JP2001234289A - Roll for hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll for hot rolling in which the wear resistance of a high speed steel type alloy is secured, pit-like flaws on the surface of the roll are minimized to improve surface roughing resistance, and no carbide segregation is brought about. SOLUTION: In the hot roll, the shell of the roll is composed of a high speed steel type alloy having a composition satisfying inequalities, by weight, 1.7%<=C<=2.2%, 4.0%<=Cr<=7.0%, C-0.2 (V+0.55 Nb)<=1.1%, (V+0.55 Nb)>=5.5%, 2Mo+W>10% and Mo+2W<8%. Further, MC-type carbides are dispersed in the structure of the alloy, and the carbides of M2C, M6C, M7C3 and M23C6 type satisfy inequalities, by area percentage, (M2C+M6C)+(M7C3+M23C6)<=15% and (M2C+ M6C)>(M7C3+M23C6), respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling roll having an outer shell layer made of a high-speed alloy and having excellent wear resistance and surface roughening resistance. In particular, it is a roll most suitable for use in a finishing row for hot plate rolling.

[0002]

2. Description of the Related Art A roll for hot rolling needs to have both wear resistance and toughness at the same time. Therefore, a roll in which an outer layer and an inner layer are combined by a centrifugal casting method or the like is used. It is widely practiced to use a wear-resistant material and a tough material for the inner layer. In particular, a high-speed alloy as an outer shell layer has, in a metal structure, an MC-based high-hardness carbide mainly composed of V, a multi-carbide such as an M ₂ C-based or an M ₆ C-based carbide, and a matrix having a high-temperature softening resistance. Therefore, it exhibits excellent wear resistance as a roll material for hot rolling.

[0003]

In the conventional hot rolling using a high-speed roll, particularly in a hot-rolled finishing row,
There was a problem that pit-like deep dent flaws were easily formed on the surface of the outer shell layer of the roll. If these pit-like flaws occur significantly, the surface of the material to be rolled, such as a thin steel sheet, becomes rough and deteriorates the quality of the product. Worsen.

Further, at the time of manufacturing by the centrifugal casting method,
V, Nb, M added to impart abrasion resistance to the outer shell layer
There was a problem that carbide generated by o and W was not uniformly crystallized and segregation was easily caused.

Accordingly, the present invention has been made in view of the above circumstances, and has ensured the wear resistance of a high-speed alloy and has reduced pit-like flaws on the roll surface to improve the surface roughness resistance. It is another object of the present invention to provide a hot rolling roll free of carbide segregation.

[0006]

Means for Solving the Problems (1) In order to secure the wear resistance of a high-speed alloy, a high-hardness MC-based carbide is uniformly dispersed in a matrix. The hardness of the MC-based carbide is several times higher than that of the matrix, and by dispersing the hardness, wear is prevented from progressing mainly at the matrix. MC-based carbide is, for example, VC
, The Vickers hardness is about 2900 and M ₂ C
, M ₆ C, M ₇ C ₃ and M ₂₃ C ₆ carbides are most effective in ensuring wear resistance because they have higher hardness.

(2) M ₂ C, M ₆ C in the outer shell tissue
System, M ₇ C ₃ type and M ₂₃ C ₆ type carbide is likely to fall chipped during rolling. This chipping is the cause of the occurrence of pit-like flaws on the roll surface. Therefore, M ₂ C system, M ₆ C system, M ₇ C ₃
It was less chipping by reducing the abundance of systems and M ₂₃ C ₆ type carbides.

(3) Since the hardness of the M ₂ C-based carbide and the M ₆ C-based carbide in the structure of the outer shell layer is higher than that of the M ₇ C ₃ -based and M ₂₃ C ₆ -based carbides, the wear resistance is secured. M ₇ C _{3 for}
More than systems and M ₂₃ C ₆ type carbides were present.

(4) Among the elements added to impart wear resistance to the outer shell layer, the contents of V, Cr, Mo, W, and Nb are set particularly within the optimum range, and while ensuring wear resistance, In the case of centrifugal casting, segregation of carbide was prevented.

That is, the hot-rolling roll of the present invention comprises:
1.7% ≦ C ≦ 2.2% by weight of the outer shell layer of the roll,
4.0% ≦ Cr ≦ 7.0%, C−0.2 (V + 0.55
Nb) ≦ 1.1%, (V + 0.55Nb) ≧ 5.5%,
This is a high-speed alloy satisfying the formulas of 2Mo + W> 10% and Mo + 2W <8%. In this alloy structure, MC-based carbides are dispersed, and M ₂ C-based, M ₆ C-based, M ₇ C ₃ -based, and M ₂₃ C ₆
(M ₂ C + M ₆ C) + (M ₇ C ₃₎
+ M ₂₃ C ₆ ) ≦ 15%, (M ₂ C + M ₆ C)> (M ₇ C ₃ +
M ₂₃ C ₆ ).

In the above, (M ₂ C + M ₆ C) + (M ₇
C ₃ + M ₂₃ C ₆ ) ≦ 15% means that the content of M
₂ C carbides, M ₆ C carbides, M ₇ C ₃ carbides, and the total area percent of the M ₂₃ C ₆ type carbides which means that more than 15%. Also, (M ₂ C + M ₆ C)> (M ₇ C ₃ + M
₂₃ C ₆ ) means that the total area% of M ₂ C-based carbide and M ₆ C-based carbide in the HSS-based alloy structure is greater than the total area% of M ₇ C ₃ -based carbide and M ₂₃ C ₆ -based carbide. It means big.

In the hot-rolling roll of the present invention, it is desirable that the MC-based carbide is dispersed in an area% of 7 to 15%.

[0013]

The MC-based carbides include VC, WC, NbC and the like, and are fine-grained carbides that crystallize in the matrix or at the grain boundaries. These carbides have high hardness and impart excellent wear resistance to the roll. If the area ratio is less than 7%, the wear resistance is insufficient, and if it exceeds 15%, segregation of carbide tends to occur during centrifugal casting.

The total area% of M ₂ C-based carbide, M ₆ C-based carbide, M ₇ C ₃ -based carbide and M ₂₃ C _6- based carbide is 15%.
%, It is not preferable because carbides are easily chipped off during rolling. When the total area% of the M ₇ C ₃ carbide and the M ₂₃ C ₆ carbide is larger than the total area% of the M ₂ C carbide and the M ₆ C carbide, the chip is easily chipped off and the wear resistance is lowered. But not preferred.

C combines with Cr, Mo, W, V, and Nb to form carbide with high hardness (MC, M ₂ C, M ₆ C, M ₇ C _3, etc.) and enhances wear resistance. If C is less than 1.7%, a sufficient amount of carbides will not be generated, and sufficient wear resistance cannot be obtained. When C exceeds 2.2%, segregation of VC carbide occurs during centrifugal casting in view of the balance with the V content, which is not preferable.

Cr combines with C to form an M ₇ C ₃ system, M ₂₃ C ₆
Generates systemic carbides. Cr is an element effective for hardening the base structure into bainite or martensite and maintaining the wear resistance. If Cr is less than 4.0%, this effect is insufficient. When Cr exceeds 7.0%, M ₇ C
_It is not preferable because carbides of type ₃ and M ₂₃ C ₆ are excessive and chipping easily occurs.

V and Nb combine with C to form an MC-based carbide which is effective in improving wear resistance. V and N
b is an element having a very strong carbide-forming action,
Form C and NbC carbides. If it is too large, VC and NbC carbides become excessive and segregation is liable to occur. C-0.
2 (V + 0.55Nb) exceeds 1.1%, M ₂ C
System, M ₆ C-based, M ₇ C ₃ -based, and M ₂₃ C ₆ -based carbides are not preferred because the total area% becomes too high and the carbides are easily chipped off during rolling. Also, (V + 0.55N
If b) is less than 5.5%, MC carbides are not uniformly dispersed and wear resistance is insufficient, which is not preferable. In the high-speed alloy of the present invention, the content of Nb may be 0%.

Mo forms a solid solution in the base structure to strengthen the base structure and combines with C to form hard M ₂ C-based and M ₆ C-based carbides. W increases the high-temperature softening resistance of the matrix and combines with C to form hard M ₂ C-based and M ₆ C-based carbides.

Odor content satisfying 2Mo + W> 10%
M_TwoC system, M₆C-based carbides are sufficiently generated, and
For the balance with the Cr content, (M_TwoC + M₆C)>
(M ₇C_Three+ M_{twenty three}C₆), To ensure wear resistance,
This is preferable because chipping hardly occurs.

A content satisfying Mo + 2W <8% is preferable because segregation of M ₂ C-based and M ₆ C-based carbides can be suppressed. In the high-speed alloy of the present invention, the content of W is preferably 0.5% or less, and may be 0%.

In the hot-rolling roll of the present invention, the outer shell layer which is subjected to rolling in contact with the rolled material is formed of a high-speed alloy having the characteristics of the present invention. In this case, the present invention can be applied to a hollow or solid composite roll in which an outer shell layer and an inner layer material (or a core material) are welded and joined. In the case of a composite roll, a tough material such as ductile cast iron, ordinary cast iron, graphite cast iron, and spheroidal graphite cast iron is used as the inner layer material or the core material. In addition,
Instead of a composite roll, a single roll, that is, the entire roll may be formed of a high-speed alloy having the characteristics of the present invention.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The roll for hot rolling of the present invention will be described in detail based on examples.

The molten metal for the outer shell layer is poured into a centrifugal casting mold having a diameter of 435 mm and a height of 800 mm, and the thickness of the molten metal is 110 mm.
Was manufactured by a centrifugal casting method. After applying an appropriate heat treatment to this material, the outer diameter is 60m by machining.
A small sleeve roll (example of the present invention) for testing having a length of m, an inner diameter of 35 mm, and a length of 40 mm was prepared. In the comparative example, similarly, small test sleeve rolls having the same dimensions were prepared.

Table 1 shows the chemical composition (% by weight) of the outer shell layer of the prepared hot rolling roll.

Table 1 Chemical composition of outer shell layer No C Si Mn PS Cr Mo V Invention Example 1 1.72 0.90 0.53 0.02 0.02 5.58 5.34 5.74 Invention Example 2 1.88 0.82 0.43 0.02 0.02 4.36 6.33 6.51 Invention Example 3 2.01 0.85 0.51 0.01 0.01 6.94 4.09 7.10 Inventive Example 4 2.14 0.77 0.35 0.01 0.02 4.27 5.38 4.89 Comparative Example 1 2.19 0.84 0.46 0.01 0.02 8.15 4.99 5.09 Comparative Example 2 1.88 0.87 0.35 0.02 0.02 4.82 5.22 5.43

(Continuation of Table 1) No W Ni Co Nb Ti Zr Fe Invention Example 1 − − − − − − Bal Invention Example 2 0.45 − − − − − Bal Invention Example 3 1.91 1.83 − − − − Bal Invention Example 4 0.22 0.59 6.61 1.21 0.32 0.22 Bal Comparative Example 1 0.38 − − − − − Bal Comparative Example 2 5.03 0.63 − − − − Bal

Measurement of Area Ratio of Carbide A test piece was cut out from each test roll, and the base tissue was decomposed.
Blackened by eclipse, image analysis method in 20 visual fields, MC
Series carbide, M_TwoC + M₆C-based carbide, M₇C_Three+ M _{twenty three}C₆system
The area ratio of the carbide was measured, and the average value was obtained. as a result
Are shown in Table 3.

Hardness Measurement The surface hardness of each test roll was measured with a Shore hardness tester. Table 3 shows the results.

Rolling Wear Test A rolling roll was tested by incorporating a test roll into a rolling wear tester. After rolling, the depth of wear generated on the surface of the test roll was measured by a stylus type surface roughness meter (SURFCOM).
Table 3 shows the results.

FIG. 2 shows a schematic view of a rolling wear tester. Table 2 shows the rolling wear test conditions. In FIG. 2, the rolling wear tester includes a rolling mill 31 and a heating furnace 3 for preheating the rolled material S.
2, a cooling water tank 33 for cooling the rolled material S, a winder 34 for the rolled material S, and a tension controller 35. The test rolls 311 and 312 are incorporated in the rolling mill 31.

Table 2 Rolling wear test conditions Rolling material Rolling distance Rolling temperature Rolling rate Rolling speed Roll cooling SUS304 800m 900 ° C 25% 150m / min Water cooling

Table 3 Amount of carbide (area%) Hardness Wear depth Rmax Chipping No MC M ₂ C + M ₆ CM ₇ C ₃ + M ₂₃ C ₆ (HS) (μm) (μm) Invention Example 1 8.3 3.8 2.9 76 4.9 2 None Inventive Example 2 9.2 4.5 2.5 78 3.8 4 None Inventive Example 3 13.1 4.1 3.5 86 1.8 4 None Inventive Example 4 12.6 6.7 5.2 80 2.7 6 None Comparative Example 1 11.3 7.3 7.9 82 3.5 31 Yes Compare Example 2 7.9 5.4 3.7 83 5.6 5 None

In Table 3, the presence or absence of chipping was determined to be the case where the degree of pit-like flaws due to chipping was severe.

In the present invention (Examples 1 to 4), 1.7%
≤ C ≤ 2.2%, 4.0% ≤ Cr ≤ 7.0%, C-0.
2 (V + 0.55Nb) ≦ 1.1%, (V + 0.55N)
b) ≧ 5.5%, 2Mo + W> 10%, Mo + 2W <8
% Alloy that satisfies the formula of
And MC-based carbides are dispersed in the range of 7 to 15
_TwoC system, M₆C system, M₇C_ThreeSystem, and M_{twenty three}C₆Each carbonization of the system
Object is area%, (M_TwoC + M₆C) + (M₇C_Three+ M
_{twenty three}C₆) ≦ 15%, (M_TwoC + M₆C)> (M₇C_Three+ M_{twenty three}
C ₆), Good wear resistance and lack of carbide
There was no downfall. Also, as a result of observing the metal structure,
It was confirmed that there was no precipitation.

In Comparative Example 1, since Cr was added in excess of 7% by weight, (M ₂ C + M ₆ C) + (M ₇ C ₃ + M ₂₃ C ₆ )
Exceeds 15 area% and (M ₂ C + M ₆ C) <(M ₇ C ₃
+ M _{2 3} C _6), and the flaw degree pit-like violently chipping was deep.

In Comparative Example 2, since Mo + 2W> 8%, as a result of observing the metal structure, segregation of carbide was found.

FIG. 1 shows the measurement results of the depth of wear generated on the surface of the roll after the rolling wear test of Example 1 of the present invention and Comparative Example 1. In FIG. 1, (a) shows the measurement result of the present invention example 1, and (b) shows the measurement result of the comparative example 1. In Comparative Example 1, M ₇ C ₃ system, M
It was confirmed that pit-shaped flaw 1 due to chipping of ₂₃ C ₆ carbide was deep.

[0038]

According to the present invention, the outer shell layer is excellent in abrasion resistance, and since the chipping of carbide and the segregation of carbide do not occur, the surface texture of the material to be rolled such as a thin steel plate is improved, and the rolled product Quality is improved. Further, conventionally, the pit-shaped flaw due to the lack of carbide has been deep, so that a large amount of roll modification has been required. However, the modification can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a measurement result of a depth of wear generated on a roll surface after a rolling wear test.

FIG. 2 is a schematic view of a rolling wear tester.

[Explanation of symbols]

 1 pit-like flaw

Claims (2)

[Claims] 1. The outer shell layer of the roll is 1.7% ≦% by weight.
C ≦ 2.2%, 4.0% ≦ Cr ≦ 7.0%, C-0.2
(V + 0.55Nb) ≦ 1.1%, (V + 0.55N)
b) ≧ 5.5%, 2Mo + W> 10%, Mo + 2W <8
%, Which is a high-speed alloy that satisfies the following formula: MC alloy carbide is dispersed in this alloy structure, and M ₂ C, M ₆ C, M ₇ C ₃
System and each carbide of M ₂₃ C ₆ system is area%, (M ₂ C +
(M ₆ C) + (M ₇ C ₃ + M ₂₃ C ₆ ) ≦ 15%, (M ₂ C + M ₆
C) A hot-rolling roll characterized by satisfying the formula: (M ₇ C ₃ + M ₂₃ C ₆ ). 2. The method according to claim 1, wherein the MC-based carbide has an area percentage of 7 to 15%.
The hot-rolling roll according to claim 1, wherein the hot-rolling roll is dispersed.