JPH08246059A - Roll for hot rolling - Google Patents

Abstract

PURPOSE: To produce an inexpensive roll for hot rolling, excellent in resistance to wear and fracture loss, for use in the intermediate and the finishing stand at the time of rolling for steel bar, such as round bar and flat bar, and wire rod rolling. CONSTITUTION: This roll is constituted of an outer layer, having a composition consisting of, by weight, 1.7-2.5% C, 0.3-2.0% Si, 0.3-1.5% Mn, 0.2-1.5% Ni, 3-6% Cr, 3-10% Mo, 3-10% W, 3-7% V, 0.5-10% Co, <=0.020% P, <=0.020% S, other inevitable impurities, and the balance Fe and in which the value of M=C%-0.24×V% satisfies 0.3<=M<1.0, and an inner layer made of cast steel or forged steel is metallically joined to the outer layer. This roll is produced by a continuous tinkering padding method. Subsequently, this roll is cooled from a hardening temp. of 1000-1130 deg.C down to 100 deg.C at (300 to 600) deg.C/hr cooling rate and then tempered at 500-550 deg.C several times, by which the hardness of the outer layer is regulated to 85-95HsC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a rolling roll used in an intermediate and finishing stand for rolling of bar steel such as round steel or flat steel and rolling for wire rod, and a rolling speed of 5 to 3
It relates to a hot rolling roll used at 0 m / sec.

[0002]

2. Description of the Related Art Since hot rolling rolls used in the intermediate and finishing stands of bar steel rolling such as round steel or flat steel and wire rod rolling require a high degree of wear resistance, tungsten produced by a sintering method is used. A high-hardness cemented carbide roll mainly composed of a carbide (WC) is used. Further, cast iron rolls such as chilled rolls are partially used. Since this cemented carbide roll is manufactured by sintering hard tungsten carbide (WC) powder, it achieves extremely high wear resistance and rough surface resistance compared to cast iron rolls such as chilled rolls. It is widely applied in the middle and finishing stands of steel bars and wire mills.

[0003]

However, although the cemented carbide roll has excellent wear resistance, it has a drawback that it has poor toughness. Therefore, during rolling, especially when the rolled material is caught between the rolls, there is a problem that the rolled material is cracked or broken due to a mechanical impact force when the rolled material collides with the roll. Another problem is that the cost of the cemented carbide roll, which uses a large amount of expensive tungsten carbide (WC) powder, is several ten times as high as that of the cast iron roll. Further, since the tungsten carbide (WC) has a large specific gravity, the weight of the roll becomes large, and there is a problem in that the handling property during roll repair and maintenance work is poor.

On the other hand, cast iron-based rolls such as chilled rolls cannot ensure high hardness and roll wear during rolling is large, and frequent roll replacement is required to secure the product shape. It was Furthermore, it cannot be used for finishing stands with strict dimensional accuracy and products with strict dimensional accuracy. The hardness level of the high speed steel roll used in the hot rolling for steel sheets was 75 to 85 HsC. Therefore, it cannot be applied to the intermediate and finishing stands of steel bars and wire rod mills that require a high degree of wear resistance.

The present invention solves such a problem and provides an inexpensive roll excellent in wear resistance and fracture resistance in place of a super hard roll. Further, the purpose of the present invention is to reduce the weight of tungsten (W), which has a large specific gravity, to 10% or less to reduce the weight of the roll, and to improve the handling workability when repairing and caring for the roll.

[0006]

That is, in order to solve the above-mentioned problems, the roll of the present invention has been solved, and the first essential point of the present invention is to secure the hardness comparable to that of a conventional cemented carbide roll. That is, in the conventional cast iron roll, the limit is 80 HsC in the case of using the M ₃ C type carbide like the chilled roll, and it is impossible to secure the hardness of 85 HsC or more.

In order to achieve this object, the gist of the present invention is that in a rolling roll produced by casting a molten metal for the outer layer around the core material by using high frequency induction heating, the outer layer component is C: 1 by weight%. .7 to 2.5% Si: 0.3 to 2.0% Mn: 0.3 to 1.5% Ni: 0.2 to 1.5% Cr: 3 to 6% Mo: 3 to 10% W : 3 to 10% V: 3 to 7% Co: 0.5 to 10% P ≦ 0.020% S ≦ 0.020% and the value of M = C% −0.24 × V% is 0. Satisfying 3 ≦ M <1.0, other continuous layers formed by unavoidable impurities and the balance Fe and an outer layer made of cast steel or forged steel metallically bonded to the outer layer and a roll comprising a shaft Manufactured at a quenching temperature of 100
From 0 to 1130 ℃ to 100 ℃, 300 to 600 ℃ /
It is a hot-rolling roll excellent in wear resistance which is cooled at a cooling rate of Hr and tempered at a temperature of 500 to 550 ° C. several times to have an outer layer hardness of 85 to 95 HsC.

[0008]

With the above composition, MC type granular carbide having extremely high wear resistance and M ₆ C type (partly M ₂ C)
The eutectic carbide is crystallized and further heat-treated to secure the outer layer hardness of 85 to 95 HsC to improve the wear resistance, the rough surface resistance and the toughness. Material hardness 85HsC
In order to find the heat treatment conditions that secure the above, φ100 × 200 h ingots were manufactured with the chemical components shown in Table 1, and the quenching temperatures were set to three levels of 950 ° C., 1000 ° C., and 1100 ° C. from 200, 250, 300, 500, 1000. ℃ / H
After cooling to room temperature at a cooling rate of r, 10 at 500 ° C.
It tempered for time and measured the hardness.

[0009]

[Table 1]

The results are shown in FIG. From the experimental results, the quenching temperature should be at least 1000 ℃ to ensure the hardness of 85HsC.
It is necessary to secure it. Further, when the quenching temperature was finished at 1200 ° C., there was a problem that part of the ingot started to melt. Therefore, the quenching temperature of 1130 ° C., which is lower than the solidification completion temperature of the material, is the limit in quenching the actual roll. On the other hand, with respect to the cooling rate, at 200 and 250 ° C./Hr, a soft upper bainite structure is formed, so that the hardness is 85.
It was found that HsC could not be achieved. Therefore, hardness 8
To secure 5HsC, 300 from quenching temperature to room temperature
It is necessary to cool at a cooling rate of ° C / Hr or higher. Although the hardness increases as the cooling rate increases, 600 ° C./Hr is the limit for quenching of actual rolls.

Next, the effect of chemical components is shown in FIG.
When the value M obtained by subtracting C% (0.24 x V%) taken as VC carbide from 0.3 to M ≤ 1.0 is 85HsC
Can be secured. That is, it has been found that when the V content is too large, the VC carbides can take up carbon, so that the C content of the ground structure is insufficient and the hardness after quenching becomes low. On the other hand, when the V content is too small, VC carbides decrease and the hardness decreases.

Cr, Mo, and W other than V are VC carbonized.
After the substance crystallizes, it combines with C and becomes hard M ₆C, M₂C carbide
To contribute to increasing hardness. In addition, Cr, Mo,
W improves the hardenability of the ground structure and is 500 to
Secondary hardening by precipitation of hard carbides by tempering at 550 ° C
There is a function to make it. Therefore, the hardness of 85 HsC is secured.
Is M = C% − (0.24 × V%), and 0.3 ≦ M
≤1.0, and quenching temperature 1000 to 1130 ° C
(Because the material partially melts above 1200 ° C,
It was set to 30 ° C. ) Cooling rate from quenching temperature to normal temperature
It is necessary to control at 300 to 600 ° C./min.

The reason why the alloy components are limited to the above range will be described below. When C is less than 1.7%, the amount of crystallized carbide is small, high hardness cannot be secured, and wear resistance is insufficient. On the other hand, when it is 2.5% or more, the amount of M ₆ C-based eutectic carbide increases,
It is segregated into lumps and peels off from that part during rolling use, causing rough skin. Further, in order to control the amount of carbide and the hardness within an appropriate range, 0.3 ≦ C% − (0.24 × V
%) <1.0 is satisfied.

Si: Si affects the castability, and if it is too small, the flowability of the molten metal deteriorates and casting defects are likely to occur.
It was set to 0.3% or more. Also, it has a deoxidizing effect by combining with oxygen in the molten metal. Further, if it is 2% or more, the hardenability is impaired and the hardness becomes low, so 2% was made the upper limit. Mn: Mn, like Si, combines with oxygen in the molten metal and prevents gas defects. Further, it is combined with S to form MnS and has a desulfurizing action, so that the grain boundary is cleaned, so that it is 0.3% or more. Further, when Mn is 2% or more, the retained austenite increases and the structure becomes unstable, so the content is made 2% or less.

Cr: Cr, like carbon, improves the hardenability of the matrix and increases the hardness. If it is 3% or less, hardenability is poor and wear resistance is poor. On the other hand, if it is 6% or more, the carbides become coarse, and the thermal fatigue properties deteriorate, causing rough skin. Mo: Mo is an effective element that increases the quenching hardness of the matrix. Further, Mo is an element having excellent tempering resistance and forms a high hardness composite carbide together with Cr and W to increase high temperature hardness and improve wear resistance. If it exceeds 10%, the effect is almost unchanged.

W: W, like Mo, enhances the hardenability of the matrix and hardens. Therefore, if the content is 3% or less, the effect is small, and the content is 3% or more. Further, hard carbides are formed to improve the material hardness, but if it is 10% or more, coarse carbides are formed, which causes rough skin. V: V combines with carbon to crystallize MC type hard and fine carbide, and significantly improves wear resistance. C becomes 7% or more
The effect disappears in the balance with. If it is 3% or less, the effect of V becomes small. Further, in order to control the amount of carbide and the hardness within an appropriate range, 0.3 ≦ C% − (0.24
XV%) <1.0 is satisfied.

Co: Co has the same effect as Ni, and has the effects of improving hardenability, making the matrix structure dense, and increasing the high temperature hardness. However, if the amount is too large, the hardness becomes low. Further, Co is effective in oxidation resistance and is effective in preventing scale generation at a high temperature for a material containing a large amount of V. If Co is 0.5% or less, there is almost no effect, so 0.5% or more is necessary. On the other hand, if it is 10% or more, the hardenability is deteriorated, so the content is set to 10% or less. Ni: Ni improves the hardenability and is added to secure the hardness. At 1.5% or more, the effect disappears,
On the contrary, since the structure becomes unstable such that the amount of retained austenite increases, the content is set to 1.5% or less. Further, if the content is 0.2% or less, the quenching effect will not be obtained, so at least 0.2% or more is required.

Next, specific examples of the present invention will be shown.

【Example】

Example 1 First, as the first step of the present invention, test materials of the present invention material, a cemented carbide roll material, and a chilled roll material were manufactured by the following method, and an abrasion test at high temperature was performed. The material of the present invention was cast into a small steel ingot of φ100 × 200 h with the chemical composition shown in Table 1. After the steel ingot was softened and annealed, it was held at 1100 ° C. for 10 hours and then cooled to room temperature in 2 hours. Then, the test material which tempered 2-3 times in the temperature range of 500 degreeC-650 degreeC, and adjusted in the range of 70-95HsC was produced. Moreover, as a comparative material, 8
Carbide roll material with hardness of 6,90,94HsC and 70,7
A chilled roll material having a hardness of 4HsC was prepared. Table 2 shows the chemical composition of the cemented carbide roll material and the chilled roll material as comparative materials.

[0019]

[Table 2]

FIG. 3 shows the results of the hot wear test. The figure shows the effects of wear loss and hardness of the roll material of the present invention, the cemented carbide roll material, and the chilled roll material. In the hot wear test, the disc-shaped mating material was induction-heated to a predetermined temperature, the test material was pressed against the mating material and rotated, and the weight of the test piece after 20,000 rolling was measured, Abrasion resistance was evaluated by determining the amount of wear loss by the difference from the weight before the test. Furthermore, the peripheral speed of the test piece was changed, the abrasion test was conducted, the abrasion loss and the surface roughness were measured, and the influence of the rolling speed in the actual rolling was investigated.

[Test conditions] Test temperature (heating temperature of mating material) 600 ° C. mating material S45C load 500 N (maximum Hertz pressure: 240 MPa) Test piece peripheral speed 10,1,50 m / sec Slip rate 4% Rolling number 20,000 Times

[Test Results] Test 1. When the hardness of the material of the present invention is 85 or more, the amount of wear reduction becomes small, and the amount of wear is 1.5 to 2 times that of the cemented carbide roll material. When the hardness is low, the amount of wear loss is large and the difference from the carbide roll material is large. Further, the chilled roll material wears 20 times or more than the cemented carbide roll material. Therefore, it has been found that if the hardness is set to 85 HsC or more, the wear resistance of about 1/2 of the cemented carbide roll material can be secured.

Test 2. The test results obtained by changing the peripheral speed of the test piece are shown in FIG. The material of the present invention having a hardness of 90 HsC or higher has a greater wear reduction than the cemented carbide roll material, but was about 1.5 times on average. Further, when the peripheral speed of the test piece was 1 m / sec, the wear reduction was large as a whole. FIG. 5 shows the results of measuring the surface roughness. When the peripheral speed of the test piece is 1 m / sec, the surface roughness is large as a whole, and the roll material of the present invention has Rma
x. The value is close to 100 μm. Test piece peripheral speed is 5m / se
becomes more than c _Rmax. In becomes 30μm or less, it was clear the target value of the actual roll. The cemented carbide roll material of the comparative material was at a level of 10 to 20 μm. However, when the peripheral speed of the test piece was 1 m / sec, both the cemented carbide and the high speed steel had large surface roughness.

Example 2 Next, the test results of an actual roll are shown. φ300 x 10
A 0 mm sleeve type test roll was manufactured and a rolling test of an actual machine was performed. The chemical composition of the test roll is shown in Table 3 and the M value is 0.66. Heat treatment is 1030
After holding at 20 ° C. for 20 hours, it was cooled to room temperature in 2 hours and 30 minutes. Tempered at 540 ° C 3 times, surface hardness 9
It was set to 0HsC.

[0025]

[Table 3]

[Test roll] (a) Roll size φ300 × 100 mm (b) Chemical composition (c) Heat treatment condition Quenching temperature: 1030 ° C. Quenching condition: Quenching speed 1000 to 400 ° C. to normal temperature
/ Hr cooled. Tempering temperature: 540 ° C. × 3 times (d) Hardness 90 HsC The results of using this roll for actual rolling are shown below. The results of cemented carbide rolls and chilled rolls are also shown as comparative materials.

[Use conditions] Rolling speed 10 m / sec Kal shape Oval Rolling material temperature 820 ° C. Rolling amount 1200 ton Roll of the present invention, Carbide roll 240 ton Chilled roll

The results of the use are shown in Table 4 and FIGS.
FIG. 6 shows wear resistance (ton / mm) in which the amount of rolling is compared with the amount of roll consumption.
The wear amount of the ton-rolled roll was 0.15 mm on one side, and the wear amount was about twice as large as that of the super-hard roll having the same amount rolled as 1. Further, when the chilled roll was compared with the wear amount (compared with the same rolling amount), it was about 1/13. FIG. 7 shows a comparison of the roll current unit price with the current roll unit price kept constant.
Comparing the current unit prices of the rolls, the rolls of the present invention showed about twice as much wear resistance as that of the cemented carbide roll. Further, the surface roughness of the roll was slightly inferior to that of the cemented carbide roll rolled by the same amount, but there was no problem in use. In comparison with the chilled roll, the level was almost the same as when rolling 5 times the amount of the chilled roll.

[0029]

[Table 4]

Example 3 A composite type test roll of φ430 × 700 mm × 1900 L was manufactured, and a rolling test of an actual machine was conducted. The chemical composition of the test roll is as shown in Table 5, and the M value is 0.82. The heat treatment was held at 1050 ° C. for 20 hours and then cooled to room temperature in 2 hours and 30 minutes. The tempering treatment was performed 4 times at 530 ° C., and the surface hardness was 87 HsC.

[0031]

[Table 5]

[Test roll] (a) Roll size φ430 × 700 mm × 190
0L (b) Chemical composition (c) Heat treatment condition Quenching temperature: 1050 ° C Quenching condition: Quenching speed 1000 to normal temperature 380 ° C
/ Hr cooled. Tempering temperature: 530 ° C. × 3 times (d) Hardness 87 HsC Table 6 shows the results of using this roll for actual rolling. The results of cemented carbide rolls and chilled rolls are also shown as comparative materials.

[Use Conditions] Rolling speed 8 m / sec Kal shape Round Rolled material temperature 900 ° C. Rolling amount 12000 ton Rolls of the present invention, 15
As a result of using 000 ton cemented carbide roll and 2400 ton chilled roll, the roll of the present invention was rolled at about 12000 ton and the wear amount of the roll was 1.0 mm on one side, which was 0.37 times the wear resistance of the cemented carbide roll. In addition, the wear resistance was 7.5 times that of the chilled roll. Further, when compared with the original unit price of the roll, the wear resistance of the cemented carbide roll was about 1.8 times as high.

[0034]

[Table 6]

FIG. 8 compares the fracture toughness values of the roll material of the present invention with the cemented carbide roll material and the chilled roll material. It can be seen that the roll material of the present invention has a high fracture toughness value. Although 18 rolls of the present invention were used in an actual mill, it was confirmed that there were no troubles such as cracks and fractures that occurred in the cemented carbide rolls during rolling use, and that it was excellent in accident resistance. did it. Further, FIG. 9 compares the densities of the roll material of the present invention with the cemented carbide roll material and the chilled roll material. The roll of the present invention has a weight of about 1/2 that of the cemented carbide roll, and a great improvement in handling work can be expected.

[0036]

As a result of using the roll of the present invention as an actual rolling roll, the wear resistance of the roll was about 1/2 of that of the cemented carbide roll. On the contrary, double wear resistance can be achieved,
The roll cost can be dramatically reduced. Also, problems such as cracks during use could be resolved. In addition, the lighter roll weight has greatly improved the handling work during roll maintenance and refurbishment work.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between hardness and quenching temperature and cooling rate in a heat treatment test,

FIG. 2 is a diagram showing the relationship between hardness and chemical composition and M value by a heat treatment test,

FIG. 3 is a diagram showing a relationship between hardness and wear reduction of the material of the present invention, a cemented carbide roll material, and a chilled roll material;

FIG. 4 is a diagram showing the relationship between the peripheral speed and wear reduction of the material of the present invention and a cemented carbide roll;

FIG. 5 is a diagram showing the relationship between the peripheral velocity and the surface roughness of the material of the present invention and a cemented carbide roll;

FIG. 6 is a diagram showing wear resistance in which rolling amount is compared with roll consumption amount,

FIG. 7 is a diagram comparing abrasion resistance when the roll cost is constant,

FIG. 8 is a diagram showing a comparison of fracture toughness values of roll materials,

FIG. 9 is a diagram showing a comparison of densities of roll materials.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C22C 37/08 C22C 37/08 Z 38/00 302 38/00 302E 38/56 38/56

Claims (1)

[Claims] 1. Hot rolling rolls used in intermediate and finishing stands of rolling mills for bar steel and rolling mills for wire rods such as round steel or flat steel, wherein the outer layer component is C: 1.7 to 1.0% by weight. 2.5% Si: 0.3 to 2.0% Mn: 0.3 to 1.5% Ni: 0.2 to 1.5% Cr: 3 to 6% Mo: 3 to 10% W: 3 to 10% V: 3 to 7% Co: 0.5 to 10% P ≦ 0.020% S ≦ 0.020% and the value of M = C% −0.24 × V% is 0.3 ≦ Satisfying M <1.0, manufacturing a roll consisting of an outer layer composed of other unavoidable impurities and the balance Fe and an inner layer made of cast steel or forged metal metallurgically bonded to the outer layer by a continuous casting overlay method, Quenching temperature 1000-1
Hot rolling with excellent wear resistance, cooling from 130 ° C to 100 ° C at a cooling rate of 300 to 600 ° C / Hr, tempering several times at a temperature of 500 to 550 ° C, and an outer layer hardness of 85 to 95 HsC. roll.