Specifications: diameter: 320 to 127 mm thickness: 0.4 to 12.7 mm Length: 6 m above, and, in accordance with customer demand, supply and other specifications of steel pipe

Thesis of heat resistant steel pipe


Heat-resistant steel pipe

Braden Shield, Adrian McKinney ※, Reese O'Connor (Key Thesis of heat resistant steel pipe, Ministry of Education,Williams College, Williams NO. 79200325) 

[1] [2] under high temperature oxidation resistance and high temperature strength the Lord enough, and good heat resistance of steel called a Heat steel pipe. The heat-resistant steel including steel anti-oxidation and thermal strength steel two types. The antioxidant Steel referred to can not afford leather steel. Thermal strength steel has good oxidation resistance at high temperatures and has high temperature strength of steel. The Heat steel pipe is mainly used for long-term use of parts at high temperatures
heat-resisting steels
Alloy steel with high strength and excellent chemical stability at high temperatures. It includes antioxidant steel (or high temperature can not afford leather steel) and thermal strength steel categories. The antioxidant Steel general requirements of good chemical stability, but to bear the load is low. Hot-strength steel requires high temperature strength and oxidation resistance. Heat steel pipe is commonly used in parts of the work at high temperatures in the manufacture of boilers, steam turbines, power machinery, industrial furnace and aviation, petroleum and chemical industrial sectors. These components in addition to the requirements of high temperature strength and high temperature oxidation corrosion, according to different purposes require sufficient toughness, good machinability and weldability, and a certain degree of organizational stability. China since 1952, the production of heat-resistant steel. Later developed a new type of low-alloy hot-strength steel, so that the operating temperature of the pearlite hot-strength steel to 600 to 620 ℃; In addition, the development of some new low-chromium-nickel antioxidant steel.
Heat-resistant steel and stainless steel acid in the range of overlap each other, some stainless steel combines the characteristics of heat-resistant steel, and can use as a stainless steel acid can also be used as a heat-resistant steel.
Role of alloying elements
Chromium, aluminum, silicon, elements of these ferrite formation at high temperatures can induce the metal surface to generate a dense oxide film to prevent the continued oxidation, the main elements to improve the steel's resistance to oxidation and corrosion resistance to high temperature gas. Serious deterioration of the aluminum and silicon content is too high room temperature ductility and thermoplastic. Chromium can significantly improve the recrystallization temperature of the low-alloy steel, the content of 2%, the strengthening effect.
Nickel, manganese and the formation and stability of the austenite. Nickel austenitic steel can improve the high temperature strength and improve resistance to carburization. Manganese may be able to nickel formation of austenite, but the damage the oxidation resistance of the Heat steel pipe.
Vanadium, titanium, niobium is a strong carbide forming elements to form a fine dispersion of carbides and improve high temperature strength of steel. The combination of titanium, niobium and carbon can also prevent the austenitic steels to intergranular corrosion in high temperatures or after welding.
Carbon, nitrogen expansion and stability of austenite, thereby improving the high temperature strength of the Heat steel pipe. Steel containing chromium, manganese more significantly improve the solubility of nitrogen, and can use the nitrogen alloying in lieu of the more expensive nickel.
Boron, rare earth are heat-resistant steel pipe in the trace elements. Boron dissolved in solid solution manipulation crystal lattice distortion of boron on the grain boundaries can prevent the element diffusion and grain boundary migration, thereby improving the high temperature strength of steel; rare earth elements can significantly improve the oxidation resistance of the steel to improve the thermoplastic.
Class heat-resistant steel according to the organization can be divided into four categories:
Pearlite steel alloy elements chromium, molybdenum, total not more than 5%. Their organization in addition to the pearlite, ferrite in vitro, as well as bainite. Such steel in the 500 ~ 600 ℃ high temperature strength and process performance, lower prices, are widely used in the production of below 600 ℃ heat-resistant components. Such as boiler tube, turbine impeller, rotor, fasteners and pressure vessels, piping, etc. Typical steel: 16Mo, 15CrMo, 12Cr1MoV, 12Cr2MoWVTiB, 10Cr2Mo1, 25Cr2Mo1V, 20Cr3MoWV and so on.
Martensitic steels containing chromium content is generally 7 to 13 percent below 650 ℃ high temperature strength, oxidation resistance and corrosion resistance to water vapor, but the poor weldability. Containing about 12% of the chromium 1Cr13 2Cr13, as well as steel developed on this basis, such as 1Cr11MoV, 1Cr12WMoV, 2Cr12WMoNbVB, etc., usually used to make turbine blades, wheel, shaft, fasteners. In addition, as the manufacture of internal combustion engine exhaust valve 4Cr9Si2, 4Cr10Si2Mo, such as a martensitic heat-resistant steel.
Ferritic steels containing more chromium, aluminum, silicon and other elements to form a single-phase ferritic structure, the ability to have good resistance to oxidation and high temperature gas corrosion, but the low temperature strength, room temperature brittle, welding is poor. 1Cr13SiAl, 1Cr25Si2. Generally used to produce a lower load bearing and high temperature oxidation resistance components.
Austenitic steels contain more nickel, manganese, nitrogen austenite forming elements, more than 600 ℃, high temperature strength and organizational stability, and good weldability. Usually used as a strong material in the heat above 600 ℃. Typical steels 1Cr18Ni9Ti, 1Cr23Ni13, 1Cr25Ni20Si2, 2Cr20Mn9Ni2Si2N, 4Cr14Ni14W2Mo.
Production process
Smelting Heat steel pipe is generally in the electric arc furnace or induction furnace melting. Quality requirements, often using high vacuum refining furnace refining process.
Casting some high-alloy heat-resistant steel processing difficult deformation of the casting is not only cost-effective than the rolled and casting lasting strength. Occupy a large proportion of heat-resistant cast steel in the Heat steel pipe. Apart from using sand casting, casting methods, but also with a precision casting process to obtain a smooth surface, precise size of the product. The high-temperature furnace tube of synthetic ammonia and ethylene cracking often centrifugal casting method.
Pearlite hot-strength steel for heat treatment is usually used after normalizing or quenching and tempering; martensitic heat-resistant steel with quenching and tempering treatment in order to stabilize the organization, good mechanical properties and high temperature strength.
Ferritic steel can be heat strengthened. To eliminate the internal stress caused by the machining and welding, due to cold plastic deformation and annealing at 650 ~ 830 ℃, the rapid cooling after annealing, in order to quickly after the brittle temperature range of 475 ℃.
Austenite antioxidant steel most of the high-temperature solution heat treatment, to get a good cold deformation. Austenitic heat-strength steel using high temperature solution treatment, and above the use temperature of 60 ~ 100 ℃ under the conditions of the aging treatment, so that the organizational stability of simultaneous deposition of the second phase, in order to strengthen the matrix. The heat-resistant cast steel is mostly cast, depending on the type of Heat steel pipe using the appropriate heat treatment.
[Edit this paragraph] the Heat steel pipe welding process
A boiler and pressure vessel steel performance requirements
Working conditions, divided into two categories:
To components of manufacturing at room temperature and the temperature and pressure plate and steel pipe
 heat exchanger boiler pipe With the characteristics:
1 has a higher room temperature strength
Usually yield limit σs and the ultimate strength of σb for the design basis requires a large σs and the σb good toughness properties
Materials need to have sufficient toughness to prevent brittle fracture, can not be ignored while considering the strength of toughness,
(1) The toughness of the material is usually with the impact toughness of the αk said.
The impact toughness of pressure vessel steel requirements
Impact toughness value of αk (N · m/cm2)
20 ℃ -40 ℃
> = 60> = 35
(2) also need to consider timeliness toughness
Aging steel by cold deformation at room temperature or higher temperatures, the impact toughness change over time. Usually in the 200-300 ° C, impact toughness values ​​were significantly reduced. General requirements for the decreased rate does not exceed 50%.
Container rupture process including the formation of defects at the crack and crack propagation in two phases, corresponding are two ways to prevent fracture method
(1) selection of sufficient toughness of steel to prevent cracks requirements of the above table shown
(2) selection of the higher toughness of the material, in order to be able to prevent cracks crack propagation. (The required temperature than the non-plastic transition temperature NPT certain value, such as component design stress for the yield limit σs half to 17 ℃
3 low notch sensitivity
Manufacturing process, opening and welding will produce local stress concentration, the material has a low notch sensitivity, to prevent cracks
4 good processing performance and welding performance
Due to the welding thermal cycle,
(1) reduce the heat affected zone toughness of the material, plastic
(2) produce a variety of defects in the weld
One (1), (2) cracks
Election materials to be considered
(1) the material of carbon equivalent (to ensure that the material has good weldability)
(2) the appropriate welding materials and welding
(3) The material has good plasticity (carbon and carbon manganese steel δs of not less than 16%, alloy steel, the δs not less than 14%)
(4) low magnification
(5) stratification of the steel, non-metallic inclusions to minimize defects such as objects, holes, loose (to prevent cracks)
Second, the steel pipe used in the manufacture of high temperature and pressure components
1 have sufficient creep strength, rupture strength and durable plastic
Usually lasting strength for the design basis, to ensure safe operation in the conditions of creep
2 has a good high-temperature structure stability
Organizational change in long-term high temperature
3 has good high temperature oxidation resistance
Requirements of materials under high temperature oxidation corrosion rate of less than 0.1mm / a
4 has a good process
Requirements of the cold (cold bending) and weldability
(2) boiler and pressure vessel steel.
An operating temperature below 500 ° C steel
Carbon steel and low alloy structural steel
A ferrite - pearlite structure of steel
Yield strength σs 300-450MPa
16Mn, 15MnV, 15MnVN adding alloying elements, solid solution strengthening, strengthening effect of crystallization
2 low-carbon bainite type steel
Yield strength σs 500-700Mpa
14CrMnMoVB delay austenite decomposition, bainite, increasing the strength
3 martensite quenched and tempered high carbon steel
Yield strength σs for more than 600Mpa
18MnMoNb and 14MnMoNbB normalized and tempered, good low-temperature toughness
Second, the operating temperature above 500 ° C steel
Low-alloy hot-strength steel and austenitic stainless steel
A low-alloy pearlitic hot strength steel
15CrMo and 12Cr1MoV, the crystallization of strengthening, precipitation strengthening
Two low-alloy bainitic heat strong steel
The 12Cr2MoWVTiB and 12Cr3MoVSiTiB features: alloy the number of many small, high temperature strength, oxidation resistance
3 austenitic stainless steel
18-8 chrome-nickel austenitic stainless steel: 1Cr18Ni9Ti and 0Cr18Ni9Ti, high temperature strength, oxidation resistance and high toughness and good processing technology
(3) Carbon Steel Pipe
, Carbon Steel Pipe, the main component of the performance impact of
The impact of a carbon
Carbon increases, the intensity increases, the plastic to reduce deterioration of weldability limitation reduced sensitivity
The impact of the two manganese
Deoxy (FeO) desulfurization, and to improve the hot workability
3 silicon
Deoxidation
4 sulfur
Temper Embrittlement of
5 phosphorus
Cold brittleness
6 oxygen
Reduce the strength, plasticity
7 nitrogen
Improve the strength, hardness, lower plasticity
The impact of the eight hydrogen
Hydrogen embrittlement
Second, carbon steel classification
Chemical Composition: (carbon content is 0.65%), (carbon content of 0.25-0.65%), low carbon steel (carbon content less than 0.25%)
Purposes: ordinary carbon steel, quality carbon structural steel and carbon tool steel
An ordinary carbon structural steel
A steel: mechanical properties of supply (A), steel plate, angle iron, etc.
Quality carbon structural steel
Supply of mechanical properties and chemical composition
The low carbon content: steel, container, screws, nuts
Carbon content: gears, shafts
The high carbon content: springs, wire rope
3-carbon tool steel (T)
High hardness and wear resistance, tool manufacturing, measuring tools, molds
Boilers and pressure vessels commonly used carbon steel pipe
Pressure components is the use of low carbon steel, ductility, toughness, processing and weldability
(1) high-quality carbon structural steel
Seamless steel pipe on the 10th and the 20th
On the 20th carbon steel than 10 gauge steel, double, high strength, yield limit σs and strength limit the σb high 20%, low aging sensitivity, and more on the 20th of steel
(2) for carbon steel pipe
A3g A3R 15g 20g, impact toughness, less metal surface and internal defects
4 ordinary low-alloy structural steel
Low alloy steel is composed of a small amount of Si, Mn, Cu, Ti, V, Nb, P and other alloying elements on the basis of the carbon steel pipes, and its low carbon content, the majority of less than 0.2%. Their organization the majority of remains of F + P Since the accession of a small amount of alloying elements can greatly enhance the strength of steel, and improved the steel's corrosion resistance and low temperature performance.
Low alloy steel can be rolled into various steel products, such as plates, tubes, rods and profiles. It is widely used in the manufacture of ocean going vessels, long-span bridges, high-pressure boiler, large containers, automotive, mining machinery and agricultural machinery and so on.
Large chemical container materials used in 16MnR, raw compared to carbon steel can reduce 1/3. 15MnV manufacturing the spherical tank, save 45% compared with the carbon steel.
Welding
(5) low-alloy hot-strength steel
Crude oil heating, cracking, catalytic devices, common to many of the high temperature of the steel. Cracking tube is required to withstand the high temperature of 650 ~ 800 ℃.
No. 20 steel at 540 ℃ in oxidizing gases, only due to oxidation strength 50MPa. Graphite.
Commonly used anti-oxidation of steel
- Cr13SiAl, Cr25Ti, Cr17Ti, Cr25Ni2
Hot-strength steel
- 12CrMo, Cr5Mo, 1Cr18Ni9Ti, Cr25Ni20
6 stainless acid resistant steel
Is a general term for stainless steel (resistant to the atmosphere) and acid-resistant steel (stainless steel)
Chrome stainless steel - 1Cr13 and more used as a large force of the chemical machinery corrosion-resistant parts such as shafts, piston rods, valves, bolts, float valve
0Cr13, Cr17Ti F organization, there are good plastic
Chrome-nickel stainless steel - 1Cr18Ni9 18-8 stainless steel
High tensile strength and lower yield point, excellent ductility and toughness, weldability and formability of cold-formed, and used to make tanks, towers, reactor, and the most widely used.
7 low-temperature steel
Cryogenic separation, air separation, and low temperature liquefied gas tank.
Average low temperature steel carbon content of 0.08 to 0.18 percent, single-phase F organization, adding an appropriate amount of Mn, Al, Ti, Nb, Cu, V, N and other elements to improve the mechanical properties of steel.
Common low-temperature steel
1) low-alloy low temperature steel
16MnDR -40 ° C mechanical properties superior to other low-carbon steel
2) nickel steel
2.25% -60 ° C
3.5% -100 ° C
9% -200 ° C
3) high manganese austenitic steel
15Mn25Al4 where Mn is the basic element of the form A, Al as the stability of A's elements.
4) chrome-nickel austenitic stainless steel
18-8 austenitic stainless steel
Foreign low-temperature equipment, steel, high chrome-nickel-based, followed by nickel steel, copper, aluminum.

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