JPH11342407A - Hot plate rolling roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent a roll from damaging even when it is used for a hot plate rolling and, restrain a roll damage while the operation of a rolling machine is stopped by sintering a high-speed system alloyed powder to a roll outer layer and specifying a sintered high speed organization and its physical property. SOLUTION: This hot plate rolling roll comprises a compound sleeve 1 being composed of an outer layer 11 and an inner layer 12, and a shaft member 2. A material of the inner layer 12 and the shaft member is preferable to be a cast steel, a forged steel or a graphite cast steel. Diameter of the compound sleeve 1 is larger than that of a bearing part 4, and the sleeve 1 is fixed with the shaft member 2 by thermal insertion. A driving part 5 of smaller diameter exists at at the outside of the bearing part 4. The outer layer 11 is made by sintering the high speed system alloyed powder by means of a hot isotropic pressurization method. In the sintered high speed organization, a carbide, an average grain size of which is 10 μm or less, is dispersed substantially even and the outer layer 11 has a fracture toughness value Klc of 15.5 MPao.m<1/2> or more, and a remained compression stress of 100 MPa or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll for hot rolling in which an outer layer made of a sintered alloy of a high-speed alloy powder is formed on the outer periphery of a shaft or inner layer made of cast steel, forged steel or graphite cast steel, and in particular, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolling roll suitable for use as a work roll of a continuous hot-rolling-sheet finishing rolling mill because of its excellent abrasion resistance, surface roughening resistance and crack resistance.

[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 alloy material (W088 / 07594). This has the problem that the wear resistance is excellent but the crack resistance is not yet sufficient. Further, in the case of a centrifugally cast roll in which the outer layer is made of a high-speed alloy material, there is a problem in that the solidification during casting tends to cause coarsening of the structure and segregation of carbides due to uneven solidification, thereby deteriorating the surface roughness resistance.

[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. Due to the poor crack resistance, rolls made of high-speed sintered alloys have not been applied to hot-rolled rolls.

[0005] However, since the hard carbide is uniformly and finely dispersed in the high-speed sintered alloy, the high-speed sintered alloy has excellent wear resistance and rough surface resistance as compared with the conventional ingot-formed high-speed steel, and has a high crack resistance. It is expected that the applicable stand will be expanded by improving the performance.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the ingot-made high-speed roll, and to provide a roll for hot strip rolling which has improved toughness and excellent crack resistance.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above problems, an outer layer constituting a body of a rolling roll is formed by hot isostatic pressing (HIP) of a high-speed alloy powder. In this case, by controlling the HIP temperature, it is possible to obtain a microstructure without uniform segregation of carbide particles, and by controlling the heat treatment conditions, the fracture toughness value K1c and the residual compressive stress can be adjusted. The present inventors have discovered that a rolling roll having abrasion resistance, surface roughening resistance and crack resistance can be obtained, and completed the present invention.

That is, the hot-rolling roll of the present invention is a hot-rolling roll having an outer layer diffusion-bonded to the outer periphery of a shaft made of cast steel, forged steel or graphite cast steel, wherein the outer layer is made of a high-speed steel. The alloy powder is sintered by hot isostatic pressing. The average grain size is 10μ in the structure of sintered high-speed steel.
m or less of carbides are substantially uniformly dispersed, and the outer layer has a fracture toughness value K1c of 15.5 MPa · m ^1/2 or more and a residual compressive stress of 100 MPa or more.

Further, the hot plate rolling roll of the present invention is formed by shrink-fitting a shaft having a composite sleeve having an outer layer diffusion-bonded to an outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel. A roll for hot rolling, wherein the outer layer is obtained by sintering a high-speed steel alloy powder by a hot isostatic pressing method, and in the structure of the sintered high-speed steel, a carbide having an average particle size of 10 μm or less is substantially contained. And the outer layer is 1
Fracture toughness values K1c and 10 of 5.5 MPa · m ^1/2 or more
It has a residual compressive stress of 0 MPa or more.

In the present invention, the chemical composition of the high-speed sintered alloy forming the outer layer is C: 1 to 4% by weight, Si:
0.2-3%, Mn: 0.1-1.5%, Cr: 2-1
4%, Mo: 9% or less, V: 3 to 15%, W: 20% or less, the balance being substantially composed of Fe and unavoidable impurities. Further, by weight ratio, 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 may be contained. It is desirable that the hardness Hs of the outer layer is 70 or more.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view in the direction of a rotating shaft when the present invention is applied to a roll for assembling hot strip rolling, and FIG. This hot plate rolling roll comprises a composite sleeve 1 comprising an outer layer 11 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, in which the outer layer 11 and the inner layer 12 are diffusion-bonded, has a diameter equal to or larger than the bearing 4 and is fixed to the shaft 2 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.

When a composite sleeve is formed, the outer periphery of a hollow cylindrical inner layer is filled with a high-speed powder and subjected to HIP treatment to sinter the high-speed powder on the inner layer surface and at the same time diffusion bonding. In the case of a composite roll of a type in which a high-speed powder is sintered and diffusion-bonded directly to the outer periphery of the roll shaft, when the high-speed powder is HIPed, the high-speed powder is filled around the roll shaft. Then, the high-speed powder is sintered at the outer periphery of the shaft material and diffusion-bonded.

The shaft material and the hollow cylindrical inner layer used here are:
It 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. When the carbon content is 0.1
%, The required strength is not secured. In order to produce a high-speed powder, the 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. Also,
This high-speed powder may further contain 20% by weight or less of one or more hard particles of a carbide powder such as V, W, Mo, Ti, etc., a carbonitride powder and a boride powder.

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 required to combine with Cr, V, Mo, and W contained simultaneously 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 is hardened, and has an effect of forming M ₇ C ₃ and M ₂₃ C ₆ carbides to enhance 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 element that is important for bonding with C to form carbides and improving 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%.

V: 3 to 15% V combines with C to form VC, that is, 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%.

W: 20% or less Like W, 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%.

In the present invention, the HSS composition may further contain the following alloying elements singly or in combination with the above alloying 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 similarly to 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 except for 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.

When the high-speed sintered alloy of the present invention is applied to a work roll for hot plate rolling, a cylindrical body made of a steel plate or the like is welded to the inner layer 12 or the periphery of the shaft member, and the resulting can is filled in the gap of the can. Is filled with the above-mentioned HSS powder and subjected to the following HIP treatment.

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. Temperature control is important because the roughness of the fracture surface changes with the HIP temperature. Also HI
If the P sintering pressure is less than 50 MPa, the resulting material has a high porosity, which is not preferable. More preferred HI
The P 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 0.1 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 is easily broken 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 is rounded and its average particle size is 10μ.
m or less. If the average particle size of the carbide exceeds 10 μm, the components in the matrix around the carbide will decrease, and the wear will preferentially occur. For this reason, the rough surface resistance is inferior. The average particle size of the carbide was determined by image analysis in 20 visual fields after the base structure was blackened by corrosion.

The fracture toughness value K 1c is 15.5 MPa · m ^1/2.
If it is less than 10, when used as a work roll for hot plate rolling, the toughness is insufficient, and when an accident or the like is encountered, if a crack occurs, the entire roll may be damaged.

It is preferable that a compressive stress of 100 MPa or more is always applied, regardless of the diameter of the outer layer used at the time of rolling. As a result, even when a situation where a tensile stress acts on the surface due to abnormal rolling or the like to generate a crack is encountered, the crack is counteracted by the compressive stress, so that the growth of the crack is prevented. When the compressive stress is less than 100 MPa, a crack is easily developed. The residual stress can be measured by a Sax method or the like.

[0034]

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 size (μm), carbide area ratio, and fracture toughness value (K1c, M
Pa · m ^1/2 ) and abrasion resistance (μm).

The HIP treatment was performed at a temperature of 1150 ° C. and a pressure of 120
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 Hs70-90
Met.

The abrasion 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 determined by the American Society for Testing Materials (A
It was measured by a test method based on ASTM E399 defined in (STM).

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3] From these results, all of the high-speed sintered alloys used in the hot plate rolling roll of the present invention have an average carbide particle size of 10
The particles were fine and substantially uniformly dispersed with a particle size of not more than μm, and the fracture toughness value K1c was able to secure 15.5 MPa · m ^1/2 or more, and was excellent in rough surface resistance and wear resistance.

Even in the case of a high-speed sintered alloy, Comparative Example 1 did not have the required toughness for the outer layer of the hot-rolling roll because the area ratio of carbide was too large. Further, Comparative Examples 2 and 3 of the infused high-speed steel material were excellent in toughness, but were inferior in wear resistance and rough surface resistance.

Example 2 A forged steel ring body equivalent to SCM440 was used, and a high-speed alloy powder having the composition of Example 2 of the present invention shown in Table 1 was HIP-coated around its periphery.
A composite sleeve having an outer layer sintered and diffusion-bonded was formed by the method. Then, the composite sleeve was fitted to a forged steel roll shaft by shrink fitting to produce a composite roll having an integrated assembly structure. The specifications of this roll are as follows:
5 mm x 900 mm length, boundary diameter of outer layer and inner layer φ272
mm, sleeve inner diameter φ132mm, shrink fit rate 1/100
0.

The roll was subjected to surface low / medium frequency quenching at 1080 ° C., and then twice tempered at 500 to 550 ° C. Next, as a result of measuring the stress in the outer layer of this roll by the sax method, the stress in the circumferential direction of the roll in the outer layer was -250 MPa on the surface of the outer layer, and a maximum of -300 M in the outer layer.
Pa was measured. In addition, a negative pressure means a compressive stress. Even when a situation where a tensile stress acts on the surface due to abnormal rolling or the like and a crack is generated is encountered, the crack is canceled by the compressive stress, so that the growth of the crack can be sufficiently prevented.

As a result of using the roll of the present invention as a work roll of an actual continuous hot-sheet finishing rolling mill, the rough surface resistance was 2.3 times and the abrasion resistance was 2.7 times as compared with the smelting high-speed roll. The effect was obtained.

[0045]

The hot-rolling roll of the present invention has a uniform structure without segregation by adopting a high-speed sintered alloy for the outer layer, thereby improving the wear resistance and the surface roughness resistance. The outer layer is provided with a fracture toughness value K1c and a residual compressive stress suitable for a hot plate rolling roll.
As a result, even when used in hot strip rolling, damage to the roll in the event of an abnormality is effectively prevented, so that stoppage of the rolling mill and damage to the roll can be suppressed.

[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 (5)

[Claims] 1. A hot-rolling roll having an outer layer diffusion-bonded to the outer periphery of a shaft made of cast steel, forged steel or graphite cast steel, wherein the outer layer is formed by pressing a high-speed steel alloy powder by a hot isostatic pressing method. obtained by sintering, the average carbide grain size below 10μm in tissues of the sintered high speed steel have substantially uniformly dispersed, the outer layer is 15.5MPa · m ^1/2 or more fracture toughness K1c And a roll for hot strip rolling, having a residual compressive stress of 100 MPa or more. 2. A hot-rolling roll formed by shrink-fitting a shaft with a composite sleeve having an outer layer diffusion-bonded to the outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel, wherein the outer layer Is obtained by sintering a high-speed alloy powder by a hot isostatic pressing method, in which the carbide having an average particle size of 10 μm or less is substantially uniformly dispersed in the structure of the sintered high-speed steel. A roll for hot strip rolling, having a fracture toughness value K1c of 15.5 MPa · m ^1/2 or more and a residual compressive stress of 100 MPa or more. 3. The chemical composition of the high-speed sintered alloy forming the outer layer is as follows: C: 1-4%, Si: 0.2-3, by weight.
%, Mn: 0.1 to 1.5%, Cr: 2 to 14%, M
The hot-rolling roll according to claim 1 or 2, wherein o: 9% or less, V: 3 to 15%, W: 20% or less, and the balance substantially consists of Fe and unavoidable impurities. 4. The high-speed sintered alloy for forming the outer layer further comprises, by weight ratio, Ni: 5% or less, Co: 10% or less,
The composition according to claim 1, further comprising at least one of Nb: 5% or less, Ti: 5% or less, and Zr: 5% or less.
3. The roll for hot plate rolling according to any one of 3. 5. The hot plate rolling roll according to claim 1, wherein the hardness Hs of the outer layer is 70 or more.