JP3211348B2 - 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 roll for rolling comprising an outer shell layer made of a hard material having abrasion resistance and rough surface 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, as the material of the outer shell layer by centrifugal casting, mainly high alloy cast iron, high chromium cast iron, high chromium cast steel, etc. are used. .

[0005]

Among the materials for forming the outer shell layer, for example, a high chromium cast steel-based rolling roll used for a rough stand and a finishing pre-roll in a hot tandem rolling mill has a casting property. When non-uniformity due to coarsening or segregation of the structure occurs, abrasion resistance and surface roughening resistance are deteriorated, and the basic unit of the rolling roll is deteriorated and 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. .

In the high chromium cast steel, when the outer shell layer is formed, 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. Become. For this reason, near the surface of the outer shell layer, the metal structure is fine,
It has excellent surface roughness resistance, and has a problem that the metal structure is rough inside the outer shell layer, so that the abrasion resistance is reduced and the surface roughness tends to be 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 solidification of the molten metal, and segregation of carbides, segregation in which a coarse metal structure exists, gas defects, and the like are generated.

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, according to the first aspect of the present invention, there is provided a rolling roll comprising an outer shell layer made of a hard material having abrasion resistance and surface roughness resistance and an inner layer or a shaft made of a tough material. The layer is C0.8 by weight.
-2.0%, Si 0.3-1.5%, Mn 0.5-1.
5%, P0.1% or less, S0.05% or less, Ni0.5
~ 2.0%, Cr 8 ~ 18%, Mo 0.5 ~ 5.0%,
The balance is substantially formed of a cast steel material composed of Fe and unavoidable impurity elements, and the average size of the base structure of the outer shell layer exceeds 30 μm by image analysis in a range of a depth of 50 mm from the surface of the product outer shell layer. Assuming that the average diameter of the matrix is 100 μm or less, and the dimensions of the matrix at the surface of the product outer layer and at a position 50 mm deep from the surface are m ₁ and m ₂ , respectively, m ₂ ≦ 1. 2
It adopted the technical means of m _1.

Further, in the second invention, the chemical component is C-0.8-2.0% by weight by centrifugal casting.
Si 0.3 to 1.5%, Mn 0.5 to 1.5%, P0.
1% or less, S0.05% or less, Ni 0.5 to 2.0%,
In the method for producing a roll for forming a shell layer comprising 8 to 18% of Cr, 0.5 to 5.0% of Mo and the balance substantially consisting of Fe and an unavoidable impurity element, the roll has a hollow cylindrical shape and its axis. rotatably formed and the temperature T for supplying a melt of the shell layer into the mold T _C ≦ T ≦ T _C around the
+ 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. Adopted.

[0012]

In the first aspect of the present invention, if the average size of the base structure of the outer shell layer exceeds 100 μm, the wear resistance and rough surface resistance required for the roll for rolling are unpreferably 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. The chemical composition of the outer shell layer defines and clarifies the chemical composition of the rolling roll to which the present invention is applied.

Next, the reasons for limiting the supply temperature of the molten metal and the lamination 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 molten metal for forming an outer shell layer is cast into a casting funnel from a ladle, that is, a 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 T _{C of the} material.

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.
When 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 because it is a thin layer, 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 in the conventional case, 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.

[0018]

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. .

[0020]

[Table 1]

In each case, the thickness of the coating material on the inner surface of the mold was set to 2.5 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 140 G. In addition, when the primary crystal formation temperature was measured by differential thermal analysis, it was T _C = 1395 ° C. in Invention Method 1, and T _C = 1360 ° C. in Invention Method 2. The supply temperature of the molten metal is T _C + 40 ° C. in the conventional method and the invention method 1,
In Invention Method 2, it is T _C + 35 ° C. Next, at the time of supplying the molten metal in the invention method, the molten metal was supplied at a laminating speed of 15 mm / min, and the casting was completed in a required time of 4 minutes and 05 seconds.

In the invention method 1, in order to measure the advancing speed of the solidification interface of the molten metal, the thickness of the molten metal is set to 10 mm and 4 mm.
At the time of forming 0 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.

[0023]

[Table 2]

As shown in FIG. 2, when the melt thickness was 10 mm, the position of 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 12.0 mm / min (0.2 m
m / sec). When the melt thickness was 40 mm, the solidification interface position of the melt was 35 mm. Therefore, the layer thickness of the unsolidified melt pool was 5 mm, and the average traveling speed of the solidification interface was 13.1 mm / min (0.1 mm). 22mm / 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, an outer shell layer having the chemical composition shown in Table 3 was cast to a thickness of 110 mm by the same centrifugal casting method as in Example 1 using a mold having an inner diameter of 1275 mm and a body length of 2563 mm. A sleeve roll was manufactured.

[0027]

[Table 3]

In each case, the thickness of the coating material on the inner surface of the mold was 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. When the primary crystal formation temperature was measured by differential thermal analysis, it was T _C = 1380 ° C. The supply temperature of the molten metal is T _C +4 in both the conventional method and the invention method.
5 ° C.

The supply of the molten metal in the method of the present invention was performed in the same manner as in Example 1. However, the thickness of the entire molten metal (the thickness of the outer shell layer is 110 m
m), which is equivalent to 30% of the melt thickness, is 33 mm.
The molten metal was supplied at 0 mm / min, and the molten metal was supplied at a lamination speed of 11 mm / min for the remaining molten metal having a thickness of 77 mm, and the casting was completed in a required time of 7 minutes and 20 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 the position of one wall depth 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,
The presence or absence of casting defects was investigated by ultrasonic internal flaw detection, visual inspection, and macro etching over a total length of 2500 mm.

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 in which the corrosion is deep at the portion 50 mm deep 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 size of the base tissue was 80 μm at the surface portion, but was coarsened to 110 μm at a portion having a depth of 50 mm. On the other hand, in the method of the present invention, the size of the base tissue was 77 μm at the surface and 89 μm even at a portion with a depth of 50 mm. 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, a slight abnormal waveform was recognized in the outer shell layer by the conventional method. When a sample was taken from the relevant portion and investigated, a fine cavity defect was found. On the other hand, no abnormality was recognized from the outer shell layer according to the invention method.

[0033]

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.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B22D 13/02 502 B22D 13/02 502E C22C 38/44 C22C 38/44 (56) References JP-A-5-247582 (JP, A) JP-A-62-24806 (JP, A) JP-A-57-101643 (JP, A) JP-A-4-176841 (JP, A) JP-A-3-53043 (JP, A) JP-A-58 -110166 (JP, A) JP-A-4-350143 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 302 C22C 38/44

Claims (2)

(57) [Claims] 1. 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, wherein the outer shell layer has a weight ratio of C0.8. ~ 2.0%, Si 0.3 ~ 1.5
%, Mn 0.5-1.5%, P 0.1% or less, S0.0
5% or less, Ni 0.5 to 2.0%, Cr 8 to 18%, M
o 0.5 to 5.0%, the balance being substantially formed of a cast steel material composed of Fe and inevitable impurity elements,
The average size of the base structure of the outer shell layer was set to 30 μm by an image analysis method in a range of a depth of 50 mm from the surface of the product outer layer.
When the average diameter of the base exceeding 100 μm is formed to be 100 μm or less, and the dimensions of the base structure at the surface of the product outer layer and at a position 50 mm deep from the surface are respectively m ₁ and m ₂ , m ₂ ≦ A roll for rolling, characterized in that the roll is 1.2 m ₁ . 2. A centrifugal casting method wherein the chemical components are C-0.8-2.0%, Si 0.3-1.5%, Mn by weight ratio.
0.5 to 1.5%, P 0.1% or less, S 0.05% or less, Ni 0.5 to 2.0%, Cr 8 to 18%, MoO.
A method for producing a rolling roll for forming an outer shell layer composed of 5 to 5.0% with the balance being substantially Fe and unavoidable impurity elements, wherein the roll is formed into a hollow cylindrical shape and is rotatable around its axis. The temperature T at which the molten metal of the outer shell layer is supplied to the cast mold 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). A method for producing a rolling roll, wherein the average laminating speed of the outer shell layer is 2 to 40 mm / min.