JPS63114937A - Composite roll for rolling and its outer layer material - Google Patents

Abstract

PURPOSE:To provide a roll excellent in wear resistance and resistance to surface roughness and further combining superior slip resistance with cracking resistance, by specifying a composition by incorporating V in a low-carbon high- chromium cast iron material as an outer layer material of a composite roll. CONSTITUTION:The outer layer material of a composite roll is constituted of the low-carbon high-chromium cast iron material consisting of, by weight, 0.8-1.2% C, 0.5-1.5% Si, 0.5-1.5% Mn, <=0.08% P, <=0.06% S, 0.5-2.0% Ni, 8-16% Cr, 0.8-2.5% Mo, 2.0-6.0% V, and the balance Fe. Subsequently, a core part composed of ferrous casting excellent in toughness is integrated with the outer layer material composed of the above cast iron material by welding, so that a composite roll for rolling in which the ratio of cross-sectional area between the outer layer and the core part is regulated to <=0.7 can be obtained. In the high-chromium cast iron of the above composition, sufficient amounts of high-hardness Cr carbides are formed though C content is reduced, and further, structure is refined and V carbides are formed owing to the incorporation of V, so that desired roll can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a composite roll in which an outer layer and a core are integrally welded, and a composite roll with good slip resistance suitable for use in a roughing stand of a hot strip mill. It relates to a roll and its outer layer material.

(Prior art) The properties required for the outer layer (rolling layer) of a composite roll used in the roughing stand of a hot strip mill are as follows:
Abrasion resistance, accident resistance, roughness resistance, slip resistance (biting resistance), etc. can be mentioned, but in recent years, in thin plate rolling, there has been a trend towards higher quality and energy saving. Among the properties, there is a growing demand for improved wear resistance and roughness resistance.

Conventionally, the outer layer material has been special cast steel, adamite material,
Hardened forged steel, graphite steel, spheroidal graphite cast iron, grain materials, etc. are used (some are also used as single roll materials). Furthermore, recently, in some mills, high chromium cast iron rolls used as rolling rolls before the finishing stand are used as they are in the roughing stand.

(Problems to be Solved by the Invention) However, the hardness of the adamite material and the outer layer material of the steel thread is less than Is55, and although the slip resistance is good, there are problems in abrasion resistance and roughness resistance. be.

In addition, Hs50-75 is used in some places for spheroidal graphite cast iron, but it has poor wear resistance and crack resistance, and furthermore, for grain materials, Is65-75 is used.
However, there are problems with crack resistance and rough skin resistance.

On the other hand, high chromium cast iron rolls used as rolling rolls in the front stage of the finishing stand have problems in that they tend to slip with the rolled material, have poor bite into the rolled material, and are prone to fatigue cranks.

Therefore, in Japanese Patent Application No. 60-163725, the present inventor proposed a low carbon, high chromium cast iron material having the above properties as an outer layer material of a composite roll. Although this cast iron material has solved the above-mentioned problems to a certain extent, it is desired to further improve the wear resistance.

The present invention has been made in view of such problems, and an object of the present invention is to provide an outer layer material for a composite roll for rolling which has excellent wear resistance and roughness resistance, and also has excellent slip resistance and crack resistance. Another object of the present invention is to provide a suitable composite roll using such an outer layer material.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an outer layer material of a composite roll having C: 0.8 to 1.2%, Ni: 0.5 to 2.0% by weight.
%Si: 0.5-1.5% Cr:
8-16%Mn: 0.5-1.5%
Mo: 0.8-2.5% P: 0.0
8% or less V:2. O~6.0%S: 0.06%
It was constructed from a low carbon, high chromium cast iron material with the remainder being Fe and normal impurities.

In addition, as a suitable composite roll using the above-mentioned outer layer material as the outer layer, a core made of iron-based cast material with excellent toughness is integrally welded to the outer layer formed of the above-mentioned outer layer material, and the outer layer cross-sectional area is a sieve and a core. The ratio to the cross-sectional area Ai ^o / A i is 0.7
It is configured as below.

(Actions and Examples) First, the reasons for limiting the components of the outer layer material of the present invention will be described.

Hereinafter, the unit is weight %.

C: 0.8-1.2% C is determined by the desired amount of carbide while keeping a balance with the Cr content within the range that stabilizes the high hardness (Fe, Cr) 7c3 type carbide. If the amount of carbide is less than 0.8%, the amount of carbide will be too small, resulting in insufficient wear resistance, while if it exceeds 1.2%, the amount of carbide will be too large, resulting in decreased slip resistance, roughness resistance, and crack resistance.

Si: 0.5-1.5% Si is an element necessary for deoxidizing the molten metal, and must be contained at least 0.5%. However, since Si reduces the solubility of C in austenite, excessive Si content will result in insufficient carbide formation, making it difficult to obtain hardness and deteriorating mechanical properties, so Si should be kept at 1.5% or less.

Mn: 0.5-1.5% Mn is required at least 0.5% for deoxidizing the molten metal and removing harmful S. However, if it exceeds 1.5%, mechanical properties, particularly toughness, will deteriorate significantly.

P: 0.08% or less P is an element that is preferably as small as possible in the roll material, and is set to 0.08% or less in order to prevent the material from becoming brittle.

S: 0.06% or less Similarly to P, the lower the S content, the more desirable it is, and the content should be 0.06% or less to prevent embrittlement.

Ni: 0.5-2.0% Ni is contained to improve hardenability and actively adjust hardness, and if its content is less than 0.5%, it will not have sufficient effect; If the content exceeds 2.0%, it will stabilize austenite and increase residual austenite, making it difficult to adjust the hardness by heat treatment after casting.

Cr: 8 to 16% Cr is contained to improve toughness and wear resistance, but in order to obtain high hardness (Fe, Cr)7Ci type carbide, it is necessary to balance it with the C content. . In the C content of the present invention, when Cr is less than 8%, the M7C3
It is not possible to obtain enough carbide of the type, while 16%
If the content exceeds 20%, the amount of M 23 C6 type carbide increases. Since this carbide has a lower hardness than the M7C3 type carbide, it becomes difficult to obtain sufficient wear resistance.

Base o: 0.8 to 2.5% Mo increases tempering resistance and at the same time enters into the carbide and is effective in increasing carbide hardness, but the content is 0.8% to 2.5%.
If the content is less than 8%, such effects will be small, while if the content exceeds 2.5%, austenite will be stabilized, making it difficult to obtain hardness.

V: 2.0 to 6.0% ■ is effective in refining the casting structure, and ■ is expected to improve hardness due to the precipitation of carbides, which in turn improves the roll's crack resistance, wear resistance, and biconcave structure. It has the effect of improving sex, etc. 2.
If it is less than 0%, the refinement of MlVa and the precipitation of carbides will not be significant, and no contribution to hardness or improvement in wear resistance can be expected. On the other hand, if it exceeds 6%, the above effect is saturated and the toughness of the outer layer material deteriorates. In addition, excessive amount of (2) mixed into the core deteriorates the toughness of the core material, which in turn deteriorates the accident resistance of the roll.

The outer layer material according to the present invention is formed from the above components, with the remainder being Fe and ordinary impurities.

The outer layer material is cast into a composite roll and then subjected to high-temperature diffusion annealing and quenching and tempering heat treatment, as in the case of conventional high chromium cast iron.

That is, in high rom steel, the matrix exhibits an austenitic structure when it is as-cast, or it is not suitable as a roll material in terms of roughness resistance and abrasion resistance. In order to transform this austenite structure into a martensite or bainite structure, it is necessary to destabilize this austenite by maintaining it at a temperature of 5 points or higher in the bladder. At this time, Ac
By maintaining the temperature at one or more points, Cr carbide and V carbide precipitate in the matrix, and the concentrations of C, Cr, and V in the matrix decrease.

For this reason, the matrix becomes more likely to undergo transformation, and in the CC7 diagram, Ps4. When cooled at a critical cooling rate that does not intersect 'i, a martensite or bainite structure is obtained.

In the case of a high chromium system, the Ps line does not intersect even with relatively slow cooling, but a cooling rate of 250° C./1]r or higher is required. Furthermore, tempering is preferably carried out at a temperature of 400 to 600°C in view of the balance between obtaining a thermally stable structure and the hardness of the product. In addition, the strain relief heat treatment reduces the residual stress of the roll in balance with the thermal stress generated in the roll.
0°C is appropriate.

As a result of the above heat treatment, the structure of the outer layer material becomes a mixed structure of IJ Fuchs eutectic carbide, the matrix structure consists of precipitated Cr and V carbides, tempered martensite, and bainite structure, and the hardness becomes Hs65 to 90.

Rolls for rough stands are particularly required to have abrasion resistance, roughness resistance, and slip resistance, but if Hs is less than 60, the abrasion resistance is poor, while if Hs exceeds 90, a quenched structure remains, making it difficult to be affected by heat. Roughness resistance becomes an issue when using large rough stands. Furthermore, although the inventor has confirmed that the slip resistance is influenced by the C content rather than the hardness, no problem occurs with the low C content of the present invention.

The core material of the composite roll using the outer layer material of the present invention is generally made of iron with excellent toughness, such as ductile cast iron, high-grade cast iron, and graphite steel, with a tensile strength of 20 kg/d or more and an elongation of 0.3% or more. Appropriately selected from cast materials.

For example, suitable ductile cast iron includes the following components (wt%):

C: 3.0-3.8% Ni: 2.0% or less Si
: L, 6-3.0% Cr: 1.5% or less Mn: 1.0% or less Mo: 1.0% or less p
: o, t% or less Mg: 0.02-0.1
%S: 0.02% or less The balance is essentially Fe and the content of Cr is preferably as low as possible from the viewpoint of the material quality of the inner layer material, but a certain amount is required to melt a part of the inner surface of the outer layer and weld it to the shaft core material. Contamination and diffusion cannot be avoided. Since the above components contain 1.6 to 3.0% of the graphitization promoting element Si, up to 1.5% is allowed in this St range. 1.5%
If it exceeds this amount, cementite will be excessive even if a large amount of St is contained, and the toughness will deteriorate significantly. In addition, other reasons for limiting the components are described below.

C: 3.0 to 3.8% If C is less than 3.0%, Cr mixed in from the outer layer will cause the material to become chilled, leading to a significant decrease in toughness, and if it exceeds 3.8%, graphite will form. As aging progresses, the strength of the inner layer material becomes insufficient and the neck hardness decreases, making the neck more likely to become rough during use.

Si: 1.6-3.0% When St is less than 1.6%, graphitization is poor and a large amount of cementite precipitates, leading to deterioration of the strength of the inner layer, and when it exceeds 3.0%, graphitization is promoted and the strength is reduced. Deterioration occurs.

Mn: 1.0% or less Mn combines with S and removes the adverse effects of S as MnS, but 1.0% or less.
．． If it exceeds 0%, the deterioration of the material will be significant.

P: 0.1% or less It increases the fluidity of the molten metal, but since it makes the material brittle, it is desirable to have it as low as possible, and it is set to 0.1% or less from a cost perspective.

S: 0.02% or less Similar to P, the lower the content, the more desirable it is, and since the inner layer material is ductile cast iron, in order to make graphite spheroidal, it is necessary to reduce S, which is an element that inhibits spheroidization, to 0.02% or less. is necessary.

Ni:2. 0% or less It is added from the viewpoint of stabilization and toughness of graphite, but there is no noticeable effect even if it exceeds 2.0%, and 2.0% is added from the viewpoint of cost.
% or less.

Mo: 1.0% or less Mo is undesirable because it inhibits the crystallization of graphite, but it is set to 1.0% or less as a range that does not cause any actual damage.

Gate g: o, 02-0.1% 0.02% is necessary for graphite spheroidization, and if it is less than this, spheroidization will be poor and strong ductile cast iron will not be obtained. However, if it exceeds 0.1%, it is undesirable in terms of the chilling effect of Mg and dross.

In addition, when the inner layer material of ductile cast iron is used, Cr is mixed and diffused from the outer layer to the inner layer, and the inner layer material becomes high in Cr.
In order to reliably prevent the toughness from deteriorating, it is effective to interpose an intermediate layer made of a cast iron material having the following specific composition (% by weight) between the two.

C: 1.0-2.5% Ni: 1.5% or less Si
: Q, 5 to 1.5% Cr: 3 to % or less Mn: 0.5 to 1.5% Gate o: 1.0% or less P: o, 1% or less Balance substantially FeS: 0.1
% or less The reasons for limiting the components of the above-mentioned intermediate layer are described below.

C:1. O ~ 2.5% C Assuming that the Cr in the outer layer is melted by the molten metal in the intermediate layer and mixed completely uniformly, the Cr in the intermediate layer is 3 to 3% in total.
It becomes lO%. If the C content is less than 1.0%, the casting temperature of the intermediate layer will be high and the outer layer will be easily melted, reducing the Cr%
further increases, the intermediate layer for preventing Cr from diffusing into the shaft core material becomes meaningless, and the C content increases to 2.5
%, the amount of carbides increases and the intermediate layer itself lacks toughness, meaning that there is no point in providing the intermediate layer. Therefore, C is 1.0~
It shall be 2.5%.

Si: 0.5-1.5% 0.5% is necessary for deoxidizing the molten metal. If it exceeds 1.5%, it becomes brittle and causes deterioration of mechanical properties.

Mn: 0.5-1.5% 0.5% is necessary because it has the same effect as Si and becomes MnS and eliminates the negative effects of S, but 1.5%
If the content exceeds this amount, the effect will be saturated and the mechanical properties will deteriorate.

p: o, i % or less P increases the fluidity of the molten metal, but in the case of roll materials, it reduces the toughness of the material, so it should be kept at 0.1% or less.

S: 0.1% or less Similar to P, S makes the roll material brittle, so the content should be 0.1% or less without causing any actual damage.

Ni: 1.5% or less Ni is included to provide hardenability and toughness, and even if it is not actively added, it is mixed in from the outer layer and reaches 0.3%.
However, if the content is up to 1.5%, there is no problem and this effect is achieved. However, if the content exceeds 1.5%, the hardenability is good and the matrix becomes too hard, which is not desirable from the viewpoint of toughness and residual stress. Therefore, the Ni content is set to 1.5% or less.

Cr: 3 to 10% or less From the point of view of providing an intermediate layer, a lower Cr content is desirable;
The chemical composition of the ladle before casting the intermediate layer is preferably less than 1.0%, which is easy to control industrially.

In this case, in the composition after casting, the Cr content increases to 3 to 10% due to the addition of Cr that enters from the outer layer. If it exceeds 10%, the material quality of the intermediate layer itself will deteriorate significantly.

Furthermore, in order to suppress the Cr content of the inner layer material to 1.5% or less, the Cr content of the intermediate layer must be adjusted to a range of 3 to 10% under casting conditions. Therefore, the Cr content is set to 3 to 10%.

Mo: 1.0% or less MO has the same effect as Ni, and if it is contained in excess of 1.0%, the intermediate layer will become too hard, so this content should be 1.0% or less.
．． 0% or less.

When using an intermediate layer on ridges, Cr is transferred from the outer layer to the inner layer.
In addition to reliably preventing mixing and diffusion, it also effectively prevents embrittlement at the boundary. In other words, when no intermediate layer is used,
The boundary area has an intermediate composition between the low C% of the outer layer and the high C% of the inner layer (
Relatively high C% and high Cr%), carbide crystallizes in a layered manner at the boundary between the outer layer and the inner layer, and the boundary becomes brittle, but the crystallization of this layered carbide can be prevented by the interposition of an intermediate layer. .

By the way, when the outer layer material of the present invention is applied to the outer layer, tensile residual stress is generated in the core due to expansion behavior accompanying martensitic transformation of the outer layer, but if the outer layer is thick, the residual stress in the core becomes excessive. It may break from the core, leading to roll breakage accidents.

Therefore, in the composite roll according to the second aspect of the present invention, the ratio AO/Ai of the outer layer cross-sectional area rib and the core cross-sectional area Ai is set to 0.
．． Must be 7 or less. If it exceeds 0.7, the area ratio of the outer layer that exhibits the expansion behavior of martensitic transformation and bainite transformation increases, causing the stress balance inside the roll to collapse and the tensile residual stress acting on the core to become excessive, leading to fracture. .

In addition, if the intermediate layer is provided between the outer layer and the core, the intermediate layer will undergo martensitic or bainite transformation due to heat treatment due to the mixing of Cr, Mo, and V from the outer layer, so it will not be the same as the outer layer. shows the expansion behavior of Therefore, in this case, assuming that the intermediate layer cross-sectional area is static, it is necessary to satisfy (Ao + Am)/Ai≦0.7.

Next, a method for casting the composite roll will be described.

Generally, it is convenient to use centrifugal casting as a method for casting composite rolls. That is, as shown in FIG. 1, first, the outer layer material molten metal is poured into a predetermined centrifugal casting mold to centrifugally cast the outer layer A, and then, depending on the case,
The intermediate layer is centrifugally cast on the inner surface of the outer layer A, and then, as shown in Fig. 2, this mold is stood up vertically or in an inclined manner, and a suitable tough inner layer material molten metal is poured into the mold having the outer layer A. A composite roll in which the outer layer A and the inner layer B are welded and integrated is cast. Thus, an integral composite roll is obtained in which the inner layer is made of a material with excellent breakage resistance, while the outer layer has excellent slip resistance, abrasion resistance, etc.

In Fig. 1, 1 is a centrifugal casting mold, 2 is a sand mold for forming the neck, 3 is a rotating roller, 4 is a drive motor, 5 is a pouring gutter, and 6 is a ladle. In Figure 2, 7 indicates a surface plate and 8 indicates a garden bowl.

Next, specific examples will be listed and explained.

[Example 1] Body diameter 900w x body length 1500tm (total length 3800 fins)
Example of manufacturing a 2N composite roll (a centrifugal casting mold with a resin sand coating of 112.5 mm thick formed on the inner surface was rotated at G No. 140, as shown in Fig. 1). The outer layer material molten metal shown in Table 1 is 1
It was cast at 530°C to a thickness of 10,011 mm.

(After 2122 minutes, the rotation of the mold was stopped and the mold was stood vertically as shown in Figure 2, and 27 minutes after the start of outer layer casting, the core material (ductile cast iron) molten metal shown in Table 1 was poured.

Note to Table 1: Unit weight %, remaining trade m average The mold was demolded 3 days after Fe(3) casting. The Cr in the inner layer of the casting roll is
The inner surface of the outer layer was melted by an average of 181 m, and some of the Cr in the outer layer was mixed into the inner layer, so the Cr content was 0.6%, which was 0.5% higher than the molten metal Cr content.

(4) After rough processing the casting roll, it was subjected to heat treatment.

Heat treatment involves expansion (annealing) at a high temperature above the transformation point.
Hardening and tempering treatments were performed. After rough processing (during heat treatment)
The outer layer thickness is 70 to 74NN, and the outer layer cross-sectional area Ao/
The core cross-sectional area At was 0.40 to 0.43.

(5) After the heat treatment, finishing was performed and the surface hardness was measured to be Hs78-85.

Furthermore, when the surface structure of the body was observed under a microscope, it was found that it consisted of eutectic carbide and matrix structure, and tempered martensite, precipitated carbides (secondary carbides) of Cr and V were observed in the matrix structure.

(6) As a result of using the above composite roll in an actual hot strip mill roughing stand, the result was 7,500 to 7,700 tons.
/fl results were obtained. This value greatly exceeds the average rolling performance of conventional Adamite rolls (body surface hardness Hs 50-55) of 4000 Ton/m.

In addition, the rolling performance of a composite roll in which the outer layer is formed from a low carbon, high chromium cast iron material having the composition shown in Table 2 above, which is in the outer layer material composition range disclosed in Japanese Patent Application No. 60-163725, is 7000-72.
00 Ton/Tsuru, but it was confirmed that better results than this can be obtained in the case of the present invention.

Table 2 Also, although the hardness was greatly increased compared to the conventional Adamite roll, the problems of biting and slipping still persisted (but did not occur).

(Effect of the invention) As explained above, the high chromium cast iron according to the present invention has C:
Despite keeping the content as low as 0.8 to 1.2%, a sufficient amount of high-hardness Cr carbide is generated, and the inclusion of (■) refines the structure and generates V carbide, making it resistant to skin. Abrasion resistance and slip resistance can be improved without impairing roughness or biconcavity, and since the amount of carbide is not excessive, crack resistance can also be improved.

On the other hand, although the composite roll according to the present invention uses the outer layer material having transformation expansion characteristics, the outer layer cross-sectional area Ao
/Since the value of the core cross-sectional area ^i is within a specific range, excessive residual stress will not be generated in the inner layer during heat treatment and during use of the roll, and breakage accidents can be reliably prevented.

In this way, the composite roll using the outer layer material of the present invention is
It has excellent wear resistance and surface roughness resistance, as well as good slip resistance and crack resistance, so it is suitable for rolling fields where both of these properties are required, such as as a composite roll for the rough stand of hot strip mills. The utility value is significant.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a centrifugal casting mold showing the process of casting a composite roll. Patent applicant Kubota Iron Works Co., Ltd. Figure 1 Figure 2

Claims (3)

[Claims] (1) Chemical composition in weight percent: C: 0.8-1.2% Ni: 0.5-2.0% Si:
0.5-1.5% Cr: 8-16% Mn: 0.5-1
．． 5% Mo: 0.8-2.5% P: 0.08% or less
V: 2.0 to 6.0% S: 0.06% or less An outer layer material of a composite roll for rolling, characterized in that it is a low carbon, high chromium cast iron material consisting of the balance Fe and normal impurities. (2) Chemical composition in weight%: C: 0.8-1.2% Ni: 0.5-2.0% Si:
0.5-1.5% Cr: 8-16% Mn: 0.5-1
．． 5% Mo: 0.8-2.5% P: 0.08% or less
V: 2.0 to 6.0% S: 0.06% or less The outer layer is made of a low carbon, high chromium cast iron material with the balance Fe and normal impurities, and the core is made of an iron-based cast material with excellent toughness. A composite roll for rolling, characterized in that the outer layer cross-sectional area Ao and the core cross-sectional area Ai have a ratio Ao/Ai of 0.7 or less. (3) An intermediate layer is provided between the outer layer and the core, and the outer layer and the core are welded together through the intermediate layer, and the sum Ao+Am of the outer layer cross-sectional area Ao and the intermediate layer cross-sectional area Am and the core cross-sectional area are The composite roll for rolling according to claim 2, wherein the ratio (Ao+Am)/Ai to area Ai is 0.7 or less.