JPH08192254A - Rolls for continuous casting that are cooled internally and externally - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a roll for continuous casting, which has high strength, is excellent in corrosion resistance, wear resistance and toughness and is used by being cooled from the inside and the outside. [Structure] C: 0.07 wt% or less, Si: 1.00 wt% or less, Mn: 1.00 wt% or less, P: 0.04 wt% or less, S: 0.03 wt% or less, Ni: 3.00
5.00% by weight, Cr: 15.5 to 17.5% by weight, C
u: 3.00 to 5.00% by weight, Nb: 0.15 to 0.
It is a solid and solid roll obtained by hot forging precipitation hardening type stainless steel containing 45% by weight and the balance being Fe and inevitable impurities, and having through holes for cooling therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll for continuous casting used in a corrosive environment, and more specifically, it has high strength, excellent corrosion resistance, wear resistance, and toughness. The present invention relates to a continuous casting roll that is used by being cooled from the outside.

[0002]

2. Description of the Related Art A continuous casting roll is subject to thermal influence from a continuous cast piece and mechanical load such as straightening reaction force. When these loads become excessive, the rolls are worn or deformed to cause irregularities in the pass line, which eventually leads to internal defects such as internal cracks in the slab.

Regarding the continuous casting roll used under such a severe environment, "Iron and Steel" (1972 (198)
6) No. 16, p. 2225), in selecting the roll material, the thermal stress generated inside the roll and the allowable stress based on "stress fluctuation" and "repetition" in each process of casting are considered. It should be stated that it should.

On the other hand, many inventions relating to the material of the continuous casting roll in consideration of these have been proposed, and many have been put into practical use. As an example, (1) a heat-resistant steel that withstands high-temperature use is used as a sleeve or padding material for a sleeve roll, and a non-water-cooled roll is used, or its composition is specified to be an austenitic heat-resistant steel. Things (Japanese Patent Publication No. 61-32107)
issue),

(2) As a material for sleeve rolls, 10 to 18% Cr steel (V, N with 5 to 10% Ni on the roll shaft)
b, Ti, Mo content), and 20 to 30 for the sleeve
% Ni steel containing 20 to 30% Cr (containing Nb, N, Mo) and provided with a plurality of cooling water grooves parallel to the roll axis between the roll axis and the sleeve (Japanese Patent Publication No. 61-2130).
3),

(3) As a build-up roll, in order to secure roll breakage resistance, Ni-based or Co-based self-fluxing alloy type thermal spraying is applied to the surface of the body of a stainless steel roll containing 7-20% Cr. The metal is sprayed to a thickness of 0.05 to 0.80 mm, and then the sprayed layer is melted to be metallurgically bonded so that cracks generated on the surface do not propagate to the deep part of the roll ( Japanese Patent Publication 59-141
01),

(4) As a non-magnetic roll, Mn15
-30% high Mn non-magnetic steel as the base material (Japanese Patent Publication 2
-4387) or high Mn non-magnetic steel containing Ni or Cu (Japanese Patent Publication No. 60-58777),

(5) Those using 13Cr-0.5Ni-Cu-V type alloys (Japanese Patent Publication No. 60-58778, Japanese Patent Publication No. 59-35427) and the like are known.

[0009]

However, in a continuous casting machine for casting high-strength steel such as SUS304 or 13Mn steel, a completely solidified slab, a casting start part, a casting end part, etc. When trying to bend and straighten a cast slab or the like, a very large bending stress acts on the neck portion of the roll. However, the continuous casting rolls made of the materials that have been proposed so far have a problem that the roll is broken from the neck portion when such a phenomenon occurs repeatedly. By the way, the continuous casting roll is usually incorporated in a roll assembly called a segment that supports and conveys the continuous cast piece, and once incorporated, it is continuously used for about one and a half to two years. In the meantime, the roll is kept in contact with the high hardness steel and the oxide scale generated on the surface of the slab for a total length of 1,000 to 1,500 km.

Further, corrosive water in which Na, F, Li and the like contained in the mold powder are dissolved is constantly sprayed as secondary cooling water on the roll in the continuous casting machine. This roll rotates as the slab is pulled out and comes into contact with the hot slab,
Repeat withdrawal. Therefore, the surface of the roll becomes hot,
The concentration of cooling water increases due to evaporation and solidification, resulting in a very severe corrosive environment. That is, the roll is in a highly corrosive high temperature atmosphere, and is continuously exposed to a severe environment in terms of both corrosion and wear.

From the above, it can be easily judged that a material having high strength at high temperature is selected as the material for the roll.
Furthermore, unless cooling is performed from inside the roll and from outside the roll (including so-called secondary cooling water), the temperature of the entire roll rises, and the neck of the roll, where stress is concentrated, may break. It may reach. In addition, the sealing material (generally made of synthetic resin) for cooling and lubricating the neck portion is solidified and burned out, often shortening the life of the roll.

As described above, the roll is always in contact with the hot slab, and in order to maintain the strength, it is essential to maintain the low temperature by cooling from the inside of the roll (cooling inside the machine) in addition to the secondary cooling water. . This internal cooling is often carried out by passing cooling water through a through hole formed in the axial direction of the roll center, but if ordinary steel is used as the roll material, the inner wall surface of the through hole that contacts the cooling water Is corroded, and there is a problem that a large amount of scale adheres to the inner wall surface of the hole. Due to the generation of this scale, the cooling effect inside the roll is drastically reduced, and as a result, the temperature of the roll as a whole is increased and the strength is reduced, and the life of the roll is shortened.

These are problems that act in a complex manner, and fatigue may be induced by repeated loading over a long period of time, and sometimes an impact load may be applied due to sudden drawing of the slab, and these may endure. It is necessary to have the characteristics to obtain.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a continuous casting roll having high strength, corrosion resistance, wear resistance, and toughness. .

[0015]

In order to solve the above-mentioned problems, the present inventors have proposed a material satisfying the high strength, corrosion resistance, wear resistance and toughness characteristics required for continuous casting rolls. Diligent research was conducted.

First, as a material satisfying the strength and toughness, 13Cr-based martensitic stainless steel is specifically mentioned. In fact, Ni, Cu, V, etc. are added to this material to improve its characteristics. Is used as a base. However, this material has a drawback that when it is welded, it tends to crack due to local heat input and strain due to transformation.

Next, as a material satisfying the corrosion resistance, austenitic stainless steel can be mentioned, which can sufficiently satisfy the required strength for general purposes, but for continuous casting. It may be insufficient as a roll.

Therefore, the present inventors have paid attention to precipitation hardening type stainless steel as a roll material for continuous casting which satisfies such a composite requirement. This type of steel is a stainless steel that is provided with corrosion resistance as stainless steel and strength by precipitation hardening. This material is hot forged and processed into a roll material, and if the heat treatment method is optimized, the knowledge that strength, hardness, and toughness that can sufficiently withstand the use of continuous casting can be obtained, The present invention has been completed based on this finding. It has not been attempted to use this material in a roll for continuous casting. Moreover, it can be said that it was never used as a solid solid roll.

That is, according to the present invention, C: 0.07
Wt% or less, Si: 1.00 wt% or less, Mn: 1.0
0% by weight or less, P: 0.04% by weight or less, S: 0.03
% By weight, Ni: 3.00 to 5.00% by weight, Cr:
15.5 to 17.5% by weight, Cu: 3.00 to 5.00
% By weight, Nb: 0.15 to 0.45% by weight, and the balance being a solid solid roll obtained by hot forging precipitation hardening type stainless steel consisting of Fe and inevitable impurities.
Provided is a continuous casting roll which is characterized by having a through hole for cooling inside, and which is used by being cooled from the inside and the outside.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the continuous casting roll of the present invention. In the figure, a continuous casting roll 1
Comprises a roll main body 2 and a through hole 3 for cooling formed in the axial center of the roll main body 2 in the axial direction, and both axial ends of the roll main body 2 form a tapered neck portion.

In the present invention, the roll main body 2 is C:
0.07 wt% or less, Si: 1.00 wt% or less, M
n: 1.00 wt% or less, P: 0.04 wt% or less,
S: 0.03 wt% or less, Ni: 3.00 to 5.00 wt%, Cr: 15.5 to 17.5 wt%, Cu: 3.0
0-5.00% by weight, Nb: 0.15-0.45% by weight
And the balance is a solid solid member obtained by hot forging precipitation hardening type stainless steel containing Fe and unavoidable impurities.

By using the precipitation hardening stainless steel having the above composition, both the corrosion resistance as stainless steel and the strength by precipitation hardening can be combined. Further, since it has high toughness, breakage from the roll neck can be prevented.

Here, the precipitation hardening stainless steel is a steel type in which the strength is increased by precipitating an intermetallic compound such as Cu or Nb in the material. Further, the heat treatment for obtaining the member of the present invention may be performed by rapidly cooling from 1020 ° C to 1060 ° C, then holding at 610 ° C to 630 ° C, and then air cooling. There are other points in this point depending on the desired mechanical properties.

The reasons for limiting the components of the precipitation hardening stainless steel having the above composition used in the present invention will be described below. C: When it is more than 0.07% by weight, the hardness after forming a solid solution is too high, which makes the processing difficult. Therefore, the C content is limited to 0.07% by weight or less.

Si: If it is more than 1.00% by weight, non-metallic inclusions increase and cleanliness deteriorates. Therefore, the Si amount is limited to 1.00% by weight or less.

If Mn is more than 1.00% by weight, non-metallic inclusions increase like Si. Therefore, the Mn content is limited to 1.00% by weight or less.

If P is more than 0.04% by weight, hot workability deteriorates and toughness also deteriorates. Therefore, the P amount is 0.
It was limited to 04% by weight or less.

If S: more than 0.03% by weight, hot workability deteriorates like P. Therefore, the S amount is limited to 0.03% by weight or less.

Ni and Cr are determined in order to obtain a martensitic structure by the balance between them. These are as specified in the so-called Sheckler phase diagram.

Cu: essential for producing a precipitation phase,
If it is less than 3.00% by weight, the precipitation phase becomes insufficient, while
If it exceeds 5.00% by weight, the toughness decreases and the weldability also deteriorates. Therefore, the Cu content should be 3.00 to 5.00.
Limited to weight percent.

Necessary for stabilization of Nb: C,
If it is less than 0.15% by weight, the stabilization becomes insufficient, while if it exceeds 0.45% by weight, the toughness deteriorates. Therefore, the Nb content is limited to 0.15 to 0.45% by weight.

The size of the roll body 2 thus produced is usually 300 to 2000 mm in total length and 150 to 550 mm in roll diameter. The diameter of the neck portion (end portion) is about 60 to 250 mm.

However, even if a roll is formed by using a solid member obtained by hot forging a precipitation hardening stainless steel having the above composition, under a high temperature condition such that the roll itself reaches 600 ° C. or more, it should be cooled for a long time. If left unattended, the mechanical properties are almost the same as those of the conventional continuous casting roll material (for example, 13Cr-0.5Ni system), and its effectiveness is drastically reduced. That is, when using the continuous casting roll of the present invention, it is essential to always perform internal cooling and external cooling including secondary cooling at the same time, and always maintain the roll temperature at about 400 ° C. or less. Becomes

In the roll of the present invention, for internal cooling, a through hole 3 for cooling is formed in the axial center portion of the roll in the axial direction. This through hole 3 is usually 20 mmφ to 8
The diameter is about 0 mmφ. When using continuous casting, the cooling water is usually supplied to the cooling through hole 3 at 20 to 100 L / min.
Cool the roll from the inside by passing it at the flow rate of the book,
Prevents roll temperature rise. As the cooling water used,
What is conventionally used can be used, water being the most common. As a result, the cooling effect inside the roll is not reduced, and it is possible to prevent the temperature of the entire roll from increasing and the strength from decreasing.

The continuous casting roll of the present invention is shown in FIG.
The padding 4 may be formed on the outer peripheral surface of the roll body 2 as shown in FIG. The member used for the padding 4 may be the member used for the roll body 2 or may be a member commonly used as a padding member for rolls. As such a member, for example, a built-up material (C: 0.15 wt%, Si:
12 wt%, Ni: 2.0 wt%, Mo: 2.0 wt
%, V: 0.15 wt%) and the like. The padding 4 can be formed by a conventional method.
In addition, normally, the buildup 4 has a thickness of about 2 to 50 mm.

Even in a conventional roll, an alloy steel based on ordinary steel is often overlaid on the outer peripheral surface of the roll body (roll shaft). However, if ordinary steel is used in the center of the shaft in such a two-layer structure, there is a limit to improvement in strength, and the problem of corrosion of the inner wall surface of the cooling through hole provided in the center of the shaft cannot be solved. In the end, however, the internal cooling was insufficient, and the temperature of the roll itself during use also increased. Therefore, it was difficult to achieve a dramatic improvement in roll life.

That is, the conventional two-layer structure using the ordinary steel in the center of the shaft is advantageous in reducing the initial purchase cost, but in terms of the total cost including the roll life, The use of solid precipitation hardening stainless steel has proven beneficial. In addition, when expensive stainless steel is overlay-welded on the roll surface, the initial cost is reversed depending on the range of build-up, and conventional rolls using plain steel are more producible than rolls according to the present invention. It can be costly.

On the other hand, with the recent increase in the temperature of the slab, near the machine end of the continuous casting machine, the temperature of the slab as a whole is made uniform by the internal heat of the slab, without performing secondary cooling, which is referred to as retroping. In many cases, the operation method is used to raise it. Even in such an operating method, in order to effectively use the precipitation hardening stainless steel of the present invention, it is necessary to cool the roll from the outside even in the cooling zone where the secondary cooling is not performed.

(Experimental Example) A roll was manufactured using the materials having the compositions shown in Table 1. This was continuously cast at 2500 charges with a single charge amount of 250 t, and the characteristics of rolls were evaluated. (Experimental conditions) Roll for continuous casting Roll length 200 cm Roll diameter 28 cm Neck part (end) diameter 14 cm Through hole diameter for internal cooling 5 cm Flow rate for internal cooling water 60 L / min · book (25 ° C) Secondary cooling method Steam spray Cooling slab drawing speed 1.6m / min

[0040]

[Table 1]

[Wearability evaluation] The results are shown in FIG. As is clear from FIG. 3, in the roll of the present invention, the wear amount of the roll was hardly observed even after 2500 charging. On the other hand, in the comparative roll, the degree of wear increased as the number of times of charging increased, and the wear amount reached to 0.2 mm or more after 2500 charging.

[Result of Observation of Roll Surface] The state of the surface of the roll after 2500 charging was visually observed. With the roll of the present invention, no defects were found in almost the same state as the roll surface at the start of use. On the other hand, in the comparative roll, the surface of the roll was cracked like a turtle and it was impossible to continue the use.

[Measurement Result of Roll Deformation] The appearance of the outer shape of the roll after 2500 charging was visually observed. No deformation was observed in the roll of the present invention, which was within the precision of the roll at the start of use. On the other hand, in the comparison roll, ±
A whirling of 1.0 mm occurred, reaching the limit that affects the quality of the slab.

[Differences with and without External Cooling of Roll] With respect to this, the results of the case where the external cooling of the roll was performed and the case where the external cooling of the roll was not performed were compared using only the roll of the present invention. The method of external cooling of the roll was a means for spraying 5 L / min of water spray to the portion immediately after the contact with the slab was completed. In any case, internal cooling was performed under the conditions described above. As a result, if the rolls are cooled at the same time,
Even after 2500 charging, it was in almost the same state as the roll surface at the start of use, and no defect was observed. On the other hand, if the roll is not cooled, 1000
At the time of charging, the roll neck had already broken and had to be replaced with another roll.

[0045]

As described in detail above, according to the present invention,
C: 0.07 wt% or less, Si: 1.00 wt% or less,
Mn: 1.00% by weight or less, P: 0.04% by weight or less,
S: 0.03 wt% or less, Ni: 3.00 to 5.00 wt%, Cr: 15.5 to 17.5 wt%, Cu: 3.0
0-5.00% by weight, Nb: 0.15-0.45% by weight
Is a solid and solid roll obtained by hot forging a precipitation hardening type stainless steel containing the balance of Fe and inevitable impurities, and a continuous casting roll having a through hole for cooling therein. Since it is provided, it is possible to provide a continuous casting roll having high strength and excellent in corrosion resistance, wear resistance, and toughness.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a continuous casting roll according to the present invention.

FIG. 2 is a sectional view showing another embodiment of the continuous casting roll according to the present invention.

FIG. 3 is a graph showing the results of a roll wear test using a roll of the present invention and a comparative roll.

[Explanation of symbols]

 1 roll for continuous casting 2 roll body 3 through hole for cooling 4 build-up

Claims (2)

[Claims] 1. C: 0.07% by weight or less, Si: 1.00
Wt% or less, Mn: 1.00 wt% or less, P: 0.04
Wt% or less, S: 0.03 wt% or less, Ni: 3.00
~ 5.00% by weight, Cr: 15.5 to 17.5% by weight,
Cu: 3.00 to 5.00% by weight, Nb: 0.15
A solid, solid roll containing 0.45% by weight and the balance being hot forged precipitation hardening stainless steel consisting of Fe and unavoidable impurities, characterized by having through holes for cooling inside. The continuous casting roll used by cooling from the inside and the outside. 2. The roll outer peripheral surface is provided with a padding.
A roll for continuous casting, which is used by being cooled from the inside and the outside as described in 1.