JPH03122251A - Composite roll for rolling metal and its production - Google Patents

Abstract

PURPOSE:To allow a composite roll to combine high thermal shock cracking resistance with high wear resistance by constituting the composite roll of a core material made of low alloy steel having a specific hardness lower than that of outer layer material and an outer layer material made of high alloy steel in which hardness, structure, and residual stress are specified, respectively. CONSTITUTION:This composite roll is constituted of a core material made of low alloy steel having a hardness of >=35 Shore hardness and lower than the hardness of outer layer material and an outer layer material made of high alloy steel having a martensitic structure of >=80 Shore hardness and <=15vol.% retained austenite content and also having a compressive stress of >=70kg/mm<2> residual stress at the outermost surface. In order to produce this roll, progressive hardening in which, while applying progressive heating to the outer layer material alone up to a temp. not lower than the austenite transformation point, a liquid refrigerant is sprayed on the heated part is performed. Then, high-temp. tempering treatment in which the amount of retained austenite phase in the outer layer material is regulated to <=15vol.% is carried out. Since tempering at a temp. as high as >=300 deg.C is made possible even if the surface hardness is regulated to a value equal to that of the conventional roll, resistance to thermal shock can be improved while maintaining wear resistance equal to that of the conventional roll.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a novel composite roll for a metal rolling mill and a method for manufacturing the same, and in particular to a shift type six-high rolling mill with high shaft strength suitable for metal cold rolling. Concerning machine work rolls and their manufacturing method.

[Conventional technology]

In rolls for metal rolling mills, thermal shock is applied to the roll surface due to slips that occur between the roll and the rolled material during rolling, rolling accidents where the rolled material wraps around the roll, and in severe cases, cracks may occur. Occur.

In addition to resistance to thermal shock, work rolls are required to have excellent wear resistance in order to maintain good rolling performance.

In order to improve thermal shock resistance, it is effective to improve the tempering resistance of the roll itself and to perform tempering at a higher temperature.

A conventional work roll has C1.2 to 2.5% and Si 0.8 to 3.5%, as described in JP-A No. 63-60258.
0%, Mn51%, Cr3.0-6.0%, M.

A roll material consisting of 0.2% or less was tempered after quenching, but in order to obtain a hardness of Hs 93 or higher, the tempering temperature was set to 160° C. or lower.

[Problem to be solved by the invention]

In the above conventional technology, in order to improve heat resistance and thermal shock resistance, when the tempering temperature is raised to 160°C or higher, hardness of Hs93 or higher cannot be obtained, wear resistance decreases, and good rolling cannot be maintained. Ta.

An object of the present invention is to provide a work roll for metal rolling that has both high resistance and high wear resistance against thermal shock cracking, and a method for manufacturing the same.

[Means to solve the problem]

The present invention provides a composite roll for metal rolling in which the outer periphery of a core material is covered with an outer layer material, wherein the core material is made of low alloy steel having a Shore hardness of 35 or more and lower than the outer layer material, and the outer layer material is characterized by being made of high-alloy steel having a martensitic structure with a Shore hardness of 8° or more and a retained austenite content of 15% by volume or less, and a compressive stress of 70 kg/nu" or more with a residual stress on the outermost surface. Composite rolls for metal rolling.

In the present invention, by weight, C015~1.5%, Si0.5~
3%, Mn 1.5% or less, Cr 2-7%.

MO1-5%, V0.5-2.0%, W2. A work roll for metal rolling, characterized in that the outer layer is made of high speed steel containing 0% or less, and the core material is made of low alloy steel.

The present invention provides a method for manufacturing a composite roll for metal rolling, in which an outer layer material made of high alloy steel, which is harder than the low alloy steel, is welded to the outer periphery of a core material made of low alloy steel, in which only the outer layer material is made of austenite. A quenching process in which a liquid refrigerant is injected into the heated portion while gradually heating it to a temperature above the transformation point, and after the quenching, the retained austenite phase of the outer layer material is reduced to 15%.
A method for manufacturing a composite roll for metal rolling, characterized by including a step of performing high temperature tempering treatment to reduce the temperature to % by volume or less.

Furthermore, in the present invention, C0.7 to 1.5% per weight.

Si 0.5-3.0%, Mn 1.5% or less, Cr 2.
0-7.0%, Mo1-5%, V0.5-2.0%, W
The surface layer of a roll material with an outer layer of high-speed steel containing 2.0% or less and a core material of low-alloy steel is heated to a temperature above the transformation point, and after fountain quenching, a temperature of 300℃ or above is applied. The present invention provides a method for manufacturing a work roll for metal rolling, which is characterized by tempering the work roll.

If a roll is made of the above material, there is a risk of it breaking from the inside due to thermal stress during fountain quenching, and the shaft has poor toughness, making it disadvantageous against neck breakage during use. . Therefore, the roll has a composite structure in which the surface layer is made of the above-mentioned material and the core material is made of alloy steel with high toughness.

In addition, after providing an outer layer made of high-speed tool steel around the outer periphery of the core shaft made of low-alloy steel, the outer layer is subjected to hot forging in order to disperse the carbides contained in the outer layer and to make the structure uniform. It is preferable to apply

The roll of the present invention is a composite roll consisting of a core shaft and an outer layer that covers the core shaft, but if the entire roll is made of the above-mentioned high-speed tool steel (i.e., if it is an integrated roll made of high-speed tool steel) ), there is a risk of internal breakage (cracking) due to the thermal stress generated during fountain quenching, and the roll neck may break during use due to poor toughness of the shaft. easy. Therefore, the above-mentioned composite roll structure was adopted.

Regarding the quenching treatment, when blast cooling or oil cooling is performed, even if the above-mentioned materials are used, the compressive residual stress in the surface layer is insufficient. That is, if tempering treatment is performed at a temperature of 300°C or higher after the quenching treatment, Hs 93
It is difficult to obtain a hardness higher than that. This is why, in the method of the invention, quenching is carried out by fountain cooling.

The tempering temperature in the present invention is preferably 450°C to 550°C, more preferably 500°C to 550°C. In addition,
In the case of cold rolling rolls, it is said that a surface hardness of approximately Hs 90 or higher is required, and in the case of hot rolling rolls, those having a surface hardness of approximately Hs 80 to 85 are used.

When only the outer layer is heated above the transformation point and quenched by rapid cooling as in the present invention, the residual stress is a combination of residual stress due to thermal stress and residual stress due to transformation stress.

When the outer layer is rapidly cooled, compressive plastic strain occurs in the internal plastic deformation temperature range due to its volumetric contraction. As a result, when the inside and outside temperatures are cooled to the same temperature, compressive residual stress occurs in the outer layer and tensile residual stress occurs inside. This is residual stress due to thermal stress. In addition, martensite produced in the outer layer due to transformation has a relatively large specific volume, so due to the difference in specific volume from the core shaft, tensile residual stress is generated in the core shaft, and compressive residual stress is generated in the hardened outer layer. arise. As described above, the residual stress caused by thermal stress and transformation stress is considerably larger than the residual stress caused only by martensitic transformation (usually about -20 kg/m), and the residual stress caused by the compressive residual stress, which is the target of the present invention, is 'lok
g/Pus 2 to -120 kg/field 2 (when sub-zero treatment is applied) can be obtained.

Further, if only water jet quenching is applied, about 40% of austenite remains, and in order to accelerate the decomposition of this residual austenite, sub-zero treatment is performed at a temperature of -50° C. or lower. Sub-zero treatment is performed by suspending a roll in a vertical sub-zero treatment tank and spraying liquid nitrogen onto the roll surface while rotating the roll. The amount of retained austenite after sub-zero treatment is approximately 15% or less.

After this, when tempering treatment is performed at a temperature of 300°C or higher,
The amount of retained austenite decreases by about several percent from the above value of about 15%. The austenite that ultimately remains serves as a buffer that alleviates thermal expansion and contraction of the roll surface while the roll is in use, and functions to prevent cracks from occurring on the roll surface. In addition, if the roll is tempered at a high temperature, when the roll is used for hot rolling, even if an accident occurs and a high-temperature steel plate wraps around the roll and the roll temperature rises, the roll surface will not change. Cracks caused by decomposition of retained austenite are effectively prevented.

In general, the higher the tempering treatment is performed, the easier it is to relax the distortion caused by quenching.
It is known that the amount of reduction in residual stress increases. However, the high speed tool steel used in the present invention contains alloying elements Si, Cr, M0. V
Compared to general low alloy steel, the steel contains less strain release during tempering at a temperature of about 500°C, and can maintain high residual stress.

In addition, the core material in the present invention has a tensile strength of 60 and g
/ m” or more, impact value 1, 5 kg-m/a
1 or more low alloy steels are preferred, especially C065 at 1% by weight.
~1.0%, Si1% or less, Mn1% or less, Cr1-5
%, M o 0 , 5% or less is preferred.

[Effect]

The work roll for cold rolling with the above configuration is wear resistant even when used for rolling that involves large bends.

It is sufficiently durable in terms of skin roughness resistance 2 and toughness. In particular, since this is a roll whose outer layer is welded to the shaft material by electroslag remelting, the carbides that crystallize from the molten metal solidify rapidly without floating, precipitating, or segregation, so that they are finely and evenly dispersed in the outer layer. becomes. These allow for high pressure reduction of rolled materials.

High shape control can be carried out soundly and the quality of the surface properties of the rolled material is improved.

In order to solve the problems of the prior art and achieve the above object, the present inventors conducted experiments and obtained the following findings.

In order to ensure wear resistance and roughness resistance, the outer layer must be made of semi-high-speed steel and must be heat treated to maintain a hardness of Hs 90 or higher.

In addition, the chemical components of the semi-high-speed steel in the outer layer are specified for the following reasons.

C is necessary for forming carbides to improve wear resistance and ensuring base hardness. When the amount is less than 0.5%, the amount of carbide is small and the wear resistance is not sufficient. On the other hand, C is 1.
When it exceeds 5%, network carbides precipitate at grain boundaries increase, resulting in poor roughness resistance and toughness. In particular, 0.
8 to 1.2% is preferred.

Si is an element necessary as a deoxidizing agent, has a content of 0.5% or more, and also improves tempering resistance. However, the amount is 3.
If it exceeds 0%, embrittlement tends to occur. In particular, 1 to 3
% is preferable, and 1.5 to 2.5% is more preferable.

Mn has a deoxidizing effect and also has the effect of fixing impurity S as MnS, but if its amount exceeds 1.5%, retained austenite increases, making it impossible to maintain stable and sufficient hardness, and reducing toughness. . In particular, 0.2 to 1.0
% is preferred, and 0.2 to 0.5% is more preferred.

If C'r is less than 2%, the hardenability is poor, and if it exceeds 7%, there will be too much Cr-based carbide, which is disadvantageous. especially,
3 to 6% is preferable, and 3.5 to 5% is more preferable.

Mo and W combine with C to form M z C or M s C-based carbides, and also form a solid solution in the base to strengthen the base and improve wear resistance and tempering resistance. However, if it is excessive, M a C-based carbides increase and toughness and roughness resistance decrease. M.

The upper limits of and W are 5% and 2%, respectively, and Mo is 1
% or more. Mo is preferably 1.5 to 4.5%, and W is preferably 0.1 to 1%, 0.15%.
~0.5% is more preferred.

V forms MC-based carbides and contributes to improving wear resistance, but
If it is less than 0.5%, there is no sufficient effect, and if it exceeds 2%,
Significantly inhibits grindability. In particular, 0.7 to 1.5% is preferable.

CO is an element for obtaining high hardness by solid solution in the matrix and high temperature tempering, but the effect is sufficient when it is less than 5%.

Note that the semi-high-speed steel used for the outer layer of the present invention may contain Ni in addition to the above-mentioned elements. Since Ni has the effect of improving hardenability, it can be added in an amount of 5% or less. Exceeding this will lead to an increase in retained austenite, resulting in a decrease in hardness and roughness resistance. In particular, 1% or less is preferable, and 0.1 to 0.5% is more preferable.

In addition, in the present invention, Hs 35 is used as the material for the core shaft.
It is preferable to use forged steel having the above properties. That is, the roll of the present invention has a nominal stress of 10 kg/o
When a net stress of wn2 is applied, the size effect coefficient is 0
．． 8. Assuming a surface effect coefficient of 0.9 and a notch coefficient of 2.0, the required fatigue limit is 36 kg/nwn'', and in order to obtain this, the hardness should be Hs35 or higher.

The nominal stress σ1 in the roll net portion is determined by the following equation.

πd3 P: Load applied to the bearing + 2 = Moment arm from the center of the bearing d: Diameter of the relevant shaft and allowable stress (Allowable 5tress)
aa* is determined by the following formula.

η ・ ξ 1 σ・0: Rotating bending fatigue limit of smooth test piece η: Size effect coefficient = 0.8 ξ: Surface effect coefficient = 0.9 β: Notch coefficient = 2.0 S: Safety factor = 1.3 Since it is considered safe if σ, ≧σ, β M: bending moment = pu from the above two equations.

σ. When = 10 kg/Den2, σ. ≧36kg/
It becomes m2.

As a method of providing an outer layer on the core shaft,
The outer layer is formed by hot isostatic pressing using a continuous overlay method using high-frequency heating disclosed in JP-A No. 03 and others, and a powder metallurgy method disclosed in JP-A-47-2851 and others. There is a method of overlaying using an electroslag remelting method disclosed in Japanese Patent Application Laid-Open No. 57-2862. Particularly preferred is the electroslab remelt overlay method.

〔Example〕

A roll with a body diameter of 385n+m and a body length of 1480am is
An ingot for a composite roll having an outer diameter of 485 nwn was manufactured using a shaft material of 00 mm in diameter by the electro-remelting method as follows.

FIG. 7 is a schematic diagram of an apparatus for manufacturing a composite roll by the electroslag overlay method. This device is a welding machine with 9.
Amplifier 172 energizing wiring 12. carbon brush 12a,
Thermocouple for temperature measurement 13. Includes a DC motor 18 and a manipulator 19. The manipulator 19 is moved by a DC motor 18 such that the tubular electrode 8, a consumable electrode made of high speed tool steel, supported by the manipulator arm 12a, is moved upwards. A core shaft 7 made of low alloy steel is installed on a surface plate ll. A water-cooled mold 10 is installed concentrically with this core shaft 7,
In the space between the two, an annular bottom hole (that is, a mold bottom) 16 is installed close to the lower end of the core shaft 7. The core shaft 7 and the water-cooled mold 10 are rotated in the circumferential direction.

A tubular electrode 8 supported by a manipulator 19 is inserted into the space defined by the core shaft 7 and the water-cooled mold 10, that is, into the melting chamber, and is connected between the core shaft 7 and the tubular electrode 8 via the wiring 12. The tubular electrode 8 is melted and consumed by the current supplied to the tube. When an arc is generated by energization, the slag 15 melts due to its resistance heat generation, and a molten metal 14 is formed, which is cooled and solidified by contact with the water-cooled mold 10, and a build-up layer is formed on the surface of the core shaft 7. Ru.

During this time, the water-cooled mold 1o is moved upward coaxially with respect to the core shaft 7. The slag 15 always has a thickness of 50~
It is adjusted to 60nn. Further, the molten metal 14 is prevented from dripping downward by the annular bottom plate 16.

The built-up layer of the composite roll obtained in this way was forged at 1100°C, with an outer diameter of 415 mm and an outer layer thickness of 42.5 mm.
mm. Furthermore, the built-up layer is subjected to quenching and tempering heat treatment, thereby making it possible to obtain a surface hardness of the built-up layer of Is90 or more.

After heat treatment, the finished outer diameter is 385 by cutting and polishing.
It is cut and polished to a diameter of approximately 2 to 3 m.

The chemical components of the outer layer material are shown in Table 1 (% by weight).

The remainder is Fe. This roll is further 1000-120
Quenching from 0°C and 120-520°C.

A tempering heat treatment was performed for 10 to 20 hours. For comparison, rolls with the same dimensions were also manufactured using conventional 5% Cr forged steel. The chemical composition of this material is also shown in Table 1.

The heat treatment was performed in a manner appropriate for this material. In addition, C009%, 3%Cr forged steel was used for the shaft material of the roll of the present invention,
Its hardness was H540.

FIG. 8 shows the fountain hardening method. roll 20
The outer layer 21, which is the overlay layer, is the part to be hardened. Surrounding the outer layer 21 of the roll 20 set vertically, an annular device including an induction coil 22, which is a low frequency inductor, and a water injection cylinder 23 is set. With a low frequency current flowing through the induction coil 22, the roll 20 is rotated and moved downward. The outer layer 21 is progressively quenched by being heated by the generated induced current and continuously cooled and quenched by the cooling water injected from the water injection tube 23. As a result, rapid cooling with a cooling rate of 10° C./sec or more is achieved. The cooling rate can be controlled by the amount of water injected, the injection speed, etc.

Only the outer layer 21 was heated to the quenching temperature, and the temperature at the boundary with the core material was below the austenite transformation point.

As a result, the toughness of the core material at the boundary can be maintained high.

Table 1 Figure 1 shows the relationship between tempering temperature and hardness, and Figure 2 shows the relationship between tempering temperature and residual stress. In the case of invention examples 1 and 2, the quenching temperature was 1060°C,
By the method shown in FIG. 8, gradual quenching was performed by low-frequency induction heating of only the outer layer and subsequent fountain cooling. Thereafter, subzero treatment was performed at -50°C, and tempering was performed at each temperature. The cooling rate at this time is approximately 15
℃/SeC.

Comparing FIG. 1 and FIG. 2, it is clear that residual stress contributes to the hardness of the roll surface after tempering. With conventional rolls, the tempering to obtain a hardness of Hs 93 is 1
60°C, but in the case of Inventive Example 1, it was 520°C,
It can be seen that the tempering temperature at which the same hardness can be obtained is significantly higher than that of conventional rolls. Also, the tempering temperature is 50
The residual stress on the roll surface of the present inventions 1 and 2 at 0°C is greater than -70 kg/mm, whereas the residual stress on the roll surface of the conventional roll is approximately -30 kg/mm".
It can be seen that a large residual stress can be secured by the present invention.

The amount of retained austenite in Examples 1 and 2 is 10 to 15
It was % by volume.

In the case of Example 2, the hardness after returning at 500° C. was Hs88, clearly demonstrating the effect of Si addition.

Figure 2 shows a comparison of thermal shock resistance between Example 1 and a conventional roll.In the test, material was taken from the surface of the roll material after forging, processed, and then quenched. The rolls were each tempered and tested at 160°C. The test method was to rotate a test piece with a diameter of 80 mm and a thickness of 40 mm at 1420 rpm, and cool the test piece with water while pressing a 20 AA square mild steel material against the test piece with a load of 500 g/pus.

The crack length on the vertical axis in Fig. 2 is the total length of cracks that occurred on the surface of the test piece, and while the crack length of the conventional material was 54+s+, in the case of Example 1, it was 23n.
m, which is less than half that of conventional materials, demonstrating the effectiveness of high-temperature tempering.

Figure 3 shows a comparison of wear resistance. In the test, the sliding surface had a diameter of 1
A test piece of 8n+o+ was subjected to the same heat treatment and slid on #100 emery paper under a load of 500 g. It can be seen that the wear resistance of the conventional roll is 230 cm, whereas in the case of Example 1 it is 120 cm, indicating excellent wear resistance.

The roll of Example 1 has the shape shown in FIG. 4, and is rolled to a thickness of sub-m, especially 20 mm, using the rolling mill shown in FIG.
As a result of cold rolling stainless steel 11 foil and thin tinplate steel sheets with a thickness of 0 μm or less, it was confirmed that the abrasion resistance was more than 5 times that of conventional integrated rolls.

1 is a rolled material, 2 is a work roll according to this embodiment, 3 is an intermediate roll, 4 is a backup roll, 5 is an outer layer, and 6 is a core material. The intermediate roll 3 can be shifted left and right.

〔Effect of the invention〕

According to the present invention, even if the surface hardness is the same as that of conventional rolls, it is possible to perform tempering at a high temperature of 300°C or higher.
It is possible to significantly increase the resistance to wear while maintaining abrasion resistance comparable to that of conventional rolls.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the tempering temperature and hardness of the rolls of the present invention and conventional rolls, Figure 2 is a graph comparing the thermal shock resistance of the rolls of the present invention and conventional rolls, and Figure 3 is , a graph comparing the wear resistance of the roll according to the present invention and a conventional roll, FIG. 4 is a sectional view of the main part of the work roll according to the present invention, and FIG. Rolling mill (cold 5trip m1
ll), FIG. 6 is a graph showing the relationship between the tempering temperature and residual stress of the roll according to the present invention and the conventional roll, and FIG. 7 is a schematic diagram of a composite roll manufacturing apparatus using the electroslag welding method. and FIG. 8 are schematic diagrams showing a fountain quenching method for rolling rolls. 1... Rolled material, 2... Composite roll, 3... Intermediate roll, 4... Backup roll, 5... Outer layer material,
6... Core material. 7... Core shaft, 8... Tubular electrode, 22... Induction coil, Fig. 1 00 00 300 400 Tempering temperature +! (℃) 00 00 Fig. Conventional material Example 1 301- (3) Residual stress Fig. Fig. Tempering temperature (℃) Fig. Fig.

Claims (1)

[Claims] 1. A composite roll for metal rolling in which the outer periphery of a core material is covered with an outer layer material, wherein the core material is made of low alloy steel having a shore hardness of 35 or more and a hardness lower than that of the outer layer material. , the outer layer material has a shore hardness of 80 or more and a retained austenite amount of 1
A composite roll for metal rolling, characterized in that it is made of a high alloy steel having a martensitic structure of 5% by volume or less and a compressive stress of 70 kg/mm^2 or more residual stress on the outermost surface. 2. By weight, C0.5-1.5%, Si0.5-3.0
%, Mn 1.5% or less, Cr 2-7%, Mo 1-5%,
A composite roll for metal rolling, characterized in that the outer layer is made of high alloy steel containing 0.5 to 2.0% of V and 2.0% or less of W, and the core material is made of low alloy steel. 3. In a composite roll for metal rolling in which the outer periphery of a core material is covered with an outer layer material, the core material contains 0.5 to 1.0% C and Si by weight.
1% or less, Mn 1% or less, Cr 1-5%, Mo 0.5%
It is made of low-alloy steel having a lower hardness than the outer layer material, and the outer layer material contains 0.5 to 1.5% of C and Si by weight.
0.5 to 3.0%, Mn 1.5% or less, Cr 2 to 7%,
A composite roll for metal rolling, characterized in that it is made of high alloy steel containing 1 to 5% Mo, 0.5 to 2.0% V, and 2.0% or less of W. 4. By weight, C0.5-1.5%, Si0.5-3.0
%, Mn 1.5% or less, Cr 2-7%, Mo 1-5%,
The outer layer is a welded layer made of high-alloy steel containing V0.5-2.0%, W2.0% or less, and Ni5% or less, and the core material is low-alloy steel having a lower hardness than the outer layer. Composite roll for metal rolling. 5. In a method for manufacturing a composite roll for metal rolling, in which an outer layer material made of high alloy steel, which is harder than the low alloy steel, is welded to the outer periphery of a core material made of low alloy steel, only the outer layer material is heated to the austenite transformation point. A quenching step in which a liquid refrigerant is injected into the heated portion while being gradually heated to a temperature above, and a residual austenite phase of the outer layer material is reduced to 15% by volume after the quenching.
A method for manufacturing a composite roll for metal rolling, comprising the following step of performing high-temperature tempering treatment. 6. By weight, C0.7-1.5%, Si0.5-3.0
%, Mn 1.5% or less, Cr 2.0-7.0%, Mo1
~5%, V0.5-2.0%, W2.0% or less as an outer layer material of high alloy steel, and a core material of low alloy steel with a lower hardness than the outer layer material.The surface layer of a roll material. 1. A method for producing a composite roll for metal rolling, which comprises heating the roll to a temperature above its transformation point, performing fountain quenching, and then tempering at a temperature of 300°C or above. 7. The method for manufacturing a metal rolling composite roll according to claim 5 or 6, wherein hot forging is performed before the quenching step of the outer layer material. 8. The method for manufacturing a composite roll for metal rolling according to any one of claims 5 to 7, wherein sub-zero treatment is performed after the quenching step and before the tempering treatment. 9. A rolling mill equipped with a work roll and a backup roll supported in contact with the work roll, wherein the work roll has a core material made of low alloy steel on its outer periphery and has a hardness higher than that of the core material; A rolling mill comprising a composite roll to which an outer layer material made of high alloy steel having a hardness of 80 or more is welded.