JPH0810922A - Roll for continuous casting - Google Patents

Abstract

PURPOSE:To provide a roll for continuous casting, in which a buildup material is used with the low Ni material in the chemical component and both of the crack resistance and the wear resistance are possessed. CONSTITUTION:The buildup layer of a precipitation hardening type martensitic stainless steel composed of by wt.%, <=0.07 C, <=1.00 Si, <=1.00 Mn, 3.00-5.00 Ni, 15.5-17.5 Cr, 3.0-5.0 Cu, 0.10-0.30 Nb + Ta, <=0.030 P, <=0.030 S and the balance Fe with inevitable impurities, is formed on the surface of a core material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting roll used for continuous casting of steel or the like, and is intended to improve heat crack resistance and abrasion resistance in the environment of use thereof. is there.

[0002]

2. Description of the Related Art A large number of rolls are provided in a cooling support guide section or a drawing section of a continuous casting facility. These rolls are used in a harsh environment where they come into contact with hot slabs and are exposed to water and steam.
For example, the temperature history received during one rotation of the roll is about 200 ° C. when the roll does not come into contact with the slab, as shown in the measurement example of FIG.
It is a harsh thing that rises to about 00 ° C. That is,
This roll is used in an extremely harsh environment because, in addition to being repeatedly subjected to the above-mentioned heat history during operation, it is in direct contact with the high temperature slab to which the scale adheres.

For the above-mentioned reasons, continuous casting rolls are so worn out that it is necessary to regularly replace the rolls or the segments incorporating the rolls.
However, it is said that the cost required for exchanging rolls or segments accounts for about 30% of the cost required for maintenance of the continuous casting apparatus, including repair and regeneration costs. Therefore, reducing the cost required for the continuous casting roll greatly contributes to the reduction of the continuous casting cost and further the cost of the steel product, and the extension of the roll life has been a problem for many years.

Generally, it is necessary to have the following material properties in order to extend the life of the roll used in the above-mentioned harsh use environment. 1) There are few heat cracks generated on the roll surface due to thermal shock and thermal fatigue caused by repeated thermal history (heat crack resistance). 2) Less wear caused by contact with the slab (wear resistance). 3) Less oxidation and corrosion in water and steam environment (corrosion resistance / oxidation resistance). 4) Must be able to withstand the load received from the slab (mechanical strength).

By the way, many proposals have been made so far for improving the life of the continuous casting roll.
For example, SC materials were used in the early stages of development, but then DI
By using materials such as N standard 21CrMoV511 and JIS standard SUS 431, the mechanical strength (including mechanical strength at high temperature) has been improved. Furthermore, recently, in order to improve the heat crack resistance and wear resistance of these materials, the material is used as the core material and 13Cr of several mm is used on the surface of the core material.
-(1-4) Ni-based build-up welding has also been used. Further, a surfacing roll of SUH 660 (15Cr-25Ni) may be used.

However, even a roll having a low-Ni overlay, that is, a 13Cr- (1-4) Ni overlay on the surface of the core material, is still poor in crack resistance and abrasion resistance. Is not sufficient, and the reality is that it has not reached the point where the continuous casting cost is significantly reduced. Also, the above SUH
The 660 overlay has improved crack resistance and abrasion resistance, but the chemical composition of the overlay material is high Ni in the first place, which increases the cost of the roll itself. Therefore, the continuous casting cost was not significantly reduced. As explained above, for example, when the chemical composition of the cladding material is low Ni material (low cost material), the crack resistance and abrasion resistance are not sufficient, while the high Ni material costs the cost of the roll itself. I had the problem of inviting highs.

[0007]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a continuous casting roll which does not cause the above-mentioned problems of the above-mentioned known techniques even if the chemical composition of the cladding material is low Ni. To provide. Another object of the present invention is to provide a continuous casting roll in which the chemical composition of the overlay material is a low Ni material and has both crack resistance and abrasion resistance.

[0008]

[Means for Solving the Problems] Now, as a result of intensive research aimed at realizing the above-mentioned object, the inventors of the present invention have surprisingly found that if precipitation hardening type martensitic stainless steel is applied to a cladding material. The inventors have found that it is possible to improve crack resistance and abrasion resistance, and have completed the present invention.

That is, the gist of the present invention is the following configuration embodying the above findings. (1) A roll for continuous casting comprising a core material and a build-up layer of precipitation hardening type martensitic stainless steel on the surface of the core material.

(2) The chemical composition of the overlay is C: 0.07 wt% or less, Si: 1.00 wt% or less, Mn: 1.00 wt% or less,
Ni: 3.00 to 5.00 wt%, Cr: 15.5 to 17.5 wt%, Cu:
3.0 to 5.0 wt%, Nb + Ta: 0.10 to 0.30 wt%, P: 0.030
The continuous casting roll according to claim 1, containing less than wt% and S: less than 0.030 wt%, and the balance being Fe and inevitable impurities.

(3) The continuous casting roll according to claim 1 or 2, wherein the build-up layer has a thickness of 3 to 6 mm.

[0012]

The inventors of the present invention have conducted extensive experiments using stainless steel having various chemical compositions as a cladding material. As a result, conventionally, it has never been considered as a cladding material for continuous casting rolls, precipitation hardening type martensitic stainless steel, especially
We have found that 17-4 PH type (SUS 630 type) stainless steel is effective. That is, it was found that when this steel was used as a surfacing material for a roll for continuous casting, heat crack resistance and abrasion resistance were remarkably improved, and excellent characteristics were also exhibited in terms of corrosion resistance. Precipitation hardening type martensitic stainless steel represented by the above 17-4 PH type stainless steel has been conventionally used as a material for limited special applications such as shafts and aircraft parts by taking advantage of its high strength property at room temperature. Was used as.
However, it has not been studied at all as a continuous casting roll. The reason is that the use temperature of these precipitation hardening type martensitic stainless steels is relatively low, and the characteristics at high temperature as well as the use at high temperature have not been originally noticed.

In order to verify the above findings, the inventors first selected 17-4 PH PH stainless steel as the precipitation hardening type martensitic stainless steel, and
% Yield strength was investigated up to a temperature range of 600 ° C. The results are shown in FIG. 1 in comparison with the 13Cr-4Ni material and 21CrMoV511. From Fig. 1, the strength of 17-4 PH stainless steel shows almost the same strength as the conventionally used 13Cr-4Ni material at room temperature, but it corresponds to the temperature at which the continuous casting roll contacts the slab. It was found that in the high temperature range, the strength was 50 N / mm ² or more higher than the 13Cr-4Ni material. So-called precipitation hardening type martensitic stainless steel has such properties, that is, high strength in a high temperature range. Therefore, when such a steel is formed on the roll surface as a buildup layer, continuous casting results. It is possible to improve the crack resistance and abrasion resistance of the roll for use. Table 1 shows the test results of the corrosion resistance (seawater) of 17-4 PH type stainless steel together with that of the comparative material. From Table 1, it was found that the 17-4 PH type stainless steel is also superior in corrosion resistance to the SUS 410 and SUS 431 stainless steels.

[0014]

[Table 1]

Next, in the present invention, the reason why the preferable chemical composition of the precipitation hardening type martensitic stainless steel which is the overlay layer is limited to the above-mentioned essential constitution will be explained.

C: 0.07 wt% or less; C is an element necessary for improving the strength and wear resistance, but if added in excess of 0.07 wt%, hardening of the matrix and precipitation of carbides become excessive, Since heat cracks easily occur due to thermal shock and thermal fatigue during use, and welding workability during overlay welding deteriorates, the range of addition is 0.07.
It should be less than wt%, preferably less than 0.05 wt%.

Si: 1.00 wt% or less; Si is an element effective as a deoxidizing agent for steel, but if added in excess, not only the effect is saturated but also weld cracking is likely to occur. Is 1.00 wt% or less, preferably 0.20 to 0.60 wt%.

Mn: 1.00 wt% or less; Mn is an element effective as a deoxidizing agent for steel and for forming a uniform martensitic structure. However, if added in excess of 1.00 wt%, ductility, toughness, and high-temperature oxidative property deteriorate, so the addition range is 1.00 wt% or less. The preferable addition range of Mn is 0.40 to 0.80 wt% in consideration of ensuring strength.

Ni: 3.00 to 5.00 wt%; Ni is an element that forms a uniform martensite structure and improves the strength. To obtain this effect, it is necessary to add at least 3.00 wt%, but even if added over 5.00 wt%, the effect will be saturated, so it is necessary to add Ni in the range of 3.00 to 5.00 wt%. is there. The preferable range of addition of Ni is 3.50 to 4.50 wt%
Is.

Cr: 15.5 to 17.5 wt%; Cr is an indispensable element for ensuring high temperature strength, abrasion resistance, oxidation resistance and corrosion resistance. These characteristics show that the Cr addition amount is 15.5 to 1
It is achieved in the range of 7.5 wt%. That is, if it is less than 15.5 wt%, the oxidation resistance and corrosion resistance are reduced, while if it exceeds 17.5 wt%, the strength is reduced.

Cu: 3.0 to 5.0 wt%; Cu is an extremely effective element for improving the high temperature strength without impairing the high temperature oxidation, and also contributes to the improvement of the corrosion resistance through the precipitate containing Cu. Is. To obtain this effect, Cu must be added at least 3.0 wt%, but if it exceeds 5.0 wt%, the weldability deteriorates, so the range of addition is 3.0 to 5.
0 wt%

Nb + Ta: 0.10 to 0.30 wt%; Nb and Ta are
Both contribute to the refinement of the structure, and their effects can be replaced with each other. To obtain the above effect, set Nb + Ta to 0.
10 wt% or more is required, but if it exceeds 0.30 wt%, the weldability deteriorates. Therefore, the addition range is Nb + Ta and is 0.
10 to 0.30 wt%.

P: 0.030 wt% or less; P is a harmful element that deteriorates toughness, and its effect becomes remarkable when it exceeds 0.030 wt%, so 0.030 wt% or less, preferably 0.015 wt% or less.
Must be less than wt%.

S: 0.030 wt% or less; S is the same as P,
It is a harmful element that deteriorates toughness, and its effect is 0.030.
Since it becomes remarkable when it exceeds wt%, it is necessary to set it to 0.030 wt% or less, preferably 0.010 wt% or less.

Further, the preferable thickness of the overlay layer made of precipitation hardening type martensitic stainless steel is set within the range of 3 to 6 mm. This is because the one-time renewal cost is high.

Next, the method for forming the built-up layer of the present invention will be described. First, as a build-up method, a welding method, particularly a submerged arc welding using a strip electrode is suitable. The chemical composition of the electrode used at this time may be determined in consideration of the dilution rate of the core material. After welding, combined post heat treatment and precipitation 4
Heat treatment is performed at 50 to 650 ° C. for 4 to 8 hours. In that case, strength, ductility, hardness, etc. can be adjusted to a desired range by changing the heat treatment temperature. The steel type of the core material need not be specified, but as mentioned above,
It is required that the roll has sufficient strength to withstand the load received from the slab. From this, the steel grade suitable for the core material has different required strength levels depending on the place of use of the roll, but for example, the tensile strength of 60 kg / mm ²
The low alloy steels having good weldability described above can be mentioned. Similarly, the chemical composition of the core material does not need to be specifically defined, but for example, a suitable steel type is DIN21CrMo.
V511 (C: 0.17 to 0.25 wt%, Si: 0.30 to 0.60 wt%,
Mn: 0.30 to 0.50 wt%, P: 0.035 wt% or less, S: 0.035
wt% or less, Ni: 0.60 wt% or less, Cr: 1.2 to 1.5 wt%, M
o: 1.0 to 1.2 wt%, V: 0.25 to 0.35 wt%) is recommended.

[0027]

EXAMPLES Example 1 A test piece of 15 mmφ × 5 mm was sampled from two kinds of materials for the overlay material and the core material having the chemical composition shown in Table 2, and the test piece was heated and cooled under the conditions shown in Table 3. After applying the heat cycle, the size distribution of cracks generated on the longitudinal section of the test piece was observed. The result is shown in FIG. From FIG. 2, it was found that the precipitation hardening type martensitic stainless steel applied to the overlay layer of the present invention is significantly superior in heat crack resistance to the 13Cr-4Ni material (comparative material) and the core material. .

[0028]

[Table 2]

[0029]

[Table 3]

Example 2 The surface of a core material having the chemical composition shown in Table 2 was subjected to overlay welding by submerged arc welding using the two types of strip electrodes shown in the same table as overlay material, and then at 600 ° C. for 8 hours. Was heat treated and finished by mechanical grinding to form a built-up layer of 4.5 mm and finished as a roll of 380 mmφ x 2350 mm. Similarly, Table 2 shows the chemical composition of the overlay layer of the obtained continuous casting roll. This roll was installed in the horizontal position of the continuous casting equipment, and the state of changes in crack depth and wear amount due to the casting process was investigated. The results are shown in FIGS. 3 and 4, respectively. From FIGS. 3 and 4, the continuous casting roll according to the present invention has a crack depth and an abrasion amount of about 1 / third compared to those of the conventional 13Cr-4Ni material in which the overlay layer is formed (comparative material).
It was confirmed that the number had decreased sharply to 5.

[0031]

As described above, according to the present invention, the heat crack resistance and abrasion resistance of the continuous casting roll can be remarkably improved. Moreover, since a continuous casting roll having such excellent characteristics can be achieved by overlaying with low Ni, it greatly contributes to reduction of maintenance cost of the continuous casting apparatus. Further, the present invention can be applied to the case where a surfacing roll for continuous casting is worn, and the surfacing roll is repeatedly ground again to obtain a product.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature dependence of 0.2% proof stress of overlay materials and core materials.

FIG. 2 is a graph showing a crack size distribution of a cladding material and a core material.

FIG. 3 is a graph showing changes in crack depth with the progress of casting of a built-up continuous casting roll.

FIG. 4 is a graph showing changes in the amount of wear of a built-up continuous casting roll with the progress of casting.

FIG. 5 is a graph showing a temperature change of a continuous casting roll during operation.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Onishi 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (no address) Inside the Mizushima Works, Kawasaki Steel Co., Ltd. (72) Fumikazu Ohara Mizushima-Kawasaki Street, Kurashiki-shi, Okayama Prefecture 1-chome (without street number) Inside Kawashima Steel Co., Ltd. Mizushima Steel Works (72) Inventor Isao Matsui 1-chome (without street number) Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi (prefecture) Inside Kawashima Steel Co., Ltd. Mizushima Works (72) Inventor Koro Emoto 3-26-29 Higashi-Namba-cho, Amagasaki-shi, Hyogo Special electrode company (72) Inventor Kazuyuki Takahashi 3-26-29, Higashi-Namba-cho, Amagasaki-shi, Hyogo Special electrode company

Claims (3)

[Claims] 1. A continuous casting roll comprising a core material and a build-up layer of precipitation hardening type martensitic stainless steel on the surface of the core material. 2. The chemical composition of the overlay is C: 0.07 wt% or less, Si: 1.00 wt% or less, Mn: 1.00 wt% or less,
Ni: 3.00 to 5.00 wt%, Cr: 15.5 to 17.5 wt%, Cu:
3.0 to 5.0 wt%, Nb + Ta: 0.10 to 0.30 wt%, P: 0.030
The continuous casting roll according to claim 1, containing less than wt% and S: less than 0.030 wt%, and the balance being Fe and inevitable impurities. 3. The overlaying layer has a thickness of 3 to 6 mm.
Alternatively, the continuous casting roll according to claim 2.