minimum, from the very beginning, an intensive search was begun to improve the technology. However, after 13 years of experience in the production of high-strength cast iron, relying on their own research, having studied domestic and foreign literature in the amount of 536 sources, Vashchenko and Safroni had to recognize the need "to continue hard work to improve the technology for obtaining and expanding the areas of application of this promising material." And 22 years later, in 1982, in the generalized work "High-quality cast iron for castings" (M. Mashinostroenie, 1982), a group of authors edited by Dr. N.N. Aleksandrov, also relying on their own experience and with reference to 93 literary sources, we concluded that the decision to produce high-quality high-strength cast iron by this time depended entirely on "further improving the technology for producing high-strength cast iron." Unfortunately, we have to admit that the tasks set have remained unfulfilled to this day. This is confirmed by the data of its production, which is only less than 1% of the total production of castings in the CIS countries per year. Magnesium is not used at all for the desulphurization of cast iron and steel. This unsatisfactory position may continue in the future, if you do not make a radical change in the technology of processing molten iron with magnesium. Attempts were made, dozens of different equipment designs and methods were proposed. Among them is a method for treating cast iron with magnesium rods without facing directly on the trough of cupola cupboards or by bus. St. N 104269 from 09.26.56. The specified method is intended for the continuous production of high-strength cast iron in the stream when it is recruited into casting ladles. However, practice has shown that the mechanization of the supply of bars and the design of the pocket itself has several disadvantages. Continuous supply of rods requires the use of a complex machine, and its passage through a graphite sleeve causes an increase in the through hole with the ingress of liquid metal into the gap formed. But the most important thing is that without a protective shell the possibility of immersion of the bar in the deep layers of the metal is excluded.

 Later, in 1981, a group of authors received certificates N 836114 for "Device for processing molten iron in a stream of magnesium" and N 863653 for "Method for continuous processing of molten iron with magnesium", consisting of funnels with tangential inlets of metal and drain water-cooled metal pipelines.

 Over the past 12 years from the date of issue of copyright certificates, these devices have not received any practical application.

 The main reasons for this phenomenon were the difficulties in manufacturing the water-cooled magnesium cartridge itself, which is associated with pouring magnesium melt into its casing, organizing the supply and removal of water directly to the molding areas with danger during operation during cooling of the casing.

 Equally important for the quality of ductile iron is the fact that air and slag get into the metal and are sucked in by the vortex flow from the rotation of the jet. The accelerated metal flow under the recess of the funnel quickly carries along with the slag and air the formed magnesium vapor along the axis, preventing the magnesium vapor from processing the incoming metal into the funnel.

 In addition, the supply of molten iron through a straight and single channel in the center of the cartridge creates such conditions when the passing stream practically does not have enough time to saturate the metal with magnesium. This is greatly facilitated by the fact that in the very first seconds the diameter of the channel expands, the jet moves away from the walls, which means that the very important process of heat transfer between directly contacting parts of the body completely terminates the thermal conductivity. After this, only less effective laws of heat transfer, convective and thermal radiation, begin to apply, which in this case is completely insufficient. The specified drawback was erroneously repeated in the application for the invention of November 15, 90 g N 4883094 / 02.110481 "Method for producing high-strength cast iron with spherical shape of graphite."

 Repeated tests have convinced that the supply of metal through a direct center channel cannot provide stable results on the absorption of magnesium.

 To eliminate these shortcomings, application No. 93034183 was submitted on 1.07.93 for “A method for producing high-strength cast iron with spherical graphite form” also in the stream, but with the help of vapors obtained from magnesium in the form of a fraction or powder located in the cavity of a steel tube entering in the metal receiver. However, it should be noted that, despite the presence of indisputable advantages, this method remains time-consuming and expensive, which is caused by the preparation of the shot, laying it in the tube and using a special feeding mechanism.

 In concluding a brief review of the existing methods for the production of ductile iron, one cannot but emphasize that they turn out to have great disadvantages: lowering the temperature of the metal being treated, increased consumption of magnesium, and the use of special equipment and devices. The imperfection of the ways of saturation of cast iron with magnesium is indicated by the very fact of the existence of numerous technological methods used in production for this.

 The invention proposes, while maintaining the processing of a jet of cast iron in a stream at the root, to change the nature of the production of magnesium vapor. For this, it is planned to use a strip billet of standard metallic magnesium or its alloys with silicon 15-20 mm thick, 85,100 mm wide and a length depending on the required weight of 0.09 0.1 of the weight of the treated volume of molten iron. The thickness will vary depending on the silicon content in the ligature. The strip blank can be obtained by extruding, rolling, casting or cutting standard ingots into plates.

 The essence of the method lies in the fact that high-strength spheroidal graphite cast iron is obtained directly when the jet flows through the chute by treating it with magnesium vapor, which is formed as a result of the contact of liquid cast iron with the surface along the entire length of the strip billet. For this, a strip blank in the form of a whole piece or cut into parts is laid in the body of rod blocks made of mixtures on liquid glass or using other known fasteners. After drying and painting, the rods are placed in the body of the gutter as a lining so that the surface of one of the ribs remains bare along the entire length and serves as the bottom of the channel of the gutter, and all other surfaces of the workpiece are covered with a rod mass.

 The gutter can be attached to the main, in the case of a set of metal from the melting units in the ladle, or to the casting bowl with direct pouring of molds.

 In any case, it should consist, as can be seen from the drawing, of the housing 1 and the cover 2, made of steel sheet, of the core blocks 3, with the strip blanks 4 made of magnesium or its ligature with silicon embedded in the lining.

 The method of producing ductile iron by the proposed method is very simple and does not require any equipment.

 Its essence lies in the fact that the flowing stream along the entire length of the strip billet is exposed to magnesium vapor and, bathing in them, turns from gray plate to cast iron with spherical graphite. The process goes on stream and continues until the pouring of metal into the bucket or into the mold stops.

 With a new portion of cast iron to be treated with magnesium vapor, another trough is placed, and the used one will be in reserve.

 The developed method is completely safe, simple, does not require any capital costs, there is no temperature loss, magnesium consumption is reduced by 2 3 times, the quality of the metal is sharply improved.

Claims (3)

 1. A method of producing high-strength cast iron with spherical shape of graphite, including processing in a stream of cast iron flowing through the drain channel of the lined chute when cast iron is drained from the smelter or mold is poured by contacting the surface of a strip insert from a modifier located in the lining body of the drain channel of the chute with the exit of the bare surface to the bottom of the drain channel of the trough, characterized in that the treatment is carried out by magnesium vapor, formed upon contact of molten iron with a longitudinal surface the second rib of the strip insert of a magnesium-containing modifier.  2. The method according to claim 1, characterized in that the treatment is carried out with magnesium vapors formed upon contact of molten iron with the surface of the longitudinal rib of the magnesium metal insert.  3. The method according to claim 1, characterized in that the treatment is carried out by magnesium vapors formed upon contact of molten iron with the surface of the longitudinal rib of the magnesium-silicon alloy insert.