JPH11246950A - Hot-strip mill roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-strip mill roll which has an outer layer of high speed steel type sintered alloy having high toughness and excellent in wear resistance and surface roughing resistance as well as in crack resistance and resistance to loss by fracture. SOLUTION: In this roll whose outer layer 11 consisting of a sintered alloy of high speed steel type powder is formed by hot isostatic pressing method on the outer periphery of a sleeve-like inner layer 12 consisting of cast steel, forged steel or graphite cast steel, or a solid shaft material 2, the average grain size of carbides in the structure of the sintered alloy is regulated to <=8 μm, and also the average spacing between mutual carbides is regulated to 3-25 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolling roll in which a sleeve made of cast steel, forged steel or graphite cast steel or an outer layer made of a sintered alloy of high-speed powder is formed on the outer periphery of a solid shaft. .

[0002]

2. Description of the Related Art Conventionally, as a work roll for hot plate rolling, there is a continuous cast overlaying roll in which an outer layer is made of a high-speed steel material (W088 / 07594). This has a problem in that the abrasion resistance is excellent, but the surface roughness resistance is not yet sufficient. In addition, a centrifugal casting roll whose outer layer is made of a high-speed steel material has a problem in that coarsening of the structure and segregation of carbides due to uneven solidification are apt to occur due to solidification during casting, so that the surface roughening resistance is deteriorated.

[0003]

The demand for the wear resistance of hot plate rolling rolls is becoming more and more severe, and as a further wear-resistant material, a high-speed sintered alloy based on the hot isostatic pressing (HIP) method is used. Is attracting attention. However, since the high-speed sintered alloy has low toughness, the rolling load is high, the thermal load is large, and it is difficult to apply it to a stand where thermal cracks are generated, and its application is mainly limited to strip rolls. Had become.

[0004] In hot plate rolling rolls, deep cracks are likely to occur on the roll surface due to accidents in the rolling operation, such as biting and squeezing. When a load is repeatedly applied during rolling with the cracks remaining, a roll made of a high-speed sintered alloy has low toughness, and may cause spalling. For this reason, rolls made of high-speed sintered alloys have not been applied to hot-rolled rolls.

However, since the hard carbide is uniformly and finely dispersed in the high-speed sintered alloy, the high-speed sintered alloy has superior wear resistance and rough surface resistance as compared with the conventional molten high-speed stainless steel material, and has a low toughness. Improvements are expected to expand the applicable stand.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the ingot-made high-speed roll, and in particular to improve the toughness of the high-speed sintered alloy used for the outer layer, thereby making it possible to apply the hot-rolled steel to rolling. To provide a roll for use.

[0007]

SUMMARY OF THE INVENTION The present inventor has carried out HIP sintering of a high-speed powder as an outer layer material on the inner layer of a sleeve of a rolling roll or the outer periphery of a shaft material and diffusion bonding,
By uniformly dispersing fine hard carbides in a sintered alloy, a roll for hot strip rolling with improved wear resistance and surface roughening resistance having improved fracture toughness value K1c has been developed.

[0008] The hot plate rolling roll of the present invention is a hot-isostatic pressing (HIP) method for forming a high-speed powder on a sleeve-shaped inner layer or an outer periphery of a solid shaft made of cast steel, forged steel or graphite cast steel. A roll on which an outer layer made of a sintered alloy is formed, wherein the average particle diameter of carbide in the sintered alloy structure is 8 μm.
m or less, and the average spacing between carbides is 3 to 25.
μm.

Further, in the present invention, it is preferable that the area ratio of carbide in the high-speed sintered alloy structure is more than 10% and less than 30%. The chemical composition of the high-speed sintered alloy is as follows: C: 1-4%, Si: 0.2-3%, M
n: 0.1 to 1.5%, Cr: 2 to 14%, Mo: 9%
Hereinafter, it is preferable that V: 3 to 15%, W: 20% or less, and the balance substantially consist of Fe and unavoidable impurities. The high-speed sintered alloy further has a weight ratio of Ni: 5% or less,
Co: 10% or less, Nb: 5% or less, Ti: 5% or less,
Zr: Any one or more of 5% or less can be contained.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The high-speed sintered alloy of the present invention can be applied to a composite roll obtained by sintering a high-speed powder directly on the outer periphery of a shaft of a roll and diffusion bonding. Further, the present invention can also be applied to an assembly type composite roll of a type in which a composite sleeve formed by sintering and diffusion bonding a high-speed steel powder on the outer periphery of a sleeve-shaped inner layer and shrink-fitting a separately prepared shaft member. In the case of composite rolls in which high-speed powder is sintered and diffusion-bonded directly to the outer periphery of the solid shaft material of the roll,
When the HSS powder is HIPed, the HSS powder is filled around the shaft of the roll, and the HSS powder is sintered on the outer periphery of the shaft and simultaneously diffusion bonded. When a composite sleeve is made, the outer periphery of the sleeve-shaped inner layer is filled with a high-speed powder and subjected to HIP treatment to simultaneously sinter the high-speed powder on the inner layer surface and simultaneously perform diffusion bonding. The shaft or sleeve-like inner layer used here is preferably any of cast steel, forged steel and graphite cast steel containing 0.1 to 2% by weight of carbon. If the amount of carbon exceeds 2%, the amount of carbide or graphite becomes excessive, so that the necessary tensile strength, toughness and the like are not secured. If the amount of carbon is less than 0.1%, the required strength cannot be secured.

FIG. 1 is a cross-sectional view in the direction of the rotation axis when the present invention is applied to a roll for assembling hot strip rolling.
The cross section is shown in FIG. This hot plate rolling roll is made of an outer layer 1
A composite sleeve 1 including an inner layer 1 and an inner layer 12 and a shaft 2. The material of the inner layer 12 and the shaft member 2 is preferably cast steel, forged steel or graphite cast steel as described above. The composite sleeve 1 for forming the body portion, in which the outer layer 11 and the inner layer 12 are diffusion bonded, has a diameter equal to or larger than the bearing portion 4 on the shaft member 2 and is fixed by shrink fitting. Outside each bearing 4, there is a drive unit 5 having a smaller diameter than the bearing 4.

The outer layer 11 of the composite sleeve is made of a high-speed powdery sintered alloy. As the composition of the high-speed sintered alloy,
C: 1-4%, Si: 0.2-3%, Mn:
0.1 to 1.5%, Cr: 2 to 14%, Mo: 9% or less, V: 3 to 15%, W: 20% or less, balance substantially F
Those having a chemical component consisting of e and unavoidable impurities are preferred. The high-speed steel may further contain at least one of Ni: 5% or less, Co: 10% or less, Nb: 5% or less, Ti: 5% or less, and Zr: 5% or less.

In order to produce a high-speed powder, a mixture of the above components is preferably melted and powdered by a gas atomizing method or a water atomizing method. The average particle size of the alloy powder obtained by such a method is desirably 20 to 150 μm. In addition, V,
At least 20% by weight of hard particles of at least one of carbide powders such as W, Mo, and Ti, carbonitride powders, and boride powders may be blended.

The chemical composition of the high-speed sintered alloy for forming the outer layer is preferably as follows in order to secure the wear resistance, hardness and toughness required by the outer layer. C: 1 to 4% C is an element necessary to combine with simultaneously contained Cr, V, Mo, and W to form a hard carbide and exhibit wear resistance. If C is less than 1%, the amount of hard carbide will be insufficient and wear resistance will not be obtained, and if it exceeds 4%, hard carbide will be excessive and the toughness will be reduced.

Si: 0.2-3% Si has a deoxidizing effect and an effect of improving the atomizing workability. If the content of Si is less than 0.2%, a sufficient deoxidizing effect cannot be obtained, and if it exceeds 3%, the sintered high-speed alloy becomes brittle.

Mn: 0.1 to 1.5% Mn also has a deoxidizing effect like Si, and also has an effect of improving hardenability. For this purpose, 0.1% or more is necessary. However, if it exceeds 1.5%, the sintered high-speed alloy is embrittled, which is not preferable.

Cr: 2 to 14% Cr has a base structure of bainite or martensite and hardens, and forms M ₇ C ₃ and M ₂₃ C ₆ carbides to increase wear resistance. In addition, it forms a quenchability by forming a solid solution in the matrix. However, if it is less than 2%, the effect is not sufficient, and if it exceeds 14%, not only the toughness of the base structure is reduced, but also the generation of hard MC-based carbide such as VC is reduced, so that the effect of improving the wear resistance is improved. Saturates.

Mo: 9% or less Mo is an important element that combines with C to form carbides and enhance wear resistance. In addition, part of the matrix is solid-dissolved in the matrix during quenching, and then precipitates as fine carbides by tempering, and has an effect of increasing the hardness of the matrix by secondary hardening. However, if it exceeds 9%, the toughness is reduced, and the VC
Since the formation of hard MC-based carbide such as
The effect of improving wear resistance is saturated. The preferred Mo content is 1 to 8%.

W: 20% or less Like Mo, W is also an important element to combine with C to form carbides and to enhance wear resistance. In addition, part of the matrix is solid-dissolved in the matrix during quenching, and then precipitates as fine carbides by tempering, and has an effect of increasing the hardness of the matrix by secondary hardening. However, if it exceeds 20%, the toughness is reduced, and the generation of hard MC-based carbide such as VC is reduced, so that the effect of improving wear resistance is saturated. The preferred W content is 2 to 16%.

V: 3 to 15% V combines with C to form VC, that is, an MC-based carbide.
VC has a hardness of Hv 2500 to 3000 and is the hardest of carbides. For this reason, V is an essential element most effective for improving the wear resistance. If the amount of V is less than 3%, the amount of VC becomes insufficient, and if it exceeds 15%, the sintered high-speed alloy becomes brittle.
The preferred V content is 4 to 12%.

In the present invention, the HSS composition may further contain the following alloy elements singly or in combination with the above alloy elements. Ni: 5% or less Ni is an austenite stabilizing element and improves hardenability. It is particularly effective when quenching a large-sized thick roll. However, if it exceeds 5%, austenite is stabilized, and it becomes difficult to transform a hard base structure into bainite or martensite, so that hardness is not obtained and wear resistance cannot be obtained. A more preferred Ni content is 0.1 to 4%.

Co: 10% or less Co forms a solid solution in the matrix and has an effect of increasing tempering hardness and high-temperature hardness. When used in hot rolling, it is effective in improving wear resistance and surface roughness resistance. However, if it exceeds 10%, the toughness is reduced, and the above effect is not improved. Therefore, the upper limit is 10%. A more preferable Co content is 1 to 8%.

Nb: 5% or less, Ti: 5% or less, Zr:
5% or less Each of these elements forms a hard carbide like V, so that the wear resistance can be improved by adding 5% or less individually or in combination.

The balance other than the above elements is substantially Fe, excluding impurities. The main elements as impurities are P and S. In order to prevent a decrease in toughness, P is desirably 0.05% or less and S is desirably 0.03% or less.

The hot-rolling roll of the present invention has an inner layer 12
Alternatively, a cylindrical body made of a steel plate or the like is welded around a shaft member, and the above-mentioned high-speed steel powder is filled in the voids of the obtained can, followed by HIP processing described below.

A lid material is welded to the opening of the can filled with the high-speed powder, and the inside of the can is depressurized from a vent tube provided in the lid material, and then the vent tube is sealed by welding. This is set in a HIP apparatus, and at a temperature of 1250 ° C. or lower, particularly 1000 to 1250 ° C., and 50 to 2 ° C. in an argon atmosphere.
Sinter at a pressure of 00 MPa. The carbide can be finely dispersed at a HIP temperature of 1000 to 1250 ° C. If the HIP sintering pressure is less than 50 MPa, the resulting material has a high porosity, which is not preferable.
A more preferred HIP sintering pressure is 100 to 150 MPa. The HIP sintering time under the above conditions is preferably 2 to 10 hours. The can on the surface of the sintered material thus obtained is removed by machining, and the surface of the HIP-sintered high-speed material is polished.

The heat treatment of the roughened high-speed sintered alloy consists of quenching and tempering.
The temperature is preferably set to 0 ° C. or lower. Maximum quenching temperature is 12
If the temperature exceeds 50 ° C., carbides grow and become excessive, which is not preferable. Further, it is preferable that the maximum temperature of the tempering is set to 600 ° C. or lower and the minimum temperature is set to 150 ° C. or higher. If the minimum temperature is lower than 150 ° C., a martensite phase appears in the HSS structure and expands, and stress is generated in the diffusion bonding portion, which is not preferable. The quenching time is preferably from 1 to 10 hours. The tempering is preferably performed in two or more stages, and the temperature conditions may be the same, but the tempering time is preferably 1 to 10 hours.

In the case of the assembly type roll shown in FIG. 1, the heat-treated composite sleeve is shrink-fitted to the shaft. After shrink fitting, finishing work is performed to obtain a roll for assembling hot plate rolling. The shrink fitting rate is 0.5 / 1000 to 2.2 / 10.
It is desirable to set it in the range of 00. 0.5 shrink fit
If it is / 1000 or less, slippage occurs between the composite sleeve and the shaft during rolling, and if it exceeds 2.2 / 1000, the composite sleeve tends to break from the inner surface.

Fine carbides are uniformly dispersed in the structure of the obtained outer layer of the roll, and there is almost no segregation. The dispersed carbide particles are rounded and have an average particle size of 8
μm or less. The average spacing between carbides is 3 to 2
5 μm. The average particle size and the average interval of the carbides were measured by an image analysis method in 20 visual fields after the base structure was blackened by corrosion, and the average value was obtained.

If the average particle size of the carbide exceeds 8 μm, the content of matrix in the vicinity of the carbide is reduced, and wear is preferentially caused. For this reason, the rough surface resistance is inferior. When the average spacing between carbides is less than 3 μm, the fracture toughness value K
1c is less than 15.5 MPa · m ^1/2, and the toughness of a hot plate rolling roll is insufficient. When the average spacing of the carbides exceeds 25 μm, the wear resistance and the rough surface resistance become insufficient.

In the high-speed sintered alloy of the hot-rolling roll of the present invention, the area ratio of the precipitated carbide is preferably more than 10% and less than 30% of the whole structure. When the area of the carbide is 10% or less, the amount of the carbide is small and the wear resistance is not sufficient. On the other hand, if the area of the carbide is 30% or more, the fracture toughness value K1c cannot be 15.5 MPa · m ^1/2 or more because the base structure binding the carbide is small.

[0032]

EXAMPLES Example 1 As shown in Table 1, test materials of a high-speed sintered high-alloy material and a molten high-speed stainless steel material by casting were produced. Table 2 shows the average particle diameter (μm) of the carbide, the average spacing (μm) of the carbide, the area ratio of the carbide, the fracture toughness (K1c, MPa · m ^1/2 ), and the wear resistance (μm).

All of the high-speed sintered alloy samples were subjected to the HIP treatment at a temperature of 1150 ° C. and a pressure of 120 in an argon atmosphere.
Performed for 2 hours at MPa. After quenching at 1150 ° C for 15 minutes, tempering at 580 ° C for 3 hours is performed for 3 hours.
Steps were taken to obtain test pieces. Hardness is Hs80-90
Met.

The wear resistance was determined by assembling a test roll into a rolling wear tester shown in FIG. 3 and conducting a test under the test conditions shown in Table 3, and then measuring the depth of wear generated on the surface of the test roll. The measurement was performed using a needle type surface roughness meter (SURFCOM). Here, the rolling wear tester shown in FIG.
1, a heating furnace 32 for preheating the rolled material s, a cooling water tank 33 for cooling the rolled material s, a winding machine 34 for the rolled material s, and a tension controller 35. Here, the test rolls 311 and 312 are incorporated in the rolling mill 31.

Further, the fracture toughness value is measured by the American Society for Testing Materials (A
It was measured by a test method based on ASTM E399 defined in (STM).

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

From these results, all of the high-speed sintered alloys used in the hot-rolling roll of the present invention have an average carbide grain size of 8 μm or less and an average spacing between carbides of 3 to 25 μm. Since it is uniformly distributed and the area ratio of carbide is more than 10% and less than 30%, the fracture toughness value K1c can secure 15.5 MPa · m ^1/2 or more, and furthermore, the rough surface resistance and the wear resistance Was excellent.

Even in the case of a high-speed sintered alloy, Comparative Example 1 did not have sufficient toughness required for the outer layer of the sheet rolling roll because the average distance between carbides was too small. Further, Comparative Example 2 was inferior in wear resistance because the average distance between carbides was too large. Comparative Example 3 was insufficient in toughness because the area ratio of carbide was too large.
In addition, Comparative Examples 4 and 5 of the infused high-speed steel material were excellent in toughness, but were inferior in wear resistance and rough surface resistance.

Example 2 A hot-rolling roll having a diameter of 600 mm and a body length of 1,830 mm was prepared from the high-speed sintered alloy of Example 2 of the present invention shown in Table 1, and was produced in the same manner as Comparative Example 4 shown in Table 1. As a result, about 2.5 times the effect of the abrasion resistance was obtained. Significantly good results were also obtained in terms of skin roughness resistance.

[0042]

The hot-rolling roll of the present invention has a high toughness of the high-speed sintered alloy used for the outer layer and is excellent in crack resistance and breakage resistance, and also has excellent surface roughening resistance and wear resistance. Things.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in the rotation axis direction when the present invention is applied to an assembling type hot plate rolling roll.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a schematic view of an apparatus for measuring the wear resistance of a roll.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite sleeve 11 Outer layer 12 Inner layer 2 Shaft material 4 Bearing part 5 Drive part 31 Rolling machine 311, 312 Test roll 32 Heating furnace 33 Cooling water tank 34 Winding machine 35 Tension controller s Rolled material

Claims (7)

[Claims] 1. A roll having a sleeve-shaped inner layer made of cast steel, forged steel or graphite cast steel or an outer layer made of a sintered alloy of a high-speed steel powder formed on the outer periphery of a solid shaft material by a hot isostatic pressing method. A roll for hot strip rolling, wherein the average grain size of carbides in the structure of the sintered alloy is 8 μm or less, and the average interval between carbides is 3 to 25 μm. 2. The hot plate rolling roll according to claim 1, wherein the area ratio of carbide in the structure of the high-speed sintered alloy is more than 10% and less than 30%. 3. The high-speed sintered alloy according to claim 1, wherein said high-speed sintered alloy is ASTM E3.
The fracture toughness value K1c was 15.5 by a test method based on 99.
Hot plate for rolling rolls according to claim 1 or 2, characterized in that it MPa · m ^1/2 or more. 4. The chemical composition of said high-speed sintered alloy is as follows: C: 1-4%, Si: 0.2-3%, Mn: 0.
1 to 1.5%, Cr: 2 to 14%, Mo: 9% or less,
V: 3 to 15%, W: 20% or less, the balance substantially consisting of Fe and unavoidable impurities.
4. The roll for hot plate rolling according to any one of claims 1 to 3. 5. The high-speed sintered alloy according to claim 1, further comprising a weight ratio of N
i: 5% or less, Co: 10% or less, Nb: 5% or less, T
The hot-rolling roll according to claim 4, comprising at least one of i: 5% or less and Zr: 5% or less. 6. The hot plate rolling roll according to claim 1, wherein said high-speed sintered alloy is formed on an outer periphery of a solid shaft material of the roll. 7. The hot plate according to claim 1, wherein a composite sleeve in which the high-speed sintered alloy is formed on the outer periphery of a sleeve-shaped inner layer is shrink-fitted to a roll shaft. Roll for rolling.