JP2005068465A - Outer layer material of roll for rolling, and roll for rolling using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an outer layer material of a roll for rolling superior in abrasion resistance, surface roughening resistance and accident resistance, and to provide the roll for rolling using it. <P>SOLUTION: This outer layer material has a chemical composition comprising, by mass%, more than 3.0% but 4.0% or less C, 3.0% or less Si, 2.3-5.5% Ni, 0.1-2.0% Cr, 0.3-10.0% V, 0.005-0.500% one or two of Mg and Ca and the balance Fe with impurity elements; and has a metallographic structure containing, by area%, 0.5-5.0% graphite. <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

  The hot rolling roll of Patent Document 1 is obtained by crystallizing hard MC carbide to improve wear resistance. However, when the alloy is simply contained at a high concentration, MC carbides are likely to crystallize in a non-uniform manner, so the wear form of the roll becomes non-uniform, and the wear resistance and rough skin resistance are still insufficient. In addition, there is a problem that the shape of the hard carbide is not easily formed into 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 inventor has improved the roll outer layer material of Patent Document 1 excellent in seizure resistance, and in particular, by containing Mg or Ca, the shape of the MC-based carbide is made into a fine granular shape, and the metal structure It was found that it could be dispersed uniformly in the inside, and improved wear resistance, rough skin resistance and accident resistance.

  That is, the outer layer material of the rolling roll of the first aspect of the present invention has a chemical composition of mass%, C: more than 3.0%, 4.0% or less, Si: 3.0% or less, Ni: 2. 3 to 5.5%, Cr: 0.1 to 2.0%, V: 0.3 to 10.0%, containing one or two of Mg or Ca 0.005 to 0.5%, It consists of the remaining Fe and impurity elements, and has graphite in the metal structure.

  The outer layer material of the roll for rolling of the second aspect of the present invention has a chemical component of mass%, C: more than 3.0%, 4.0% or less, Si: 3.0% or less, Ni: 2.3 to 5.5%, Cr: 0.1 to 2.0%, 0.3 to 10.0% in total of V and Nb, 0.005 to 0.5% of one or two of Mg or Ca And the balance Fe and impurity elements, and having a metal structure with graphite.

  In the first and second aspects of the present invention, 0.005 to 0.5% of rare earth element (REM) is contained by mass%. In addition, by mass, Mn: 0.3 to 2.0%, Mo: 0.2 to 3.0%, W: 0.1 to 3.0%, Co: 0.1 to 10.0% , Ti: 0.01 to 2.0%, B: 0.002 to 0.2%, Cu: 0.02 to 1.0%, or one or more thereof.

  In addition, the metal structure of the outer layer material according to the present invention is characterized by having graphite in an area% of 0.5 to 5%. Furthermore, it is a roll for rolling using the outer layer material of the present invention. The rolling roll of the present invention is desirably used as a work roll for the subsequent stage of the finishing row of a hot sheet rolling mill.

The reason for limiting the content range (% by mass) of each chemical component in 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%, more preferably 4.0 to 5.0%.

Cr: 0.1 to 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 0.1% 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%. The content of Cr is more preferably 1.0 to 1.8%.

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%.

Mg, Ca: 0.005 to 0.5%
Mg and Ca are the most characteristic elements in the roll outer layer material of the present invention. These are elements having a strong deoxidation and desulfurization action, and form oxides and sulfides. Although the detailed phenomenon is unknown, these are suspended in the molten metal to become nuclei and cause MC-based carbides to crystallize uniformly and finely. In addition, the MC-based carbide crystallized is assumed to be granular, just like the graphite of spheroidal graphite cast iron is spheroidized by adding Mg or the like. In order to make the shape of the MC carbide fine particles and uniformly disperse it in the metal structure, one or two of Mg and Ca needs to be 0.005% or more. On the other hand, if it exceeds 0.5%, the effect is saturated, and addition of a large amount makes the reaction with the molten metal difficult and makes it difficult to work.

V + Nb: 0.3 to 10.0%
In the outer layer material of the second present invention, V and Nb can be 0.3 to 10.0% in total content. 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.

Rare earth element (REM): 0.005 to 0.5%
In the outer layer material of the first and second inventions, 0.005 to 0.5% of rare earth element (REM) may be added. Although details are not yet clear, rare earth elements (REM) have the effect of granulating MC carbides and spheroidizing graphite in the same manner as Mg and Ca.

  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%.

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%.

Ti: 0.01 to 2.0%
Ti combines with N and O, which are graphitization inhibiting elements, to form oxynitrides. If Ti is less than 0.01%, the effect cannot be expected, and 2.0% is sufficient for Ti from the amount of N and O contained. The content of Ti is preferably 0.05 to 0.5%.

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.

  In order to ensure the accident resistance of the outer layer material of the roll, it is necessary to improve the seizure resistance and the fracture toughness value. The seizure resistance and fracture toughness values are improved according to the amount of graphite in the metal structure. 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 5.0%, the effect of improving seizure resistance and fracture toughness value is saturated and wear resistance is lowered. The amount of graphite is preferably 1.0 to 3.0%.

  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 inoculant 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, Mg, and Ca to a molten metal, Fe-Si inoculum, Ni-Mg inoculum, and Ca-Si inoculum were added to the molten metal after tapping from a furnace. 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.

  Specimens were collected from these test materials, the area percentage of the structural components was measured by an image analyzer, and the fracture toughness value and tensile strength were measured. Also, 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.

  Since the roll outer layer material of the present invention example contains Mg or Ca, the shape of the MC-based carbide is finely granulated and uniformly dispersed in the metal structure, so that the wear resistance, rough skin resistance and Good results were obtained in terms of 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. Since Comparative Example 25 has a large baking area ratio and a large skin roughness, it is inferior in seizure resistance and rough skin resistance.

  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 hard carbide and making the shape granular. The outer layer material of the roll for rolling according to the present invention exhibits excellent performance in the entire work roll for hot rolling, particularly in the latter stage of the finishing row of the hot sheet rolling mill, and contributes to the improvement of productivity in the rolling mill.

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.

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

Claims (7)

Chemical component is mass%, C: more than 3.0% and 4.0% or less, Si: 3.0% or less, Ni: 2.3-5.5%, Cr: 0.1-2.0 %, V: 0.3 to 10.0%, containing one or two of Mg or Ca in an amount of 0.005 to 0.5%, the balance being Fe and impurity elements, and having a metal structure with graphite. The outer layer material of the roll for rolling characterized. Chemical component is mass%, C: more than 3.0% and 4.0% or less, Si: 3.0% or less, Ni: 2.3-5.5%, Cr: 0.1-2.0 %, V and Nb in total 0.3 to 10.0%, Mg or Ca one or two kinds are contained 0.005 to 0.5%, the balance is Fe and impurity elements, and the metal structure is graphite. An outer layer material of a roll for rolling, comprising: Furthermore, 0.005 to 0.5% of rare earth elements (REM) are contained by mass%, and the outer layer material of the roll for rolling according to claim 1 or 2. Furthermore, in mass%, Mn: 0.3 to 2.0%, Mo: 0.2 to 3.0%, W: 0.1 to 3.0%, Co: 0.1 to 10.0%, 2. One or more of Ti: 0.01 to 2.0%, B: 0.002 to 0.2%, and Cu: 0.02 to 1.0% are contained. The outer-layer material of the roll for rolling in any one of -3. The outer layer material of the roll for rolling according to any one of claims 1 to 4, wherein the graphite has an area% of 0.5 to 5.0%. A rolling roll using the outer layer material of the rolling roll according to any one of claims 1 to 5. The roll for rolling according to claim 6, which is a work roll for a subsequent stage of a finishing row of a hot sheet rolling machine.