JP2006095595A - Centrifugal casting method for composite roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centrifugal casting method for a composite roll which has a longer life than the conventional one and which hardly causes a rough surface on a rolled product. <P>SOLUTION: In this improved centrifugal casting method for the composite roll, a casting mold is equipped with a die for forming the working portion of a roll, and an upper and a lower dies made of sand for forming both ends of the roll. While rotating the casting mold tilted at a certain angle, a material in a molten state for an external layer is poured into the casting mold first, and then a core material is poured after the material for the external layer is solidified. In this case, a convex stripe protruding toward the center in a cross-sectional view is formed on a part of the inner face of the lower die, where the material is cut away as a crop after the material is solidified, so that the stir of the molten material poured is promoted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for centrifugal casting of a composite roll, and more particularly to a technique for producing a composite roll that has excellent wear resistance and has a longer life than conventional ones.

  In general, a metal material, for example, a steel material or a steel plate is manufactured by rolling a steel slab obtained by continuously casting molten steel, hot or cold. A roll is used for the rolling, but the quality of the roll has a great influence on the quality and price of the manufactured steel, steel plate and the like. In particular, in recent years, the progress of hot rolling technology has been remarkable, and accordingly, the characteristics of the hot rolling roll to be used, particularly the improvement of wear resistance, has been strongly demanded.

  In response to such demands for improving wear resistance, the roll has a double structure of an outer layer (also referred to as a work layer) in contact with the core material and the material to be rolled, and the material of the outer layer is similar to the composition of high-speed tool steel. A high-performance composite roll (high-speed roll) that has a composition and precipitates hard carbides during the production of the roll to significantly improve the wear resistance has been developed and put into practical use. For example, on a roll core material, C: 2.4-2.9 mass%, Si: 1 mass% or less, Mn: 1 mass% or less, Cr: 12-18 mass%, Mo: 3-9 mass% , V: 3 to 8% by mass, Nb: 0.5 to 4% by mass, and a high-speed system having a composition satisfying 0.27 ≦ Mo / Cr ≦ 0.7 and (C + 0.2Cr) ≦ 6.2 A hot rolling roll having an outer layer has been proposed (Patent Document 1). Here, a centrifugal casting method as shown in FIG. 3 is used for manufacturing such a composite roll. That is, the material is melted in an electric furnace (for example, a low frequency melting furnace) 1, poured into a rotating mold 2 inclined at a constant angle, solidified in a state where a centrifugal force is applied, and then a heat treatment furnace 3. And it is set as the roll 11 through the processing machine 4. At that time, two kinds of materials, that is, an outer layer to be injected first and a core material to be injected later are used.

  Further, the present applicant is also manufactured by a centrifugal casting method, and C: 1.6 to 2.9% by mass, Si: 1% by mass or less, Mn: 1% by mass or less, Cr: 4 to 18% by mass, Mo: 1 to 9% by mass, V: 3 to 8% by mass, Nb: A roll formed by forming an outer shell with iron of 0.5% by mass or less, in which the iron is further insoluble in the iron A roll for hot rolling of a metal material, characterized by containing a fine metal and dispersing fine particles of metal insoluble in iron in a roll use layer after solidification (see Patent Document 2) ). According to this roll, the seizure frequency with the material to be rolled is reduced, the occurrence of cracks is reduced, and the life of the roll can be extended.

However, recently, demands for improving the quality and productivity of rolled products have further increased, and accordingly, the life of rolls used for rolling has been eagerly extended.
Japanese Patent Laid-Open No. 10-183289 JP 2003-306740 A

  In view of such circumstances, an object of the present invention is to provide a centrifugal roll casting method capable of producing a roll that has a longer life than conventional ones and is less likely to cause rough skin on a rolled product.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

  That is, the present invention is configured to incline and rotate a mold having a mold for forming a work part of a roll and an upper mold and a lower mold for forming both ends at a predetermined angle. In the centrifugal casting method of a composite roll in which a material for an outer layer is injected and the core material is injected after the outer layer material is solidified, the material is used so as to promote stirring of the molten material injected for the outer layer. Is a centrifugal casting method of a composite roll characterized in that a lower mold is used in which a protrusion protruding toward the center in a cross-sectional view is formed on the inner surface of a lower mold that is cut off as a crop after solidification. In this case, the shape of the ridge is preferably a mountain shape. Further, it is preferable that the inclination of the mold is 5 ° or more and the rotation speed is 300 to 1000 rpm, or the outer layer material is a high-speed alloy and the core material is ductile cast iron.

  According to the present invention, the rotational force of the mold is quickly and reliably transmitted to the molten material accumulated in the lower mold at the beginning of injection, and the time until the centrifugal force acts on the material is accelerated. As a result, the crystal grains on the surface of the outer layer of the roll become fine and the wear resistance is improved. That is, it becomes possible to stably manufacture a roll that has a longer life than conventional ones and is less likely to cause rough skin on a rolled product.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  When a roll is manufactured by centrifugal casting, when a molten material (hereinafter referred to as a molten metal 5) is poured into a general mold 2 configured by combining an upper mold 6, a mold 7 and a lower mold 8, the molten metal 2, the flow of the molten metal is once accumulated in the lower mold 8 of the mold as shown by the arrows in FIG. 2, and the rotation of the mold 2 is transmitted to the molten metal 5 so that the centrifugal force acts and moves to the mold 7 to form a cylindrical shape. To spread. The rotational force to the molten metal 5 is applied only by the frictional force between the molten metal 5 and the mold 2, but the frictional force is greatly influenced by the inner surface properties of the mold 2, and the mold 7 is filled with the molten metal 5 in a cylindrical shape. There was a tendency that the behavior of the molten metal 5 was not constant during the period until it was made. Therefore, unevenness occurred in the solidification form. In other words, it was considered that the roll surface had a large and small crystal grain size, had a non-uniform particle size distribution, had not only rough skin, but was unfavorable for wear resistance. However, conventionally, no countermeasure has been taken for strengthening the stirring power of the molten metal in the lower mold, which is considered to be effective in eliminating this unevenness.

  Therefore, if the inventor can strengthen the stirring force of the molten metal 5 in the lower mold 8, not only the reverse upward flow of the molten metal 5 to the mold 7 is increased particularly in the initial stage of pouring, but also nucleation of crystals is caused. It was thought that the crystal structure could be increased and made uniform with fine grains. First, several steel fins (plate-shaped stirring blades) are provided at the inner surface position of the lower mold corresponding to the length (indicated by symbol L in FIG. 2) where the injected molten metal is cut off as a crop after solidification. Was provided along the longitudinal direction of the lower mold to try to strengthen the stirring of the molten metal.

  However, the attempt was unsuccessful because the fins melted and deformed immediately after the molten metal was poured. Therefore, the inventor continued to study various alternatives and found that, instead of the fins, the ridges 9 projecting toward the center in a cross-sectional view were formed of sand, and as a result, the rotation of the molten metal 5 was strengthened. Then, as the ridge 9, a lower mold 8 having various shapes as shown in cross-sectional views in FIGS. 1 (b) to 1 (c) is manufactured as a prototype, and the melt casting 5 is actually cast by the mold 2 incorporating the same. To produce a roll. That is, in the lower mold of FIG. 1 (a), the region indicated by the symbol L is a cross-section (FIG. 1 (b) or (c)) having a ridge 9 as seen from BB, and the mold 7 side thereof The region is a circular cross section (FIG. 1D) as seen in AA. The length of L is usually 100 mm or less from the bottom surface of the lower mold, but in order to increase the stirring effect, the length of L is set to about 200 mm.

  As a result, the ridges 9 act like stirring blades, and the outer layer of the roll has finer, more uniform and dense skin than conventional crystals. Moreover, when the steel slab is hot-rolled with such a roll, it has been confirmed that the life of the roll is about 20% longer than before and the rough surface generated on the surface of the manufactured steel sheet is reduced. The present invention is a centrifugal casting method using a mold.

  In the present invention, various shapes such as a mountain shape, a screw shape, a weir shape and the like can be adopted as the shape of the ridge 9, but a mountain shape is most preferable. This is because, when observed with the naked eye after the completion of casting, it is expected that the effect will be great because there is little deformation of the shape. Further, the length (L in FIGS. 1 and 2), the height, the cross-sectional area, the size protruding to the inner surface, and the like are not particularly limited in the present invention. This is because it may be determined in advance by a preliminary test or the like.

  Furthermore, in this invention, it is preferable that the inclination of the said casting_mold | template 2 shall be 5 degrees or more, and a rotational speed shall be 300-1000 rpm. When the inclination of the mold 2 is less than 5 °, the injected molten metal does not sufficiently fill the stirring strengthening portion (that is, the portion provided with the ridges), and the intended stirring cannot be obtained. Further, if the rotational speed of the mold is less than 300 rpm, the stirring force is too weak and the intended effect does not appear, and if it exceeds 1000 rpm, the effect is saturated and meaningless, and the lower inward convex shape by stirring The adverse effect of increasing the damage of the product occurs.

  The rotational speed of the mold when centrifugally casting the roll is determined by the centrifugal force applied to the molten metal in the mold. If the centrifugal force applied to the molten metal is insufficient compared to gravity, the shape of the molten metal is uniform in the mold. The problem of not becoming.

  In addition, in the present invention, the composition of the molten metal 5 is not particularly limited. This is because the lower mold 8 provided with the ridges 9 was effective for any of molten steel, various metals, and alloys that can be used as a roll material. However, the results of using the trial roll showed the best results when the outer layer material was a high-speed alloy and the core material was ductile cast iron. Decided to add.

  C: 2.5 mass%, Si: 0.8 mass% or less, Mn: 0.9 mass% or less, Cr: 13 mass%, Mo: 5 mass%, V: 3 mass%, Nb: 0.3 mass A composite roll was produced using a high-speed alloy containing the remaining iron and inevitable impurity elements as the outer layer material of the roll and ductile cast iron as the core material. At that time, the centrifugal casting method according to the present invention shown in FIG. 2 was applied to the casting of the outer layer. The above material is melted by using a low frequency induction furnace as the electric furnace 1 and poured into a rotating inclined mold 2 as a molten metal having a temperature of 1450 ° C. After the solidification of the high speed alloy for the outer layer is completed. The mold was stopped and kept upright to cast the core material. The high-speed alloy for the outer layer of the roll to be cast first was 3.6 tons, and the ductile cast iron for the core material to be cast later was 7.6 tons. Note that the upper mold 6 and the lower mold 8 of the mold 2 were manufactured by solidifying sand in a frame, and the mold was manufactured of forged steel. Further, the inclination angle of the mold was 20 °, and the rotation speed was 550 rpm. Further, the mold has a special shape on the inner surface of the lower mold 8 according to the present invention. In other words, a mountain-shaped convex strip having an L of 200 mm and a height of 50 mm was formed on a cylindrical inner surface having an inner diameter of 450 mmφ. And it compared with the case of the conventional casting method using the normal lower mold | type of an inner surface (inside diameter 450mmphi).

  The result of rolling the steel material using the manufactured roll, and evaluating the “surface fatigue layer thickness” and “uncut maximum rolling amount” of the roll used when the rolling amount exceeded 10,000 tons, Organized into one. Here, the “surface fatigue layer thickness” is a region where fine cracks generated in the roll surface layer several tens of μm thick when used for rolling, and is considered to be caused by rolling Hertz stress and rapid quenching It is. The surface fatigue layer has a thickness that can be confirmed in the ultrasonic flaw detection of the roll by surface waves. Further, the “uncut maximum rolling amount” is the maximum value of the rolling amount when the roll can be repeatedly used without being polished.

  From Table 1, according to the centrifugal casting method of the composite roll according to the present invention, the crystal grains on the outer layer surface of the roll become fine, the wear resistance is improved, the life is longer than before, and the rolled product has rough skin. It is clear that rolls that are difficult to produce can be produced stably.

It is a figure explaining the centrifugal casting method of the composite roll which concerns on this invention, (a) is a side of the whole casting_mold | template, (b)-(c) is a BB view of (a), and is the inner surface of a lower mold | type. (D) is a portion where no ridges are provided in the AA view of (a). It is a side view which shows the condition before pouring the first molten metal into a casting_mold | template and starting rotation. It is a flowchart which shows the general process of manufacturing a roll by centrifugal casting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Mold 3 Heat treatment furnace 4 Processing machine 5 Molten metal 6 Upper mold 7 Mold 8 Lower mold 9 Convex strip 10 Roll

Claims (4)

The mold with the work part of the roll, and the upper and lower molds made of sand that form both ends are tilted and rotated at a fixed angle, and the molten outer layer material is initially injected into the mold. In the centrifugal casting method of the composite roll in which the core material is injected after the outer layer material is solidified,
In order to promote stirring of the injected molten material, a lower mold is used in which a protrusion protruding toward the center in a sectional view is formed on the inner surface of the lower mold where the material is cut off as a crop after solidification. A method for centrifugal casting of a composite roll.   The method of centrifugal casting of a composite roll according to claim 1, wherein the shape of the ridges is a mountain shape.   The method of centrifugal casting of a composite roll according to claim 1 or 2, wherein the mold has an inclination of 5 ° or more and a rotational speed of 300 to 1000 rpm.   The composite roll centrifugal casting method according to claim 1, wherein the outer layer material is a high-speed alloy, and the core material is ductile cast iron.

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