JP2003055726A - Thermocouple, material for protection tube thereof, and use of the material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermocouple capable of stably performing temperature monitoring in the vicinity of the bottom of a blast furnace over a long period, a material for a protection tube thereof, and the use of the material. SOLUTION: (1) A protection tube composed of a material having a composition consisting of, by mass, >=15% Ni, >=15% Cr, further total >=3% of either or both of Mo and W and the balance Fe with inevitable impurities is provided. (2) A protection tube composed of a material having a composition consisting of, by mass, >=15% Ni, >=15% Cr, further >=10% Co and the balance Fe with inevitable impurities is also provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermocouple, a protective tube material thereof and a method of using the material, and more particularly to a thermocouple used near the bottom of a blast furnace, a protective tube material thereof and a method of using the material. .

[0002]

2. Description of the Related Art Since a large amount of capital investment is required to construct a new blast furnace, it is essential to extend the life of the blast furnace as much as possible for cost reduction. For that purpose, the erosion condition of the brick at the bottom of the blast furnace is monitored in real time, and when an abnormality occurs,
Appropriate changes in operating conditions and repairs are required. As a means for indirectly inspecting the erosion state of this brick, a method using a thermocouple buried in the bottom of the furnace is generally used. This method estimates the brick thickness that reaches the hot metal temperature, that is, the brick residual thickness, from the temperature measurement values of thermocouples buried in two or more locations in the direction of heat conduction and the thermal conductivity of the bricks obtained in advance. is there.

This thermocouple is covered with a protective tube so as to withstand the corrosive environment in the furnace, and an electrical insulator (for example, MgO) is packed between the protective tube and the thermocouple.
As the protective tube material, for example, SUS310S, Inconel 600 or the like is used. Hereinafter, a thermocouple of the type in which the thermocouple is inserted into the protective tube is referred to as a sheath thermocouple.

[0004]

However, in the conventional sheath thermocouple, 10 years after the blast furnace was burned, and in some cases 3
Deterioration occurs in about 5 years, the thermocouple is broken, and the insulation performance of the insulator is deteriorated, so that a predetermined temperature measurement accuracy cannot be obtained. In recent years, the blast furnace life has exceeded 10 years, and further blast furnaces constructed in the future are expected to have a life of 20 years or more. It is practical to repair or renew the sheath thermocouple buried in the bottom of the blast furnace. It will be difficult. For this reason, it has become essential to develop a sheath thermocouple that has stable performance for a long period of 20 years or more at the bottom of the blast furnace.

An object of the present invention is to provide a thermocouple capable of stably monitoring the temperature of the bottom of a blast furnace for a long period of time, a protective tube material for the thermocouple, and a method for using the material.

[0006]

Means for Solving the Problems The present inventors have obtained the following findings as a result of collecting sheath thermocouples from the blast furnace bottom at rest and diligently investigating and examining the damage factors. (A) The main cause of the deterioration of the sheath thermocouple is corrosion of the sheath thermocouple protection tube due to the gas in the blast furnace (hereinafter, also referred to as blast furnace gas). (B) At high temperature (200-500 ° C), due to carburization by CO and high temperature sulfide corrosion by H ₂ S, on the other hand, at low temperature (<200 ° C), acid components (hydrochloric acid and sulfuric acid) in blast furnace gas are protected by the surface of the protective tube. Corrosion damage to the protective tube is caused by corrosion (hereinafter also referred to as acid dew point corrosion) that occurs when dew condensation occurs.

Based on the above knowledge, various test materials were
A material evaluation test was conducted and the following findings were obtained. (A) Carburization resistance in a blast furnace gas environment (≧ 200 ° C.) is
It is remarkably improved in a test material containing 15% by mass or more of Ni and Cr (hereinafter simply referred to as% by mass).

(B) The corrosion resistance to the acid generated when the blast furnace gas condenses is a test material containing 15% or more of each of Ni and Cr and 3% or more in total of one or more of Mo and W. improves. Further, when Ta is contained in the test material in an amount of 1% or more, the corrosion resistance against acid is further improved.

(C) In a blast furnace gas environment, the corrosion resistance against high temperature sulfidation corrosion is remarkably improved in the test material containing 15% or more of each of Ni and Cr and 10% or more of Co.

(D) Further, one or more of Si and Al
% Or more in the test material, the corrosion resistance to high temperature sulfidation corrosion is further improved. The present invention has been made on the basis of the above findings, and the summary thereof is as follows. (1) Containing 15% by mass or more of Ni and Cr, respectively,
Furthermore, a protective tube material for a sheath thermocouple for a blast furnace, which contains one or more kinds of Mo and W in a total amount of 3% by mass or more and the balance is Fe and inevitable impurities. (2) The protective tube material for the sheath thermocouple for blast furnace according to (1) above, which further contains Ta in an amount of 1 mass% or more. (3) Containing 15% by mass or more of Ni and Cr, respectively,
Furthermore, a protective tube material for a sheath thermocouple for a blast furnace, characterized in that it contains 10% by mass or more of Co, and the balance is Fe and inevitable impurities. (4) The protective tube material for the sheath thermocouple for blast furnace according to (3) above, further containing one or more kinds of Si and Al in a total amount of 1% by mass or more. (5) A protective tube material for a sheath thermocouple for a blast furnace, comprising a protective tube material for a sheath thermocouple for a blast furnace according to any one of (1) to (4) above how to use. (6) Containing 15% by mass or more of Ni and Cr, respectively,
Furthermore, a sheath thermocouple for a blast furnace, comprising a protective tube containing one or more kinds of Mo and W in a total amount of 3% by mass or more and the balance being Fe and inevitable impurities. (7) The sheath thermocouple for blast furnace according to (6) above, which further contains Ta in an amount of 1% by mass or more. (8) Containing 15% by mass or more of Ni and Cr, respectively,
A sheath thermocouple for a blast furnace, further comprising a protective tube containing Co in an amount of 10% by mass or more and the balance being Fe and inevitable impurities. (9) The sheath thermocouple for blast furnace according to (8) above, further containing one or more kinds of Si and Al in a total amount of 1 mass% or more. (10) A sheath thermocouple for a blast furnace, which comprises a protective tube material for a sheath thermocouple for a blast furnace according to any one of (6) to (9) to form a multiple protective tube.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram of a sheath thermocouple showing the application site of the protective tube material of the present invention. here,
1: Sheath thermocouple, 2: Protective tube, 3: Thermocouple element, 4:
Insulator, 5: insulator in sleeve, 6: sleeve and 7: compensating lead.

The material of the present invention is used for the protective tube 2, but the protective tube used in the low temperature part of the furnace bottom (temperature: less than 200 ° C.) is
When a material containing one or more kinds of Mo and W in a total amount of 3% or more in a Ni-Cr base alloy or a material containing 1% or more of Ta is used, the corrosion resistance to acid dew point corrosion is improved. From the bottom of the furnace to the high temperature (temperature: 200
Protective tube to be buried so that it extends over ℃) is Ni-C
A material containing one or more kinds of Mo and W in a total amount of 3% or more in an r-based alloy, or a material containing 1% or more of Ta in addition, and a material containing 10% or more of Co in a Ni-Cr based alloy, Alternatively, when a multi-layered tube in which a material containing one or more kinds of Si and Al in a total amount of 1% or more is layered is used, the corrosion resistance against acid dew point corrosion and the corrosion resistance against high temperature sulfidation corrosion are improved.

The action of each element constituting the protective tube material of the sheath thermocouple for a blast furnace of the present invention and the preferable range of the content are described below. (1) Cr: Cr is an alloying element that tends to uniformly form a Cr ₂ O ₃ coating on the alloy surface and enhances the corrosion resistance of the alloy against carburization by high-temperature furnace gas and high temperature sulfide corrosion.
Further, Cr is an important constituent element of the passivation film and contributes to the improvement of the corrosion resistance of the alloy under the acid dew point corrosion environment. The effect of enhancing the durability against carburization and high temperature sulfidation corrosion by blast furnace gas is 15% or more, so the lower limit is 1
It was set to 5%. The upper limit is not particularly limited, but is preferably 30%. The reason is that the effect is saturated even if Cr exceeds 30%. The preferred range is 18 to 30%.

(2) Ni: Ni has poor reactivity with carbon atoms at high temperatures and has an action of reducing the diffusion rate of carbon atoms in the alloy. Therefore, it is an alloying element that improves the corrosion resistance of the alloy in a carburizing environment. Is. Carburization resistance by blast furnace gas,
Since the effect of enhancing the corrosion resistance against acid dew point corrosion is seen at 15% or more, the lower limit was made 15%. The upper limit is 70%
Is preferred. The reason is that it does not exceed 70% in consideration of the other element concentrations necessary for the present invention. More preferably, it is 40 to 70%.

(3) Mo, W: Mo is an important alloying element that constitutes a passivation film in an acid dew point corrosive environment, and is an element that contributes to the improvement of the corrosion resistance of the alloy in an acid dew point corrosive environment. Mo is an alloying element whose sulfide contributes to corrosion resistance and has an effect of suppressing high-temperature sulfide corrosion. W is
It is an alloying element that has the same effect as Mo.

That is, both Mo and W are alloying elements necessary for enhancing the high temperature sulfide corrosion resistance by blast furnace gas and the corrosion resistance against acid dew point corrosion, and the effect is Mo,
The lower limit was set to 3% because it is found in a total of 3% or more of any one or more of W. The upper limit is preferably 30%. The reason is that if it exceeds 30%, the workability becomes poor and it becomes difficult to manufacture a sheath thermocouple for a blast furnace. A more preferable range is 10 to 20%.

(4) Ta: If Ta is contained by 1% or more,
Corrosion resistance to acid dew point corrosion is further improved. The upper limit is 10
% Is preferable. The reason is that if it is added in a large amount, workability deteriorates, and if it exceeds 10%, it becomes difficult to manufacture a sheath thermocouple for a blast furnace. A more preferable range is 1 to 5%.

(5) Co: Co is an alloying element which has the effect of enhancing the corrosion resistance of alloys at high temperature sulfide corrosion because it forms a protective film of CoS which has excellent corrosion resistance in high temperature sulfide corrosion environments. The effect sharply increases at 10% or more, and the effect does not change so much even if it exceeds 30%. The preferred range is 10-30
%.

(6) Si, Al: Si and Al are all
Al with blast furnace gas₂O₃, SiO ₂Protective acid such as
In order to form a chemical film, the high temperature sulfidation corrosion resistance of the alloy is
It is an alloying element that has the effect of enhancing The effect is Si
And when one or more kinds of Al are contained in a total amount of 1% or more,
Therefore, the lower limit was set to 1% or more. The upper limit is 3%
Is preferred. The reason is that even if it exceeds 3%,
This is because the high temperature sulfidation corrosion performance is saturated.

(7) The unavoidable impurities include about 0.5% of Mn and Si mixed during deoxidation refining. The general basic structure of the sheath thermocouple is as shown in FIG. 1, but each part will be described below.

Thermocouple element: As the thermocouple element, K type, N type or the like is used, and N type which is relatively small in deterioration of temperature measurement accuracy is preferable. Insulator: As the insulator, MgO, Al ₂ O ₃ or the like is used, and MgO, which is inexpensive, is preferable in terms of cost.

Insulator in sleeve: As the insulator in the sleeve, epoxy resin, glass or the like is used, but epoxy resin is preferable from the viewpoint of ease of construction. Compensation lead wire: As a compensation lead wire, a K-type thermocouple made of a combination of copper and a copper-nickel alloy, a combination of iron and a copper-nickel alloy, or an N-type made of two kinds of copper-nickel alloys. Thermocouples are used, and each compensating wire is usually vinyl coated.

Sleeve: The material of the sleeve is SU
S304, SUS310S, SUS316, etc. are used. It is empirically known that when the outer diameter of the protective tube exceeds 12 mm, the hot metal in the blast furnace flows out through the thermocouple, so the outer diameter of the protective tube is preferably 12 mm or less.
On the other hand, if the outer diameter of the protective tube is less than 6 mm, the heat resistance of the thermocouple may deteriorate. Therefore, the outer diameter of the protective tube is preferably 6 to 12 mm.

The thermocouple is classified into a ground type and a non-ground type. The grounding type thermocouple is one in which the tip of the thermocouple is electrically connected to the protective tube, and is characterized by excellent responsiveness. On the other hand, the non-grounded thermocouple is one in which the thermocouple and the protective tube are electrically insulated from each other, and is characterized by excellent noise resistance. Therefore, when a thermocouple is used in a blast furnace, noise resistance superior to high response is often required, and a non-grounded thermocouple is desirable.

[0025]

EXAMPLES As a conventional example, an example of the present invention and a comparative example, an evaluation test was conducted using four kinds of commercially available materials and 14 kinds of newly melted materials.

The evaluation items are hydrochloric acid resistance, sulfuric acid resistance, high temperature sulfidation corrosion resistance and carburization resistance. The manufacturing method of the test material used for these evaluation tests is as follows. (1) 50 test materials with specified chemical composition in a vacuum induction heating furnace
kg was melted and cast into an ingot.

(2) After cutting and removing the outer surface of this ingot, it is heated at 1200 ° C. for 5 hours and hot forged in the temperature range of 1200 ° C. to 1050 ° C., and the size of the forged test material is 20 mm. , Width 100mm, length about 3m
And

(3) The forged material was heated at 1200 ° C. for 2 hours to be softened and annealed, and then cold-rolled to a thickness of 14
mm cold rolled sheet. The solution heat treatment after cold rolling is 11
After heating and holding at 80 ° C. for 1 hour, water cooling was performed.

(4) Test Material No. 1: Inconel 600,
Test Material No. 2: SUS310S, Test Material No. 3: SS4
00 (carbon steel), test material No. 4: SUS304 is a commercially available hot-rolled sheet, and the thickness is 2 from the center of the rolled sheet of various test materials.
mm, width 10 mm, length 25 mm strip test piece is cut out and evaluated for hydrochloric acid resistance, sulfuric acid resistance and high temperature sulfidation corrosion resistance. Carburization resistance test is 4 mm thick, 20 mm wide and 30 mm long strip. The test piece was cut out and subjected to an evaluation test.

The evaluation test conditions are as follows. (A) Hydrochloric acid resistance test: The test piece was immersed in a 5% hydrochloric acid solution (temperature: 60 ° C.) for 5 hours, and the corrosion weight loss was measured.

(B) Sulfuric acid resistance test: The test piece was immersed in a 70% sulfuric acid solution (temperature 100 ° C.) for 5 hours to measure the corrosion weight loss. (C) High temperature sulfide corrosion test: 1.5 simulating blast furnace gas
_{% H 2 S-20% CO} -20% CO 2 -1.6% H 2 O-
The test piece after the test was chemically descaled by heating in the remaining 56.9% N ₂ gas stream at 500 ° C. for 100 hours, and the weight loss at that time was measured.

(D) Carburization resistance test: 90% CO-10%
Heat treatment was performed at 550 ° C. for 100 hours while passing H ₂ gas, and after the treatment, the test piece surface was cut to a depth of about 0.5 mm, and the C content of the cut was determined by chemical analysis.
The difference from the content was determined as the amount of C increase, and the value was used to evaluate the carburization resistance.

Table 1 shows the chemical composition (% by mass) of the materials used in the test. Table 2 shows the acid dew point corrosion test results. Table 3
The high temperature sulfidation corrosion test results are shown in.

Table 4 shows the carburizing test results.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

The targets of each test are as follows. (A) Hydrochloric acid resistance: Corrosion weight loss of 10 mg / cm ² or less (b) Sulfuric acid resistance: Corrosion weight loss of 100 mg / cm ² or less (c) High temperature sulfidation corrosion resistance: Corrosion weight loss of 50 mg / cm ²
(D) Carburization resistance: C content is 0.5% or less. As shown in Tables 1 to 4, test material numbers 10 to 14 of the present invention.
Met the goals of hydrochloric acid resistance and sulfuric acid resistance, and also achieved high temperature sulfidation corrosion resistance and carburization resistance.

In particular, the test material No. 14 containing 1.81% Ta had further improved hydrochloric acid resistance and sulfuric acid resistance. The test materials Nos. 15 to 18 achieved the target though the hydrochloric acid resistance and the sulfuric acid resistance were lower than those of the test materials Nos. 10 to 14, and the high temperature sulfidation resistance was higher than that of the test materials Nos. 10 to 14. Improved. In particular, Si is 2.76 each.
%, 1.08% in test material numbers 16, 17 and A
Test Material No. 18 containing 1.1% of 1 further improved the high temperature sulfidation corrosion resistance.

The test materials Nos. 10 to 18 all had good carburization resistance and achieved the target.

[0042]

EFFECTS OF THE INVENTION The thermocouple of the present invention, the protective tube material thereof, and the method of using the material enable stable temperature monitoring near the bottom of the blast furnace for a long period of time.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a sheath thermocouple showing an application place of a protective tube material of the present invention.

[Explanation of symbols]

1: Sheath thermocouple, 2: Protective tube, 3: Thermocouple wire, 4: insulator, 5: resin, 6: sleeve, 7: Compensation lead wire.

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[Procedure amendment]

[Submission date] August 20, 2001 (2001.8.2)
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

[0037]

[Table 3]

Continued front page    (72) Inventor Nobuo Otsuka             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. (72) Inventor ▲ Taka ▼ Kozo Ta             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. (72) Inventor Tamane Abe             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. F term (reference) 2F056 BP01 BP03 KA03 KC06

Claims (10)

[Claims] 1. Ni and Cr are contained in an amount of 15% by mass or more, respectively, and one or more kinds of Mo and W are added in a total amount of 3 or less.
A protective tube material for a sheath thermocouple for a blast furnace, characterized by containing at least mass% and the balance being Fe and unavoidable impurities. 2. The protective tube material for a sheath thermocouple for a blast furnace according to claim 1, which further contains Ta in an amount of 1% by mass or more. 3. Ni and Cr are contained in an amount of 15% by mass or more, Co is further contained in an amount of 10% by mass or more, and the balance is F.
A protective tube material for a sheath thermocouple for a blast furnace, characterized by being e and unavoidable impurities. 4. The protective tube material for a sheath thermocouple for a blast furnace according to claim 3, further containing one or more kinds of Si and Al in a total amount of 1% by mass or more. 5. A protective tube material for a sheath thermocouple for a blast furnace, wherein the protective tube material for a sheath thermocouple for a blast furnace according to any one of claims 1 to 4 is used as a multiple protective tube. how to use. 6. Ni and Cr are contained in an amount of 15% by mass or more, respectively, and one or more kinds of Mo and W are added in a total amount of 3 or less.
A sheath thermocouple for a blast furnace, comprising a protective tube made of a material containing at least mass% and the balance being Fe and inevitable impurities. 7. The sheath thermocouple for a blast furnace according to claim 6, which further contains Ta in an amount of 1% by mass or more. 8. Ni and Cr are contained in an amount of 15% by mass or more, Co is further contained in an amount of 10% by mass or more, and the balance is F.
A sheath thermocouple for a blast furnace, comprising a protective tube made of e and a material that is an unavoidable impurity. 9. The sheath thermocouple for a blast furnace according to claim 8, further comprising one or more kinds of Si and Al in a total amount of 1% by mass or more. 10. A sheath thermocouple for a blast furnace, wherein the sheath thermocouple for a blast furnace according to any one of claims 6 to 9 is made into a multiple protective tube by using a material for the protective tube of the sheath thermocouple for a blast furnace.