JP2778896B2 - Roll for rolling and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling roll comprising an outer shell layer made of a hard material having abrasion resistance and surface roughening resistance and an inner layer or a shaft made of a tough material, and a centrifugal casting method. The present invention relates to a method for manufacturing a roll for forming an outer shell layer, and more particularly to a roll for rolling having an outer shell layer having excellent microstructure and homogeneity, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A roll for hot or cold rolling used for rolling a structural material such as a steel material has a uniform casting structure with respect to an outer shell layer which is in direct contact with a material to be rolled, and has a high durability. It is required to have abrasion resistance, rough surface resistance, and crack resistance. In order to meet such demands, it is effective to form the outer shell layer by a centrifugal casting method, which has been widely used. In this centrifugal casting method, it is most common to supply a molten metal for forming an outer shell layer into a mold having a hollow cylindrical shape and configured to rotate at high speed around its axis, and to solidify it. It is a target.

[0003] In this case, the molten metal in contact with the inner surface of a mold (die) usually made of a steel material is rapidly cooled, so that a fine metal structure can be obtained on the outer surface constituting the roll. However, since the cooling rate becomes lower and the temperature gradient becomes smaller from the outer surface to the inside, the metal structure gradually becomes coarse. Initially, the surface of the outer shell layer has a fine structure and has abrasion resistance, rough surface resistance, and crack resistance,
If the refining is repeated after using for a long time, the metal structure on the surface of the outer shell layer becomes coarse, and there is a problem that the above-mentioned properties such as abrasion resistance deteriorate. In order to solve such a problem, it is effective to increase the cooling rate of the molten metal for forming the outer shell layer, and to make the casting structure uniform, the cooling rate at each position in the radial direction is increased. It is necessary to be as uniform as possible.

[0004] As means for increasing the cooling rate of the molten metal for forming the outer shell layer, there have been proposed means for casting the molten metal by spraying the molten metal on the inner peripheral surface of the mold, including means for cooling the mold with water. (See, for example, JP-A-1-254363). In order to prevent segregation and other material defects generated in the outer shell layer and to improve homogeneity, there is a proposal to move the pouring position of the molten metal in the centrifugal casting means (for example, Japanese Patent Publication No. 50-33021). Reference).
Furthermore, research and development has been actively conducted on the material forming the outer shell layer, but at present, high alloy cast iron, high chromium cast iron, high chromium cast steel, etc. are mainly used as the material of the outer shell layer by the centrifugal casting method. . Recently, high-speed steel-based materials have also been proposed (for example, Japanese Patent Application Laid-Open No. 60-12440).
No. 7).

[0005]

Among the materials forming the outer shell layer, among the rolls used for hot rolling or cold rolling, non-uniformity due to coarsening and segregation of the cast structure is observed. When it occurs, abrasion resistance and surface roughening resistance are reduced, and the basic unit of the rolling roll is deteriorated or increased, or the quality of the material to be rolled is deteriorated. On the other hand, in recent years, since the rolled material has a tendency to gradually become higher grade, the demand for the roll for rolling is frequently becoming stricter, and it is necessary to further refine the structure and uniformity of the outer shell layer more than before. .

When the outer shell layer is formed from the above high-speed steel-based material, the metal structure becomes finer due to the quenching action from the mold near the surface, but the quenching action becomes slow inside, so that the metal structure becomes Coarse. For this reason, near the surface of the outer shell layer, the metal structure is fine, so it has excellent wear resistance and rough surface resistance. On the other hand, inside the outer shell layer, the metal structure is rough, There is a problem that the tendency of occurrence of deterioration and rough skin is large.

Next, when the outer shell layer is formed by the centrifugal casting method, there is a problem that casting defects and uneven metal structure may occur inside. That is, since the cooling rate is lower and the temperature gradient is smaller inside the outer shell layer than at the surface, it is difficult to discharge gases, solute elements, impurities, and the like contained in the molten metal to the inner surface side. For this reason, these are trapped during the solidification of the molten metal, and carbide segregation, segregation in which a coarse metal structure is present, gas defects, and the like occur.

An object of the present invention is to solve the above problems and to provide a rolling roll having a fine metal structure and a shell layer excellent in homogeneity, and a method for producing the same.

[0009]

In order to achieve the above object, the present inventors conducted various experiments and examinations by a centrifugal casting method. By appropriately controlling the speed, it is possible to increase the cooling rate and temperature gradient of the solidified portion of the outer shell layer, prevent the inner structure of the outer shell layer from becoming coarse, and obtain an outer shell layer free of casting defects. I found that I can do it.

That is, in the first aspect of the present invention, an outer shell layer made of a hard material having abrasion resistance and abrasion resistance and manufactured by a centrifugal casting method and an inner layer or a shaft made of a tough material are formed. In the roll for rolling, the outer shell layer was C-1.0-3.0% by weight and Si2.
0% or less, Mn 2.0% or less, Cr 2.0 to 15.0
%, Mo 10.0% or less, V 2.0 to 8.0%, and in addition, W 20.0% or less, Ni 3.0% or less, Co 10.0% or less, N 0.03 to 0.2% , Each of which can be contained alone or in combination, the balance being substantially formed of a casting material composed of Fe and unavoidable impurity elements, and the average size of the base structure of the outer shell layer being deeper from the surface of the product outer shell layer. In the range of 50mm
The average diameter of the base exceeding 30 μm by the image analysis method was set to 10
When the dimensions of the matrix formed at 0 μm or less and at the surface of the product outer layer and at a depth of 50 mm from the surface are respectively m ₁ and m ₂ , m ₂ ≦ 1.2 m ₁ , The technical means that was adopted.

Further, in the second invention, the weight ratio of C is 1.0 to 3.0% and Si is 2.0% by centrifugal casting.
Mn 2.0% or less, Cr 2.0-15.0%, M
o 10.0% or less, V2.0 to 8.0%, and in addition, W20.0% or less, Ni3.0% or less, Co1
0.03% or less and 0.03-0.2% of N can be contained alone or in combination.
And a method for producing a roll for forming an outer shell layer made of an unavoidable impurity element, wherein the molten metal of the outer shell layer is supplied to a mold having a hollow cylindrical shape and rotatably formed around its axis. When the temperature T is T _C ≦ T ≦ T _C +90
° C (where T _C is the primary crystal formation temperature of the material forming the outer shell layer) and the average lamination speed of the outer shell layer is 2 to 40 mm / min. did.

[0012]

The reasons for limiting the composition ranges of the respective alloying elements in the outer shell layer made of a hard material having wear resistance and surface roughness resistance according to the present invention will now be described in detail.

C: 1.0 to 3.0% by weight C is necessary for the formation of carbides for improving wear resistance, but the crack resistance decreases as the amount of C increases. Therefore, it is necessary to be within the range of 1.0 to 3.0%. If the amount is less than 1.0%, the amount of crystallization or precipitated carbide is too small, which is not sufficient in terms of wear resistance.
On the other hand, when C exceeds 3.0%, the abrasion resistance is good, but the crack resistance tends to decrease. A more preferred amount of C is 1.3 to 2.0%.

Si: 2.0% by weight or less Si is an element necessary as a deoxidizing agent. Further, it is effective for dissolving in N ₆ C carbide to replace expensive elements such as W and Mo and to save energy. If the amount is large, embrittlement is likely to occur. If the amount is small, there is no deoxidizing effect, and casting defects are likely to occur. A more preferred amount of Si is 0.3-1.5%.

Mn: 2.0% by weight or less Mn has a deoxidizing action and an action of fixing S as an impurity as MnS. However, if the content exceeds 2.0%, retained austenite is likely to be generated, and sufficient hardness cannot be stably maintained. If the amount is small, deacidification is poor, which is not preferable. A more preferred amount of Mn is 0.3-1.5%.

Cr: 2.0 to 15.0% by weight Cr is less than 2.0% and is inferior in hardenability, and 15.0%
When it exceeds, it is inconvenient because chromium-based carbide becomes excessive. Cr-based carbide, for example, N ₂₃ C ₆ has lower hardness than MC and M ₂ C and lowers wear resistance. The more preferred amount of Cr is 3.0 to 10.0%.

Mo: 10.0 wt% or less Mo is necessary for obtaining hardenability and high-temperature hardness.
If it exceeds 10%, the balance between C, V and Mo becomes M
₆ C, M ₂ C carbides increases, since not preferable in terms of toughness and耐肌Arasei, the upper limit of the Mo content is 10.0%. A more preferable Mo content is 2.0 to 8.0%.

V: 2.0 to 8.0% by weight V is an essential element for forming an MC-based carbide which is effective in improving wear resistance. Therefore, if the content is less than 2.0%, a sufficient effect is not obtained. If the content is more than 8.0%, oxidation of the molten metal becomes severe, and it becomes difficult to obtain a sound cast product due to an increase in viscosity. A more preferred amount of V is 2.0-6.0%.

Further, the casting material for an outer shell layer of the present invention can contain W, Ni, Co, and N, alone or in combination, in addition to the above elements.

W: not more than 20.0% by weight W is necessary for maintaining high-temperature hardness, but if it exceeds 20.0%, M ₆ C-based carbides increase and the toughness and the roughening resistance are lowered. Therefore, the upper limit is set to 20.0%. A more preferable amount of W is 2.0 to 15.0%.

Ni: 3.0% by weight or less Ni has an effect of improving hardenability. Therefore, 3.0
% Or less. However, if it is more than that, the amount of retained austenite increases, and problems such as cracking and surface roughness during rolling occur, so that the content can be up to 3.0%. Preferably it is 0.1 to 1.5%.

Co: 10.0% by weight or less Co can form a solid solution in the matrix to delay the precipitation of carbide and prevent the matrix from softening. That is, it is a useful element in terms of tempering softening resistance and secondary hardening. However, if the content exceeds 10.0%, the effect is saturated and the production cost is increased.
0 to 7.0%.

N: 0.03 to 0.2% by weight The N content is preferably 0.03 to 0.2%.
N in this range is effective in improving the tempering hardness in the material of the present invention. However, when the content is excessive, the material becomes brittle, so the upper limit of the content is 0.2% or less. More preferably, it is 0.03 to 0.1%.

Other than the above elements, except for impurities, they are substantially made of iron. The main impurities are P and S,
P is 0.1% or less for preventing embrittlement, and S is similarly 0.06% or less.

Further, in the first invention, when the average size of the matrix structure of the outer shell layer exceeds 100 μm, it is not preferable because the abrasion resistance and the rough surface resistance required for the rolling roll are significantly reduced. The above requirement is defined in the range of a depth of 50 mm from the surface of the outer shell layer in order to correspond to the depth (maximum cutting allowance) used by the rolling roll. On the other hand, if m ₂ > 1.2 m ₁ , when the outer shell layer is processed by re-cutting, the abrasion resistance and the surface roughening resistance are remarkably reduced, and the roll basic unit is disadvantageously reduced.

Next, the reasons for limiting the supply temperature of the molten metal and the laminating speed of the outer shell layer in the second invention will be described.

(1) T _c ≦ T ≦ T _c + 90 ° C. In a normal centrifugal casting method, a temperature at which a casting ladle containing a molten metal for forming an outer shell layer is cast into a casting funnel, so-called casting temperature, is controlled. However, the supply temperature of the molten metal in the present invention is the temperature of the molten metal when it falls onto the inner surface of a mold (usually a mold is used). Then, the so-called casting temperature needs to be set higher than the supply temperature in consideration of the temperature drop. The molten metal for forming the outer shell layer needs to be supplied to the mold in a temperature range of + 0 ° C. to + 90 ° C. with respect to the primary crystal formation temperature _{Tc of the} material. Since solidification starts in the nozzle, a healthy shell layer cannot be formed, which is inconvenient.

In this case, the primary crystal austenite is generated immediately after the molten metal is supplied into the mold, and the molten metal supplied into the mold immediately starts solidification.
If T> T _c + 90 ° C., the time until the molten metal solidifies is too long, so that a large cooling rate cannot be obtained and the metal structure becomes coarse, which is not preferable. On the other hand, if T <T _c ° C., the molten metal starts to solidify in the casting nozzle, so that a healthy outer shell layer cannot be formed, which is inconvenient.

(2) Average Laminating Speed of Outer Shell Layer 2 to 40 mm / min The average laminating speed of the outer shell layer in the present invention means the time required for casting the thickness of the outer shell layer formed by casting the outer shell layer. That is, the rate at which the thickness of the outer shell layer increases due to the lamination of the molten metal per unit time. Generally, the casting speed of the outer shell layer in the centrifugal casting method is set to an average lamination speed of 50 to 200 mm / min in consideration of the fact that the cast molten metal is surely wound around the inner surface of the rotating mold. On the other hand, the reason why the average laminating speed in the present invention is set to be much lower is to supply the molten metal in synchronization with the progress speed of the solidification interface of the molten metal for forming the outer shell layer. In this way, the molten metal for forming the outer shell layer is supplied at a speed corresponding to the traveling speed of the solidification interface, and the outer shell layers are sequentially laminated, so that a thin layered molten pool is always held in front of the solidification interface. However, it can be moved in the radial direction.

Since the molten metal pool has a small heat capacity due to its thin layer shape, a large cooling rate can be obtained by heat conduction or heat radiation to the mold and the already solidified outer shell layer. In the thin layered molten pool, the temperature changes from the vicinity of the primary crystal forming temperature to the solidification temperature, so that a large temperature gradient can be obtained. If the thin layered molten pool is kept constant during the lamination of the outer shell layer and is moved in parallel, such a large cooling rate and temperature gradient as described above can be ensured even at a position inside the outer shell layer. And contributes to miniaturization and uniformity of the metal structure and prevention of casting defects. However, if the average laminating speed of the outer shell layer exceeds 40 mm / min, the above effect cannot be expected, and the outer shell layer is formed in the same manner as the conventional one, and the metal structure inside the outer shell layer is undesirably coarsened. On the other hand, if the laminating speed of the outer shell layer is less than 2 mm / min, the supply of the molten metal cannot follow the progress of the solidification interface of the molten metal, so that a sound outer shell layer cannot be formed, which is inconvenient.

[0031]

The present invention will be described in more detail with reference to the following examples.

Example 1 Using a mold having an inner diameter of 420 mm and a body length of 1530 mm, a sleeve roll having a total casting weight of 700 kg and a wall thickness of 60 mm was produced by centrifugal casting to form an outer shell layer having the composition shown in Table 1. .

[0033]

[Table 1]

In each case, the thickness of the coating material on the inner surface of the casting was set to 2.5 mm, and the rotation speed of the casting mold was set so that the gravity multiple of the centrifugal force on the surface of the molten metal on which the outer shell layer was to be formed was 140 G. The primary crystal formation temperature was measured by differential thermal analysis and found to be T _c = 1390 ° C. The supply temperature of the molten metal is T _c + 85 ° C. in the conventional method, and T _c + 50 ° C. in the invention method. Next, at the time of supplying the molten metal in the invention method, the molten metal was supplied at a laminating speed of 12 mm / min, and the casting was completed in a required time of 5 minutes.

In the method of the present invention, in order to measure the speed of progress of the solidification interface of the molten metal, a thickness of the molten metal of 10 mm and a thickness of 40 mm are used.
At the time of forming mm, 200 g of iron sulfide was added to the remaining molten metal in the casting port, and detection by sulfur printing was attempted. Test specimens were collected from the outer shell layer cast as described above by machining. FIG. 2 is a diagram schematically showing the results of a sulfur print test in an example of the present invention. Table 2 shows the test results of the test pieces.

[0036]

[Table 2]

As shown in FIG. 2, when the melt thickness was 10 mm, the solidification interface of the melt was 8 mm from the surface of the outer shell layer (the inner surface of the mold). The thickness of the pool of unsolidified molten metal is 2 mm,
The average traveling speed of the solidification interface is 9.6 mm / min (0.16 m
m / sec). Further, when the melt thickness was formed to be 40 mm, the position of the solidification interface of the melt was at the position of 33 mm. Therefore, the layer thickness of the unsolidified melt pool was 7 mm, and the average traveling speed of the solidification interface was 10.0 mm / min (0. 17mm / sec)
Is recognized.

The metal structure of the outer shell layer was observed. As a result, it was confirmed that the base tissue was fine and homogeneous not only at the outer surface of the outer shell layer but also at a portion 50 mm deep from the outer surface.

Example 2 Next, using a mold having an inner diameter of 1130 mm and a body length of 1593 mm, an outer shell layer having the chemical composition shown in Table 3 was cast to a thickness of 100 mm by the same centrifugal casting method as in Example 1. A sleeve roll was manufactured.

[0040]

[Table 3]

In each case, the thickness of the coating material on the inner surface of the mold was set to 2.0 mm, and the rotation speed of the mold was set so that the gravity multiple of the centrifugal force on the surface of the molten metal on which the outer shell layer was to be formed was 120 G. The primary crystal formation temperature was measured by differential thermal analysis and found to be T _c = 1335 ° C. The supply temperature of the molten metal is T _c + 85 ° C. in the conventional method and T
_c + 50 ° C.

The supply of the molten metal in the method of the invention was performed in the same manner as in Example 1. However, the thickness of the entire molten metal (100 m
m), which is 30% of the melt thickness, corresponds to a lamination speed of 12
The molten metal was supplied at 0 mm / min, and the molten metal was supplied at a laminating speed of 11 mm / min for the remaining molten metal having a thickness of 70 mm, and the casting was completed in a required time of 6 minutes and 37 seconds. Therefore, the average lamination speed is about 15 mm / min.

In the same manner as in Example 1, a test piece was sampled from the cast outer shell layer by machining and examined. In addition, at a position at a depth of 25 mm and 50 mm from the outer surface of the product outer shell layer obtained by cutting and grinding the finishing allowance at the time of as-cast, ultrasonic internal flaw detection over a total length of 1530 mm, visual inspection,
The existence of casting defects and segregation were investigated by macro etching.

FIG. 1 shows the metal structure of the outer shell layer of the invention method according to the second embodiment and the conventional method, and the metal structure of the corroded portion at the depth of 50 mm from the surface. In these metal structures, a portion that looks black is a base structure, and a portion that looks white is carbide. In addition, the size of the metal structure at the surface of the product outer layer of the invention method of Example 2 and the conventional method and the portion 50 mm deep from the surface was quantified by an image analysis method. The size (area) of the base tissue was converted into a perfect circle, and the diameter of the base tissue exceeded 30 μm was measured, and the average diameter was determined. The measurement was performed in 20 visual fields by darkening the base structure portion due to heavy corrosion, and the average value was defined as the base structure size. As a result, in the conventional method, the dimension of the base tissue was 83 μm at the surface portion, but was coarsened to 113 μm at a portion having a depth of 50 mm. On the other hand, in the method of the invention, the size of the base tissue was 75 μm, and even at a portion with a depth of 50 mm, it was 88 μm. From these results, it was confirmed that the roll of the present invention formed a fine metal structure from the surface to the inside.

Next, as a result of the ultrasonic internal flaw detection, no abnormality was recognized in any of the outer shell layers. However, the outer shell layer according to the conventional method has a depth of 25 mm from the surface.
Segregation of carbide having a diameter of 1 mm at a position of φ1 mm and a depth of 50 mm was observed by visual inspection. Further, as a result of the visual inspection and the macro-etching, it was confirmed that in the case of the conventional method, there was tissue unevenness (segregation) at a position 25 mm deep from the surface. On the other hand, in the outer shell layer of the invention method, no abnormality was recognized by visual inspection and micro-etching, and there was no casting defect and no segregation, and it was confirmed that the outer shell layer was sound.

[0046]

Since the present invention has the above-described structure and operation, it has been a problem in the prior art that the internal metallographic structure of the rolling roll having the outer shell layer made by centrifugal casting is coarsened and casting defects. In addition, it is possible to eliminate non-uniformity of the structure such as segregation and segregation, thereby improving the quality of the rolling roll and reducing the unit consumption of the roll.

[Brief description of the drawings]

FIG. 1 shows the surface of a product outer layer and a depth of 50 mm from the surface in Example 2 of the present invention and a conventional method, respectively.
3 is a micrograph showing the metal structure at the position of FIG.

FIG. 2 is a diagram schematically showing the results of a sulfur print test.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B22D 13/02 502 B22D 13/02 502K 19/16 19/16 F C22C 37/08 C22C 37/08 Z 38/00 301 38 / 00301L 302 302E 38/24 38/24 (56) References JP-A-2-258949 (JP, A) JP-A-3-53041 (JP, A) JP-A-63-290608 (JP, A) JP JP-A-1-195260 (JP, A) JP-A-1-254363 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 37/00-38/60 B21B 27/00-27 / 02 B22D 13/02 502 B22D 19/16

Claims (10)

(57) [Claims] 1. A rolling roll made of a hard material having abrasion resistance and abrasion resistance and comprising an outer shell layer manufactured by centrifugal casting and an inner layer or a shaft made of a tough material. The layers are C1.0 to
3.0%, Si 2.0% or less, Mn 2.0% or less, Cr
2.0-15.0%, Mo 10.0% or less, V2.0-
8.0%, the balance being substantially formed of a casting material composed of Fe and unavoidable impurity elements, and having an average size of the base structure of the outer shell layer of 50 mm from the surface of the product outer layer.
In the range, the average diameter of the matrix exceeding 30 μm by the image analysis method is formed to 100 μm or less, and the dimensions of the matrix structure at the surface of the product outer layer and at a position 50 mm deep from the surface are m ₁ and m, respectively. When m is ₂ , m
_A roll for rolling, characterized in that ₂ ≦ 1.2 m ₁ . 2. The rolling roll according to claim 1, wherein the outer shell layer further contains 20.0% by weight or less of W. 3. The rolling roll according to claim 1, wherein the outer shell layer further contains 3.0% Ni.
Rolls for rolling, characterized in that they contain not more than% by weight. 4. One of claims 1 to 3
3. The rolling roll according to claim 1, wherein the outer shell layer further contains Co in a weight ratio of 10.0% or less. 5. The method according to claim 1, wherein:
3. The rolling roll according to any one of claims 1 to 3, wherein the outer shell layer further contains 0.03 to 0.2% of N by weight. 6. The method according to claim 1, wherein the weight ratio is C1.0 to
3.0%, Si 2.0% or less, Mn 2.0% or less, Cr
2.0-15.0%, Mo 10.0% or less, V2.0-
8. A method for producing a roll for forming a shell comprising 8.0%, the balance being substantially composed of Fe and unavoidable impurity elements, wherein the mold has a hollow cylindrical shape and is formed rotatably around its axis. _{T C ≦ T ≦ T C +} 90 ℃ temperature T for supplying a melt of the shell layer to the (however, T _C is the primary crystal formation temperature of the material forming the outer shell layer.) and while, the outer A method for producing a roll for rolling, wherein the average laminating speed of the shell layer is 2 to 40 mm / min. 7. The method for producing a rolling roll according to claim 6, wherein the outer shell layer further contains 20.0% by weight or less of W. 8. The method for producing a rolling roll according to claim 6, wherein the outer shell layer further comprises N
A method for producing a rolling roll, wherein i is contained in an amount of 3.0% by weight or less. 9. Any one of claims 6 to 8
The method for producing a rolling roll according to any one of the first to third aspects, wherein the outer shell layer further contains Co in a weight ratio of 10.0% or less. 10. The method for producing a rolling roll according to claim 6, wherein the outer shell layer further contains 0.03 to 0.2% of N in a weight ratio. A method for producing a roll for rolling.