JP2888041B2 - Composite roll and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention, composite roll and its manufacturing method, used in particular, such as the hot finish rolling mill work roll of steel material such as a steel plate, composite roll your Durable
Yobiso relates to a process for the preparation of.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for steel rolling technology to improve the quality and economic efficiency of rolled products. In particular, those requirements in hot strip rolling technology have been increasing load stress during rolling. From that
We are looking for a roll for rolling that has even better wear resistance and toughness.

[0003] Conventionally, a roll composite roll formed from an outer layer having excellent wear resistance and a shaft core steel having excellent toughness has been used for such an application. A high alloy material melt is cast around the core material to form an outer layer to obtain a composite material, which is then annealed.
There is known a method in which roughing, quenching, tempering and finishing are performed to impart sufficient surface hardness and shape.

That is, Japanese Patent Publication No. 44903/1984 discloses a continuous overlay welding method as a method for producing a suitable composite material in which an outer layer and a shaft steel material are welded and integrated. Also,
Japanese Patent Application Laid-Open No. 1-96355 discloses a high-carbon high-alloy material that ensures the wear resistance of a rolled layer corresponding to the outer layer.

[0005]

However, the above-mentioned conventional method for producing a composite roll has the following problems.

[0006] First, the continuous overlay welding method is a method of manufacturing a composite material whose main purpose is to weld and integrate an outer layer and a shaft core steel material, and comprises a refractory material frame having a built-in annular induction heating coil. Inside a mold composed of a cooling mold, a core material made of steel is inserted concentrically, and an outer layer material molten metal is injected into an annular gap between the mold and the core material, and the molten metal is welded to the core material. This is a method of continuously building up while solidifying. Since the solidification of the outer layer material melt proceeds not only from the outer peripheral part in contact with the cooling mold but also from part of the core material side, the outer layer where the solid-liquid coexistence temperature range during solidification, that is, the difference between the primary crystallization start temperature and the solidification completion temperature is large In the case of molten metal, there is a problem that casting defects such as shrinkage cavities are likely to occur in the final solidified portion of the outer layer near the boundary between the outer layer and the core material.

As a method of reducing the occurrence of such casting defects, it is proposed that the outer layer material disclosed in Japanese Patent Application Laid-Open No. 1-96355 be limited to a composition range in which the solid-liquid coexistence temperature range becomes small. . However, the C content is 1.
In a high-carbon high-alloy material of 5% or more, a composition that reduces the solid-liquid coexistence temperature range necessarily increases the amount of coarse eutectic carbide crystallized at the time of solidification. Has the effect of remarkably deteriorating the abrasion resistance and heat resistance (skin roughness resistance and thermal shock resistance), which are important properties of hot rolled roll materials, and may reduce the occurrence of casting defects. Although it is, performance is degraded.

On the other hand, as a roll material for hot rolling having excellent wear resistance, there is a high carbon high vanadium wear resistant material disclosed in Japanese Patent Application Laid-Open No. 3-56642. This was developed for the purpose of an integrated high-durability hot rolling roll or the like in which the inside of the body and the shaft part are rich in toughness and the surface layer part is excellent in wear resistance and heat resistance. Therefore, a large amount of granular and high-hardness V carbide is dispersed to ensure wear resistance, and toughness,
The composition is such that the crystallization amount of the coarse eutectic carbide which significantly deteriorates the wear resistance and heat resistance is limited. Therefore, it is also suitable as an outer layer material of a composite roll for hot rolling having both abrasion resistance and heat resistance, but the solid-liquid coexistence temperature range becomes larger as the composition reduces the amount of crystallization of coarse eutectic carbide. Due to the tendency, occurrence of casting defects is inevitable.

Therefore, when a composite roll having an outer layer having excellent wear resistance and heat resistance is manufactured using the above-described cast composite material, the amount of coarse eutectic carbide crystallized in the outer layer is reduced. As a result of the composition, the solid-liquid coexistence temperature range is large, casting defects are likely to occur near the boundary of the obtained cast composite material, and as a work roll used for a long time under severe rolling conditions, casting defects In some cases, the outer layer as a starting point was peeled off, and the reliability was lacking. In particular, such a tendency becomes remarkable when the crystallization amount of the coarse eutectic carbide has to be reduced as much as possible in performance as in today, and a solution is required.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a process for producing highly durable composite roll and its capable of eliminating casting defects occurring in the casting composite material .

More specifically, according to the present invention, when a composite roll is produced from a cast composite material, even when an outer layer material having a composition that minimizes the amount of coarse eutectic carbides to be crystallized is used, casting defects can be finally obtained. durable composite roll and does not remain in
An object of the present invention is to provide its manufacturing method.

[0012] Here, "durability" means that the so-called roll service life is long by comprehensively judging abrasion resistance, skin roughness resistance and accident resistance. Therefore, the high durability in the present invention means that, for example, the rolling amount per one roll is conventionally 600,000 t, but can be extended to 3 million t.

[0013]

Various studies have been made to achieve the above object. Rather, the crystallization of coarse eutectic carbides is actively reduced to achieve not only wear resistance but also toughness and heat resistance. Casting defects such as shrinkage cavities resulting from the expansion of the solid-liquid coexistence temperature range resulting from the improvement of the castability are eliminated by forging the outer layer afterwards, resulting in high durability overall The present invention has been completed by knowing that it can be realized.

[0014] Forging processing has conventionally been performed on cast materials in some cases, but the object is originally a roll material for cold rolling or an integral material, and the forging is performed by destroying the casting structure. It is intended to be a structure, not intended for those having a composite structure mainly used for hot rolling rolls as described above, and also for those mainly intended for repair of casting defects such as shrinkage cavities. Absent.

[0015] Here, it is an aspect of the present invention, strength
Around the core steel excellent in toughness, C: 1.5 ~
A steel composition having 2.5% and V: 4.5-8.0%,
Outer layer with excellent wear resistance and heat resistance is applied by continuous overlay welding
To obtain a composite material.
At a heating temperature of ~ 1150 ° C, it occurs in the final solidification zone of the outer layer
Forging to eliminate compressed shrinkage cavities
A composite roll characterized by the following. Also, from another side,
The present invention is, around the excellent axial steel in toughness, weight%
With C: 1.5-2.5% and V: 4.5-8.0%
It has a steel composition, connecting an excellent outer wear resistance and heat resistance
Was cast by continued build-up welding method to obtain a composite material, then the said composite material, at a heating temperature of 900 to 1150 ° C., the final outer layer
This is a method for producing a composite roll, which comprises performing a forging process for eliminating pressure-bonding of shrinkage cavities generated in a solidification region .

[0016]

According to the present invention, forging processing is performed at a heating temperature of 900 to 1150 ° C. on a composite material obtained by casting an outer layer around a shaft core steel material by means of, for example, a conventionally known continuous overlay welding method. According to the present invention, casting defects occurring near the boundary of the cast composite material can be eliminated by press bonding.

Further, it is possible to refine the crystal grains of the surface layer of the shaft core steel material which has been coarsened by heating at a high temperature during casting, to improve the toughness of the boundary portion, and to further enhance the reliability as a highly durable roll. Can be.

Therefore, according to the present invention, it is possible to select a wide range of compositions from low alloy steel to high alloy steel as the outer layer material, but from the practical point of view, it is used for the outer layer of the composite roll according to the present invention. As the high alloy material, the above-mentioned JP-A-3-56
There is one having the following composition (wt%) disclosed in Japanese Patent No. 642 which can ensure abrasion resistance and heat resistance.

That is, in terms of% by weight, C: 1.5 to 2.5%, Si: 1.2% or less, Mn: 1.2% or less, Cr: 1.5 to 6.0%, Mo + 0.5W: 1.5 to 6.0%, V: 4.5 to 8.0% And, if desired, at least one selected from the group consisting of Ni: 3.0% or less, Co: 5.0% or less, Nb: 2.0% or less, and Ti: 2.0% or less. Steel composition consisting essentially of Fe It is.

As for the method for producing a composite material by outer layer casting , the aforementioned continuous overlay welding method is used.

According to the conventional continuous overlay welding method, not only restrictions on the composition of components sacrificing performance but also accurate setting of casting conditions for minimizing the occurrence of casting defects such as shrinkage cavities. In addition, measures such as elimination of materials having casting defects by strictly inspecting products have been important management items. However, according to the present invention, rolling which directly affects roll performance is performed. The setting of casting conditions for making the used layer have an appropriate solidified structure is almost the only control item.

[0022] While performing the forging for the composite material thus obtained, the heating temperature at the time of forging 900-11
The reason why the temperature is set to 50 ° C. is that if the temperature is lower than 900 ° C., the plastic deformation resistance is large, and it is difficult to eliminate the press-fit of the casting defect.
If the temperature exceeds the limit, the temperature may exceed the solidification completion temperature of the outer layer. In the present invention, the forging heating temperature is 11
It is preferable that the temperature is 00 ± 20 ° C. and the forging finish temperature is 900 ° C. or higher.

The degree of working at the time of forging, that is, the forging ratio, is usually about 1.1 to 1.5 because the main purpose is to press the casting defects by compression, and when the casting structure is to be destroyed and the structure is refined. The forging ratio is preferably 1.5 or more.

The forging is usually performed using a press, but may be performed using a hammer when the composite material is small.

[0025]

EXAMPLES Specific examples will be described below.

Example 1 In this example, the body was made of steel (SCM440) and the outer layer molten metal component shown in Table 1 by a continuous overlay welding method disclosed in Japanese Patent Publication No. × length 1500mm, outer layer thickness
A 40mm composite material was cast.

FIG. 1 shows a photograph of a metallographic structure obtained by subjecting the obtained composite material to macro corrosion in a cross section at a position of 400 mm from the body end. Magnification is 1: 1. As can be seen from FIG.
Due to macro-corrosion, significant casting defects are observed in the final solidification of the outer layer up to about 12 mm from the boundary.

[0028] FIG. 2 is its a expansion <br/> casting defect by microscopic size and metal structure photograph showing (magnification 30 times), it casting defects is obtained by a set of shrinkage porosity according to which I understand.

After turning the remaining 600 mm of this composite material to a diameter of 220, it was uniformly heated to 1080 ° C., and forged with a hammer to a diameter of 200 mm. The forging ratio was 1.21.

A metal group showing the position of 200 mm from the body end of the composite material thus forged by macro- corrosion in section.
Gold woven photograph and boundary vicinity shown enlarged by a microscope
The genus photographs are shown in FIGS. 3 and 4, respectively.

As can be seen from each of the figures, it is understood that the casting defect that has occurred in the cast composite material has been eliminated by the forging process.

Next, in order to compare the toughness of the boundary with or without forging, a specimen was taken from a disk on which a macroscopic cross-section of these composite materials had been subjected to a bending test. While the transverse rupture force is 641MPa as it is, it becomes 864MPa for forged material,
An improvement in toughness of 200 MPa or more was observed. That is, it can be seen that not only the casting defect is eliminated by the forging process but also the forging process is extremely useful for improving the toughness of the boundary.

[0033]

[Table 1]

Example 2 In this example, the same tests as in Example 1 were conducted using the outer layer materials of the respective steel compositions shown in Table 2 in place of the outer layer materials shown in Example 1.

Although the composite material had shrinkage cavities, they were repaired by forging.

[0036]

[Table 2]

[0037]

As described above, according to the present invention , casting defects generated in a cast composite material can be eliminated by pressure bonding, so that high durability having both abrasion resistance and heat resistance and markedly improved reliability has been achieved. The roll can be supplied stably.

[Brief description of the drawings]

FIG. 1 is a metallographic photograph showing a state of a casting defect generated near a boundary portion of a cast composite material by macro corrosion in a cross section .

2 is a metallographic photograph showing casting defects in cast composite material observed in FIG. 1 on an enlarged scale by microscopy <br/> microscope.

FIG. 3 is a metallographic structure photograph of a forged cast composite material according to an embodiment of the present invention, which is shown by macro-corrosion in a cross section.

[4] The vicinity of the border of the forged construction composite material of Figure 3 the microscope
It is a metal structure photograph shown in a larger scale.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-122251 (JP, A) JP-A-50-29453 (JP, A) JP-A-57-2862 (JP, A) JP-A 61-122 284527 (JP, A) JP-A-54-120260 (JP, A) JP-A-6-210434 (JP, A) JP-A-6-226306 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 27/04 B22D 19/19 B21B 27/00

Claims (2)

(57) [Claims] 1. A steel composition having C: 1.5 to 2.5% and V: 4.5 to 8.0% by weight around a shaft core steel material having excellent toughness, and having excellent wear resistance and heat resistance. The outer layer is cast by a continuous overlay welding method to obtain a composite material, and the composite material is subjected to a forging process at a heating temperature of 900 to 1150 ° C. to eliminate pressure shrinkage cavities generated in a final solidified region of the outer layer. A composite roll characterized by being performed. 2. A steel composition having C: 1.5 to 2.5% and V: 4.5 to 8.0% by weight around a shaft core steel material having excellent toughness, and having excellent wear resistance and heat resistance. The outer layer is cast by a continuous overlay welding method to obtain a composite material, and the composite material is subjected to a forging process at a heating temperature of 900 to 1150 ° C. to eliminate pressure shrinkage cavities generated in a final solidified region of the outer layer. A method for producing a composite roll, comprising: