JP2005169460A - Compound sleeved roll for hot finish rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound sleeved roll for hot finish rolling which is used for a finish rolling mill array of a hot strip mill. <P>SOLUTION: In the compound sleeved roll for hot finish rolling to perform hot finish rolling of a steel strip or a steel plate, a compound sleeve formed by arranging an outer layer containing, by mass, 1.0-3.0% C, 0.2-2.0% Si, 0.2-2.0% Mn, 3.0-10.0% V, 3.0-10.0% Cr and 2.0-10% one or two kinds of Mo and W, and the balance Fe with inevitable impurities around an inner layer formed of forged steel, cast steel or a rolled steel pipe containing ≤ 1% C by a continuous tinkering method is shrinkage-fitted to a shaft of high toughness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a work roll used in steel rolling, in particular, hot strip steel or hot continuous finish rolling of a steel sheet, that is, a hot strip mill finish rolling train.

  Conventionally, as a roll for finishing rolling of a hot rolling mill, a composite roll manufactured by centrifugal casting method using an outer layer material of nihard cast iron and high chrome cast iron and high-grade cast iron or ductile cast iron as an inner layer material is used. I came. Further, in recent years, white cast iron containing a large amount of V, Cr, Mo, W called a high-speed roll material has been adopted as a composite roll excellent in wear resistance. For example, patent international publication WO88 / 7594 (patent document 1), patent international publication WO91 / 19824 (patent document 2) and the like are disclosed, and around a tough cylindrical inner layer (also referred to as a core material). A composite solid roll having both wear resistance and toughness has been developed and put into practical use (hereinafter referred to as “high speed roll”) by casting a high-speed outer layer and completely welding both materials metallurgically.

  However, when the high-speed roll is used in a hot finish rolling mill for hot finish rolling a strip or steel plate, the outer surface has a residual compressive stress exceeding 300 MPa, which is larger than that of a conventional roll. Such a problem occurred. That is, in an actual rolling operation, the rolling operation due to various factors becomes unstable, and a situation where a part of the steel plate is rolled up and rolled over a plurality of sheets (hereinafter referred to as a drawing accident) may occur. is there. At this time, there was a risk of deep cracks entering the surface of the roll and inducing delayed fracture after a certain period of time. Therefore, despite having both wear resistance and toughness, the performance of the overall rolling roll was significantly impaired, and the management of the rolling roll once cracked was extremely complicated. .

Patent International Publication WO88 / 7594 Patent International Publication No. WO91 / 19824

  As described above, in view of the problems of the prior art, the present inventors have made extensive developments. As a result, in continuous hot finish rolling of steel strip or steel plate, even when a squeeze accident is encountered in the rolling operation, It is possible to provide a rolling roll with a shallow crack on the roll surface and a low risk of causing delayed fracture, thereby enabling a highly productive and economical rolling method.

The gist of the invention is that
(1) In a hot finish rolling roll for hot finish rolling a steel strip or steel plate, the C content is about 1% by mass around the inner layer made of forged steel, cast steel or rolled steel pipe having a C content of 1% or less by mass. : 1.0-3.0%, Si: 0.2-2.0%, Mn: 0.2-2.0%, V: 3.0-10.0%, Cr: 3.0-10 A composite sleeve comprising 0.0% and 2.0 to 10% of Mo or W, or 2.0 to 10%, and the outer layer consisting of the remaining Fe and inevitable impurities formed by a continuous casting method, and a tough shaft A composite sleeve roll for hot finish rolling, characterized by being shrink-fitted.

(2) A hot-rolling composite sleeve roll characterized by further containing, as an outer layer material according to (1), Nb: 0.5 to 2.0% by mass.
(3) In addition to the outer layer material according to (1) or (2), in addition, Ni: 0.2 to 5.0% by mass, Ni: 0.2 to 5.0% composite sleeve for hot finish rolling roll.
(4) In addition to the outer layer material described in (1) to (3) above, the composite sleeve for hot finish rolling characterized by containing Co: 0.5 to 10.0% by mass%. In the roll.

  As described above, according to the present invention, it is possible to perform rolling with a roll having high performance and excellent accident resistance in the post-rolling mill row after finishing of the hot strip mill, and it is economical and productivity can be improved. The quality of rolled products has been improved and has great industrial value.

Hereinafter, the present invention will be described in detail. First, the metal structure of the outer layer material in the rolling roll material of the present invention will be described.
The outer layer material may be basically the same as the so-called high-speed material disclosed in Patent Document 1 and Patent Document 2 described above. First, in order to ensure wear resistance, it is desirable that the carbide is hard, and MC, M ₆ C and M ₇ C ₃ type carbides are mainly used. In particular, in order to realize good wear resistance in a hot strip finish rolling mill to which the present invention is applied, the amount of carbide crystallization is expressed as an area ratio, MC type carbide alone is 5% or more, and total carbide is 10%. It is necessary to secure the above. A small amount of M ₂ C or cementite (Fe ₃ C) carbide that crystallizes during casting does not impair the effects of the present invention, but it is preferably 5% or less.

Hereinafter, the reason which limited the chemical component of the outer-layer material which concerns on this invention is demonstrated.
C is the most important element for obtaining hardness that directly affects the performance of the roll. If the amount of C is less than 1.0%, there is little crystallization and precipitation of hard carbides effective for improving wear resistance and rough skin resistance, and there is not enough C to dissolve in the base. Hardness cannot be obtained, and at the same time, the effect of alloy addition cannot be sufficiently exhibited, wear resistance is remarkably deteriorated, and improvement cannot be expected. On the other hand, if it exceeds 3.0%, the crystallization amount of brittle carbides will increase, especially coarse carbides will aggregate and crystallize at the grain boundaries. Therefore, 3.0% was made the upper limit.

V binds preferentially to C, and crystallizes extremely hard and granular MC type carbide, that is, VC carbide compared with cementite and chromium carbide (Cr ₇ C ₃ ) found in the existing rolls, and improves wear resistance. This is an extremely useful element. Further, VC carbide crystallizes out as a primary crystal preferentially over the molten metal, and V is an important element for the reason of determining the solidification structure, and its content is selected in relation to C. In the range of C: 1.0 to 3.0% of the present invention, if less than 3.0%, VC carbide does not crystallize and the wear resistance cannot be improved, so the lower limit is 3.0%. did. On the other hand, if it exceeds 10%, as described above, a large amount of primary carbides crystallize, and the strength of the material is impaired, and the carbides segregate at the grain boundaries, which are chipped off during rolling and impair the rough skin resistance. Therefore, the upper limit was set.

Cr alone binds to C and agglomerates and crystallizes as a Cr ₇ C ₃ carbide in the form of a network in the form of a network, so that this is not generated, so it is limited to 10% or less. Further, a hard M ₂ C-type eutectic carbide is formed together with Mo and W. As will be described later, this is used after being changed to M ₆ C by heat treatment. On the other hand, Cr is a solid element that dissolves in the base structure and improves the hardness by quenching, and is a useful element for accelerating precipitation hardening in tempering. It is necessary to contain.

Mo and W mainly form hard M ₂ C type eutectic carbides to improve wear resistance, and have been actively used in the above-mentioned patents. This carbide is rod-like and crystallizes at the grain boundary. In the present invention material, the M ₂ C type carbide crystallized during casting becomes a M ₆ C type carbide through a subsequent heat treatment step. On the other hand, Mo, like Cr, partly dissolves in the base structure and improves hardness by quenching, and further promotes precipitation hardening in tempering, and W also partly dissolves in the base structure at high temperature. In order to improve the strength and hardness of the steel, when it is subjected to hot rolling, it has an effect of improving the wear resistance, and in order to exhibit the effect, it contains 2 to 10% of 1 type or 2 types In consideration of the amount of the crystallized carbide, the total amount of both elements is desirably 4% or more and 15% or less.

  Both Si and Mn are preferably contained in amounts of 0.2 to 2.0% of general high-speed steel from the viewpoint of improving the deoxidation effect and the fluidity of the molten metal. The basic components of the outer layer material in the present invention are as described above, but in addition to the chemical components described above, depending on the size of the roll to be applied, the roll characteristics required by the hot strip mill, etc. The following components may be appropriately selected and added.

  Nb has the same action as V, and forms hard MC carbide. Therefore, even if a part of V is replaced with Nb, the effect of the present invention is obtained. However, when the Nb content increases, the eutectic point of the material of the present invention rapidly moves to low C, and when the C content exceeds the eutectic point, coarse MC carbides crystallize as primary crystals and segregate. In particular, the surface properties during use are significantly impaired. Therefore, in the present invention, the Nb content is limited to 2% or less in order to obtain a homogeneous structure within the range of the C content. In order to exhibit the effect, it is necessary to contain 0.5% or more.

  Ni has the effect of improving hardenability when added in an amount of 0.2% or more. When a large curing depth is required, such as a roll having a large diameter, it may be added according to the requirement. However, if added in a large amount, the retained austenite becomes excessive and high hardness cannot be obtained.

When Co is added in an amount of 0.5% or more, it improves the hardness and strength of the base when used at a high temperature, and it is particularly effective to use it in a range of 10% or less for a roll for hot finish rolling. For example, the necessity of selection may be determined in consideration of high temperature hardness and friction coefficient reduction in use characteristics.
Al, Ti, Zr, and Mg have the effects of generating crystallization nuclei of MC type carbides, reducing the size of the carbides, and causing dispersive crystallization. Therefore, especially in the roll for hot finish rolling to which the rolling roll of the present invention is applied, particularly when the rough surface resistance is strongly required, the effect becomes greater when added.

  The outer layer material is used after being cured to a Shore hardness (HS) of 80 or more by heat treatment. In the present invention, since it is a hollow sleeve, a large cooling rate is obtained during quench hardening, and the residual stress is solid. Since it can be kept relatively small as compared with the roll, it is preferably cured to HS85 or higher and used with improved wear resistance.

  FIG. 1 is a view showing a sleeve roll according to the present invention and a conventional solid roll. FIG. 1A is a diagram showing a conventional solid roll, which is a so-called conventional technique in which core materials that are an outer layer 1 and an inner layer 2 (solid roll) are welded and integrated metallurgically. As described above, this roll was a solid roll, and there was a risk that a deep crack would occur on the roll surface or a delayed fracture would occur when a squeeze accident was encountered. This is because when the composite roll for rolling is manufactured, there is a large temperature difference in the inner and outer layers and a transformation expansion difference in the outer and inner layers that occur during heat treatment. And promoted the possibility of delayed destruction.

  Therefore, in the present invention, as shown in FIG. 1B, the outer layer 1 and the inner layer are metallurgically welded to form a sleeve 3, which is assembled by a shrink-fitting portion 5 on a shaft 4 (also referred to as an arbor). It was a roll. As a result, the compressive residual stress generated in the outer layer during the manufacture of the sleeve can be reduced, and when there is a crack in the outer layer on the surface of the roll for rolling, the constraint of the inner layer is relaxed and delayed fracture occurs. Risk can be reduced.

  On the other hand, as a sleeve assembling roll for hot rolling, it is used in a rolling roll for rough rolling, but is not used at all for normal finish rolling. Compared with the roll for rough rolling mill, the roll for finish rolling mill has a small diameter, so the thickness of the sleeve is reduced, and the rolling number (the number of rotations at which the rolling operation is performed in contact with the rolled steel material and the reinforcing roll) This is because the conventional sleeve roll cannot ensure toughness, especially high fatigue strength. Furthermore, in particular, in the finishing post-rolling mill, that is, the rear three to four rolling mills, the thickness of the steel sheet is thin and the demand for the dimensional accuracy is high, so the rigidity of the roll is high. That is, solid rolls that are difficult to deform were preferred.

  In addition, in conventional composite sleeves by centrifugal casting, which employs abradite with excellent wear resistance and various cast irons as the outer layer material, graphite cast steel with a high C content and a low solidification temperature (1.4 to 2.0%) Or, ductile cast iron (3% C or more) had to be adopted as the inner layer material. Therefore, it cannot be used at all from the viewpoint of toughness, fatigue strength and rigidity. Therefore, in the present invention, the outer layer material having excellent wear resistance is employed, while the inner layer material has a low C of 1% or less, which has not been able to be employed by the centrifugal casting method, has high tensile strength, and has high toughness. Forged steel, cast steel, and rolled steel pipe that have high fatigue strength and can provide high rigidity with high Young's modulus are employed. It is manufactured by a continuous casting method in which a sound sleeve can be manufactured by such a combination. For example, SCM material, SNCM material, adamite cast steel, and ductile cast iron are suitable as the tough shaft material for shrink fitting the composite sleeve in the present invention.

  Next, a manufacturing method will be described. First, the outer layer molten metal composed of the chemical component of the present invention is injected between a refractory frame and a core material made of a forged steel, cast steel or rolled steel pipe manufactured in advance to perform induction heating, and then a water cooling mold provided below the refractory frame Then, the molten metal is solidified to form an outer layer portion, and then the integrated outer peripheral portion and core material are sequentially drawn downward to produce a composite roll. Thereby, it becomes an ideal cast structure as the outer layer material of the present invention, and an extremely dense structure can be obtained.

Next, heat treatment for achieving the base structure of the present invention will be described.
As described above, in the present invention, the base structure must first be martensite or bainite by quenching. Therefore, the entire roll is heated to 1000 to 1100 ° C. in a heat treatment furnace, held for a certain period of time, and then cooled to near normal temperature in the air or in a blast, thereby being hardened and hardened. Of course, the cooling rate may be increased as long as cracking does not occur during quenching, and the effect of the present invention is not impaired.

  However, martensite or bainite produced by quenching is very hard, but is an unstable structure at high temperatures. Therefore, particularly in the present invention used for hot rolling, it is heated to a high temperature during use and is not affected by another structure. It transforms uniformly and is undesirable. Therefore, after quenching, tempering is continued at least twice at 500 to 600 ° C. to impart precipitation hardening action and appropriate toughness, and to reduce the large residual stress caused by quenching and to improve accident resistance. It is essential.

  Note that the sleeve roll of the present invention differs from the solid high-speed roll described in the prior art because of its thin wall thickness, the temperature difference inside and outside during heat treatment is small, so that the residual stress is small, especially the outer layer. , The compressive stress is reduced. Furthermore, tensile stress due to shrink fitting is also added during use. As a result, the residual stress is equal to or less than that of Nihard cast iron and high chrome cast iron rolls, which are conventional rolls, thereby eliminating the occurrence of deep cracks at the time of a squeeze accident and eliminating the risk of delayed fracture.

  On the other hand, a sleeve roll requires sufficient fatigue strength on the inner surface that is repeatedly subjected to tensile stress by rolling. In particular, in the roll for a finishing mill, since the sleeve roll is thin, the generated stress is large and high fatigue strength is required. Also in this respect, the present invention employs a tough steel-based inner layer material, and it has become possible to obtain sufficient strength by heat treatment.

  FIG. 2 is a diagram showing the generated stress applied to the inner surface of the sleeve and the required strength in a typical finish rolling mill. This is a Soderberg diagram that is generally used for examining the presence or absence of fatigue failure. As shown in this figure, in the figure, when the generated stress is plotted with the average stress on the horizontal axis and the stress amplitude on the vertical axis, the one-point diagonal line passing through the dot ● indicates the required intensity. It is safe if the straight line (solid line in the figure) connecting the tensile strength shown on the horizontal axis and the fatigue strength shown on the vertical axis is on the upper right side of the single-point diagonal line. Yes, if it is in the lower left, it was judged dangerous. As the fatigue strength, a commonly used rotating bending fatigue strength was adopted.

  As the stress generated in the sleeve, a rolling stress that varies repeatedly at each rotation due to shrinkage fitting stress, residual stress, and rolling load is considered. Here, although the roll diameter is the smallest in a normal hot strip finish rolling mill, the result of the trial calculation at the time of small diameter disposal where the wall thickness of the sleeve becomes thin is shown for the roll to which the largest stress is applied. The shrinkage stress is 150 MPa, the residual stress is 35 MPa, the rolling stress is 0 to 330 MPa, the average stress is 350 MPa, and the stress amplitude (1/2 of the rolling stress) is 165 MPa. The graphite steel (a) and the ductile cast iron (b) employed in the conventional sleeve cannot be used at all. In the present invention, the strength required for the inner layer material is 280 MPa in terms of fatigue strength and 700 MPa (indicated by a broken line in the figure) or more in terms of tensile strength. In addition, although the shrink-fit rate was set to 1/1000 which is larger than the value (0.7 / 1000) generally used for a rough rolling mill, it is preferable to select a value that can withstand the rolling torque depending on the application.

  FIG. 3 is a view showing the residual stress and the inner surface strength of the sleeve of the present invention roll and the conventional roll. The present invention is required to have a compressive residual stress of 300 MPa or less and an inner layer fatigue strength of 280 MPa or more, which are equivalent to those of conventional rolls, and ensure sufficient accident resistance. In addition, although a thermal crack is generated on the surface of the hot finish rolling roll due to contact with the high-temperature steel material, it is necessary to impart an appropriate compressive residual stress because it does not propagate inside, and also in the present invention. The lower limit value was 100 MPa shown in the figure. The figure shows the values for the various rolls described in the prior art. The composite solid roll of nihard cast iron (a and b) and high chromium cast iron (c) by centrifugal casting has a residual compressive stress of 300 MPa. In all cases, the inner layer fatigue strength is as low as 150 MPa or less, and it cannot be used.

  On the other hand, although the high-speed roll (d) by the continuous casting method has a high inner layer fatigue strength of about 350 MPa, the residual compressive stress is as high as 350 MPa, and as described above, there is a problem in accident resistance. Further, it is clear that the inner layer fatigue strengths of the high-speed (e) and nihard cast iron (f) composite sleeve rolls by centrifugal casting are as low as 250 MPa and 100 MPa, respectively, and cannot be used. The residual stress of the present invention is the one at the time of use. Therefore, the stress (tensile) due to shrink fitting is added to the residual stress (compression) of the sleeve itself.

  For the measurement of the residual stress, a method using an open strain by processing using a strain gauge and a method using X-rays are generally performed. In the former case, the measured value can be used as it is, but in the latter case, since it is a value obtained by measuring a minute crystal strain, the measured value is often converted into a macroscopic stress value. The optimum value of (macro true stress / measured value by X-ray) is optimally 0.6.

  As described above, the sleeve roll cannot be used because of its low rigidity. Therefore, in the present invention, both the high-speed material employed for the outer layer and the steel employed for the inner layer have increased rigidity by a combination having a high longitudinal elastic modulus (Young's modulus). Thereby, the required rigidity can be obtained although the cross-sectional area is smaller than that of the conventional solid roll.

Hereinafter, the present invention will be specifically described with reference to examples.
Table 1 shows chemical components. No. 1-4 are conventional examples. 1-3 are centrifugal casting methods, 4 is a case where a composite solid roll is manufactured by a continuous casting method. No. Nos. 5 to 12 are examples of the present invention. 13 to 14 are comparative examples, each of which produced composite sleeve rolls by centrifugal casting. Thereafter, the same heat treatment was applied to the high-speed rolls, and Nihard cast iron and high chromium cast iron were each subjected to appropriate heat treatment. . The invention example No. Nos. 5 to 12 were produced as rolling rolls for a rear rolling mill in a hot strip mill having seven hot finish rolling mills.

  The diameters of the rolls for rolling were all 615 mm at the time of new production and 525 mm at the time of disposal, the sleeve inner diameter was 360 mm, and the sleeve length was 1850 mm. For the outer layer, a hardness and metal structure equivalent to a solid high-speed roll were obtained. Here, FIG. 2 and FIG. Although the tensile strength, fatigue strength, and residual stress of the inner layer in 5 to 12 are shown together, it is clear that the target sufficient strength and low residual stress can be achieved.

  FIG. 4 is a view showing the rigidity of the roll of the present invention and the conventional roll. As shown in this figure, the bending stiffness (El: Young's modulus x cross-sectional secondary moment) representing rigidity is compared. The outer layer material of the present invention has a high Young's modulus as well as 230 GPa and the inner layer material has 210 GPa. As a result, the present invention is the most commonly used inner layer in the past, even in the smallest diameter (575 mm) of the most severe range of use in the finishing mill with the highest dimensional accuracy requirements and the highest importance of rigidity. It has rigidity equal to or higher than Nihard cast iron roll (No. 2) using ductile cast iron. Furthermore, when it was made at the maximum diameter (625 mm), it was possible to obtain a rigidity about 10% higher than that of the roll. Therefore, the Young's modulus of the inner layer material is desirably 200 GPa. Although not shown in this example, it is also possible to use an inexpensive rolled steel pipe having the necessary strength and Young's modulus as the inner layer material.

It is a figure which shows the sleeve roll which concerns on this invention, and the conventional solid roll. It is a figure which shows the generated stress added to the sleeve inner surface in a typical finishing mill, and required intensity | strength. It is the figure which showed the residual stress of this invention roll and the conventional roll, and the inner surface strength of a sleeve. It is the figure which showed the rigidity of this invention roll and the conventional roll.

Explanation of symbols

1 outer layer 2 inner layer 3 sleeve 3
4 axis 5 shrink fit


Patent applicant: Nippon Steel Corporation and 1 other
Attorney Attorney Shiina and others 1

Claims (4)

In a hot finish rolling roll for hot finish rolling a steel strip or a steel plate, the C content is 1% by mass or less around the inner layer made of forged steel, cast steel or rolled steel pipe, in mass%,
C: 1.0-3.0%,
Si: 0.2-2.0%,
Mn: 0.2 to 2.0%,
V: 3.0-10.0%,
Cr: 3.0 to 10.0%, and a composite containing 2.0 or 10% of Mo or W, and the outer layer composed of the remaining Fe and unavoidable impurities is formed by a continuous casting method. A composite sleeve roll for hot finish rolling, wherein the sleeve is shrink-fitted with a tough shaft. 2. The composite sleeve roll for hot finish rolling, wherein the outer layer material according to claim 1 is further added by mass% and Nb: 0.5 to 2.0%. A composite sleeve roll for hot finish rolling, wherein the outer layer material according to claim 1 or 2 further contains Ni: 0.2 to 5.0% by mass. A composite sleeve roll for hot finish rolling, wherein the outer layer material according to any one of claims 1 to 3 further contains Co: 0.5 to 10.0% by mass.

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