JPH08117965A - Production of composite roll made by centrifugal casting - Google Patents

Abstract

PURPOSE: To uniformly and finely disperse graphite at a shaft part in the as cast condition by using a rapidly cooling mold, at first, casting molten metal for outer shell layer of a cast iron, etc., having wear resistance in a centrifugal casting machine and successively, casting the same molten metal into an upper shaft part after the lapse of a prescribed time of casting the specific components of molten metal into a lower shaft part and a barrel core part. CONSTITUTION: After centrifugal-casting the barrel outer shell layer 1, the metallic mold for centrifugal casting is erected, and an upper mold 7 and a lower mold 6 for casting the shaft part at the upper and the lower parts thereof are arranged to form the vertical type mold and the molten metal is cast into the lower mold 6 and the barrel core part. Thereafter, at the point of time passing 10-150min, the molten metal is cast into the part of the upper mold 7 to integrally cast the barrel core part and the shaft parts. At this time, the barrel core part and the shaft parts of the composite roll is formed by wt.% of 3.0-4.0% C, 1.5-3.0% Si, 0.2-1.3% Mn, <=0.1% P, <=0.06% S, 0.7-5.0% Ni, 0.3-3.0% Cu, 0.1-1.0% Cr, 0.1-1.0% Mo, 0.02-0.8% Mg, 0.0005-0.05% Bi and Fe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a centrifugally cast composite roll having excellent toughness in the shaft portion.

[0002]

2. Description of the Related Art In steel rolling rolls, the wear resistance is required for the outer shell layer in contact with the rolled material.
In many cases, a composite roll made of different materials is used for the body shell layer 1 and the body core portion 2 and the shaft portion 3 shown in FIG. The main characteristic required for the body core 2 and the shaft 3 is toughness, and ductile cast iron is often used. As a method of manufacturing the composite roll, usually, as shown in FIG. 2, after the outer shell layer 1 is centrifugally cast, a centrifugal casting mold is erected,
After forming a vertical mold by providing an upper mold 7 and a lower mold 6 for casting the shaft portion above and below the molten metal, the molten metal for the core portion and the shaft portion is cast. As a method of strengthening the shaft portion of the composite roll, in Japanese Examined Patent Publication No. 6-27289, only the shaft portion is heated to 800 to 900 ° C. after completion of casting to austenite, and then cooled at 150 to 500 ° C./Hr. Continue to 350
It is disclosed that the material is toughened by holding it at a constant temperature of up to 600 ° C and performing a constant temperature transformation.

[0003]

In order to improve the toughness of ductile cast iron used for the shaft portion, it is considered effective to uniformly finely disperse the spheroidal graphite and use bainite as the matrix structure. ing. However, in the case of JP-B-6-27289, since the cooling rate of the shaft portion is slow, improvement of the graphite structure determined by the eutectic reaction at the time of solidification cannot be expected, so that uniform fine dispersion of spherical graphite is difficult. . Further, heat treatment of only the shaft portion increases the temperature difference in the roll axial direction, and there is a high risk of cracking during heat treatment.

An object of the present invention is to provide a method for producing a composite roll having a shaft portion of ductile cast iron in which graphite in the shaft portion is uniformly finely dispersed in an as-cast state and a part or all of the matrix structure is bainized. It is provided.

[0005]

The feature of the present invention resides in that the core portion and the shaft portion of the composite roll are in a weight ratio,
C: 3.0 to 4.0%, Si: 1.5 to
3.0%, Mn: 0.2 to 1.3%, P:
0.1% or less, S: 0.06% or less, N
i: 0.7 to 5.0%, Cu: 0.3 to 3.0%,
Cr: 0.1-1.0%, Mo: 0.1-1.0
%, Mg: 0.02 to 0.08%, Bi:
While forming 0.0005-0.05%, the balance impurities and substantially Fe, at the time of casting, a quenching mold was used for the shaft portion, and the casting timing of the shaft portion was 10 to 150 minutes after casting of the body core portion. There is a point in time.

[0006]

The ductile cast iron applied to the above-mentioned shaft portion is made as-cast to make the graphite grains finer by adding Bi.
The toughness is improved by adding appropriate amounts of Ni, Cu and Mo and then rapidly cooling with a quenching mold to bainite a part of the matrix structure in the as-cast state.

The reason why the alloy components of the shaft portion and the body portion are limited to the above range will be described below. Regarding the limitation of C: 3.0 to 4.0%, if the C content is less than 3.0%, the tendency of chilling is remarkably reduced, and if it exceeds 4.0%, the amount of graphite becomes excessive and becomes brittle. . Therefore, the range is set to 3.0 to 4.0%.

Regarding the limitation of Si: 1.5 to 3.0%,
Si is an element indispensable for crystallization of graphite, and it is necessary to suppress crystallization of carbides as much as possible, but if it is less than 1.5%, crystallization of graphite is insufficient and cementite becomes excessive.
If it exceeds, the amount of graphite becomes excessive and the strength deteriorates. Therefore, the range is 1.5 to 3.0%.

Regarding the limitation of Mn: 0.2 to 1.3%,
Mn is effective in increasing the hardness of the matrix,
If it is less than 0.2%, the effect cannot be expected. If it exceeds 1.3%, toughness is deteriorated, so the range is made 0.2 to 1.3%.

Regarding P: 0.1% or less, P is set to 0.1% or less from the viewpoint of making the material brittle.

S: About 0.06% or less, S was made 0.06% or less from the viewpoint of making the material brittle.

Ni: 0.7 to 5.0% limitation,
Ni is an element for improving the matrix structure and an element for promoting graphitization, as is clear in Nihard cast iron. If it is less than 0.7%, the effect is small, and if it is 5.0% or more, the matrix structure easily forms martensite, so that the matrix structure is improved and the graphitization promoting effect is obtained. The range was set.

Cu: Regarding the limitation of 0.3 to 3.0%,
Cu has a remarkable effect of suppressing the ferrite formation of the matrix structure, and is effective in promoting bainite transformation. 0.3%
If it is less than 3.0, the effect is small, and if it is 3.0% or more, Cu segregates, which is not preferable. Therefore, 0.3 to 3.0
The range is%.

Regarding the limitation of Cr: 0.1 to 1.0%,
Cr is a white pig iron promoting element and a graphitization inhibiting element, but it is effective for making the matrix structure finer, and if it is less than 0.1%, its effect is small. If it exceeds 1.0%, crystallization of graphite is significantly hindered.
The range was 1.0%.

Mo: Regarding the limitation of 0.1 to 1.0%,
Mo is a solid solution in the matrix structure to delay the pearlite transformation and facilitates the bainite transformation.
Although it is necessary as described above, if it exceeds 1.0%, graphitization is hindered, so the content was made 0.1 to 1.0%.

Regarding Mg: 0.02 to 0.08%, Mg is contained for spheroidizing graphite, but if it is less than 0.02%, its effect is small and 0.08%.
If it exceeds, the graphitization is hindered and casting defects are likely to occur. Therefore, the range is 0.02 to 0.08%.

Bi: Regarding the limitation of 0.0005 to 0.05%, addition of a small amount of Bi has an effect of finely crystallizing graphite, and the number of graphite particles increases. However, when it is added in an excessive amount, the amount of graphite decreases, and the tendency of embrittlement of cast iron becomes prominent. If it is less than 0.0005%, its effect is small, and if it exceeds 0.05%, graphitization is hindered. Therefore, the range is 0.0005 to 0.05%.

As the molten metal for the outer shell layer, a roll material such as a grain material, a high chromium material, a high speed material, a chilled material, a ductile material or an adamite material which is generally used as a roll material for rolling a steel material may be used. .

In addition to the above, the components of the core and shaft of the composite roll according to the present invention are composed of the balance impurities and substantially Fe.

This composite roll is shown in FIG.
After centrifugal casting, the centrifugal casting mold is erected, and upper and lower molds 7 and 6 for casting the shaft portion are provided on the upper and lower sides thereof to form a vertical mold, and the lower mold 6 and the body core portion are formed. Pour the molten metal up to. Then, after 10 to 150 minutes, the upper mold 7
The molten metal is cast in the portion of, and the body core portion and the shaft portion are cast and integrated. Here, the lower mold 6 and the upper mold 7 are formed by a quenching mold. A quenching mold is a mold (sand mold) in which a chiller is embedded or when the diameter is large, such as in a thick plate roll, the entire mold is formed. It is a mold that allows water to pass through a pipe installed at In this case, if all of the core and the shaft are cast at the same time as in the conventional case, the solidification speed in the upper die 7 portion is faster than that of the core, and the molten metal of the volume contracted by solidification is transferred to the core. Since it cannot be supplied, the direction of solidification is lost, and there is a high risk of contraction holes being generated inside. In addition,
Conventionally, a sand mold having a small thermal conductivity was used as the mold of the shaft portion, so that the solidification rate of the core portion was faster than that of the shaft portion and the directionality of solidification could be secured.

However, according to the present invention, the molten metal is cast into the upper mold 7 at a time of 10 to 150 minutes after casting up to the lower mold 6 and the core portion, so that the directionality of solidification is ensured and the inner mold shrinks. It was possible to realize the refinement of the solidification structure by rapid cooling without the generation of holes. Regarding the casting timing of the upper die 7, the directivity of solidification cannot be ensured within 10 minutes after casting up to the lower die 6 and the body core, and the solidification of the body core progresses after 150 minutes or more, and the welding is performed. The time is preferably within the above-mentioned time because there is a high risk of causing defects.

From the above, it is possible to manufacture a composite roll having a shaft portion of ductile cast iron in which graphite of the shaft portion is finely dispersed uniformly in the as-cast state without heat treatment, and a part or all of the matrix structure is bainized. Became.

[0023]

EXAMPLES Next, specific examples will be described in comparison with two conventional rolls. (1) Ni-grain cast iron was used for the outer shell layer, and ductile cast iron of Table 1 was used for the body core and the shaft to cast a work roll for a thick plate mill having the following dimensions as shown in FIG. In the examples, quenching dies were applied to the upper and lower dies forming the shaft. Further, in the conventional examples 1 and 2, the sand mold was applied to both the upper mold and the lower mold forming the shaft as in the conventional case. Roll size: Body diameter φ1000mm x body length 4800mm Shaft diameter φ700mm, total length 8800mm

[Table 1]

(2) As described above, the casting of the embodiment is performed as shown in FIG.
In 100 minutes after casting, the molten metal was cast into the upper die 7 at the height of the body core. Further, in Conventional Examples 1 and 2, the upper die 7 was cast at one time.

(3) After casting Examples and Conventional Examples 1 and 2, all three were subjected to strain relief annealing at 420 ° C. × 30 Hr.
Further, only in Conventional Example 2, only the shaft portion was subjected to austempering treatment under the following heat treatment conditions. Austenite treatment: 880 ℃ × 2Hr Cooling rate from austenite: 200 ℃ / Hr Constant temperature transformation treatment: 400 ℃ × 5Hr

(4) The tensile strength of the shafts of the three rolls of the example and the conventional examples 1 and 2 was investigated. Ten test pieces were collected from each of the positions shown below. The test piece size was JIS No. 4 size. Upper part of shaft: sampled axially at a position of 1000 mm from the body end and depth of 50 mm Lower part of shaft: sampled axially at a position of 1000 mm from the body end and a depth of 50 mm The results are shown below. Example: 650 N / mm ² Conventional example 1: 350 N / mm ² Conventional example 2: 600 N / mm ²

When the ductile cast iron of the above-mentioned specific component of the present invention is applied, a quenching die is used for the shaft portion, and only the upper side of the shaft portion is cast after a certain elapsed time, a shrinkage hole is generated inside. The shaft toughness of the composite roll made by centrifugal casting was achieved. In other words, when the sand mold is used for the shaft and there is no austempering treatment (conventional example 1), the shaft strength is 350 N /
Only mm ² can be secured, and the strength of the shaft is 6 even when the shaft is sanded and austempered (conventional example 2).
In the case of the present invention, the shaft strength of 650 N / mm ² could be secured, although it was only 00 N / mm ² . From the above results, the effect of the present invention is clarified.

[0028]

As described above, according to the manufacturing method of the present invention, a shaft which is required to be toughened by applying the above-mentioned specific component ductile cast iron to the core and the shaft of the composite roll. By using a quenching die for the part and casting only after the elapse of a certain time only on the upper side of the shaft, the directionality of solidification is secured, and the solidification structure is miniaturized and cast as it is without cooling due to shrinkage holes. The bainite of the matrix structure in the state could be realized, and the shank of the composite roll could be significantly strengthened without heat treatment.

[Brief description of drawings]

FIG. 1 is a sectional view showing an ordinary composite roll.

FIG. 2 is a diagram for explaining a method of manufacturing a composite roll by stretch casting.

[Explanation of symbols]

 1 Body Shell Layer 2 Body Core 3 Shaft 6 Shaft Lower Mold 7 Shaft Upper Mold

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B22D 27/04 F C22C 37/00 B 37/04 B

Claims (1)

[Claims] 1. A method of manufacturing a composite roll by a centrifugal casting machine, wherein a chiller is embedded in a mold (sand mold) at a shaft portion or a quenching mold which is entirely a metal mold is used, and the centrifugal casting machine is first provided with abrasion resistance. After casting the molten metal for the outer shell layer made of cast iron or cast steel having the following, and then casting the molten metal made of the following component systems in the lower shaft portion and the core portion, 10 minutes to 150 minutes after, the upper shaft portion is A method for manufacturing a centrifugally cast composite roll, which comprises casting a molten metal having the following component system.
C: 3.0 to 4.0%, Si: 1.5 to
3.0%, Mn: 0.2 to 1.3%, P:
0.1% or less, S: 0.06% or less, N
i: 0.7 to 5.0%, Cu: 0.3 to 3.0%,
Cr: 0.1-1.0%, Mo: 0.1-1.0
%, Mg: 0.02 to 0.08%, Bi:
0.0005-0.05%, balance impurities and substantially Fe