KR20080087548A - Low alloy-steel tube for boiler and manufactyring method thereof - Google Patents

Low alloy-steel tube for boiler and manufactyring method thereof Download PDF

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Publication number
KR20080087548A
KR20080087548A KR1020070029957A KR20070029957A KR20080087548A KR 20080087548 A KR20080087548 A KR 20080087548A KR 1020070029957 A KR1020070029957 A KR 1020070029957A KR 20070029957 A KR20070029957 A KR 20070029957A KR 20080087548 A KR20080087548 A KR 20080087548A
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South Korea
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steel pipe
heat
welding
boiler
temperature
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KR1020070029957A
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Korean (ko)
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김윤규
전동현
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현대하이스코 주식회사
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Priority to KR1020070029957A priority Critical patent/KR20080087548A/en
Publication of KR20080087548A publication Critical patent/KR20080087548A/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

In the present invention, by using a material whose quality is strictly controlled, it is possible to obtain stable quality by weight wt%, C: 0.05 to 0.15%, Mn: 0.3 to 0.61%, P: 0.03% or less, S: 0.02% or less, Si: 0.5 The steel pipe is prepared by welding the hot rolled steel sheet with the basic composition of% or less, Mo: 0.40 ~ 0.70%, Cr: 0.8 ~ 1.25% and strictly controlled internal quality in an oxidation-free atmosphere ERW (Electric Resistance Welding) welding. The present invention relates to a heat-resistant alloy steel pipe for a thermal power plant boiler, in which the bright constant temperature normalizing is strictly controlled within a certain temperature range.

Description

Low alloy-steel tube for boiler and manufactyring method

Schematic diagram of 1st thermal power plant boiler

2 is a process chart of manufacturing a heat-resistant alloy steel pipe as an embodiment

3 is a schematic view of an oxygen-free atmosphere welding apparatus as an embodiment

4 is a furnace temperature rising scheme and heat treatment conditions as an embodiment

Figure 5 is a microscopic histogram of before and after heat treatment as an embodiment

The present invention relates to a heat-resistant alloy steel pipe used as a heat-resistant material of the boiler, in particular to improve the efficiency of the thermal power plant boiler, to cope with energy savings and environmental problems, and to increase the high temperature and pressure of steam during thermal power generation and boiler It is related to the heat-resistant alloy steel pipe which requires weldability, high temperature strength, high temperature corrosion resistance, workability (processability), dimensional accuracy, and inspection conditions as core heat-resistant material steel pipe with increasing device role.

Heat-resistant alloy steel pipe is a heat-resistant alloy steel pipe used in water-cooled wall pipes and coal mills of the heat exchanger of the boiler to generate a heat transfer medium of the steam power plant steam turbine as shown in FIG.

Furnace is the place where the fuel and air that is supplied are burned to convert chemical energy of fossil fuel into thermal energy. The water-cooled wall is made in the form of a panel by welding a tube (pipe) to allow water to pass through all four sides of the furnace, absorbing strong heat in the furnace, heating and evaporating water, blocking flame and overheating. The furnace is protected by cooling the walls. In addition, it is a device that preheats the water supply into the boiler by using the remaining heat of the combustion gas discharged from the boiler. The lower the temperature of the exhaust gas, the more fuel is saved, and the thermal stress of the drum is reduced as the water supply temperature is increased. have.

The steel pipe according to the present invention used in the water cooling wall and the cutting machine is a low alloy steel tube of a typical 1% Cr, 0.5% Mo addition type and is manufactured through electric resistance welding (ERW), and the manufacturing process thereof is shown in FIG. 2. In this manufacturing process, the present invention adopts an oxygen-free atmosphere welding method in order to prevent side effects and deterioration in the conventional manufacturing process resulting from the formation of Cr 2 O 3 oxide inclusions described later.

Water-cooled wall steel pipe material is required for weldability, plastic workability, and the like, and site material subjected to heat load by high temperature flame requires oxidation resistance and high temperature corrosion resistance. Recently, there has been a tendency to use coated or spray coated tubes to increase the corrosion resistance of the outer surface of the tube. The coating is generally subjected to chromizing, and the thermal spraying material uses a material having high corrosion resistance and wear resistance.

Water-cooled wall steel pipe specifications vary depending on boiler type, boiler maker, boiler capacity, etc., but generally used materials are carbon steel and low alloy system.

The temperature distribution in the middle of the wall thickness of the water-cooled wall outlet is the thermal insulation of the iron oxide layer (Fe 3 O 4 ) which is provided from the water / steam in the pipe after 100,000 hours of use at 250 bar / 540 ° C steam conditions. Increases up to 455 ° C by effect. Low-alloy steel pipes are used that do not require preheating and postheating during welding in these temperature ranges. Creep characteristics need not be taken into account because the use of lower-grade steel pipe materials is lower than water-cooled wall steel pipe materials.

Since there is a problem in the supply of steel pipe material and the boiler manufacturing cost by using expensive non-bare steel pipe due to the resistance to heat, that is, heat resistance, attempts and studies have been made to solve this problem. In addition, the general carbon steel material using the conventional method was almost impossible to obtain the heat resistance strength of the steel pipe for 500 ℃ class boiler.

Therefore, in order to replace the conventional steel materials, which are expensive special metal materials, with general carbon steel materials, the present invention is characterized by 500 ° C thermal power plant boilers having excellent heat resistance and high temperature strength, among others, by specifying the composition of components, welding steel pipes, and heat treatment. The purpose is to provide heat-resistant alloy steel pipes.

In order to achieve the above object, in order to secure a stable quality, in particular, using a material whose quality is strictly controlled, the weight wt%, C: 0.05 ~ 0.15%, Mn: 0.3 ~ 0.61%, P: 0.03% or less , S: 0.02% or less, Si: 0.5% or less, Mo: 0.40 ~ 0.70%, Cr: 0.8 ~ 1.25% The hot rolled steel plate with strictly internal quality and non-oxidizing atmosphere electric resistance welding After welding steel tube through Welding (ERW), it is characterized by heat-resistant alloy steel pipe for thermal power plant boiler, which is processed by bright constant temperature normalizing.

The composition of the composition for strict management of the chemical composition of the present invention is described below.

C: 0.05 to 0.15% of the steel is an element that increases oxidation resistance and high temperature strength, and is a common carbon steel component.

The Si serves as a strong deoxidizer and is preferably limited to 0.5% or less for spherical separation of oxide-based inclusions contained in the material to ensure high cleanliness and oxidation resistance.

Mn is an element that increases strength and toughness of steel and stabilizes austenite. However, when added below 0.3%, the effect of Mn addition is less likely to occur, and excessive addition of Mn above 0.61% increases the amount of non-metallic inclusions, increases segregation, and does not maintain fast cooling rate after hot rolling. Since the light layer shows a tendency to lower the elongation in the thickness direction, the Mn content is preferably strictly limited to 0.3 to 0.61%.

The P causes softening of the material due to the formation of central segregation during the production of hot rolled steel sheet, and embrittles the stressed weave. In addition, S is preferably managed low because the compound of MnS reacted with Mn lowers the workability and weldability of steel.

The Mo content of 0.40 to 0.70% is designed to ensure the effect of the high temperature strength of the present invention by fixing a potential when subjected to tensile stress of a steel pipe at a high temperature, which generates a large number of precipitates in ferrite. In this case, it is effective to precipitate and strengthen the coagulation of carbonitrides.However, when added below 0.04%, this effect does not appear properly.When added above 0.70%, the yield strength is increased to impair processability. It is preferable to limit it to -0.70%, but especially 0.44-0.65% which is especially stable range. This is because the effect on the workability is very sensitive to the addition of Mo.

The Cr is particularly one of the most important components in the present invention to form a form of Cr nitride to suppress grain growth to refine the tissue to improve oxidation resistance. In other words, Cr has the effect of preventing the corrosion caused by the oxide film by forming Cr oxide, and less than 0.8% has an oxidation corrosion effect, but the grain growth inhibition effect is insignificant or unstable and withstands high temperature when the content exceeds 1.25% It is preferable to limit the Cr addition to 0.8-1.25% because the heat resistance and creep strength improvement effect that do not appear properly.

The product of the present invention having the above composition may remain in the weld such as impurities and Cr 2 O 3 when 1Cr-0.5Mo alloy steel is welded in the air. This is because Cr 2 O 3 is easier to form than FeO and has a higher melting point, so it does not melt well due to electric resistance welding (ERW). Make a problem.

When the Cr 2 O 3 oxide inclusion remains in the weld, a weld defect called a penetrator is created. Therefore, in order to eliminate such welding defects, it is necessary to secure an oxygen-free atmosphere welding condition.

FIG. 3 provides 100% argon gas (Ar-gas) to supply a non-oxidizing atmosphere to the welding apparatus as shown in the schematic view of the non-oxidizing atmosphere welding apparatus. It is a feature of the present invention to obtain weld weld integrity using an anoxic atmosphere welding condition method to eliminate weld defects.

Example

The products according to the present invention are shown in Tables 1 and 2 by taking the average value of the specimens divided into a plurality of specimen groups 1 and 2, as shown in the following examples.

In addition, the steel pipe prepared by the above composition was heat treated by constant temperature normalizing (Normalizing) under the conditions as shown in FIG. 4, the constant temperature holding time during the heat treatment was 13.5 minutes, and the temperature was measured and managed for each zone in the heat treatment furnace. It was.

Here, the comparative material is a non-barrier steel pipe made of a conventional expensive special heat-resistant alloy material, the present invention is a general-purpose welded steel pipe with a strictly controlled chemical composition range and strictly heat treatment, and the heat treatment results are respectively shown in the microscope structure of FIG. The photo is shown.

FIG. 4 is a diagram of the furnace temperature rising method according to the embodiment of the present invention, which shows the normalizing temperature in each zone of the furnace and the temperature tolerance to be managed as shown in the work flow chart. Here, the region division in the heat treatment furnace is a section that can set the temperature in the furnace usually carried out in this field, and the steel pipe is charged by the roll of the conveying table and heat treated while passing through each region in the furnace. 4 is a heat treatment condition showing the temperature increase temperature by time. Since the crystal structure changes rapidly with temperature, the present invention focuses on strict management of the temperature tolerance at 905 ° C to 915 ° C and constant temperature normalizing temperature to obtain uniform grains. At the heat treatment temperature of less than 905 ℃, as shown in Table 2, the physical properties after heat treatment are relatively good at 900 ℃ or more, but the structure of the welded and the base metal parts are insufficient, so that the structure becomes weak due to the generation of needle-like structure, which adversely affects the workability. Confirmed. On the other hand, at the heat treatment temperature exceeding 915 ° C decarburization of the surface layer occurs, which causes the surface layer strength deterioration and crystal grains overgrown, resulting in non-uniformity of crystal grains, particularly stretch strain defects on the surface during bending. Since the grains are severely different depending on the heat treatment temperature control, the uniformity of the grains can be increased by strictly managing the range.

The heat treatment results are shown in the microscopic tissue photograph of FIG. 5, respectively. Compared with before heat treatment, the crystal grains appearing in the stressed fibers after the heat treatment were composed of payrat and pearlite, and the grains were uniform grains having a grain size of 8, and the grains were more uniform and clearly developed.

The material of the present invention, which shows the chemical composition of Table 1 and the mechanical properties of Table 2, was fabricated into a steel pipe manufactured by applying the ERW welding method in an oxygen-free atmosphere. In order to secure the welding condition for the non-oxidizing atmosphere of the ERW welding part, argon (Ar) gas, which is inert gas, is injected into the non-oxidizing part welding machine, and the oxygen concentration is measured by the oxygen measuring device. I worked on the tube.

After the steel pipe is welded to ensure the integrity of the welded part, it is charged into a bright normalizing heat treatment furnace and DX gas (GAS), which is a non-oxidizing atmosphere gas, is used in the combustion process generated by injecting a certain amount of atmospheric air into the liquefied natural gas (LNG). During the bright normalizing heat treatment, it acts as an atmosphere gas and undergoes the final bright normalizing treatment after the heat cycle and the temperature raising step (FIG. 4) for each region, and then the non-lumped test (ECT + UT), which is the final inspection step of the product. (Flange Test), Impact Test (Crush Test), Flattening Test (Flattening Test), and High Temperature Strength Test at 510 ° C, steel pipes with a strength of 440 MPa or more could be developed.

Table 1. Chemical Composition

division Chemical composition (wt,%) C Si Mn P S Sol-Al Cr Mo Comparative material 0.07 0.08 0.5 0.017 0.010 0.04 Tr Tr Invention 0.0697 0.211 0.49 0.013 0.003 0.014 0.96 0.53

Table 2. Mechanical Properties after Bright Constant Temperature Normalizing

   division  Before heat treatment  After heat treatment (bright constant temperature normalizing) High temperature strength 510 ℃ TS (MPa) YS (MPa) EL (%) TS (MPa) YS (MPa) EL (%) TS (MPa) 900 692 661 19.2 480 263 30.2 387 901 692 661 19.2 477 260 31.0 394 902 692 661 19.2 474 258 31.6 402 903 692 661 19.2 470 256 32.2 410 904 692 661 19.2 468 253 33.0 417 905 692 661 19.2 464 251 33.6 422 906 692 661 19.2 460 250 34.4 429 907 692 661 19.2 458 248 35.3 435 908 692 661 19.2 456 246 36.1 442 909 692 661 19.2 455 244 36.6 449 910 692 661 19.2 455 243 37.0 456 911 692 661 19.2 454 241 37.2 447 912 692 661 19.2 452 239 37.5 440 913 692 661 19.2 449 236 37.8 430 914 692 661 19.2 447 234 38.0 421 915 692 661 19.2 444 233 38.3 409 916 (Decarburization)  692  661  19.2  439  230  38.6  393 917 (Decarburization)  692  661  19.2  435  228  38.9  384 918 (Decarburization)  692  661  19.2  431  226  39.1  378 919 (Decarburization)  692  661  19.2  427  224  39.3  371 920 (Decarburization)  692  661  19.2  423  221  39.5  366

DX gas was added to prevent the normalization of the steel pipe in the furnace.

Since the strength after heat treatment affects bending molding (improving curvature workability), it can be seen that the physical properties before and after heat treatment of the comparative material with little bending molding do not change significantly.

When maintaining the strength before heat treatment of the present invention material problems occur, heat treatment (bright constant temperature normalizing), it can be seen that the physical properties are represented by the appropriate level by the heat treatment. As a result, the present invention also showed that the high temperature strength was improved by about 2 times as shown in Table 2 at 510 ° C (the use temperature of the present invention is a 500 ° C thermal power plant boiler) compared to the comparative material.

According to the present invention, it is possible to provide a heat-resistant alloy steel pipe that can be used in high temperature and high pressure environment by using a material having a component range of general purpose steel. By avoiding heat-resistant steel pipe material with difficult material selection, strictly managing carbon steel pipe composition and 1Cr-0.5Mo alloy composition, and strictly managing non-oxidizing atmosphere welding condition and heat treatment condition, as described above, It is now possible to develop general-purpose thermal power plant water-cooled walls and heat-resistant alloy steel pipes for coal mills.

Claims (1)

In order to manufacture a heat-resistant alloy steel pipe suitable for heat-resistant alloy steel pipe for thermal power plants, by weight wt%, C: 0.05 ~ 0.15%, Mn: 0.3 ~ 0.61%, P: 0.03% or less, S: 0.02% or less, Si: 0.5 905 ℃ ~ 915 ℃ Brightness constant temperature after hot-rolled steel sheet strictly controlled with Mo: 0.44 ~ 0.65%, Cr: 0.8 ~ 1.25% as a basic component through non-oxidizing atmosphere electric resistance welding (ERW) A heat-resistant alloy steel pipe for a thermal power plant boiler, which is manufactured by strictly managing the temperature tolerance at the drying temperature.
KR1020070029957A 2007-03-27 2007-03-27 Low alloy-steel tube for boiler and manufactyring method thereof KR20080087548A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018011862A1 (en) * 2016-07-11 2018-01-18 新日鐵住金株式会社 Electric-resistance-welded steel pipe for boiler having excellent stress corrosion cracking resistance, and method for manufacturing same
CN107805757A (en) * 2016-09-09 2018-03-16 中国石化工程建设有限公司 A kind of low alloy steel and preparation method thereof
CN110343823A (en) * 2019-07-31 2019-10-18 北京机电研究所有限公司 A kind of isothermal normalizing heat treatment process
JP2021011611A (en) * 2019-07-08 2021-02-04 株式会社東芝 Steel, turbine rotor, and steam turbine

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018011862A1 (en) * 2016-07-11 2018-01-18 新日鐵住金株式会社 Electric-resistance-welded steel pipe for boiler having excellent stress corrosion cracking resistance, and method for manufacturing same
JPWO2018011862A1 (en) * 2016-07-11 2018-11-01 新日鐵住金株式会社 ERW steel pipe for boiler excellent in stress corrosion cracking resistance and its manufacturing method
CN109477173A (en) * 2016-07-11 2019-03-15 新日铁住金株式会社 Anticorrosion stress-resistant anti-thread breakage excellent boiler electric-resistance-welded steel pipe and its manufacturing method
CN107805757A (en) * 2016-09-09 2018-03-16 中国石化工程建设有限公司 A kind of low alloy steel and preparation method thereof
JP2021011611A (en) * 2019-07-08 2021-02-04 株式会社東芝 Steel, turbine rotor, and steam turbine
CN110343823A (en) * 2019-07-31 2019-10-18 北京机电研究所有限公司 A kind of isothermal normalizing heat treatment process
CN110343823B (en) * 2019-07-31 2021-04-16 北京机电研究所有限公司 Isothermal normalizing heat treatment process

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