JP2006181628A - Method for rolling thick steel plate and method for producing thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the seizure between a work roll and the material to be rolled and the crack or the like generated at the work roll, and to prevent the spalling of the work roll as well in thick plate rolling. <P>SOLUTION: In the method for rolling a thick steel plate, a roll comprising a ferrous material as an external layer and a cemented carbide layer at the inside is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for rolling thick steel plates and a method for producing thick steel plates using the same. Thick steel plates have a wider product width than flat steel and strip steel. While flat steel has a product width of 500 mm or less and strip steel has a width of 600-2300 mm, thick steel plates often have a product width of more than 2300 mm, which is much wider than flat steel. Although there is a region where the product width wraps, the product width is generally wider than the strip steel. Thick steel plate and strip steel have a region where some product thickness wraps, but there is a big difference that the former is not wound after rolling, while the latter is wound after rolling. ing.

  In general, in a step (thick plate rolling step) in which a steel slab is hot-rolled into a thick steel plate (hereinafter referred to as a thick plate), the steel slab is heated to, for example, 1050 to 1350 ° C. in a heating furnace, and then one or two Are subjected to hot rolling in a plurality of passes with a reversible rolling mill to obtain a thick steel plate having a desired thickness and width (product thickness range: 4.5 to 400 mm). A steel roll is usually used as a work roll of a reversible rolling mill for thick plate rolling (thick plate rolling mill).

  However, since the rolling temperature is high, seizure is likely to occur between the work roll and the material to be rolled, and the surface of the product steel plate is rough. Also, due to the large stress accompanying the rolling reaction force (rolling load) and thermal load, the surface of the work roll is likely to crack, and when cracked, it is transferred to the surface of the product thick steel plate, resulting in rough skin. In addition, there is a problem that when the roll grinding amount is increased and the roll basic unit is deteriorated or the crack is large, the roll may be broken (spoling).

  In addition, if many rollings with relatively low rolling temperatures are rolled, the rolling load is high and a relatively hard scale is generated on the surface of the material to be rolled. Therefore, the work roll is worn early and the roll profile is changed. There was also a problem that the frequency of re-polishing was high and the roll cost was high. Conventionally, as a roll having high resistance to cracking and wear resistance, as shown in Patent Document 1, a high-carbon steel high-speed steel roll in which the composition, hardness, and residual compressive stress of the roll outer shell layer are regulated, and Patent Document As shown in FIG. 2, a composite roll made of cemented carbide in which the cross-sectional area ratio of the outer layer / inner layer of a composite roll having an inner / outer two-layer sleeve having an inner layer made of steel and an outer layer made of cemented carbide is regulated.

  However, even when the roll of Patent Document 1 is used for a work roll of a thick plate rolling mill, the seizure and cracks (cracking and wear) cannot be sufficiently prevented. Further, although the roll of Patent Document 2 can effectively prevent the seizure and cracks, the composite sleeve is manufactured by sintering the mixed powder of the cemented carbide of the outer layer and simultaneously diffusion-bonding it to the inner layer. Therefore, it is difficult to manufacture with high accuracy and good workability in a size range suitable for a roll having a large diameter and long length (for example, outer diameter 1200 mmφ × rolling part width 5500 mmW) such as a work roll for thick plate rolling. It was not applicable to the work roll of a plate rolling mill. Therefore, if hundreds of rolls are to be rolled with the surface quality of the material to be rolled in good condition, the line must be stopped frequently and the rolls must be replaced to operate.

  Therefore, in order to meet both the demands of preventing work roll seizure and cracks in the plate rolling mill, improving the surface quality of the plate products, and improving the rolling efficiency in plate rolling operations. In Patent Document 3, a cylinder made of cemented carbide is further sintered, and some of them are added and HIP (hot isostatic pressing) is performed. Has proposed to manufacture a roll made of cemented carbide and use it for rolling thick steel plates.

In addition, in order to cite the best mode for carrying out the present invention which will be described later, Patent Document 4 is referred to here.
Japanese Patent Application Laid-Open No. 09-078186 Japanese Patent Laid-Open No. 10-005825 JP 2002-224715 A Japanese Patent Laid-Open No. 10-317102

  However, in the method in which the material of the surface layer of the work roll as shown in Patent Document 3 is a cemented carbide, there is a problem that the work roll is easily damaged because the cemented carbide is a brittle material. Moreover, it does not mean that the material to be rolled is immediately broken just by rolling the material to be rolled, but suddenly breaks while rolling the material to be rolled. The number of breakage varies, and once a breakage occurs, the plate rolling operation is suddenly interrupted and rolling of the material to be rolled cannot be performed for several hours. Because of such problems, it has been difficult to apply.

  The present invention has been made to solve the above-mentioned problems of the prior art.

  (1) A method for rolling a thick steel plate, characterized by using a roll having an iron-based material as an outer layer and a cemented carbide layer inside.

  (2) A method for producing a thick steel plate using the method for rolling a thick steel plate according to (1).

  According to the present invention, it is possible to prevent breakage like the work roll shown in Patent Document 3.

  In the present invention, a roll having an iron-based material as an outer layer and a cemented carbide layer inside is used as a work roll of a thick plate rolling mill.

  Cemented carbide is 5-50% added to carbide powder such as WC, TaC, TiC, etc. with one or more selected from metal powders such as Co, Ni, Cr, Ti, etc. as mass%. The cemented carbide mixed powder is sintered. As the cemented carbide mixed powder, it is assumed that the WC powder added with 5 to 50% Co in mass% is sintered, It is preferable because it has excellent resistance to rough skin and good toughness.

  The roll used for the rolling method of the thick steel plate of this invention is demonstrated below.

  The work roll (henceforth, roll) used for embodiment of this invention is shown in FIGS. In each figure, (a) is a cross-sectional view in the radial direction, and (b) is a cross-sectional view in the body length direction. The basic structural features of these rolls are that an outer layer 1 made of an iron-based material and an inner layer 2 made of a cemented carbide inside are formed.

  The roll shown in FIG. 1 is a case where the inside is the inner layer 2 made of a cemented carbide. In addition, 5 in a figure is a neck part.

  The roll shown in FIG. 2 is provided with an inner layer 2 made of cemented carbide around an axis 4 made of iron-based material and an outer layer 1 made of iron-based material on the outer side thereof.

  The rolls shown in FIGS. 3 to 5 are the same as the rolls shown in FIG. 2 in contact with the inner layer 2 made of a cemented carbide, respectively, on the inner side, the outer side, and both sides of the inner layer 2, respectively, The intermediate layer 3 made of a cemented carbide having the same or different composition is provided. This is provided for the purpose of alleviating the influence of internal stress generated on the roll due to residual stress generated when a sleeve-shaped cemented carbide layer to be described later is formed or thermal stress generated during rolling.

  The iron-based material forming the outer layer 1 may be any material as long as it contains 50% or more by mass of iron as the term iron-based. For example, the following is described in Patent Document 4 as follows: It is preferable to have various alloy components.

  By mass%, C: 1.1 to 1.5%, Si: 0.15 to 1.0%, Mn: 0.15 to 1.5%, Ni: 1.0% or less, Cr: 9. An iron-based alloy containing 0 to 15.0%, Mo: less than 1.0%, V: less than 0.8%, Ti: 0.3% or less, and the balance iron and inevitable impurities.

  On the other hand, the cemented carbide forming the inner layer 2 is composed of a cemented carbide powder such as WC, TaC or TiC and one or more selected from metal powders such as Co, Ni, Cr and Ti in the total mass. Sintered cemented carbide mixed powder added at a mass percentage of 5-50%, especially Co powder added to the WC at a mass percentage of 5-50% of the total mass It is preferable to sinter the cemented carbide mixed powder, because it has good accident resistance such as thermal characteristics at the time of use and suppression of breakage at the time of manufacture.

  Moreover, in the roll shown in FIGS. 3 to 5, the iron-based material forming the intermediate layer 3 may be the same material as the iron-based material forming the outer layer 1, or may be a different kind of iron-based material. . As the dissimilar iron-based material, for example, any of cast steel, forged steel, graphite cast iron, carbon steel, and alloy carbon steel is preferable, and it is preferable to have the following alloy components, but is not limited thereto. .

  C: 1.3% or less, Si: 1.0% or less, Mn: 1.5% or less, Ni: 1.0% or less, Cr: 10% or less, Mo: less than 1.0% V: less than 0.8%, Ti: less than 0.3%, an iron-based alloy consisting of the remaining iron and inevitable impurities.

  It is also preferable to use a cemented carbide as the intermediate layer 3, in which case the cemented carbide is a cemented carbide powder such as WC, TaC or TiC, and a metal powder such as Co, Ni, Cr or Ti. Sintered cemented carbide mixed powder in which one or two or more selected from the above is added in a proportion of 5 to 50% by mass with respect to the total mass. If the cemented carbide mixed powder to which Co powder is added at a ratio of 5 to 50% is sintered, the thermal characteristics at the time of use and the accident resistance such as the suppression of breakage at the time of manufacture are good. Therefore, it is preferable.

  In addition, since the different types of iron-based materials as described above or different types of iron-based materials are preferably melted materials, the following description will be made with reference to the case of the iron-based materials of the melted materials. The iron-based material portion of the roll used in the invention is not limited to the melted material.

  Moreover, the shaft core 4 of the roll shown in FIGS. 2-5 can also be manufactured by refining chromium steel, chromium molybdenum steel, and high-speed steel, for example.

  Based on the basic roll structure described above, the detailed structure may be appropriately determined depending on the roll dimensions, use conditions, manufacturing cost tolerance, etc. It is preferable to do as described below.

  That is, the thinner the outer layer 1 made of an iron-based material, the smaller the roll flatness, and the shorter the contact arc length between the roll and the material to be rolled during rolling. This shortens the contact time between the roll and the material to be rolled along with the rotation of the roll during rolling, reduces heat input to the roll, and reduces thermal stress, making the work roll surface layer less susceptible to cracking. Therefore, it is possible to suppress the roll grinding amount from decreasing and the roll basic unit from deteriorating.

  However, it is preferable that the thickness is 5 mm or more because of the limitation that the thinner the layer becomes, the more difficult it is to form, and the problem of rigidity during rolling. The upper limit is preferably 100 mm or less from the viewpoint of suppressing roll flatness.

  The inner layer 2 made of cemented carbide is preferably thicker from the viewpoint of suppressing roll flatness. The preferred range is 50 mm to 500 mm.

  In addition, the thickness of the intermediate layer 3 made of an iron-based material or a cemented carbide can be stabilized if there is a certain amount of thickness. Therefore, the thickness is preferably equal to or less than the thickness of the cemented carbide layer. . In production, the thinner the layer, the more difficult it is to form.

  The thickness of the roll core 4 shown in FIGS. 2 to 5 is the same as the representative dimension of the neck portion 5 (the diameter of the cylindrical portion excluding the oval cross section) due to the roll structure. It is preferable that the diameter is 1.5 to 1/4 of the diameter of the body (excluding the neck) of the roll. By adjusting the thickness of the shaft core 4, as a result, the thickness of the inner layer 2 made of cemented carbide or the intermediate layer 3 made of iron-based material can also be adjusted.

  The final dimensions of the roll are as wide as 500 to 2000 mm as the diameter of the cylindrical portion of the body at the center of the roll length direction and 2500 to 6000 mm as the length in the length direction.

  Next, taking the case of the roll shown in FIG. 3 as an example, a method for manufacturing the roll used in the present invention will be described below.

  Note that the roll dimensions used in the present invention are, as a typical example, very long in the body length direction with the outer diameter of the body 1200 mmφ × body length 5490 mmW. As shown in FIG. 6, it is preferable that (a) a body having a body length of several hundred mm manufactured in advance by sintering is (b) added in a plurality and then sintered again.

  Therefore, for example, a plurality of molded bodies having a width (body length) that is substantially equal to powder filling (size obtained by dividing the body length per roll by an integer and adding the shrinkage in the subsequent process) → CIP (cold isotropic pressure) treatment → Machining → Pre-sintering → Machining → Main sintering / HIP (hot isotropic pressure) treatment (Adding multiple compacts in the body length direction) Are integrated, hot isostatically pressed and sintered to produce a cemented carbide sleeve (cylindrical member)) → machining → diffusion bonding (iron as an intermediate layer on the inner surface of the cemented carbide sleeve) Through a series of manufacturing processes of fitting and fixing (fitting and fixing the sleeve to the shaft core member), and then a cemented carbide layer around the shaft core member. The roll member which has is manufactured. Then, a cylindrical member made of an iron-based material of the outer layer is created by casting, and the roll of the present invention is finally formed by fitting and integrating the roll member having the cemented carbide layer by shrink fitting or the like. Completed production.

  Thereafter, machining is performed to finally adjust the dimensions of each part, and polishing to adjust the roughness and gloss of the roll body does not impede this.

  A supplementary explanation will be given of a part of the manufacturing method of the roll of the present invention described above. The cemented carbide sleeve is subjected to machining such as grinding and polishing on the inner surface as necessary, and then shrink fitting. Then, a cemented carbide sleeve is fitted and fixed to the shaft core by cold fitting or the like.

  For example, the CIP molding is preferably performed at 100 to 300 MPa for 5 to 60 minutes.

  The pre-sintering condition is preferably, for example, maintained at 550 to 800 ° C. for 1 to 3 hours.

  The main sintering / HIP treatment is preferably, for example, held at 100 to 200 MPa and 1100 to 1200 ° C. in an Ar atmosphere for 0.5 to 2 hours, and further held at 1300 to 1350 ° C. for 1 to 3 hours. The main sintering / HIP treatment is not limited to simultaneous treatment, and hot isostatic pressing may be performed after sintering. For example, when diffusion-bonding forged steel equivalent to a cylindrical SCM-440 having a thickness of 50 mm on the inner surface of a cemented carbide sleeve, it is held at 1200 to 1300 ° C. for 0.5 to 1 hour in an Ar atmosphere. preferable.

  Finally, a cylindrical member made of an iron-based material for the outer layer is manufactured by casting, and fitted to the outer surface side of the cylindrical member in which forged steel equivalent to SCM440 is diffusion-bonded to the inner surface side of the above-mentioned cemented carbide sleeve by shrink fitting. Combine and integrate. It is also preferable that the cylindrical member made of the iron-based material of the outer layer is given tempering or forging by quenching or carburizing before and after the fitting as necessary to give the necessary strength and properties.

  Although the above is an example of the manufacturing method of the roll used for this invention, the method demonstrated above is an example to the last, and the manufacturing method of the roll used for this invention is not restricted to the method demonstrated above. For example, the outer layer made of the iron-based material may be formed outside the roll member by centrifugal casting, overlay welding, thermal spraying, or the like.

  Although not shown in FIGS. 1 to 5, between the layer of the iron-based material forming the outer layer 1 and the intermediate layer 3 and the cemented carbide layer forming the inner layer 2, the cemented carbide material is appropriately selected. It is also preferable to provide a buffer layer prepared by adding iron (Fe) or carbon (C). The components of the buffer layer are preferably adjusted according to the diffusion bonding conditions of the cemented carbide. The thickness of the buffer layer is preferably 10 mm or less, and more preferably 2 to 5 mm so as not to impair the effect of thermal crown suppression by the cemented carbide.

  Since the Young's modulus of the cemented carbide layer 2 is higher than that of the iron-based material, roll flatness is suppressed, and the contact arc length between the roll and the material to be rolled is shortened during rolling. The contact time between the roll and the material to be rolled along with the rotation of the roll is also shortened, the heat input to the roll is reduced and the thermal stress is reduced, so that the work roll surface layer is less likely to crack. However, since heat input to the roll is reduced, there is also an effect that occurrence of seizure between the outer layer 1 of the roll and the material to be rolled is suppressed.

  Moreover, since the outer layer 1 is made of an iron-based material that is not a brittle material such as a cemented carbide, it is possible to prevent the work roll from being damaged by the contact between the outer layer 1 of the roll and the material to be rolled.

  In a factory (thick plate rolling line) where hot steel plates are manufactured by hot rolling, one or two thick plate rolling mills are arranged, but in the case of two arrangements, at least one work roll is provided. The roll used in the present invention is used. FIG. 7 is a layout diagram showing an example of a thick plate rolling line suitable for carrying out the present invention. A heating furnace 10, a descaling device 11, a thick plate mill 12, a cooling device 13, and a cooling bed 14 are arranged in this order from the upstream side of the line. In this example, the thick plate mill 12 is composed of one quadruple reversible rolling mill having a pair of upper and lower work rolls WR and a backup roll BUR, but is composed of two reversible rolling mills. Alternatively, the reversible rolling mill may be a double type having only a pair of upper and lower work rolls.

  In the case of a thick plate rolling mill having a two-unit configuration, the present invention may be applied to any one unit, but it is more effective to apply to two units.

  In the thick plate rolling line shown in FIG. 7, a steel roll as a work roll of a thick plate rolling mill (rolling part dimension = outside diameter 1200 mmφ × width 5490 mmW), each cemented carbide roll shown in FIGS. 8A and 8B. Using the rolls of the present invention shown in A, B, FIG. 2 and FIG. 3, hot rolled steel slabs equivalent to SM490 (thickness of 300 mm) for each roll type (number of passes: 10 to 15), and product plates A thick steel plate having a thickness of 12 to 16 mm was obtained.

  The steel roll was made by tempering high speed steel.

  The cemented carbide roll A has the structure shown in FIG. 8A, and the cemented carbide joining sleeve 22 is formed by rubber molding using a material obtained by adding 20% by mass of Co to tungsten carbide (WC). Twenty-five WC-Co alloy hollow members having a thickness of 230 mmt and a width of 400 mmL were HIP-bonded in the width direction, and fitted to the steel shaft 24 to obtain a cemented carbide roll A. Reference numeral 21 denotes a steel side end ring.

  The cemented carbide roll B has the structure shown in FIG. 8B, and the cemented carbide joining sleeve 22 is formed by rubber molding using a material obtained by adding 10% by weight of Co to tungsten carbide (WC). 25 WC-Co alloy hollow members having a thickness of 230 mmt and a width of 400 mmL are joined in a HIP joint in the width direction, and are fitted into a steel cushion 25 and further fitted into a steel shaft 24 to make a cemented carbide. Roll B was obtained. Reference numeral 21 denotes a steel side end ring.

  In the example of the present invention, the work roll having the structure shown in FIG. 2 and FIG. 3 is used, and the outer layer 1 is an iron-based material having a chemical composition range described in Patent Document 4 in mass%, C: 1 .4%, Si: 0.5%, Mn: 0.5%, Ni: 0.5%, Cr: 12%, Mo: 0.8%, V: 0.4%, Ti: 0.1% The balance is an alloy composed of Fe and components that are inevitable impurities, and the thickness is 15 mm.

  The cemented carbide layer 2 was 15% by mass of Co added to WC, the thickness in FIG. 2 was 200 mm, and the thickness in FIG. 3 was 195 mm. The intermediate layer 3 shown in FIG. 3 is carbon steel containing 0.05% carbon by mass, and the thickness is 5 mm. The cemented carbide layer 2 was manufactured from the five temporary sintered bodies in the body length direction by the above HIP, and the intermediate layer 3 was fitted inside. At the time of fitting, the cemented carbide layer 2 was heated to 350 ° C., the intermediate layer 3 was cooled to −30 ° C., and tempered and fitted. As the outer layer 1, a cylinder having a thickness of 25 mm was manufactured by centrifugal casting and mechanical grinding, and this was fitted to the outer periphery of the cemented carbide layer 1. At the time of fitting, the outer cylinder 1 was heated to 250 ° C. and shrink-fitted with the integral cylinder of the cemented carbide layer 2 and the intermediate layer 3 kept at room temperature. These three-layered integrated cylinders were heated to 380 ° C. and shrink-fitted onto a steel shaft core 4 having a diameter of 750 mm. Finally, the outer layer 1 was forged and mechanically ground to finish the outer periphery of the roll.

  While observing the surface properties of the thick steel sheet rolled for the final roll for each roll type, the amount of cracks and wear on the surface of the work roll after the final roll was investigated. The amount of cracks generated was evaluated by the number of roll surface cracks detected by ultrasonic flaw detection and the maximum depth. The amount of wear was evaluated by the amount of roll radius reduction at the position in the roll body length direction where the difference in roll profile from that before rolling was maximum.

  The survey results are shown in Table 1. In the comparative example using the cemented carbide roll as the work roll and the present invention example using the work roll having the structure shown in FIGS. 2 and 3, the roll surface layer after rolling was shallow and the surface property was good. . On the other hand, the conventional steel roll had deep cracks and rough skin.

  Although the rolling was continued after the 20 rollings were finished, the cemented carbide roll A was broken at the 53rd and the cemented carbide roll B was broken at the 215th. In the example of the present invention using the steel roll which is a conventional example and the work roll having the structure shown in FIGS.

  Thick steel plates are prepared by adjusting the components of the hot metal coming from a blast furnace, etc., and then ingot after casting by ingot casting, or by direct casting into slab steel ingots directly. It can be manufactured by rolling in the thick plate rolling line as shown in FIG. 7, but when rolling in the thick plate rolling line as shown in FIG. By rolling using the rolling method of a steel plate, it is possible to produce a thick steel plate with good surface quality and to prevent operation stoppage due to breakage of the work roll.

It is sectional drawing of the roll used for this invention. It is sectional drawing of the roll used for this invention. It is sectional drawing of the roll used for this invention. It is sectional drawing of the roll used for this invention. It is sectional drawing of the roll used for this invention. It is a figure for demonstrating a part about the manufacturing method of the roll used for this invention. It is an arrangement figure showing an example of a thick plate rolling line suitable for implementation of the present invention. It is sectional drawing of the roll used for a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ferrous material 2 Cemented carbide 3 Intermediate layer 4 Shaft core 5 Neck part 10 Heating furnace 11 Descaling device 12 Thick plate mill 13 Cooling device 14 Cooling floor 21 Steel side end ring 22 Cemented carbide joining sleeve 24 Steel Axle 25 Steel cushioning material

Claims (2)

  A method for rolling a thick steel plate, comprising using a roll having an iron-based material as an outer layer and a cemented carbide layer inside.   The manufacturing method of the thick steel plate using the rolling method of the thick steel plate of Claim 1.