JP3354543B2 - Composite roll for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a composite roll for hot rolling.

[0002]

2. Description of the Related Art In a composite roll for hot rolling, an outer layer material constituting an outer layer portion is generally required to have abrasion resistance, surface roughening resistance, heat crack resistance and the like. As a roll material that can meet this demand, a high-carbon high-speed steel material as disclosed in, for example, JP-A-1-96355 is conventionally known. This high-carbon high-speed steel material contains several percent of each of Cr, Mo, W, and V, has good wear resistance at high temperatures, and is suitable as a roll for hot rolling. However, when a high-carbon high-speed material disclosed in Japanese Patent Application Laid-Open No. 1-96355 is used, a special production method having problems in productivity and economy, such as a special casting overlay method, is used. However, there is a problem that a composite roll cannot be manufactured by a centrifugal casting method. On the other hand, a composite roll using a high-carbon high-speed material as an outer layer material is disclosed in Japanese Patent Application Laid-Open No. 5-29547.
No. 9 discloses this. By the way, in general, when a composite roll is manufactured by a centrifugal casting method using a high-carbon-based high-speed material as an outer layer material, due to a difference in specific gravity between a crystallized carbide and a liquid phase, the crystallized carbide is centrifuged and segregation occurs. There's a problem. In the material disclosed in JP-A-5-295479, in order to solve the problem of the segregation, C:
1.5 to 3.1%, Si: 1.5% or less, Mn: 1.2
% Or less, Cr: 5.5 to 12.0%, Mo: 2.0 to
8.0%, V: 3.0 to 10.0%, Nb: 0.6 to
7.0%, and V + 1.8Nb ≦ 7.5C−
The greatest feature is that the components are limited to those satisfying the formula of 6.0% and 0.2 ≦ Nb / V ≧ 0.8.

[0003]

However, in the components of the material disclosed in JP-A-5-295479, a large amount of hard carbide is crystallized, and therefore, it is excellent in wear resistance and heat crack resistance. However, since it is mainly composed of granular carbide, there is a problem that the surface roughness of a projection is easily caused, and the heat crack resistance deteriorates when the area ratio of the carbide is increased. As described above, when a composite roll is manufactured by a centrifugal casting method using a high-carbon-based high-speed material as an outer layer material, conventionally, a problem due to segregation occurs, and a decrease in rough surface resistance and a decrease in heat crack resistance are caused. There was a problem.

Accordingly, the present invention has solved the above-mentioned drawbacks of the conventional hot rolled composite roll using a high-speed material as an outer layer material,
An object of the present invention is to provide a composite roll for hot rolling that can improve the quality of a material to be rolled in hot rolling and is excellent in wear resistance, heat crack resistance, and surface roughness resistance.

[0005]

According to the present invention, there is provided a hot-rolling composite roll in which an outer layer material and an inner layer material are welded and integrated by a centrifugal casting method. The composition of the outer layer material is% by weight, and C:
1.4 to 2.7%, Si: 0.3 to 1.0%, Mn:
0.3-1.0%, Ni: 1.0% or less, Cr: 5.0
１12.0%, Mo: 3.0 to 10.0%, W: 2.5
４4.5 %, V + Nb: less than 2.0% , the balance being substantially composed of Fe, and satisfying the following expressions (1) and (2) as a first feature. . (1)... Mo + 2W ≦ 1.8Cr (2)... 40% ≦ 10C + Cr + 1.5Mo + 3W ≦ 50% In addition to the first feature, the composite roll for hot rolling according to the present invention has a thickness of an outer layer material formed by centrifugal casting. (T) is 20m
A second feature is that m ≦ t ≦ 120 mm. The third feature of the composite roll for hot rolling of the present invention is that, in addition to the first or second feature, the inner layer material is made of ductile cast iron or graphite steel.

[0006] The present inventor has proposed a component composition capable of improving the surface roughness resistance without impairing the abrasion resistance and the heat crack resistance, which are the great advantages of the high-speed hot rolling roll, and the segregation in centrifugal casting. In order to obtain an outer layer material that can effectively prevent the occurrence of the above problems, the present inventors have completed the present invention as a result of repeated studies while promoting the following technical logic. That is, first considering the solidification process in a high-carbon high-speed material, in this high-carbon high-speed material, austenite (γ phase) is first crystallized in a dendrite shape as primary crystals. Next, MC type carbide is crystallized from the melt between the dendrites by the γ-MC eutectic reaction.
When the cooling further proceeds, an M ₂ C-type carbide is crystallized by a γ-M ₂ C eutectic reaction. Finally, an M ₇ C ₃ type carbide is crystallized by a γ-M ₇ C ₃ eutectic reaction. Further, depending on the components, cementite is crystallized by γ-M ₃ C eutectic. As described above, carbides are successively crystallized from the melt with the progress of solidification, and therefore, there is a problem that a segregation occurs due to a centrifugal separation due to a difference in specific gravity between the melt and the carbides. Therefore, the present inventor further promoted the logic as follows. That is,
The segregation of carbides by centrifugation is limited only when there is a liquid phase that allows the crystallized carbides to move freely, and when the solid fraction is high, the carbides can no longer move freely. Is also less likely to occur. Thus, the outer layer melt in the centrifugal casting method is cooled in one direction from the outer diameter part by the presence of the mold, and directional solidification is performed. While crystallization occurs, carbides are successively crystallized by eutectic solidification, which causes a problem of centrifugation. Then, after the entire outer layer solidifies in the primary crystal and the solid phase ratio becomes high,
By optimizing the composition of the components and the thickness of the outer layer so that carbides are crystallized by eutectic solidification, a composite roll with less segregation, excellent surface roughness resistance, good wear resistance and good heat crack resistance can be centrifugally cast. The present invention has been conceived to be able to be manufactured by the present invention.

[0007] The composite roll for hot rolling of the present invention comprises:
The reason for limiting the content range of each component element in the component composition of the high alloy outer layer material constituting the outer layer will be described below. In addition, all component compositions are shown by weight%.

The content of C is set to 1.4 to 2.7%. C
Is an important element that combines with Cr, Mo, W, V, Nb, etc. to crystallize and precipitate carbides. When the content is less than 1.4%, the amount of carbides generated is small, and sufficient wear resistance is obtained. In addition to this, there is a problem that the solidification start temperature is increased and castability is deteriorated, or shrinkage cavities due to solidification shrinkage are easily generated. On the other hand, when the content exceeds 2.7%, the amount of carbides increases, the wear resistance is excellent, and the castability is also improved. However, the crystallization amount of the primary γ phase decreases, and the solid fraction at the time of eutectic solidification decreases. In addition, there arises a problem that carbides to be crystallized later are separated by the centrifugal force of centrifugal casting to cause segregation. The content of C is more preferably 1.6 to 2.5%.

The content of Si is 0.3-1.0%.
This Si is added in an amount necessary for deoxidation of the molten metal and good castability. If it exceeds 1.0%, the toughness of the material decreases, which is not preferable. The content of Si is more preferably
The content is preferably set to 0.5 to 0.9%.

[0010] The content of Mn is 0.3 to 1.0%.
Mn is added for deoxidation and desulfurization of the molten metal. It has the effect of improving hardenability and improving wear resistance.
%, The toughness decreases, which is not preferable. The Mn content is more preferably set to 0.4 to 0.8%.

The content of Ni is set to 1.0% or less. Ni
It is effective to add a small amount to improve the hardenability. However, when the content exceeds 1.0%, the amount of retained austenite becomes excessive, and problems such as a decrease in hardness and transformation cracking occur. Ni content is more preferably 0.5%
It is better to do the following.

[0012] The content of Cr is 5.0 to 12.0%. Cr is crystallized a M ₇ C ₃ type mesh-like carbide bonded by C, thereby forming an excellent carbide structure to surface roughening resistance, improving the hardenability and solid solution in the base. Also, γ-
Since the M ₇ C ₃ eutectic reaction temperature is low, the crystallization occurs after the solid phase ratio of the outer layer increases, and thus the crystallized carbide is not centrifuged and hardly causes carbide segregation. If less than 5.0%, M ₇ C
The crystallization amount of carbides such as type ₃ is small, and the surface roughening resistance is deteriorated. If it exceeds 12.0%, carbides are excessively crystallized, causing a problem of deterioration of heat crack resistance. The content of Cr is more preferably set to 6.0 to 11.5%.

The content of Mo is set to 3.0 to 10.0%. Mo forms a solid solution in the matrix to increase the high-temperature hardness of the matrix, and forms rod-like or needle-like carbides of M ₆ C type and M ₂ C type, which is effective in improving wear resistance and heat crack resistance. Mo
If the content of is less than 3.0%, the area ratio of these carbides is small, and the effect cannot be expected. On the other hand, if it exceeds 10%, M ₆ C-type and M ₂ C-type carbides are excessively crystallized due to coexistence with W, causing a decrease in toughness, which is not preferable. The content of Mo is more preferably set to 4.0 to 9.0%.

The content of W is 2.0-6.0%. W
Like Mo, it combines with C to form M ₆ C-type and M ₂ C-type carbides, and is effective in improving wear resistance and heat crack resistance. In addition, it has a solid solution in the matrix and has the effect of improving the high-temperature softening resistance. If the content is less than 2.0%, these effects are not obtained.
If it exceeds 0%, M ₆ C-type and M ₂ C-type carbides are excessively crystallized due to coexistence with Mo, and the toughness is lowered, which is not preferable. The W content is more preferably set to 2.5 to 4.5%.

V and Nb are contained in a total amount of 2.5% or less. V combines with C to form MC-type high-hardness carbides, which is effective in improving wear resistance. However, when the area ratio of the carbides is increased, rolling-like projections are formed on the surface, causing friction. Causes an increase in coefficient and rough skin. Also, γ
-MC The eutectic reaction temperature is high, and the crystallization occurs at the time when the solid fraction of the outer layer melt is low, so that there is a problem that carbide segregation is likely to occur due to centrifugation. The contents of V and Nb are more preferably 2.0% or less in total.

The composite roll for hot rolling according to the present invention comprises:
The reason for limiting the content range of each component element in the component composition of the outer layer material of the high alloy constituting the outer layer is as described above, but in the present invention, the above formula (1) is further defined as a limiting condition for the component composition. I have. The reason for imposing this condition is that in equation (1), the value of Cr is (Mo + 2W) /
When the value exceeds 1.8, M ₇ C ₃ type Cr carbide is mainly used, and the heat crack resistance deteriorates. That is, the condition (1) needs to be satisfied in order to maintain good heat crack resistance.

Further, in the present invention, the above-mentioned formula (2) is used as a second limiting condition for the component composition.
The reason for imposing this equation (2) is that (10C + Cr + 1.5M
When the value of (o + 3W) is less than 40% by weight, the crystallization amount of the primary crystal γ phase is large, which is effective in preventing segregation, but the total amount of crystallized carbide is small and the wear resistance is deteriorated. On the other hand, (10C
If the value of (+ Cr + 1.5Mo + 3W) exceeds 50% by weight, the total amount of the crystallized carbide becomes too large, the heat crack resistance is reduced, and the crystallized amount of the primary γ phase is reduced, so that carbide segregation is liable to occur. Problem. That is, (2)
By satisfying the formula, while maintaining the heat-resistant cracking property equivalent to that of the conventionally known high-speed steel, the carbide segregation which is a problem peculiar to centrifugal casting is improved, and the adjustment of the carbide morphology according to the formula (1) is performed. In addition, the outer layer of the roll can be provided with rough surface resistance while ensuring excellent wear resistance and heat crack resistance.

The second feature of the present invention resides in that the thickness (t) of the outer layer material by centrifugal casting is set to 20 mm ≦ t ≦ 120 mm for the following reason. That is, even if the component composition of the outer layer material is limited as in the first feature, segregation due to centrifugal casting may occur in the outer layer portion of the composite roll depending on the outer layer thickness (t). In the present invention, as a mechanism for preventing segregation peculiar to centrifugal casting, it is effective to carry out eutectic solidification after the entire outer layer is primary crystal solidified and the solid phase ratio is increased. According to this idea,
As the thickness of the outer layer increases, carbide starts to crystallize before the solid phase ratio of the entire outer layer increases, so that segregation due to centrifugal force is more likely to occur. However, if the outer layer thickness (t) at the time of casting is less than 20 mm, the outer layer becomes too thin, so that when the inner layer is cast following the outer layer, the temperature of the outer layer is already lowered, and the adhesion between the outer layer and the inner layer is reduced. A problem arises. In addition, since the outer layer is too thin as an actual hot-rolling roll, the service life is short, and it is not economical. On the other hand, when the outer layer thickness (t) exceeds 120 mm, there arises a problem that carbides are segregated and minute defects are easily generated. That is, by limiting the composition of the component according to the first feature and limiting the thickness of the outer layer (t) according to the second feature, the outer layer of the roll has no segregation and has excellent adhesion to the inner layer. It can be a composite roll.

The composite roll formed by the centrifugal casting method of the present invention comprises:
1400-1650 ° C of molten metal to be an outer layer in a rotating mold
When the solidification of the outer layer is almost completed, the inner layer is manufactured by casting a molten iron of ductile cast iron or graphite steel. The composite roll thus manufactured is subjected to a quenching and tempering treatment to give appropriate hardness and toughness. The quenching and tempering treatment is, for example, quenching from about 1000 ° C to about 200 to 250 ° C,
Tempering can be performed by repeating tempering one or more times at about 550 to 600 ° C.

The hot roll composite roll of the present invention has excellent wear resistance because the outer layer is made of a high alloy and has high hardness. By using a material having excellent toughness, for example, ductile cast iron or graphite steel, as the inner layer material combined with the outer layer material, it is possible to maintain mechanical properties enough to withstand hot rolling. The ductile cast iron and graphite steel,
Conventionally known ductile cast iron and graphite steel can be used.

[0021]

EXAMPLES Examples 1 to 7 were used as outer layer materials having the component composition according to the present invention.
It was centrifugally cast into a rotating mold having a diameter of φ and a height of 300 mm. The amount of hot water was poured so that the thickness at the time of casting was 200 mm at a half height. The centrifugal force is 10 at the inner diameter of the mold.
0G. The obtained casting is from 1000 ° C to 200 ~
Quench at 250 ° C, 3 at 550 ° C, 550 ° C and 560 ° C
The tempering treatment was repeated to obtain a supply. Comparative Examples 1 to 7
Was prepared in the same manner as in the example. Table 1 shows the component compositions of Examples 1 to 7 and Comparative Examples 1 to 7, and the formulas (1) and (2).

[0022]

[Table 1]

With respect to the obtained materials of Examples and Comparative Examples, the structure was observed at a depth of 20 mm from the outer diameter, and the area ratio of carbide was determined by image analysis. The Shore hardness was also measured. Table 2 shows the results.

[0024]

[Table 2]

A ring-shaped disk was sampled from the half height of the material, the cut surface was polished, and the state of carbide segregation by macro etching and the state of porosity defects by color check were evaluated. Table 3 shows the range of each defect by the distance from the outer diameter.

No segregation or casting defects of the ring-shaped disk
From the portions, abrasion test pieces and thermal shock test pieces were collected. Wear
A wear test was performed under the following conditions to determine the loss of wear and the surface of the worn part.
The roughness was measured. Wear resistance is specific wear amount mg / cm²Reputation in
Valued. Table 3 shows the results. The smaller the value, the more wear-resistant
Excellent. Roughness resistance is the maximum height of roughness R_maxAnd inside
Core wire average height R_aWas evaluated. Table 3 shows the results. Number
The smaller the is, the more excellent the surface roughening resistance is. <Wear test> Test method Pin-on-disk method Test temperature 300 ° C Load 5kg / cm²  Rotation speed 10m / min Sliding distance 20000m

[0027]

[Table 3]

In the thermal shock test, a test piece of 20 mm × 30 mm was heated to a predetermined temperature in the atmosphere, kept for 20 minutes, dropped into ice water and rapidly cooled. After the test, a color check was performed, and the temperature drop at which cracks began to occur was defined as thermal shock resistance. Table 3 shows the results. The higher the thermal shock resistance temperature,
Excellent heat crack resistance.

From the above data, segregation defects, abrasion resistance, surface roughness resistance, and heat crack resistance of Examples 1 to 7 and Comparative Examples 1 to 7 were evaluated. Table 4 shows the evaluation. ◎ is excellent, ○ is good, Δ is usable, and × is bad.

[0030]

[Table 4]

In Comparative Examples 1 and 2 where the amount of added V or Nb was large,
Contains a large amount of MC-type carbide, which tends to segregate.
The surface roughness after the test is rough, and the rough surface resistance is poor. Low in carbide
In Comparative Examples 5 and 6, the abrasion resistance was poor, and the C content was particularly small.
In Comparative Example 6, segregation and microscopic cavities also tend to occur. C amount
In Comparative Examples 4 and 7, where segregation and micro porosity tend to occur,
In both cases, the amount of carbide increases and the heat crack resistance decreases significantly.
You. Comparative Example 3 has good segregation, abrasion resistance and heat crack resistance.
Has a low Cr content,₇C ₃Type carbide is reduced,
Poor skin resistance.

It is important to reduce the roll production cost and to reduce the amount of abrasion of the roll material and the amount of remodeling due to thermal cracks in the roll basic unit in hot rolling. Further, in order to improve the quality of the rolled steel material, it is important to improve the wear resistance and the rough surface resistance. From this perspective,
The composite roll of the present invention in which the outer layer material is a high alloy is made of Cr, M
o and W as appropriate, and M ₇ C _3- type carbide and M ₆ C
It is possible to obtain a structure in which the surface roughness and the M ₂ C type carbide are appropriately crystallized, and the abrasion resistance and the heat crack resistance are not deteriorated, and the surface roughness resistance is improved. Furthermore, by limiting the amounts of V and Nb added and adjusting the amount of C, the solidification morphology can be suppressed, and segregation, which is a problem in centrifugal casting, can be prevented. INDUSTRIAL APPLICABILITY The composite roll of the present invention has high suitability as a roll for steel pipe rolling, a roll for strip steel rolling, and in particular, a hot rolling roll requiring surface roughness resistance, in addition to a work roll for hot finishing.

[0033]

According to the present invention, the composite roll for hot rolling according to the first aspect has the same abrasion resistance and heat crack resistance as a conventional roll made of high-speed steel. Thus, it is possible to provide a hot-rolling roll with sufficient segregation, which has a disadvantage in that the rough surface resistance, which is a drawback, is low, and is suitable for centrifugal casting. Of course, the manufacturing cost is also low. According to the composite roll for hot rolling according to the second aspect, in addition to the effect of the configuration of the first aspect, segregation during centrifugal casting is effectively suppressed, and a good hot rolling roll is provided. In addition to being provided, it is possible to secure a service life enough to withstand practical use as a roll for hot rolling. According to the composite roll for hot rolling according to claim 3, in addition to the effect of the configuration according to claim 1 or 2, the inner layer material is made of ductile cast iron or graphite steel,
A good roll for hot rolling excellent in toughness can be provided.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-8-60289 (JP, A) JP-A-6-145888 (JP, A) JP-A-2-258949 (JP, A) JP-A-5-258949 339673 (JP, A) JP-A-6-179947 (JP, A) JP-A-11-279680 (JP, A) JP-A-10-183289 (JP, A) JP-A-9-41072 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 37/00 B21B 27/00 B22D 13/02 502

Claims (3)

(57) [Claims] 1. An outer layer material and an inner layer material are formed by centrifugal casting.
A composite roll for hot rolling obtained by welding and integrating,
The component composition of the outer layer material is% by weight, C: 1.4 to 2.7% Si: 0.3 to 1.0% Mn: 0.3 to 1.0% Ni: 1.0% or less Cr: 5.0 to 12.0% Mo: 3.0 to 10.0% W:2.5-4.5% V + Nb:Less than 2.0%  And the balance substantially consists of Fe; and
Heat characterized by satisfying the following expressions (1) and (2)
Composite roll for cold rolling. (1) {Mo + 2W ≦ 1.8Cr (2)} 40% ≦ 10C + Cr + 1.5Mo + 3W ≦ 50% 2. The thickness (t) of the outer layer material obtained by centrifugal casting is 2
2. The composite roll for hot rolling according to claim 1, wherein 0 mm ≦ t ≦ 120 mm. 3. 3. The composite roll for hot rolling according to claim 1, wherein the inner layer material is made of ductile cast iron or graphite steel.