JP2005169426A - Composite rolling roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite rolling roll excellent in abrasion resistance, surface roughening resistance, and accident resistance, and excellent in mechanical properties in the vicinity of the boundary between an outer layer and an inner layer. <P>SOLUTION: The outer layer of the roll has a chemical composition containing, by mass%, 2.5-3.0% C, ≤ 3.0% Si, 2.3-5.5% Ni, 0.1-2.0% Cr, 0.3-10.0% V, 0.005-0.5% of 1 or 2 kinds from Mg and Ca, and the balance Fe with impurity elements, and has graphite in its metallic structure. The inner layer of the roll consists of either of flake graphite cast iron, spheroidal graphite cast iron, or graphite steel. The roll has, between the outer and inner layers, an intermediate layer whose metallic structure contains graphite. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composite roll for rolling excellent in wear resistance, rough skin resistance and accident resistance. In particular, it is suitable as a work roll used in the subsequent stage of the finishing row of a hot sheet rolling mill.

  Conventionally, a roll having a Glen-based cast iron material as an outer layer 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, W and the like, in which a very hard MC-based carbide is crystallized.

Therefore, as a means for improving the wear resistance of the roll, a method of crystallizing or precipitating hard carbides such as MC and M ₂ C has been considered. 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.

  Furthermore, in the conventional composite roll in which the outer layer and the inner layer are metal-bonded, alloy components are mixed into the inner layer from the outer layer, and defects and carbide concentrated layers are generated at the boundary between the outer layer and the inner layer. There was also a problem that mechanical properties such as strength and toughness were easily deteriorated.

  Therefore, an object of the present invention is to eliminate the above-mentioned problems, and to provide a composite roll for rolling excellent in wear resistance, rough skin resistance and accident resistance, and excellent in mechanical properties in the vicinity of the boundary between the outer layer and the inner layer. Is to provide.

  The present inventor has improved the roll outer layer 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 fine and granular, It was found that they could be dispersed uniformly, and improved wear resistance, rough skin resistance and accident resistance.

  In addition, by providing an intermediate layer with graphite in the metal structure between the outer layer and the inner layer, we found that mixing of alloy components from the outer layer to the inner layer was suppressed, and improved the mechanical properties near the boundary between the outer layer and the inner layer It was possible to.

  That is, the chemical component is mass%, C: 2.5-3.0%, Si: 3.0% or less, Ni: 2.3-5.5%, Cr: 0.1-2.0%, V: 0.3 to 10.0%, one or two of Mg or Ca is contained in an amount of 0.005 to 0.5%, the outer layer is made of Fe and an impurity element, and has a metallographic structure, and a piece. The present invention is characterized in that an intermediate layer having graphite in the metal structure is provided between the inner layer made of any of graphite-like cast iron, spheroidal graphite cast iron and graphite steel.

  Further, in the present invention, the outer layer contains 0.005 to 0.5% of rare earth element (REM) by mass%. Further, the outer layer is 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. One of 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 It contains 2 or more types.

  Further, the metal structure of the outer layer of the present invention has graphite in an area% of 0.5 to 5.0%, and the graphite in the intermediate layer has an area% of 0.1 to 10.0%. To do. Moreover, the said intermediate | middle layer is the mass%, C: 4.0% or less, Si: 4.0% or less, Ni: 1.0-5.0%, Cr: 0.1-1.5%, V: It contains 0.1 to 8.0%, consists of the balance Fe and impurity elements, and the thickness of the intermediate layer in the roll radial direction is 10 mm or more. Furthermore, the composite roll for rolling according to the present invention is used as a work roll for a subsequent stage of a 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: 2.5-3.0%
C combines with Fe, Cr, V, etc. to produce hard carbides such as cementite, MC, M ₂ C, M ₆ C, and M ₇ C ₃ carbides to increase wear resistance and to crystallize graphite. It is an element necessary for imparting seizure resistance. If C is less than 2.5%, the amount of carbide is insufficient and the amount of crystallization of graphite is also insufficient. If it exceeds 3.0%, MC-based carbides are easily crystallized as primary crystals, so it is necessary to reduce the amount of V or Nb added, and the amount of MC-based carbides is limited.

Si: 3.0% or less Si is a graphitization promoting element. If the total amount of Si in the outer layer 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 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 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 outer roll layer 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.

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

Rare earth element (REM): 0.005 to 0.5%
In the outer layer of the present invention, 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.

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 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.

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 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 inner layer of the composite roll of the present invention is preferably excellent in toughness, and specifically, is preferably composed of any one of flake graphite cast iron, spheroidal graphite cast iron and graphite steel.

  Further, an intermediate layer having graphite in the metal structure is provided between the outer layer and the inner layer of the present invention. Desirable component ranges of the intermediate layer are mass%, C: 4.0% or less, Si: 4.0% or less, Ni: 1.0 to 5.0%, Cr: 0.1 to 1.5%, V: 0.1 to 8.0% is contained and the balance is Fe and impurity elements.

  By providing this intermediate layer, mixing of alloy components from the outer layer to the inner layer can be suppressed, and mechanical properties such as strength and toughness in the vicinity of the boundary between the outer layer and the inner layer can be improved. Further, by allowing the intermediate layer to crystallize 0.1 to 10.0% by area ratio, the elongation in the vicinity of the boundary is improved, and the strength and toughness are further strengthened. If the area ratio of the graphite in the metal structure is less than 0.1%, the effect is not exhibited, and if it exceeds 10.0%, the graphite is densely packed in the boundary portion and the boundary strength is deteriorated. Furthermore, the area ratio of the preferable graphite is 0.2 to 6.0%.

  Moreover, in order to fully exhibit the effect of the intermediate layer, the thickness of the intermediate layer is required to be 10 mm or more in the roll radial direction. A more preferable intermediate layer thickness is 15 mm or more.

  The rolling composite roll of the present invention is preferably formed by a centrifugal casting method. In casting, it is necessary to inoculate using a Si-containing inoculant.

  By adding the Fe-Si inoculum, Ni-Mg inoculum, and Ca-Si inoculum in the ladle to the outer layer molten metal of the chemical components (sample Nos. 1 to 25) shown in Table 1 Then, Si, Mg, and Ca were added, and the molten metal for outer layer was poured into a rotating mold for centrifugal casting to perform centrifugal casting. After the molten cylindrical outer layer was almost completely solidified, the molten intermediate layer composed of the chemical component of the present invention was cast by centrifugal force, and the intermediate layer was deposited on the inner surface of the outer layer. After the outer layer and the intermediate layer are almost completely solidified, stop the mold rotation, stand the mold vertically, set the upper and lower molds at both ends, and spheroidal graphite cast iron as the inner layer inside the mold Was cast. Then, the intermediate layer and the inner layer were completely welded. Thus, after the composite roll was completely cooled, it was taken out from the mold to produce the roll of the present invention.

  FIG. 3 shows a schematic cross-sectional view of the composite roll body of the present invention. In FIG. 3, the roll of the present invention is configured by providing an intermediate layer 22 between an outer layer 21 and an inner layer 23. Note that the intermediate layer may be provided not only in one layer but also in two or more layers. Further, the inner layer may have a hollow sleeve shape as well as a solid shape.

  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 pieces were collected from these obtained outer layers of the roll, the area% 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.

  From Table 2, the outer layer of the roll of the present invention contains Mg or Ca, so that the shape of the MC carbide is finely granular and uniformly dispersed in the metal structure. Good results were obtained for both safety 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. In Comparative Example 23, the area ratios of MC carbide and cementite are small and the wear resistance is poor. 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.

In addition, as the outer layer, the test material No. 1. An intermediate layer (C: 4.0% or less, Si: 4.0% or less, Ni: 1.0-5.0%, Cr: 0) using spheroidal graphite cast iron as an inner layer and having graphite in the metal structure 0.1 to 1.5%, V: 0.1 to 8.0%, balance Fe and impurity element) provided in the present invention, the boundary between the outer layer and the intermediate layer, the intermediate layer, The tensile strength at the boundary of the inner layer was measured. As a result, the tensile strength of each of the boundary ^portions, 58.9 kg / mm 2, was 61.8kg / mm ^2.

  Moreover, the said invention example has 2.9 area% of graphite in an intermediate | middle layer, It has confirmed that the tensile strength and elongation of a boundary part were enough.

In addition, as the outer layer, the test material No. 1. In a composite roll using spheroidal graphite cast iron as an inner layer, that is, a comparative roll having no intermediate layer, the tensile strength at the boundary between the outer layer and the inner layer was measured in the same manner as described above. As a result, the tensile strength at the boundary was 52.9 kg / mm ² . That is, it was found that the composite roll for rolling of the present invention was provided with an intermediate layer, so that alloy mixing from the outer layer to the inner layer was suppressed, and the strength of the boundary portion was sufficient.

  As described above, the outer layer of the rolling composite roll of the present invention has both wear resistance and accident resistance due to the coexistence of graphite and hard carbide. Moreover, wear resistance and accident resistance can be further improved by dispersing hard carbide finely and uniformly and making the shape granular. Further, by providing an intermediate layer having graphite in the metal structure, the mechanical properties near the boundary between the outer layer and the inner layer can be improved. The outer layer of the rolling roll of the present invention exhibits excellent performance in the work roll for hot rolling in general, particularly in the latter stage of the finishing row of the hot sheet rolling mill, and contributes to 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. It is a schematic sectional drawing of the composite roll trunk | drum part of this invention.

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, 21 outer layer, 22 intermediate layer, 23 inner layer

Claims (8)

Chemical component is mass%, C: 2.5-3.0%, Si: 3.0% or less, Ni: 2.3-5.5%, Cr: 0.1-2.0%, V: An outer layer containing 0.3 to 10.0%, 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 graphite in the metal structure, and flake graphite A composite roll for rolling, characterized in that an intermediate layer having graphite in a metal structure is provided between an inner layer made of cast iron, spheroidal graphite cast iron and graphite steel. Furthermore, the said outer layer is the mass%, and contains 0.005-0.5% of rare earth elements (REM), The composite roll for rolling of Claim 1 characterized by the above-mentioned. Furthermore, the said outer layer is the mass%, Mn: 0.3-2.0%, Mo: 0.2-3.0%, W: 0.1-3.0%, Nb: 0.3-10. One of 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 The composite roll for rolling according to claim 1, comprising two or more kinds. The composite roll for rolling according to any one of claims 1 to 3, wherein graphite in the outer layer has an area% of 0.5 to 5.0%. The composite roll for rolling according to any one of claims 1 to 4, wherein graphite in the intermediate layer has an area% of 0.1 to 10.0%. The intermediate layer is in mass%, C: 4.0% or less, Si: 4.0% or less, Ni: 1.0 to 5.0%, Cr: 0.1 to 1.5%, V: 0.00. The composite roll for rolling according to any one of claims 1 to 5, further comprising an intermediate layer containing 1 to 8.0% and the balance being Fe and an impurity element. The composite roll for rolling according to any one of claims 1 to 6, wherein a thickness of the intermediate layer in a roll radial direction is 10 mm or more. The composite roll for rolling according to any one of claims 1 to 7, wherein the composite roll for rolling according to any one of claims 1 to 7 is used for a work roll for a subsequent stage of a finishing row of a hot sheet rolling mill.