JP2005177808A - External layer material of rolling roll and rolling roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external layer material of a rolling roll which is excellent in wear resistance, resistance to rough surface and resistance to accident and the rolling roll using the same. <P>SOLUTION: The external layer material of the rolling roll, the chemical composition of which consists of, by mass, > 3.0 to ≤ 4.0% C, ≤ 3.0% Si, 2.3-5.5% Ni, 1.0-2.0% Cr, 0.3-10.0% V, 0.01-2.0% Ti and the balance Fe with impurity elements, which has graphite and MC base carbide in the metallic structure and the spheroidizing rate of the graphite is ≥ 0.5. Furthermore, the material contains, by mass, one or more of 0.3-2.0% Mn, 0.2-3.0% Mo, 0.1-3.0% W, 0.3-10.0% Nb, 0.1-10.0% Co, 0.002-0.2% B and 0.02-1.0% Cu. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an outer layer material of a roll for rolling excellent in wear resistance, rough skin resistance and accident resistance, and a roll for rolling using the same. In particular, it is suitable as an outer layer material of a work roll used in the subsequent stage of the finishing row of a hot sheet rolling machine.

  Conventionally, a roll using a Glen-based cast iron material as an outer layer material has been used in the subsequent stage of the finishing line of a hot sheet rolling mill. In general, the Glen-based roll has excellent seizure resistance, and has an advantage that even if a rolling accident is encountered, there is little seizure of the material to be rolled, and there is little progress of occurrence of cracks.

  However, the wear resistance is considerably inferior to that of a roll containing a high-speed material containing a large amount of an alloy such as Cr, Mo, V, and W and crystallizing a very hard MC-based carbide.

As means for improving the wear resistance of the roll, methods for crystallizing or precipitating hard carbides such as MC-based and M ₂ C-based are known. As a means for improving seizure resistance, a method of crystallizing graphite, which is a solid lubricant, is known. However, V, Mo, and W, which are elements constituting the hard carbide, are whitening elements and have been difficult to coexist with graphite. In addition, when a Glen-based roll containing V or the like is manufactured by a centrifugal casting method, there is a problem that, for example, MC-based carbide segregates on the inner surface side due to a difference in specific gravity between the crystallized carbide and the molten metal.

  Various inventions have been made to solve such problems, and the present applicant has already proposed Patent Document 1. That is, in Patent Document 1, the chemical component is mass%, C: 2.0 to 4.0%, Si: 0.5 to 4.0%, Mn: 0.1 to 1.5%, Ni: 2.0 to 6.0%, Cr: 1.0 to 7.0%, V: 2.0 to 8.0%, balance Fe and impurity elements, and 0.5 to 0.5% by area structure A wear-resistant and seizure-resistant hot rolling roll having a metal structure composed of 5.0% graphite, 0.2 to 10.0% MC-based carbide, and 10.0 to 40.0% cementite. Has been described.

JP-A-6-335712

  In the roll for hot rolling of Patent Document 1, since the shape of graphite in the metal structure is flaky and easily crystallizes non-uniformly, the wear form of the roll becomes non-uniform and wear resistance and rough skin resistance are still sufficient. It was not. In addition, there is a problem that the shape of the MC-based carbide does not easily become a fine grain having a low notch coefficient, and the accident resistance is not sufficient.

  Accordingly, an object of the present invention is to solve these problems and provide an outer layer material of a roll for rolling excellent in wear resistance, rough skin resistance and accident resistance, and a rolling roll using the same.

  The present inventor made improvements to the roll outer layer material of Patent Document 1 excellent in seizure resistance, and in particular, by making Ti essentially contained, the shape of graphite was made into a fine spherical shape, and in the metal structure. It was found that it could be uniformly dispersed, and improved wear resistance, rough skin resistance and accident resistance.

  The outer layer material of the rolling roll of the present invention has a chemical composition of mass%, C: more than 3.0% and 4.0% or less, Si: 3.0% or less, Ni: 2.3 to 5.5. %, Cr: 1.0 to 2.0%, V: 0.3 to 10.0%, Ti: 0.01 to 2.0%, the balance being Fe and impurity elements, graphite in the metal structure And MC-based carbide, and the spheroidization ratio of the graphite is 0.5 or more.

  In the present invention, in terms of mass%, Mn: 0.3 to 2.0%, Mo: 0.2 to 3.0%, W: 0.1 to 3.0%, Nb: 0.3 ~ 10.0%, Co: 0.1 to 10.0%, B: 0.002 to 0.2%, Cu: 0.02 to 1.0% Features.

Furthermore, in the present invention, the metal structure is characterized by having 1% or more of graphite having a diameter of 3 μm or less in terms of a circle in area%. Further, the number of graphite particles is 300 or more per 1 cm ^{2 in the} structure observation cross section.

  The reason for limiting the content range (% by mass) of each chemical component of the roll outer layer material of the present invention will be described.

C: More than 3.0% and 4.0% or less C combines hard carbides such as cementite, MC, M ₂ C, M ₆ C, M ₇ C ₃ carbides by combining with Fe, Cr, V, etc. It is an element necessary for generating and enhancing the wear resistance and crystallization of graphite to impart seizure resistance. When C is 3.0% or less, the amount of carbide is insufficient and the amount of crystallization of graphite is also insufficient. If it exceeds 4.0%, the amount of cementite and hard carbide increases, and the toughness decreases. The content of C is preferably more than 3.0% and not more than 3.4%.

Si: 3.0% or less Si is a graphitization promoting element. If the total amount of Si in the outer layer material exceeds 3.0%, the matrix becomes brittle and the toughness decreases. Moreover, in order to crystallize graphite, it is necessary to add 0.03% or more of the total Si amount by inoculation. The amount of Si to be inoculated is preferably 0.1 to 0.5% of the total amount of Si. The total amount of Si in the outer layer material is preferably 0.8 to 3.0%, more preferably 1.0 to 2.0%.

Ni: 2.3 to 5.5%
Ni is effective for improving the crystallization of graphite and the hardenability of the matrix structure. Since the outer layer material of the present invention does not require quenching after casting, it may be contained by 2.3% or more. If it exceeds 5.5%, austenite becomes too stable, and it becomes difficult to transform into bainite or martensite. The content of Ni is preferably 3.0 to 5.0%, and more preferably 4.0 to 5.0%.

Cr: 1.0-2.0%
Cr is an element effective for securing hardness and maintaining wear resistance by making the base structure bainite or martensite, and is required to be 1.0% or more. When Cr exceeds 2.0%, the crystallization of graphite is inhibited or the toughness of the base structure is lowered. In addition, Cr carbide (M ₇ C ₃ system, M ₂₃ C ₆ system) is formed, and since this carbide has lower hardness than MC system and M ₆ C system carbide, the effect of improving wear resistance cannot be expected. And become brittle. For this reason, the upper limit of Cr is set to 2.0%.

V: 0.3 to 10.0%
V combines with C to produce MC carbide. The hardness of this MC-based carbide is Hv 2500 to 3000, and is extremely hard among the carbides. For this reason, V is one of the essential elements that is most effective in improving wear resistance. Not only crystallized carbides but also fine precipitated carbides in the matrix contributes to improved wear resistance. However, if excessively contained, crystallization of graphite is hindered and toughness is reduced. At the same time, MC-based carbides are coarsened and the rough skin resistance is lowered, which is not preferable. The content of V is preferably 2.0 to 5.0%.

Ti: 0.01 to 2.0%
Ti is the most characteristic element in the roll outer layer material of the present invention. These have the effect of spheroidizing graphite and crystallize finely and uniformly. In order to make the shape of graphite into fine spherical particles and uniformly disperse it in the metal structure, 0.01% or more of Ti is required. On the other hand, 2.0% Ti is sufficient from the amount of N and O contained. The content of Ti is preferably 0.05 to 0.5%.

  Although the basic chemical components of the outer layer material of the present invention are as described above, the following various chemical components can be selectively added depending on the application and usage characteristics of the roll.

Mn: 0.3 to 2.0%
Mn is effective when deoxidation of molten metal and S, which is an impurity, are fixed as MnS and contained in an amount of 0.3% or more. If Mn exceeds 2.0%, retained austenite tends to be generated, and the hardness cannot be stably maintained. The Mn content is preferably 0.4 to 1.5%, more preferably 0.4 to 1.0%.

Mo: 0.2-3.0%
Mo combines with C to form hard M ₆ C-based and M ₂ C-based carbides, and dissolves in the base structure to strengthen the base structure, so it is effective in improving wear resistance. .Effective when contained in 2% or more. If it exceeds 3.0%, crystallization of graphite is inhibited, which is not preferable. The Mo content is preferably 0.2 to 1.0%.

W: 0.1-3.0%
W, like Mo, combines with C to form hard M ₆ C and M ₂ C carbides, and dissolves in the base structure to strengthen the base structure, so it is effective in improving wear resistance. Yes, containing 0.1% or more is effective. If it exceeds 3.0%, crystallization of graphite is inhibited, which is not preferable. The content of W is preferably 0.2 to 2.0%.

Nb: 0.3 to 10.0%
Nb, like V, combines with C to produce MC-based carbides. When the outer layer material of the roll is formed by a centrifugal casting method, Nb has an effect of reducing the segregation of MC carbides. What is necessary is just to select the necessity of addition of Nb according to the addition amount of V at the time of centrifugal force casting. However, excessive inclusion is not preferable because toughness is reduced and MC carbides are coarsened to deteriorate the rough skin resistance. The content of Nb is preferably 2.0 to 5.0%.

Co: 0.1-10.0%
Co is an element effective for strengthening the base structure, but when it is excessive, toughness is reduced. Therefore, the Co content is 0.1 to 10.0%. Co also has the effect of destabilizing cementite and facilitating crystallization of graphite. The content of Co is preferably 3.0 to 7.0%.

B: 0.002 to 0.2%
B has an effect of making carbide finer. If it is less than 0.002%, the effect is not sufficiently exhibited. If it exceeds 0.2%, the carbide becomes unstable. The content of B is preferably 0.01 to 0.05%.

Cu: 0.02 to 1.0%
Cu, like Co, has the effect of destabilizing cementite and facilitating crystallization of graphite. If it is less than 0.02%, the effect is not sufficient, and if it exceeds 1.0%, the toughness is lowered. The content of Cu is preferably 0.1 to 0.5%.

  Except for the above elements, the balance is substantially Fe except for impurities. The main elements as impurities are P and S. In order to prevent a decrease in toughness, the P content is preferably 0.1% or less, and the S content is preferably 0.08% or less.

  The outer layer material of the present invention has graphite in its metal structure, and excellent seizure resistance and fracture toughness values necessary for ensuring accident resistance are improved according to the amount of graphite. When the amount of graphite is less than 0.5% in area%, the seizure resistance effect is not sufficient. On the other hand, if the amount of graphite exceeds 5%, the effect of improving the seizure resistance and fracture toughness value is saturated and the wear resistance is lowered. For this reason, the amount of graphite required is 0.5 to 5%. A more preferable amount of graphite is 1 to 3%.

  In order to improve the wear resistance, it is necessary to disperse hard carbides. In particular, MC-based carbide which is a hard carbide needs to be contained in an area of 0.1 to 10%. When the area percentage of the hard carbide is less than 0.1%, the wear resistance is not sufficient. In addition, due to the coexistence with graphite, it is difficult to produce a hard carbide exceeding 10%. More preferably, the area percentage of the MC-based carbide is 0.5 to 6%.

  In addition, cementite is included in the metal structure, and cementite is softer than MC carbide, but can be easily crystallized without using an expensive alloy. Moreover, by crystallizing in a large amount, the particle size of the soft matrix can be made fine, the matrix area ratio can be reduced, and the wear resistance can be improved. If the crystallization amount of cementite is less than 10%, crystallization of graphite becomes difficult, and if it exceeds 45%, the toughness decreases. More preferable area percent of cementite is 15 to 40%.

  The roll outer layer material of the present invention makes the shape of graphite in the metal structure fine spherical and can be uniformly dispersed in the metal structure. The spheroidization rate of the graphite of the present invention is 0.5 or more. When the spheroidization ratio of graphite is less than 0.5, the wear form of the roll becomes non-uniform, and the wear resistance and rough skin resistance deteriorate. A more preferable spheroidization ratio of graphite is 0.7 to 1.0.

  Further, when the MC carbide grains are small and finely dispersed, the rough skin resistance is improved. Also, the more MC-based carbides, the better the wear resistance. Therefore, it is desirable that MC-based carbides having a diameter of 10 μm or less in terms of a circle in the metal structure are 2% or more in area%. More preferably, the MC-based carbide having a diameter of 10 μm or less in terms of a circle is 2 to 10 area%.

Further, when the graphite grain size is small and spherical and finely dispersed, the rough skin resistance is improved. Therefore, it is desirable that graphite having an area of% and a diameter of 3 μm or less in terms of a circle is 1% or more in the metal structure. More preferably, the graphite having a diameter of 3 μm or less in terms of a circle is 2 to 3%. Further, the more graphite, the better the wear resistance. The number of graphite particles is desirably 300 or more per 1 cm ^{2 in the} structure observation cross section. More preferably, the number is 1000 to 4000 per 1 cm ² .

  Moreover, it is preferable that the base structure of the outer layer material of the present invention is substantially composed of martensite, bainite, or pearlite.

  The outer layer material of the roll of the present invention can be formed by a centrifugal casting method or a continuous overlay casting method. Centrifugal casting is more preferable for further exerting the effects of the present invention. In any method, it is necessary to inoculate using a Si-containing inoculum such as an Fe-Si inoculum and a Ca-Si inoculum during casting.

  Molten metal of chemical components (test materials No. 1 to No. 25) shown in Table 1 was cast and cast in a cylindrical mold rotated at high speed by a centrifugal casting machine. About addition of Si to a molten metal, Fe-Si inoculum was added to the molten metal after the hot water was discharged from the furnace with the ladle. The sample material thus obtained was heated at 500 ° C. for 10 hours and gradually cooled to decompose and remove strain from the retained austenite.

  Specimen No. shown in Table 1 1-No. 7 is an example of the present invention; 21-No. Reference numeral 25 is a comparative example. The test material No. No. 31 is a conventional Glen-based material, test material No. 32 is a conventional high-speed material.

Test specimens were collected from these test materials, and the image analysis apparatus (SPICCA-II manufactured by Nippon Avionics Co., Ltd.) was used to convert the area percentage of the structural component, the spheroidization rate of the graphite, and the graphite with a diameter of 3 μm or less in terms of a circle into metal. The area percentage in the structure and the number of graphite grains per 1 cm ² were measured. The fracture toughness value and tensile strength were also measured. A wear test was conducted with a rolling wear tester, and a seizure test was conducted with a frictional thermal shock tester. Table 2 shows the test results.

  FIG. 1 shows a schematic view of a rolling wear tester. In FIG. 1, the rolling wear tester includes a rolling mill 1, a heating furnace 4 for preheating the rolled material S, a cooling water tank 5 for cooling the rolled material S, a winder 6 for the rolled material S, and a tension controller 7. Consists of Test rolls 2 and 3 are incorporated in the rolling mill 1. A test roll was prepared from the above-described test material, and a small sleeve roll having an outer diameter of 60 mm, an inner diameter of 40 mm, and a width of 40 mm was used. A test roll is incorporated into a rolling wear tester, and the test conditions are rolling material: SUS304, rolling reduction: 25%, rolling speed: 150 m / min, rolling temperature: 900 ° C., rolling distance: 300 m / time, roll cooling: water cooling The number of rolls: The test was performed by a quadruple type. After rolling, the depth of wear generated on the surface of the test roll was measured with a stylus type surface roughness meter.

  FIG. 2 shows a schematic diagram of a frictional thermal shock tester. In FIG. 2, the frictional thermal shock tester rotates a pinion 10 by dropping a weight 9 on a rack 8, and causes the biting material 12 to come into strong contact with the test material 11.

  FIG. 3 is a diagram for explaining the spheroidization ratio and the circle-equivalent diameter of graphite. In FIG. 3, 15 is an object to be measured, and refers to graphite in the present invention. A specimen taken from the specimen was mirror polished. Then, the portion was subjected to image analysis at 10 magnifications at a magnification of 100, and the average was defined as the spheroidization rate and the circle-equivalent diameter.

  When the area of the measurement object is A and the circumference of the measurement object is L, the spheroidization rate is expressed by Equation (1), and the closer to 1, the closer to a perfect circle. Moreover, the diameter of graphite in terms of a circle is a diameter of a circle C corresponding to an area equal to the area A of the measurement object 15, and is represented by Expression (2).

  From Table 1 and Table 2, since the roll outer layer material of the present invention example contained Ti, the shape of the graphite was made into a fine spherical shape and uniformly dispersed in the metal structure. Good results were obtained for both rough skin and accident resistance.

  Compared to the inventive example, Comparative Example 21 is inferior in fracture toughness value. Comparative Example 22 has a large amount of wear and is inferior in wear resistance. Comparative Example 23 has a large seizure area ratio and is inferior in seizure resistance. Comparative Example 24 has a large amount of wear and is inferior in wear resistance. It was found that Comparative Example 25 was inferior in seizure resistance and rough skin resistance because of a large seizure area ratio and large skin roughness.

  In addition, in FIG. 1 shows a micrograph (20 times) of the metal structure in FIG. In FIG. The microscope picture (20 time) of the metal structure in 21 is shown. Test specimens were collected from each test material, polished with alumina, and observed without corrosion. In FIG. 4, the whitish granular material is MC-based carbide, and the blackish material is graphite. In FIG. 5, the whitish petals are MC-based carbides, and the blackish flakes are graphite. In the example of the present invention, it can be seen that the graphite has a fine spherical shape and is uniformly dispersed in the metal structure.

  As described above, the outer layer material of the rolling roll of the present invention has both wear resistance and accident resistance due to the coexistence of graphite and hard carbide. Further, wear resistance and accident resistance can be further improved by finely and uniformly dispersing graphite and making the shape spherical. The rolling roll formed using the outer layer material of the rolling roll of the present invention is generally used in the work roll for hot rolling, particularly in the latter stage of the finishing row of the hot sheet rolling mill, and in the rolling mill. Contributes to improved productivity.

1 is a schematic view of a rolling wear tester used in an embodiment. It is the schematic of the friction thermal shock tester used in embodiment. It is a figure for demonstrating the spheroidization rate of MC type carbide | carbonized_material, and a circle conversion diameter. Sample No. of the present invention example. It is a microscope picture which shows 1 metal structure. Sample No. of Comparative Example It is a microscope picture which shows 21 metal structures.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling wear test machine, 2 Test roll, 3 Test roll, 4 Heating furnace,
5 Cooling water tank, 6 Winder, 7 Tension controller, S Rolled material,
8 racks, 9 weights, 10 pinions, 11 specimens,
12 Biting material, 15 Object to be measured

Claims (5)

The chemical composition is mass%, C: more than 3.0% and 4.0% or less, Si: 3.0% or less, Ni: 2.3 to 5.5%, Cr: 1.0 to 2.0 %, V: 0.3 to 10.0%, Ti: 0.01 to 2.0%, the balance being Fe and impurity elements, and having a graphite and MC carbide in the metal structure, An outer layer material of a roll for rolling, wherein the spheroidization ratio is 0.5 or more. Furthermore, in mass%, Mn: 0.3 to 2.0%, Mo: 0.2 to 3.0%, W: 0.1 to 3.0%, Nb: 0.3 to 10.0%, 2. One or more of Co: 0.1 to 10.0%, B: 0.002 to 0.2%, and Cu: 0.02 to 1.0% are contained. The outer layer material of the roll for rolling as described in 2. The outer layer material of a roll for rolling according to claim 1 or 2, wherein the metal structure contains 1% or more of graphite having a diameter of 3 µm or less in terms of a circle in area%. The outer layer material for rolling rolls according to claim 1, number of grains of graphite, characterized in that 300 or more per 1 cm ^2. A roll for rolling, which is formed using the outer layer material of the roll for rolling according to any one of claims 1 to 4.