JP2006316331A - Graphite-spheroidizing treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To add Mg into molten cast iron in high yield when the molten cast iron for ductile casting is smelted by adding an iron-coated Mg wire into the molten cast iron by a wire-feeder method and subjecting graphite to spheroidizing treatment. <P>SOLUTION: When the graphite in the molten cast iron is subjected to the spheroidizing treatment by supplying the iron-coated Mg wire 14 coated with a coating material composed of a steel sheet or a steel pipe into the molten cast iron from the upper part, the supplying speed of the iron-coated Mg wire into the molten cast iron is adjusted according to the bath depth of the molten cast iron and the thickness of the coated material so that the melting position in the molten cast iron of the coated material becomes the depth of ≥1/2 of the bath depth (L) of the molten cast iron. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention adds an iron-coated Mg wire formed by coating a molten Mg or Mg alloy with a steel plate or steel pipe to a molten cast iron melted in a melting furnace or the like, thereby spheroidizing the graphite in the molten cast iron. The present invention relates to a graphite spheroidizing method.

  Ductile casts such as ductile cast iron pipes have the same tensile strength as steel materials, and their mechanical test values such as elongation and toughness are more than ten times that of ordinary cast irons. Therefore, it is widely used in various piping materials under more severe environments such as underground pipes that require these characteristics.

  This ductile casting is made by adding an Mg alloy such as metal Mg or Fe-Si-Mg alloy as a graphite spheronizing agent to molten cast iron melted by a melting furnace such as a cupola or an electric furnace using iron scrap as a main iron source material. , C: 3-4% by mass (hereinafter referred to as “%”), Si: 2-3%, Mn: 0.2-0.5%, Mg: 0.01-0.06% It is manufactured by melting molten cast iron for casting and casting it with a casting facility such as a centrifugal casting machine (see, for example, Patent Document 1).

  Since Mg has a low boiling point (1103 ° C.) and a high vapor pressure in the temperature range of molten cast iron, it is inherently difficult to dissolve in molten cast iron. Various additions such as the pouring method, the ladle addition method with a lid, the plunger method, the pressure addition method, the wire feeder method, etc. as a method for adding metal Mg or Mg alloy having such properties to molten cast iron with a high addition yield The method is implemented (for example, refer nonpatent literature 1). All of these are addition methods that increase the pressure of the atmosphere in which the metal Mg or Mg alloy dissolves and reduce the loss of Mg gas.

  Among these, in the wire feeder method, metal-coated Mg or Mg alloy is used as a core material, and iron-coated Mg wire obtained by coating and molding the core material with a coating material such as a steel plate or a steel pipe is supplied into the molten cast iron. After the core melts, the core material and the molten cast iron come into contact with each other, so that metal Mg or an Mg alloy is added to the molten cast iron. Therefore, in the wire feeder method, by controlling the length of the supplied iron-coated Mg wire, the amount of added metal Mg or Mg alloy can be controlled, and the length of the supplied iron-coated Mg wire is Since it is automatically measured by a pinch roll or a measure roll that supplies iron-coated Mg wire, there is a merit that work addition is greatly reduced as compared with the other addition methods described above. In other words, by applying the wire feeder method, it becomes possible to unmanned the graphite spheroidization process very easily.

  However, in the past, when melting molten iron for ductile castings, there is an example using the wire feeder method (see, for example, Patent Document 2), but it is possible to add iron-coated Mg wire with a high addition yield. There is no example that proposed a new addition method.

JP-A-6-246415 JP 2004-238664 A Revised 4th edition casting manual, Japan Foundry Association, published on January 20, 1986, p. 560-565

  The present invention has been made in view of the above circumstances, and its object is to add an iron-coated Mg wire formed by coating a metal Mg or Mg alloy with a steel plate or steel pipe to a molten cast iron by a wire feeder method. Then, it is intended to provide a graphite spheronization method that can add Mg into molten cast iron at a high yield when spheroidizing graphite to melt molten cast iron for ductile castings.

  The present inventors have conducted intensive research and examinations in order to solve the above problems. As a result, the time when the coating material of the iron-coated Mg wire supplied into the molten cast iron is melted is set to a depth position of 1/2 or more of the bath depth of the molten cast iron, and the core material of the iron-coated Mg wire and the molten cast iron As a result of this contact, the static pressure of the molten cast iron contributed to suppress the generation of Mg gas, and it was found that Mg can be added with a high yield.

  Further, the dissolution time of the coating material can be uniquely determined from the thickness of the coating material, and it is always possible to cover the coating material by setting it to a predetermined supply rate or more determined according to the bath depth of the molten cast iron and the thickness of the coating material. The knowledge that the melt | dissolution position of a material can be made into the depth position more than 1/2 of bath depth was acquired.

  The present invention has been made on the basis of the above knowledge, and the graphite spheroidizing method according to the first invention supplies an iron-coated Mg wire coated with a coating material comprising a steel plate or a steel pipe into molten cast iron from above. Then, when spheroidizing the graphite in the molten cast iron, the molten cast iron bath is such that the melting position of the coating material in the molten cast iron is at a depth of 1/2 or more of the molten cast iron bath depth. The supply speed of the iron-coated Mg wire into the molten cast iron is adjusted according to the depth and the thickness of the coating material.

In the graphite spheroidizing treatment method according to the second invention, in the first invention, when the bath depth of the molten cast iron is L and the thickness of the coating material is t, the iron-coated Mg wire is converted into the following (1 ) Is supplied at a supply rate that is equal to or higher than the supply rate calculated by the equation (1). However, it is (1) In the equation, V _l is the feed rate (mm / sec), L is Yokufuka of (mm), t is the thickness of the coating material (mm).

  According to the present invention, the coating material of the iron-coated Mg wire is left undissolved at least up to a position that is 1/2 the depth of the molten cast iron bath. The molten cast iron is brought into contact with the molten cast iron at a position deeper than half the bath depth, and the static pressure of the molten cast iron acts, so that the generation of Mg gas is suppressed, and Mg can be added to the molten cast iron with a high addition yield. As a result, the amount of metal Mg and Mg alloy, which are extremely expensive, is reduced, the production cost of molten cast iron for ductile castings can be greatly reduced, and industrially beneficial effects are brought about.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic side view of a graphite spheronization treatment facility used in carrying out the graphite spheroidization treatment method according to the present invention.

  As shown in FIG. 1, the graphite spheroidizing treatment equipment 1 is constructed by a steel pedestal 2, and a ladle 15, which is a processing container, is carried in and out of the four corners surrounded by the pedestal 2. A roller table 3 is installed as a conveying means. The roller table 3 is provided with a plurality of rollers 4 which can be rotated by a roller drive motor (not shown) attached to the roller table 3. A concave groove (not shown) is provided on the surface of the roller 4, and a pair of rails 16 are installed on the bottom surface of the ladle 15. 4 is supported by the roller table 3 in a state of being placed in the concave groove 4, and moves on the roller 4 as the roller 4 rotates.

  A lid 5 for covering the upper opening of the ladle 15 is disposed immediately above the ladle 15 that has been carried to the predetermined position of the graphite spheroidizing treatment facility 1 by the roller table 3. The lid 5 is connected to the chain 7, the other end of the chain 7 is connected to the lid lifting device 6, and the lid 5 moves up and down via the chain 7 that is wound up or down by the lid lifting device 6. 15 upper openings are covered. A plurality of chains 7 are arranged, and each chain 7 is independently connected to the lid lifting device 6. The lid lifting device 6 is driven by an electric motor (not shown).

  Further, a linear guide pipe 8 is attached to the gantry 2 at a predetermined position above the ladle 15 so as to face in a vertical direction with respect to the bath surface of the molten cast iron 17 accommodated in the ladle 15. The guide pipe 8 passes through the lid 5, and a gap is provided between the lid 5 and the guide pipe 8 so that the lid 5 can sufficiently move up and down. A pair of pinches provided with a function of sandwiching the iron-coated Mg wire 14 between the opposing rolls and supplying the iron-coated Mg wire 14 by being rotated by an electric motor (not shown) on the upper side of the guide pipe 8. A roll 9 is installed. A plurality (four in FIG. 1) of guide rolls 11 are attached to the gantry 2 by the attachment jig 12. In this case, the pinch roll 9 and the plurality of guide rolls 11 are arranged along a circumference of a predetermined radius centered on a certain point (P in FIG. 1), and the upper end of the guide pipe 8 The pinch roll 9 and the plurality of guide rolls 11 form an arc-like (substantially semicircular in this case) wire supply path 10. The axial direction of the guide pipe 8 is arranged so as to coincide with the tangential direction of the arcuate wire supply path 10. Further, at a position away from the ladle 15, a wire holding base 13 for placing an iron-coated Mg wire 14a wound in a coil shape is provided.

  That is, the coiled iron-coated Mg wire 14a placed on the wire holding base 13 is sandwiched between the opposing pinch rolls 9 and rewound to form a linear iron-coated Mg wire 14, which has an arc shape. It is supplied to the molten cast iron 17 accommodated in the ladle 15 through the wire supply path 10 and the guide pipe 8. In this graphite spheroidizing treatment equipment 1, it is possible to supply two iron-coated Mg wires 14 at the same time. Therefore, the guide pipe 8, the pair of pinch rolls 9, the arc-shaped wire supply path 10, and the wire holding Although the bases 13 are independently arranged one by one, FIG. 1 shows only one of them. The supply amount of the iron-coated Mg wire 14 is automatically measured by the pinch roll 9, and the measurement result is output to a control panel (not shown).

  As shown in the schematic cross-sectional view of FIG. 2, the iron-coated Mg wire 14 is made of metal Mg, Fe—Si—Mg alloy, Fe—Si—Mg—RE (rare earth element) alloy, Fe—Si—Mg—. This is a clad wire material in which an Mg alloy such as a RE—Ca alloy or Ni—Mg alloy is used as a core material 18, and this core material 18 is coated and molded with a thin steel plate or a thin steel tube as a coating material 19. The coiled iron-coated Mg wire 14a does not need to be wound around a drum or the like, and may be simply placed on the wire holding base 13 as shown in FIG.

  A graphite spheroidizing method for molten cast iron for ductile casting using the graphite spheroidizing treatment facility 1 having such a configuration will be described below.

  Using an iron source such as iron scrap or pig iron and a carbonaceous material such as coke as raw materials, it is melted in a melting furnace such as a cupola or an electric furnace, and further desulfurized to melt molten cast iron 17 as necessary. The produced molten cast iron 17 is poured into the ladle 15. And the ladle 15 which accommodated the molten cast iron 17 is conveyed to the graphite spheroidization processing equipment 1 by suitable conveyance means, such as a crane and a conveyance cart, and the ladle 15 is mounted on the roller table 3. The embodiment shown in FIG. 1 is an example in which the ladle 15 is transported to the graphite spheroidizing treatment facility 1 using a transport cart, but the transport cart facing the roller table 3 is omitted in FIG.

  When the roller table 3 is operated and the ladle 15 is carried over the roller table 3 to a predetermined position, the ladle 15 is fixed on the roller table 3 by a stopper (not shown), and the lid lifting device 6 is moved. The lid 5 is lowered by driving, and the upper opening of the ladle 15 is covered with the lid 5. Next, the pinch roll 9 is driven at a predetermined rotational speed, and the iron-coated Mg wire 14 is supplied to the pan 15. The supply amount of the iron-coated Mg wire 14 is automatically measured from the rotational speed of the pinch roll 9.

  In this case, in order to prevent the covering material 19 of the iron-coated Mg wire 14 from melting until it reaches at least a half depth position of the bath depth (L) of the molten cast iron 17, a bath of the molten cast iron 17 is used. Depending on the depth (L) and the thickness of the covering material 19, the supply speed of the iron-coated Mg wire 14, that is, the rotational speed of the pinch roll 9 is adjusted. Specifically, it can be carried out as follows.

  FIG. 3 shows that the inventors changed the thickness of the covering material 19 and required the melting time of the covering material 19, that is, until the room temperature covering material 19 is melted after being immersed in the molten cast iron 17 at 1445 ° C. Is a result obtained by heat transfer calculation. As shown in FIG. 3, it was found that the dissolution time becomes longer as the thickness of the covering material 19 increases, and the dissolution time can be approximated by the following equation (2). In the equation (2), T is the dissolution time (second), and t is the thickness (mm) of the covering material 19.

  The inventors of the present invention instantaneously immerse the iron-coated Mg wire 14 at room temperature in the molten cast iron 17, and evaporate Mg as a core material of the iron-coated Mg wire 14 to emit light on the surface of the molten cast iron 17. It has been confirmed that the result measured by the high-speed camera and the dissolution time calculated by the equation (2) are in good agreement. Moreover, even if the temperature of the molten cast iron 17 deviates from about 1445 ° C. by about ± 50 ° C., it is confirmed that the melting time of the covering material 19 is expressed by the equation (2).

Therefore, depending on the thickness of the coating material 19 of the iron coating Mg wire 14 to be used and the bath depth (L) of the molten cast iron 17 in the ladle 15 to be used, the melting position of the coating material 19 is 1 bath depth. What is necessary is just to set the supply speed | rate of the iron covering Mg wire 14 so that it may become a depth position more than / 2. Specifically, the supply speed at which the iron-coated Mg wire 14 can be supplied to a depth position of 1/2 or more of the bath depth (L) before the melting time T determined by the thickness of the coating material 19 elapses. In other words, the product of the supply rate and the dissolution time T may be ½ or more of the bath depth (L). That may be supplied at a higher feed rate than the feed rate V _l calculated by the aforementioned equation (1). For example, when the thickness of the covering material 19 is 0.4 mm and the bath depth (L) is 590 mm, it can be seen that the supply speed may be 325 mm / sec (= 19.5 m / min) or more.

If the supply speed of the iron-coated Mg wire 14 is excessively increased, the coating material 19 of the iron-coated Mg wire 14 collides with the bottom surface of the processing container such as the ladle 15 without being dissolved, and the bottom of the processing container Since there is a possibility of damaging the refractory, it is preferable to set an upper limit of the supply rate so that the covering material 19 is dissolved before reaching the bottom surface of the processing container. That is, it is preferable to supply at a supply speed that is equal to or lower than the supply speed V _u calculated from the following equation (3). However, in the formula (3), V _u is the supply rate (mm / second), L is the bath depth (mm), and t is the thickness (mm) of the coating material.

  In this way, the iron-coated Mg wire 14 is supplied to the molten cast iron 17. The molten cast iron 17 accommodated in the ladle 15 is subjected to graphite spheroidization treatment with added Mg, and the molten cast iron 17 is, for example, C: 3-4%, Si: 2-3%, Mn: 0.00. It is melted in molten cast iron for ductile casting containing 2 to 0.5% and Mg: 0.01 to 0.06%.

  When a predetermined amount of iron-coated Mg wire 14 is supplied to the inside of the ladle 15 and the graphite spheroidization treatment with Mg is completed, the pinch roll 9 is stopped, and then the lid lifting device 6 is driven to remove the lid 5. Raise to a predetermined position. Moreover, if the lid | cover 5 and the ladle 15 are isolate | separated, the roller 4 of the roller table 3 will be driven and the ladle 15 will be carried out from the graphite spheroidization processing equipment 1. FIG. Thereafter, the ladle 15 containing the molten cast iron for ductile casting is transported to casting equipment such as a next-stage dehulling equipment and a centrifugal casting machine using appropriate transporting means such as a crane and a transport carriage.

  By subjecting the molten cast iron 17 to the graphite spheroidization treatment in this way, the coating material 19 of the iron-coated Mg wire 14 is dissolved at least up to a position half the depth of the bath depth (L) of the molten cast iron 17. Therefore, the metal Mg or Mg alloy that is the core material 18 comes into contact with the molten cast iron 17 at a position deeper than ½ of the bath depth, and the static pressure of the molten cast iron 17 acts on the Mg gas. Generation | occurrence | production is suppressed and Mg can be added to the molten cast iron 17 with a high addition yield.

  When the iron spheroidizing treatment is performed by adding the iron-coated Mg wire to the molten cast iron accommodated in a ladle having a depth of 1000 mm using the graphite spheroidizing treatment equipment shown in FIG. The relationship between the supply speed and the yield of Mg was investigated by changing the speed. The bath depth of the molten cast iron in the ladle was 590 mm. The iron-coated Mg wire used is an iron-coated Mg wire having an outer diameter of 13 mm, in which an Fe—Si—Mg—R—E—Ca alloy is used as a core material and a steel sheet having a thickness of 0.4 mm is used as a coating material. The supply rate of the iron-coated Mg wire into the molten cast iron was changed to a range of 10 to 34 m / min, and a predetermined amount of iron-coated Mg wire was added.

  The yield of Mg was calculated from the Mg concentration of the cast iron pipe obtained by casting the molten cast iron for ductile casting after the graphite spheroidizing treatment with a centrifugal casting machine and the mass of the added Mg. FIG. 4 shows the relationship between the supply rate of the iron-coated Mg wire and the Mg yield. When the temperature of the molten cast iron at the time of Mg addition is different, a difference in Mg yield occurs, and the relationship between the supply rate of the iron-coated Mg wire and the Mg yield becomes unclear, so the results shown in FIG. Only the result of the operation where the molten cast iron temperature at the time of addition is 1440 to 1449 ° C. is displayed.

  As shown in FIG. 4, as the supply rate of the iron-coated Mg wire increases, the yield of Mg increases. When the supply rate is 20 m / min or more, a high yield of about 45% can be stably obtained. I understood.

The operating conditions, i.e. Yokufuka of the at 590 mm, the condition thickness of the coating material is 0.4 mm, when obtaining the feed rate V _l is substituted into the aforementioned equation (1), 19 as feed rate V _l. A feed rate of 5 m / min is obtained. That is, it can be seen that when the supply speed is 19.5 m / min or more, the dissolution position of the coating material is deeper than the half position of the bath depth.

  As a result of comparing the result of the formula (1) by the heat transfer calculation and the result of the Mg yield shown in FIG. 4, the melting position of the coating material of the iron-coated Mg wire is a depth of 1/2 or more of the bath depth of the molten cast iron. It was confirmed that by setting the position, the yield of Mg can be stably maintained at a high level.

It is the side schematic diagram of the graphite spheroidization processing equipment used when implementing the present invention. It is a schematic sectional drawing of the iron covering Mg wire used by this invention. It is a figure which shows the result of having calculated | required the melt | dissolution time of the coating | covering material by heat transfer calculation. It is a figure which shows the relationship between the supply rate of the iron covering Mg wire in Example 1, and Mg yield.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Graphite spheroidization processing equipment 2 Base 3 Roller table 4 Roller 5 Lid 6 Lid raising / lowering device 7 Chain 8 Guide pipe 9 Pinch roll 10 Wire supply path 11 Guide roll 12 Mounting jig 13 Wire holding stand 14 Iron covering Mg wire 15 Ladle 16 Rail 17 Molten cast iron 18 Core material 19 Coating material

Claims (2)

  When the iron-coated Mg wire coated with a coating material comprising a steel plate or a steel pipe is supplied into the molten cast iron from above and the graphite in the molten cast iron is spheroidized, the melting position of the coating material in the molten cast iron is the molten cast iron. Adjusting the feed rate of the iron-coated Mg wire into the molten cast iron according to the bath depth of the molten cast iron and the thickness of the coating material so that it is at a depth of 1/2 or more of the bath depth of A characteristic graphite spheroidizing method. When the bath depth of molten cast iron is L and the thickness of the coating material is t, the iron-coated Mg wire is supplied at a supply rate equal to or higher than the supply rate calculated by the following equation (1). The graphite spheroidizing method according to claim 1.
V _l = (L / 2) × [1 / (-0.18t ² + 2.07t + 0.11)]… (1)
However, it is (1) In the equation, V _l is the feed rate (mm / sec), L is Yokufuka of (mm), t is the thickness of the coating material (mm).

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