JPH09256108A - Tool steel for hot rolling and outer layer material for centrifugally cast roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool steel combining wear resistance, crack resistance, and seizure resistance and causing no damage to the surface of a mating material by specifying the composition of a tool steel for hot rolling. SOLUTION: The tool steel for hot rolling has a composition consisting of 3.5-5.5% C, 0.1-1.5% Si, 0.1-1.2% Mn, 4.0-12.0% Cr, 2.0-8.0% Mo, 12.0-18.0% V, and the balance Fe with inevitable impurities and further containing <=8.0% Nb. The outer layer material for centrifugally cast roll, composed of the tool steel for hot rolling, further contains <=5.5% Ni. Further, in this outer layer material for centrifugally cast roll, an inequality of 0.2<=Nb/V is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has wear resistance, crack resistance, and seizure resistance, and does not cause damage to the surface of a mating material when used as a tool. The present invention relates to a tool steel for hot rolling and an outer layer material for rolling rolls which does not cause segregation or the like even when centrifugally cast.

[0002]

2. Description of the Related Art Conventionally, high-speed tool steel steel (high speed steel) as shown in JIS (JIS G 4403) etc. has been widely known as steel for hot tools, and is mainly used for cutting steel. It is used. For example, SKH10 used for cutting difficult-to-cut materials has C: 1.45 to 1.60%, Si: 0.40% or less, M
n: 0.40% or less, P: 0.030 or less, S: 0.030 or less, C
r: 3.80 to 4.50%, V: 4.20 to 5.20%, W: 11.50 to 1
3.50%, Co: 4.20-5.20%. These are manufactured by being subjected to heat treatment and hot rolling or casting after being melted by an electric furnace or the like.

Further, in the perforating process for manufacturing seamless pipes, a rolling tool called a guide shoe is used in order to suppress the bulging of the rolled material during perforation. The guide shoe heats due to direct contact with the material to be rolled at a temperature of over 1000 ° C and friction heat with the material to be rolled causes the tool surface to reach an extremely high temperature. At this time, the material to be rolled and the tool are seized, the surface of the material to be rolled is damaged, and the tool life is significantly reduced. The tool is sometimes cooled in order to protect the tool from this seizure, but at this time, the tool is subjected to thermal shock, and the tool surface is often cracked. Conventionally, ductiles, alloy ductiles, alloy grains, etc. have been used as guide shoes in order to prevent seizure as much as possible, but they have the drawback of poor wear resistance. In particular, when the material to be rolled is a high alloy steel (for example, 13Cr-based stainless steel), the rolling load is high, and it is inevitable to replace the pipe due to the progress of wear and the occurrence of cracks or seizures due to the drilling of about 10 pipes.

Further, in the finish rolling process of hot-rolled steel sheet production, there is a case where two or more sheets are stacked between stands and rolled as they are. This is called "aperture" trouble. When the roll surface temperature locally rises due to the increase in heat generated by friction between the roll and the plate and the heat generated during processing, seizure occurs and cracks occur on the roll surface due to thermal shock during water cooling (throttle crack accident ). Conventionally, centrifugal casting high alloy grain rolls have been generally used where there is a high risk of drawing cracks. The centrifugally cast high-alloy grain roll has a relatively low crack occurrence rate when encountering a drawing, and when a crack occurs, the depth is relatively shallow, but the wear resistance is poor. Recently, high-speed rolling rolls are being used, but the wear resistance is 3-5 times higher than that of centrifugally cast high-alloy grain rolls, but the drawing rate at the time of drawing encounter is high, and However, there is a drawback that the depth of cracks is deep.

Conventionally, as a high-speed rolling roll, as described in JP-A-4-365836, C: 1.5 to 3.5%, 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
It contains 7.0% and satisfies the following formulas (1) and (2), and V + 1.8Nb ≦ 7.5C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 (2) balance Fe and Disclosed is a rolling roll outer layer material composed of inevitable impurities, which has components in the outer layer even when centrifugally cast, no structure segregation, and uses a rolling roll outer layer material having both wear resistance and crack resistance. ing.

On the other hand, in the case of rolls used for cold rolling such as rolling of cold rolled steel sheet, forging rolls are generally used.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide wear resistance, crack resistance, and seizure resistance as a tool. It is intended to provide a tool steel for hot rolling that does not cause damage to the surface of a mating material when used.

Another object of the present invention is to provide an outer layer material for rolling rolls which does not cause segregation or the like even when centrifugally cast.

[0009]

The tool steel for hot rolling according to the present invention according to claim 1 has C: 3.5 to 5.5% and Si:
0.1 to 1.5%, Mn: 0.1 to 1.2%, Cr: 4.0 to 12.0
%, Mo: 2.0 to 8.0%, V: 12.0 to 18.0%, balance Fe
And inevitable impurities.

The present invention according to claim 2 is the tool steel for hot rolling according to claim 1, which further contains Nb: 8.0% or less.

The present invention according to claim 3 provides the tool steel for hot rolling according to claim 1 or 2, further comprising Ni: 5.5
% Or less.

According to a fourth aspect of the present invention, the outer layer material for centrifugal casting rolls comprising the hot-rolled tool steel according to the second or third aspect further satisfies the following expression (1). 0.2 ≤ Nb / V (1)

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

Si: 0.1 to 1.5% Si is added in an amount of 0.1% or more to secure deoxidation and castability, but if it exceeds 1.5%, the wear resistance decreases, so the upper limit is 1.5.
%.

Mn: 0.1 to 1.2% Mn is required to be 0.1% or more in order to form MnS by combining with S mixed as an impurity to prevent embrittlement due to S. If it exceeds 1.2%, crack resistance is high. The upper limit is 1.2% because it will decrease.

Cr: 4.0 to 12.0% Cr is added in an amount of 4.0% or more in order to improve wear resistance by forming carbides and strengthening the matrix, but if it exceeds 12.0%, the crack resistance decreases, so the upper limit is 12.0. %. It is more preferably 5.0 to 10.0%.

Mo: 2.0 to 8.0% Like Cr, Mo is effective in improving wear resistance by forming carbides, and also improves the hardenability and temper softening resistance of the matrix to strengthen the matrix structure. To be effective, 2.0% or more is required, but if it exceeds 8.0%, crack resistance decreases, so the upper limit is made 8.0%. It is more preferably 2.0 to 5.0%.

C: 3.5 to 5.5%, V: 12.0 to 18.0% C is an essential element for forming a hard carbide that improves the wear resistance of the outer layer material of the roll.

V is a hard MC which is most effective for improving abrasion resistance.
It is an essential element for forming (or M ₄ C ₃ ) carbides (diameter several μm to about 10 μm), and is added to most of conventional high speed steels. Addition of about 3.0% is sufficient if only improving wear resistance, but seizure resistance and crack resistance are not sufficient.

The seizure is caused by metal contact between the material to be rolled and the rolling tool. The structure of the rolling tool of the present invention is composed of granular MC (or M ₄ C ₃ ) carbide, non-granular M ₇ C ₃ carbide and matrix. It was found that increasing the amount of granular carbides is effective in improving the seizure resistance in this structure.
Therefore, as compared with the conventional high speed steel, it is necessary to add a large amount of V which is a granular carbide forming element and C corresponding to the amount of V. In order to exert its effect in the test of FIG. 1, C is
It was found that it is necessary to add 3.5% or more and V 12.0% or more. On the other hand, if V exceeds 18.0%, the effect of improving the seizure is saturated and the risk of manufacturing problems such as poor melting increases, so the upper limit of V is set to 18.0%.

Since V remains in the matrix, the crack resistance is improved. Minimum amount of V to secure seizure, 12.0
%, V remained in the matrix, and it was found that C must be 5.5% or less in the test of FIG. 2 in order to maintain the crack resistance.

In the test shown in FIG. 1, C: 2.0 to 6.0%, Si:
0.5%, Mn: 0.3%, Cr: 6.0%, Mo: 2.1%,
V: 1050 ℃ normalizing treatment for 7.0 to 20.0%, 550 ℃
A sample subjected to tempering treatment was used. In the seizure test, the mating material of φ 190 × 10 and the mating material of 55 × 40 × 10 were heated to 300 ° C by the sliding wear method, the test material was rotated at 800 rpm, and the pressure of 200 kgf was applied for 1 minute. The presence or absence of seizure was measured.

In the test shown in FIG. 2, C: 2.1 to 6.2%, Si:
0.4%, Mn: 0.5%, Cr: 5.8%, Mo: 2.5%,
V: Normalizing treatment of 1050 ℃ for 8.2 to 19.8%, 550 ℃
A sample subjected to tempering treatment was used. Thermal shock test is 1200
A 55 × 40 × 15 plate-shaped test piece is pressed against a roller rotating at 15 rpm for 15 s, then immediately cooled with water to generate cracks. The pressure contact load is 150 kgf. After the test, the test piece was cut and the crack length was measured. More preferably, C is
3.5 to 4.5% and V is 13.0 to 16.0%.

Nb: 8.0% or less Nb forms a composite carbide {V, Nb} C with V, and the wear resistance is further improved. On the other hand, if it exceeds 8.0%, manufacturing problems such as poor dissolution will occur, so the upper limit is 8.0%.

Ni: 5.5% or less Added to improve hardenability. Product is small,
Alternatively, when the wall thickness is thin or water quenching or oil quenching is possible, it is not always necessary to add it.

A rolling roll, which is a large hot rolling tool, has a maximum diameter of about 1500 mm. For rolls of this level, the range that allows quenching even with natural cooling with a slow cooling rate is 5.5% or less. 0.2 ≦ Nb / V (1)

The VC carbide has a small specific gravity with respect to the mother molten metal, and segregates when centrifugal casting is performed. Nb is also effective in preventing this segregation. Nb is V and complex carbide {V, N
b} C is formed, and the specific gravity is increased as compared with the case where the carbide is V alone. This prevents segregation due to centrifugation.
Therefore, it is necessary to change the amount of Nb added depending on the amount of V added. From FIG. 3, 0.2 ≦ Nb / V must be satisfied in order to obtain a uniform outer layer material for rolls when manufactured by the centrifugal casting method.

In FIG. 3, the "wear ratio (inner layer / outer layer)" indicates the wear amount (Iw) of the test piece taken from the inner layer side of the ring material and the wear amount (Ow) of the test piece taken from the outer layer side.
ratio (Iw / Ow) with w). The test of FIG. 3 is C:
4.0%, Si: 0.5%, Mn: 0.3%, Cr: 6.0%,
A ring sample with a wall thickness of 100 mm obtained by centrifugal casting (140G) of Mo: 2.1%, V: 14.2% and Nb: 0 to 11.0% was subjected to 1050 ° C normalizing treatment and 550 ° C tempering treatment. Using. Then, the wear test was carried out using the sliding wear method of the two-disc, φ190 × 15 mating material and φ50 × 10 mating material.
The test material was heated to 800 ° C and pressed under a load of 100 kgf.
Rotation was carried out at 800 rpm, the slip rate was set to 3.9%, and the wear reduction after 120 minutes was measured.

[0028]

【Example】

(Example 1) Chemical composition shown in Table 1 (materials A1 to A1 of the present invention)
2. The samples of Comparative Materials B1 to B9) were subjected to normalizing treatment at 1050 ° C. and tempering treatment at 540 ° C., and then hot abrasion, seizure and thermal shock tests were conducted. In this example, hot rolling or forging like high-speed steel for manufacturing the sample is not performed.

[0029]

[Table 1]

The wear test, the seizure test and the thermal shock test were carried out under the same conditions by collecting the above-mentioned test pieces.

Table 2 shows the results of the abrasion test, seizure test and thermal shock test. According to Table 2, the material of the present invention (A1
.About.A12) simultaneously satisfy the wear resistance, seizure resistance, and crack resistance of the comparative material. A9, A10, A1
Since Nb is added to the two materials, the wear resistance is further improved as compared with the case of no addition.

[0032]

[Table 2]

Since the B1 material has a small amount of C added, the amount of granular carbide is small and seizure occurs. Since the B2 material contains a large amount of C, the amount of V remaining in the matrix is small and the crack resistance is low. Since the B3 material contains a large amount of Si, its wear resistance is reduced. Since B4 material contains a large amount of Mn,
Crack resistance is reduced. Since the B5 material has a small amount of added Cr, its wear resistance is reduced. The B6 material has an excessive amount of Cr added, and thus the crack resistance is deteriorated. Since the B7 material has a small amount of Mo added, its wear resistance is reduced.
Since the B8 material contains an excessive amount of Mo, the crack resistance is deteriorated. In B9, the amount of V was insufficient, so that the amount of granular carbide was small and seizure occurred.

Example 2 A molten metal having the chemical composition shown in Table 3 (materials of the present invention: A21 to A24, comparative materials: B21 to B2)
4) was subjected to centrifugal casting (140G) to cast a ring sample having a wall thickness of 100 mm, subjected to normalizing treatment at 1050 ° C and tempering treatment at 540 ° C, followed by hot abrasion, seizure and thermal shock test. . In this example, hot rolling or casting like high speed steel is not performed in manufacturing the sample.

[0035]

[Table 3]

The wear test was carried out under the same conditions as described above, by taking test pieces of φ50 × 10 from each of the inner layer side and the outer layer side of the ring material. The seizure test and the thermal shock test were carried out under the same conditions by collecting the above-mentioned test pieces.

The results of the abrasion test, seizure test and thermal shock test are shown in Table 4. According to Table 4, the material of the present invention (A2
1 to A24), the homogeneity at the time of centrifugal casting is satisfied with respect to the comparative material.

[0038]

[Table 4]

Since the materials B21 to B24 do not satisfy the formula (1), segregation of carbides deteriorates the wear resistance of the outer layer.

[0040]

As described above, according to the present invention, a tool steel for hot rolling which has wear resistance, crack resistance, and seizure resistance and does not cause damage to the surface of the mating material when used as a tool. Can be obtained. Further, it is possible to obtain an outer layer material for a rolling roll that does not cause segregation or the like even when centrifugally cast.

[Brief description of drawings]

FIG. 1 is a diagram showing the effects of C and V on seizure properties.

FIG. 2 is a diagram showing the effects of C and V on crack depth in a thermal shock test.

FIG. 3 is a diagram showing the influence of the Nb and V content ratio Nb / V on the hot wear ratio between the outer layer and the inner layer due to the carbide distribution of the centrifugally cast ring material.

Claims (4)

[Claims] 1. C: 3.5 to 5.5%, Si: 0.1 to 1.5
%, Mn: 0.1 to 1.2%, Cr: 4.0 to 12.0%, Mo:
Tool steel for hot rolling, characterized by comprising 2.0 to 8.0%, V: 12.0 to 18.0%, balance Fe and inevitable impurities. 2. The hot-rolling tool steel according to claim 1, further containing Nb: 8.0% or less. 3. The tool steel for hot rolling according to claim 1 or 2, further comprising Ni: 5.5% or less. 4. An outer layer material for a centrifugal casting roll comprising the tool steel for hot rolling according to claim 2 or 3, further comprising:
Outer layer material for centrifugal casting rolls that satisfies the formula (1). 0.2 ≤ Nb / V (1)