JP2005297005A - Rolled cast iron manufacturing method and rolled cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality rolled cast iron while producing a large amount of a cast iron rolled material, which has been difficult to produce conventionally, at a low cost.
A cast slab is prepared by containing 0.01 to 0.50 mass% of a rare earth element in cast iron having a carbon concentration of 1.5 to 5.0 mass%. The cast slab is heated in a temperature range of 900 to 1200 ° C. for 20 minutes or more, and then rolled at a temperature of 800 ° C. or more to obtain a good rolled cast iron. A particularly stable rolled cast iron can be produced by setting the sulfur concentration in the cast iron to 0.007 to 0.700 mass%, and the rolled cast iron produced according to the present invention has excellent material properties such as elongation and strength. .
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Description

  The present invention relates to a method for producing a cast iron rolled product and a rolled cast iron product.

  In general, cast iron, which is a high carbon steel, has a wide range of usage because it has features such as a beautiful casting surface and excellent vibration damping. However, due to poor workability, casting is performed in a form close to the final shape using sand molds or wooden molds, and then processing such as surface polishing is performed, so it becomes casting of batches, and productivity is It is extremely low and its usage is strictly limited.

  Various characteristics of cast iron are described in Non-Patent Document 1, and material characteristics depending on components and heat treatment conditions are described in detail. If it is possible to produce a plate material that takes advantage of the characteristics of cast iron, it can be applied to parts that are completely different from conventional mold casting materials, and if it can be produced by existing steel making and rolling processes, productivity will jump dramatically. In addition to the increase in cost, the decarburization process in the decarburization furnace can be greatly reduced, so that the merit is very large in terms of cost.

As a casting method of a cast iron plate, a method using a twin roll casting machine as shown in Patent Document 1 has been proposed, and it is shown that continuous casting of a cast iron plate of 10 mm or less is possible. Further, Patent Document 2 discloses an attempt to roll a composite steel piece formed by laminating spheroidal graphite cast iron and a steel material to produce a new material. On the other hand, various characteristics of rolled cast iron utilizing the plastic workability of spheroidal graphite cast iron are described in Non-Patent Document 2, and mention is also made of application examples as a material of rolled cast iron.
JP 60-262923 A Japanese Patent Laid-Open No. 03-146203 Nakata et al., Metal Materials (1977), Vol. 17, No. 10, p. 46 Fukumura et al., Metal Materials (1975), Vol. 17, No. 11, p. 31

  The method using a twin roll casting machine as shown in Patent Document 1 is not only low in productivity compared with a normal casting method, but also has a small number of bases that can be put into practical use and is low in cost. Due to the high price, commercial production of cast iron has not been achieved. Moreover, the manufacturing method as disclosed in Patent Document 2 not only increases the cost of the step of laminating spheroidal graphite cast iron and steel, but also does not make use of the characteristics of the cast iron itself. Furthermore, the information described in Non-Patent Document 2 does not mention an appropriate component value or a stable production method of rolled cast iron, nor does it mention a means for further improving material properties. .

  The present invention produces cast iron under mass production type melting conditions, and cast iron pieces produced by general continuous casting or ingot casting for high production on a large-scale rolling mill, and with clean and excellent material properties And a cast iron product (including a semi-finished product) that is inexpensive and manufactured in large quantities and has excellent material properties.

The features of the present invention for solving the above-described problems are as follows.
(1) A cast slab obtained by casting cast iron containing rare earth elements in an amount of 0.01% by mass to 0.50% by mass is heated at 900 ° C. or more and 1200 ° C. or less for 20 minutes or more, and 800 ° C. or more by a rolling mill. It is a method for producing rolled cast iron characterized by carrying out rolling in the temperature range of
(2) The method for producing rolled cast iron according to (1), wherein the sulfur concentration of cast iron is 0.007 mass% or more and 0.700 mass% or less,
(3) The method for producing rolled cast iron according to (1) or (2), wherein the silicon concentration of cast iron is 0.2% by mass or more and 1.5% by mass or less,
Moreover, it is the rolled cast iron manufactured by the method in any one of (4) (1)-(3).

  According to the present invention, it becomes possible to mass-produce a cast iron rolled material at a lower cost than before, and to provide a rolled cast iron having excellent material characteristics, and its industrial value is great.

  In the present invention, cast iron molten metal (hereinafter referred to as molten metal) is used as a base material. Here, cast iron refers to iron having a carbon concentration of 1.5% by mass or more and 5.0% by mass or less with a mother phase.

  For molten metal, scrap may be added to the hot metal produced in a blast furnace, decarburized to the required composition in a converter, and then iron alloy may be added by ladle refining, or scrap and necessary components in an electric furnace. For example, a melting method that is appropriately performed by the contractor may be used. The molten metal component at this time needs to contain a rare earth element in an amount of 0.01% by mass to 0.50% by mass.

  The rare earth elements referred to here are 17 elements of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu in the periodic table of elements. That is, it is managed by the total of the mass% of one or more of these.

  The role of rare earth elements added to the molten metal is to act as the precipitation nuclei of graphite in cast iron in the heating furnace from casting to rolling (or the heat-retaining process of cast slab immediately after casting). The carbon concentration is reduced to improve workability, and the addition amount is 0.01% by mass or more and acts as an effective nucleus. If it is less than 0.01% by mass, the frequency of precipitation nuclei is low, so that it may not act as effective precipitation nuclei. Moreover, the upper limit of 0.5% by mass or less is provided for the added amount. When the amount exceeds 0.5% by mass, the frequency of precipitation nuclei becomes excessive, which may not be suitable for improvement of workability. This is to increase the cost.

  The cast iron melt can be cast using a general continuous casting machine, which can be manufactured with high yield and high production, but can be inserted into a subsequent rolling process or processed into an insertable shape. If possible, there is no problem even with ingot casting.

  The heating temperature of the slab needs to be at least 900 ° C. and 1200 ° C. or less in a heating furnace from casting to rolling (may be a heat-retaining step of the slab immediately after casting), and effective graphite below 900 ° C. It has been found by the inventors' investigation that it may not act as a precipitation nucleus. The reason why the upper limit of the heating temperature is set to 1200 ° C. is that in most cast iron compositions, the temperature exceeding 1200 ° C. exceeds the solidus temperature, and stable slab heating may be difficult.

  In addition, it is preferable to heat for 20 minutes or more for precipitation of carbon by rare earth elements. There is no particular upper limit for the deposition time, but if it exceeds 4 hours, it may be necessary to use a special heating furnace in order to increase the deposition effect. It may not be advantageous.

  As for the temperature during rolling, as a result of the inventors' tests, it is preferable to ensure that the rolling temperature is 800 ° C or higher. This is because when the rolling temperature is lower than 800 ° C., the occurrence of ear cracks may occur, which may lead to a decrease in product yield after rolling. Although there is no particular upper limit to the rolling temperature, rolling at a temperature equal to or higher than the heating furnace temperature is impossible with a normal rolling mill, and rolling at 1200 ° C. or lower is preferable.

  The sulfur concentration of cast iron is preferably 0.007% by mass or more and 0.7% by mass or less. According to the inventors' basic experiments, the presence of sulfur in the mass ratio of 0.7 to 1.4 times that of rare earth elements causes the rare earth sulfide to remain finely in the cast iron slab, resulting in better graphite precipitation. This is because it became clear that can be realized.

  In addition, the presence of silicon is advantageous for promoting the precipitation of graphite in the cast iron matrix in the heating furnace. This is because the carbon equivalent is increased by the presence of silicon, and the apparent carbon potential in the cast iron matrix is increased, so that the discharge of graphite from the cast iron matrix is promoted. In particular, good graphite precipitation was confirmed in the presence of 0.2 mass% or more of silicon. On the other hand, if the silicon concentration exceeds 1.5% by mass, the plating property of the rolled cast iron of the product may be easily deteriorated.

  These rolled cast iron products manufactured by any one of the methods (1) to (3) manufactured under the manufacturing conditions also belong to the product of the present invention.

  In rolled cast iron, precipitated graphite is elongated during rolling and forms an iron structure and a lamellar structure of the parent phase. Therefore, elongation, tensile strength, and vibration damping are remarkably improved as compared with ordinary cast iron. The term "rolled cast iron product" as used herein refers to a thin cast iron such as a hot rolled plate manufactured by a hot rolling mill, a pickled plate of a hot rolled plate, a cold rolled plate manufactured by performing cold rolling after hot rolling, or a thick plate. Thick plate cast iron that is manufactured as a predetermined size by repeatedly rolling in the longitudinal direction and width direction as necessary in a rolling mill, and strips formed into rod-like, wire-like, rail-like, mountain-like, I-type and H-type cross sections, etc. This refers to rolled cast iron products (including semi-finished products) such as cast iron.

(Example)
In order to confirm the effect of the present invention, cast iron was manufactured and a material evaluation test was conducted using a 20 kg test melting slab.

  While melting 20 kg of cast iron using an atmospheric high frequency furnace and repeating alloy addition and component analysis, carbon 2.4% by mass, sulfur 0.02% by mass, silicon 1.02% by mass and the remaining inevitable impurities (Mn: Cast iron made of 0.24% by mass, P: 0.021% by mass, and each other: 0.1% by mass or less) was melted under a temperature condition of 1400 ° C. (Missel metal (principal component Pr: 3.8% by mass)). %, Nd: 10.3 mass%, Ce: 48.2 mass%, La: 36.9 mass%) immediately after adding 40 g, cast into a metal mold (100 mm square, depth 300 mm) to create a slab did.

  As a result of analysis of the slab cut sample, almost no change was observed in the components other than the rare earth element, and the yield of the rare earth element was changed, Pr: 0.008 mass%, Nd: 0.017 mass%, Ce: 0 A cast slab of 0.078% by mass and La: 0.047% by mass (total rare earth elements 0.150% by mass) was obtained.

  The obtained slab was heated at 1100 ° C. for 60 minutes, and rolled for 11 passes in a temperature range of 1020 ° C. to 890 ° C. with a test rolling mill to obtain 4 mm thick rolled cast iron. The cast iron produced at this time showed no rolling unevenness such as ear cracks, and was able to obtain a good rolled cast iron.

From the obtained rolled cast iron, 10 test rolled pieces designated by JIS No. B were cut out, and the material properties were measured with an automatic tensile testing machine. The total elongation was 24.3% (σ = 1.7%), An excellent value of 431 N / mm ² (σ = 12 N / mm ² ) in terms of tensile strength was obtained. (Here, σ means standard deviation.) The obtained rolled cast iron was also excellent in bending workability, and the vibration damping property was confirmed to be equal to or better than the value of spheroidal graphite cast iron.

(Comparative example)
As a comparative example, cast iron was melted and rolled under the same conditions as in the previous examples except for the rare earth element addition conditions. At this time, the amount of misch metal added was 2.0 g, and the concentration of rare earth elements in the slab was 0.008 mass%.

  The obtained slab was heated at 1100 ° C. for 60 minutes, and when rolling was started at an initial temperature of 1020 ° C. using a test rolling mill, the slab was cracked in the first pass of rolling, and subsequent rolling could not be continued. Became.

  The remaining material was cut out and the structure was observed with an optical microscope after etching. From the polished surface of the cast slab obtained at the rare earth element addition amount within the range of the present invention, a structure containing a large number of spherical graphite having excellent dispersibility and a uniform shape is observed, whereas the cast used in the comparative example is used. On the polished surface of the piece, only coarse and irregularly shaped graphite with a low number density was deposited, and the appearance was clearly different from the metal structure of the present invention.

Claims (4)

  A cast slab obtained by casting a cast iron containing 0.01% by mass to 0.50% by mass of a rare earth element is heated at 900 ° C. or more and 1200 ° C. or less for 20 minutes or more, and a temperature range of 800 ° C. or more by a rolling mill. A method for producing rolled cast iron, characterized in that rolling is performed at   The method for producing rolled cast iron according to claim 1, wherein the sulfur concentration of the cast iron is 0.007 mass% or more and 0.700 mass% or less.   The method for producing rolled cast iron according to claim 1 or 2, wherein the silicon concentration of the cast iron is 0.2 mass% or more and 1.5 mass% or less.   The rolled cast iron manufactured by the method of any one of Claims 1-3.