JPH07126796A - Work roll for hot rolling - Google Patents

Abstract

PURPOSE:To develop a work roll for hot rolling excellent in wear resistance, surface roughening resistance, thermal crack resistance, slip resistance, etc., by shrinkage-fitting an intermediate cylindrical sleeve consisting of the outer shell layer made of high carbon/high chromium cast steel, intermediate layer made of high carbon cast steel and inside layer made of graphite cast steel on the axial center material made of ductile cast iron. CONSTITUTION:The outer shell layer 11 consisting of high carbon/high chromium cast steel contg., by wt., 0.8-1.2% C, 0.5-1.5% Si, 0.5-1.5% Mn, 3.0-12.0% Cr, 1.0-3.0% Mo, 0.5-2.0% V and 0.5-2.0% Ni and intermediate layer 12 made of cast steel contg. 1.0-2.0% C, 1.5-2.0% Si, <1.0% Mn and <1.0% Ni and inner layer 13 made of graphite cast steel contg. 1.0-1.5% C, 1.5-.25% Si and 0.5-2.0% Ni inside those layers are laminatedly cast by centrifugal casting method and the work roll for hot rolling the steel or the like is manufactured by shrinkage- fitting of the obtained follow-shaped cylindrical sleeve 1 on the axial center material 2 made of the ductile cast iron or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work roll used for hot rolling a steel material such as a hot strip mill,
More specifically, a hollow cylindrical body having a centrifugally cast laminated structure is used as a roll body member, and an assembled roll obtained by shrink-fitting this into a shaft core material has wear resistance, rough surface resistance,
It has improved heat crack resistance and slip resistance.

[0002]

Work rolls used in hot strip mills such as hot strip mills have a toughness that can withstand bending of rolling load and wear in order to smoothly perform hot rolling operation and ensure quality of rolled material. It is required to have resistance to rough skin, heat cracks, etc. Adamantite cast iron, nickel grain cast iron, ductile cast iron, etc. are typical roll materials that have been used so far, but they have advantages and disadvantages, wear resistance, rough surface resistance,
It is hard to say that all the properties such as heat crack resistance can be satisfied.

In recent years, high C-high Cr cast iron rolls have been widely used as hot rolling rolls. High C-High C
The roll outer shell layer made of r-cast iron has a structure in which a large amount of hard Cr-based carbide [(Fe, Cr) ₇ C ₃ ] is formed in the matrix, and is hard and has excellent wear resistance. JP 58-30382
In Japanese Patent Laid-Open Publication No. C-2.0-
3.2%, Cr: 10.0 to 25.0%, and Mn,
Axial core material containing Si, Ni, Mo, Nb, V, etc. and forming the outer shell layer of the roll body with cast iron consisting of the balance Fe, and made of ductile cast iron with an intermediate layer inside the outer shell layer There is disclosed a hot rolling roll which is a laminated cast body formed with. The roll has a high C-high Cr cast iron as the outer shell layer and has a high degree of wear resistance, while a shaft core material made of ductile cast iron ensures toughness against bending of rolling load. is there. Also, when replacing a roll whose surface has worn or deteriorated due to use for a certain period of time, if you want to discard only the body of the roll and reuse the shaft core repeatedly, roll the body of the roll. As another example, a hollow cylindrical body (sleeve) is cast, and the assembly roll is obtained by shrink-fitting the hollow cylindrical body (sleeve) separately prepared.

[0004]

The above-mentioned laminated structure roll in which the outer shell layer of the hot-rolled roll is made of high C-high Cr cast iron, can be applied to a rough rolling stand having a large thermal and mechanical load. Exhibits good wear resistance superior to conventional rolls such as adamite cast iron rolls. However, the resistance to rough skin, thermal cracking, chipping and the like cannot be said to be sufficient, and there is a problem that slippage with the material to be rolled easily occurs. According to the study of the present inventors, the above-mentioned problem regarding the surface characteristics is that the high C-high Cr cast iron forming the outer shell layer is M ₇ C ₃ type Cr.
This is due to having a coarse structure containing a large amount of carbide. That is, rough skin is likely to occur because the texture is coarse and resistance to tissue flow under hot rolling conditions with large thermal and mechanical loads is low, and thermal cracking is likely to occur in the texture. This is because the amount of hard M ₇ C ₃ type Cr carbide (area ratio) occupying 20% to 30% is high, so that sufficient toughness cannot be secured, and a large amount of hard carbide is included. Therefore, the roll surface roughness is small in the process of using the actual machine, which causes slipping with the material to be rolled. Moreover, since the M ₇ C ₃ type Cr carbide has a so-called chrysanthemum petal-like coarse shape, a phenomenon of peeling and falling off from the roll surface is likely to occur during the rolling process under high pressure and high heat load conditions.

Further, in an assembled roll having a hollow cylinder body (sleeve) which is shrink-fitted to a shaft core material so that the shaft core material can be repeatedly used, residual stress, shrinkage-fitting stress, rolling Stress, thermal stress, etc. act on the sleeve in a superimposed manner,
The action of this stress causes a breakage accident of the sleeve. In recent hot rolling operations, due to demands for improved productivity,
With the trend of high pressure and high heat load, the above problems are becoming more prominent. The present invention relates to a work roll for hot rolling having an assembled structure that enables repeated use of a shaft core material, not only to have fracture resistance and toughness capable of withstanding operating conditions under high pressure and high heat load, but also to It is an object of the present invention to provide an improved hot-rolled roll that enhances the above-mentioned properties such as wear resistance and enables improvement and stabilization of roll life and quality of rolled material.

[0006]

SUMMARY OF THE INVENTION The present invention provides a laminated cylindrical body comprising an outer shell layer, an intermediate layer and an inner layer which are centrifugally cast,
A work roll for hot rolling, which is shrink-fitted to a shaft core material, wherein an outer shell layer is C: 0.8 to 1.2%, Si: 0.5 to
1.5%, Mn: 0.5 to 1.5%, Cr: 3.0 to 1
2.0%, Mo: 1.0 to 3.0%, V: 0.5 to 2.
0%, Ni: 0.5 to 2.0%, the balance being cast steel having a molten metal composition substantially consisting of Fe, and the intermediate layer is C:
1.0 to 2.0%, Si: 1.5 to 2.5%, Mn:
1.0% or less, Ni: 1.0% or less, balance substantially Fe
Made of cast steel having a molten metal composition consisting of
C: 1.0 to 1.5%, Si: 1.5 to 2.5%, N
i: 0.5 to 2.0%, the balance being made of graphite cast steel having a molten metal composition substantially consisting of Fe.

[0007]

As shown in FIG. 1, in the hot-rolled roll of the present invention, the sleeve 1 is a three-layer laminate comprising an outer shell layer 11, an intermediate layer 12 and an inner layer 13, which is a core material 2. It has a shrink-fitted structure. The cast steel forming the outer shell layer 11 of the sleeve has a small amount of C and a small amount of Cr, which is a carbide-forming element, as compared with the high C-high Cr cast iron.
Is adjusted to a composition containing a certain amount. M ₇ C ₃ type carbide [(Fe, Cr) ₇ formed by combining Cr and C]
C ₃ ] exhibits a chrysanthemum petal-like coarse crystallization form as described above, whereas MC type V formed by the combination of V and C
The crystallization morphology of C carbide is fine and uniform. In the outer shell layer of the roll of the present invention, the dendrite growth is suppressed and the austenite crystal grains are miniaturized, as an effect of finely crystallizing VC carbides during the temperature-lowering solidification process of the casting melt. Along with the refinement of the crystal grains, the M ₇ C ₃ type Cr carbide generated at the grain boundaries is also refined. As a micronization effect of this structure, high resistance to tissue flow under high pressure / high heat load is actually imparted, and good resistance to rough skin is exhibited. Furthermore,
Since the amount of C is regulated to a small amount, the amount of carbides generated is small, and the ratio (area ratio) to the structure is about 8% or less. Therefore, it has high toughness and cracks due to thermal stress are generated.
High resistance to propagation and excellent resistance to thermal cracking.
Further, as an effect that the amount of carbides in the structure is suppressed, an appropriate surface roughness required to avoid slip with the material to be rolled is imparted in the process of using the roll in an actual machine.
Moreover, since the carbide has a fine crystallized morphology, it has excellent chipping resistance in the process of actual use.

The outer shell layer of the sleeve of the roll of the present invention has a high degree of abrasion resistance while the amount of carbide is regulated to a small amount as described above. This is because VC carbide
Micro Vickers hardness Hv is about 2400 to 3400, which is significantly higher than Hv of Cr carbide [(Fe, Cr) ₇ C ₃ ] of about 1800 to 2500, and this high hardness carbide is finely dispersed in the matrix. As an effect, it is possible to secure a high level of wear resistance equal to or higher than that of high C-high Cr cast iron, although the total amount of carbides is small. Further, since the sleeve of the roll of the present invention is provided with the inner layer made of graphite cast steel, it has a high degree of toughness capable of withstanding shrink fitting stress and the like. When the carbide forming element diffuses and mixes into the inner layer from the outer shell layer (including carbide forming elements such as Cr, Mo and V), the toughness of the inner layer is impaired, but the diffusion and invasion of the inner layer occur Is suppressed and prevented, so that the toughness of the inner layer is stably maintained. Further, the outer shell layer of the sleeve is different from the high C-high Cr cast iron,
Since it has a composition with a low content of Cr and the like, it diffuses and penetrates into the intermediate layer in a relatively small amount, which also contributes to the stable maintenance of the toughness necessary for preventing the breakage of the sleeve. .

With respect to the roll of the present invention, the reasons for limiting the components of the cast steel melt of the outer shell layer will be described below. C: 0.8 to 1.2% C combines with Cr, Mo, V, etc. to form MC type and M ₇ C ₃ type carbides, and contributes to improvement of wear resistance. 0.8
If it is less than%, the amount of carbides formed is insufficient and the wear resistance cannot be sufficiently enhanced. On the other hand, if it exceeds 1.2%, the toughness is lowered due to excessive formation of carbides, and the heat crack resistance is impaired.

Si: 0.5 to 1.5% Si is added as a deoxidizing agent for molten cast steel. If the amount is less than 0.5%, the deoxidizing effect is insufficient, while 1.5%
If it exceeds%, embrittlement is caused and the heat crack resistance is lowered.

Mn: 0.5 to 1.5% Mn is a deoxidizing agent for the molten cast steel and is an impure component of S.
As MnS, at least 0.5% is required as an element for fixing and detoxifying. However, if it exceeds 1.5%,
Residual austenite is likely to occur, resulting in insufficient hardness and wear resistance.

Cr: 3.0 to 12.0% Cr forms a solid solution in the matrix to strengthen the matrix, and partially forms a Cr-based carbide to contribute to the improvement of wear resistance. At least 3.0% is required to obtain this effect. The effect is increased by increasing the amount of addition, but if it exceeds 12.0%, the amount of Cr-based carbides is unnecessarily increased, and the amount of fine VC carbides with high hardness is insufficiently generated, resulting in a decrease in toughness. As a result, problems such as deterioration of the rough skin resistance are caused.

Mo: 1.0 to 3.0% Mo is effective as a solid solution in the matrix to improve hardenability and prevent temper embrittlement, and also has an effect of improving high temperature characteristics. It forms a Mo-based carbide and contributes to the improvement of wear resistance. To secure these effects, at least 1.0% is required. The effect increases with increasing the amount of addition, but if it exceeds 3.0%, it becomes supersaturated, and addition beyond that is not only a waste, but also leads to stabilization of retained austenite, causing a lack of hardness and wear resistance. Become.

V: 0.5 to 2.0% V is an element that contributes most to the improvement of wear resistance by forming a fine and high hardness VC carbide by combining with C. The MC type carbide is significantly finer than the M ₇ C ₃ type Cr carbide crystallized in the matrix of the high C-high Cr cast iron, and the effect of the fine crystallization is that the growth of dendrites is suppressed. At the same time that the austenite grains are refined,
The M ₇ C ₃ type Cr-based carbides generated at the grain boundaries are also refined. By making the structure fine and uniform, remarkable improvement effects of surface characteristics such as resistance to roughening of the surface are achieved. At least 0.5% is required to make the effect of adding V sufficient. The effect is increased by increasing the amount added, but 2.0%
When it exceeds, the amount of carbide produced becomes excessive, and in the centrifugal force casting step, the specific gravity separation of the carbide becomes remarkable due to centrifugal force, and the effect of improving the surface characteristics is impaired.

Ni: 0.5 to 2.0% Ni has the effect of forming a solid solution in the matrix to enhance the hardenability. If it is less than 0.5%, the effect cannot be obtained, while if it exceeds 2.0%, retained austenite is apt to occur,
It causes a lack of hardness.

Next, the intermediate layer formed between the outer shell layer and the inner layer will be described. Since the intermediate layer has a role of preventing the carbide forming elements such as Cr, Mo and V from diffusing and mixing from the outer shell layer to the inner layer, the cast steel molten metal forming the intermediate layer is composed of Cr, Even if it does not contain a carbide-forming element such as Mo or V and is accompanied by it, the amount is limited to a range (about 0.05% or less) inevitably mixed in the melting technology. Further, the intermediate layer needs to be castable at a casting temperature lower than the melting point of the outer shell layer. When the casting temperature becomes higher, the amount of melting of the outer shell layer caused by the heat effect of the molten metal at the time of casting increases, so that Cr, Mo, V, etc. in the intermediate layer increase, which means This is because it causes an increase in the amount of diffusion and mixing of the element and deterioration of its toughness. The reasons for limiting the components of the cast steel molten metal forming the intermediate layer are as follows.

C: 1.0 to 2.0% C has the effect of lowering the melting point of cast steel and lowering the casting temperature. If it is less than 1.0%, the casting temperature is high and the melting amount of the outer shell layer is large, so that the C of the intermediate layer formed is
r, Mo, V, etc. increase. This not only impairs the toughness of the intermediate layer, but also increases the amount of diffusion of these elements into the inner layer and causes the toughness of the inner layer to be impaired. On the other hand, the upper limit of 2.0% is that if it exceeds this, it becomes difficult to secure the toughness of the intermediate layer.

Si: 1.5 to 2.5% Si requires 1.5% or more as a deoxidizing agent. However, if it exceeds 2.5%, embrittlement is caused and the tensile strength of the intermediate layer is reduced.

Mn: 1.0% or less Mn has a deoxidizing effect and an effect of fixing the impurity S as MnS. This effect can be obtained in an amount of 1.0% or less, and does not require any further addition.

Ni: 1.0% or less Ni is an element effective in graphitizing and strengthening the matrix. Crystallization of graphite alleviates the volume contraction accompanying the solidification of the molten metal and is effective in preventing shrinkage cavities. This effect can be obtained in an amount of 1.0% or less, and addition beyond that is unnecessary.

The inner layer formed by laminating the intermediate layer is a layer for stably maintaining a strong coupling relationship between the roll body member (sleeve) and the shaft core material by shrink fitting.
That is, most of the accidents that occur when the shrink shrink fit roll is actually used are fractures of the sleeve, and these breakdown accidents are caused by various stresses (residual stress, shrink fit stress, rolling stress, thermal stress) that act on the inner surface of the sleeve. This occurs when the sum of (stress, etc.) exceeds the strength of the sleeve. As a countermeasure against this, the present invention provides an inner layer made of cast steel having high toughness. The use of graphite cast steel as the cast steel is because the cast steel-based material easily causes defects such as cavities due to solidification shrinkage in the casting process (the casting defects significantly impair the strength and toughness of the inner layer). To deal with. Graphite cast steel can form an inner layer that does not have casting defects such as cavities as the effect that the volumetric shrinkage due to solidification during casting is relaxed by the crystallization of graphite, and the soundness of the cast steel quality allows It is possible to guarantee the fracture resistance of the sleeve in the rolling operation under high heat load.
The graphite cast steel forming the inner layer does not contain carbide-forming elements such as Cr, Mo and V, which impair the toughness thereof, as in the case of the intermediate layer, and even when accompanied by this, the mixed amount thereof is
The amount is limited to an unavoidable range (about 0.05% or less) in terms of melting technology. The reasons for limiting the components of the melt of the graphite cast steel are as follows.

C: 1.0 to 1.5% C is an element necessary for crystallization of graphite for compensating for volumetric shrinkage in the solidification process of cast steel as described above. If it is less than 1.0%, it is difficult to crystallize graphite and the crystallization amount is insufficient. On the other hand, if the amount exceeds 1.5%, the shape of graphite will collapse, and it will be difficult to secure strength and ductility.

Si: 1.5 to 2.5% Si is an element necessary for promoting crystallization of graphite. 1.5%
If it is less, the effect is insufficient. If it exceeds 2.5%, the strength is lowered due to excessive graphitization, and the matrix structure becomes brittle.

Ni: 0.5 to 2.0% Ni is an element necessary for stabilizing graphite and strengthening the matrix structure. If less than 0.5%, the effect is insufficient. The effect increases with increasing amount, but if it exceeds 2.0%,
The effect is almost saturated.

The roll sleeve 1 consisting of the outer shell layer, the intermediate layer and the inner layer is manufactured by centrifugal casting.
In the centrifugal casting, first, as a first stage casting, a cast steel molten metal to be an outer shell layer is cast into a mold, and an outer shell layer 11 is formed on the inner surface of the mold by the action of centrifugal force. After the outer shell layer is almost solidified up to the inner surface, as a second stage casting, a cast steel melt serving as an intermediate layer is cast to form an intermediate layer 12. Furthermore, after the intermediate layer has almost solidified to the inner surface, the inner layer 13 is formed by casting the molten molten graphite cast steel as the inner layer in the third stage casting. The roll sleeve 1 which is the obtained three-layer laminated cast body is subjected to quenching / tempering treatment as heat treatment for refining. The quenching treatment is achieved by heating and holding at a temperature of 900 to 1000 ° C, followed by rapid cooling (forced air cooling), and the tempering treatment is achieved by heating and holding at a temperature of 450 to 580 ° C, followed by slow cooling (air cooling). To be done.

The sleeve 1 which has been subjected to the heat treatment is shrink-fitted on the separately prepared shaft core material 2, and then subjected to predetermined machining to be finished into a product roll. In addition, the shaft core material 2
Is a plastically worked product such as hot rolling or hot forging, or cast iron,
Cast products such as cast steel may be applied. The material type is appropriately selected according to the actual machine use condition, but as a suitable example thereof,
Examples of the plastically worked product include Cr-Mo-based tough steel such as JIS G4105 SCM440, and examples of the cast product include ductile cast iron.

[0027]

【Example】

[1] Manufacture of test rolls A roll sleeve consisting of three layers, an outer shell layer, an intermediate layer, and an inner layer, is centrifugally cast, heat-treated, then shrink-fitted onto a separately prepared shaft core material, and finish machining is applied. To produce a test roll A (invention example) and a roll B (comparative example). The surface finish roughness of the sleeve of each test roll is 6S. Table 1
Shows the composition of the molten metal (Wt%) in each layer of the sleeves of the test rolls A and B and the thickness (mm) of each layer. The material of the outer shell layer of the test roll B is high C-high Cr cast iron (Japanese Patent Publication No. 58-303).
(Corresponding to the material for the outer shell layer described in No. 82). The type of the shaft core material is SC for both roll A and roll B.
It is a forged steel product equivalent to M440 (JIS G4105).

[2] Surface Hardness of Test Roll and Structure of Outer Shell Layer (1) Surface Hardness Roll A (Invention Example): H _S 78.65 ± 1.45 Roll B (Comparative Example): H _S 72.15 ± 0.95 (2) Texture of outer shell layer The outer shells of roll A (invention example) and roll B (comparative example) are shown in FIGS. 2 (1) (2) and 3 (1) (2). The metal structure of the layer (etching: 5% nitric acid alcohol, 10 seconds) is shown (Fig. 1: Roll A, Fig. 2: Roll B, magnification is (1): × 100, in each figure).
(2): × 400). The black part in the figure is the matrix and the white part is the carbide. Roll B (comparative example) shown in FIG.
It retains the dendritic remnants that have grown during the casting and solidification process, has large carbide grains, and has a coarse structure. In contrast,
Roll A (invention example) in FIG. 2 exhibits a fine structure in which dendritic growth is suppressed. The amount of carbides in each structure is as follows. Roll A (invention example): 4.8 area% (FIG. 2) Roll B (comparative example): 29.6 area% (FIG. 3)

[3] Actual machine use test The test rolls A and B were used as work rolls of the rough rolling stand (which is the rolling stand having the largest thermal and mechanical load) in the hot strip mill, and the actual machine use test was repeated several times. (The rolling amount of each time is 25000 to 4000, respectively.
It was subjected to 0 tons) and the results shown in Table 2 were obtained. The surface roughness (R _max ) and the wear amount in the table are measured values after the test use. As is clear from the table, Roll B of Comparative Example
In the case of roll A of the invention example, there is no rough surface, chipping or slippage, whereas the body part (outer shell surface) has surface roughness, chipping or slippage with the material to be rolled. Moreover, the amount of wear loss is also reduced. As shown in FIG. 2, the excellent resistance to rough skin, slip resistance, chipping resistance, etc. is due to the fact that the structure is fine and the amount of carbide is moderately suppressed. The reason why it has a high degree of wear resistance despite being suppressed is that the hard VC carbides are finely and uniformly dispersed, and the difference from the roll B of the comparative example is It is obvious.
After the end of the use test, the chemical composition of the inner layer of the sleeve was analyzed for the roll under test A, and as a result, the increase in the amount of carbide forming elements such as Cr, Mo and V was small (Cr: 0.05% → 0.45%, M
(O: 0.02% → 0.13%, V: trace → 0.07%), and it was confirmed that the tensile strength was maintained at a sufficient level of about 642 N / mm ² .

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

The work roll for hot rolling of the present invention has been improved so as to be able to substantially completely prevent wear resistance, surface roughening resistance, heat crack resistance, chipping resistance, and slip with the material to be rolled. It has surface characteristics, sufficient toughness to withstand high-load bending, and the stability of the shrink-fitting structure is sufficient, so it can be used stably under the recent severe conditions of high pressure and high heat load. It contributes to the improvement of service life, reduction of roll maintenance, improvement of line efficiency, and improvement of rolling quality.

[Brief description of drawings]

FIG. 1 is an axial sectional view showing a laminated structure of a roll.

FIG. 2 is a drawing-substituting micrograph showing a metal structure of an outer shell layer of roll A (invention example) in Examples [(1) is a magnification of 50, and (2) is a magnification of 400].

FIG. 3 is a drawing-substituting micrograph showing a metal structure of an outer shell layer of Roll B (Comparative Example) in Examples [(1) is a magnification of × 50, (2) is a magnification of × 400].

[Explanation of symbols]

1: Sleeve, 11: Outer shell layer, 12: Intermediate layer, 13: Inner layer, 2: Shaft core material.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B23P 11/02 A 7528-3C C22C 37/08 Z 38/00 301 L 302 E 38/46

Claims (1)

[Claims] 1. A work roll for hot rolling comprising a centrifugally cast outer shell layer, an intermediate layer, and an inner layer, which are shrink-fitted onto a mandrel to form a hot-rolling work roll, the outer shell layer comprising: , C: 0.8 to 1.2%, Si: 0.5 to 1.
5%, Mn: 0.5 to 1.5%, Cr: 3.0 to 12.
0%, Mo: 1.0 to 3.0%, V: 0.5 to 2.0
%, Ni: 0.5 to 2.0%, the balance being cast steel having a molten metal composition substantially consisting of Fe, the intermediate layer being C: 1.0 to 2.0%, Si: 1.5 to 2 ．
5%, Mn: 1.0% or less, Ni: 1.0% or less, the balance being cast steel having a molten metal composition substantially consisting of Fe, and the inner layer is C: 1.0 to 1.5%, Si : 1.5-2.
A work roll for hot rolling, characterized in that it is made of graphite cast steel having a molten metal composition of 5%, Ni: 0.5 to 2.0%, and the balance being substantially Fe.