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Alloy Tube For High Temperature Service


Standard: ASTM A335/ASME SA335
Steel grade: P5, P9, P11, P12, P22, P91, P92
Size: OD (90-1200mm) x WT (25-150mm) 
Application: Used for boiler pipe, power plants and nuclear plants.

Chemical Composition (%)
Grade C Si Mn P S Cr Mo Cu Ni V Al W Nb N
P11 0.05~0.15 0.5~1.0 0.3~0.6 ≤ 0.03 ≤ 0.03 1.0~1.5 0.5~1.0              
P12 0.05~0.15 ≤ 0.5 0.3~0.61 ≤ 0.03 ≤ 0.03 0.8~1.25 0.44~0.65              
P22 0.05~0.15 ≤ 0.5 0.3~0.6 ≤ 0.03 ≤ 0.03 1.9~2.6 0.87~1.13              
P5 ≤ 0.15 ≤ 0.5 0.3~0.6 ≤ 0.03 ≤ 0.03 4.0~6.0 0.45~0.65              
P91 0.08~0.12 0.2~0.5 0.3~0.6 ≤ 0.02 ≤ 0.01 8.0~9.5 0.85~1.05   ≤ 0.4 0.18~0.25 ≤ 0.015   0.06~0.10 0.03~0.07
P92 0.07~0.13 ≤ 0.5 0.3~0.6 ≤ 0.02 ≤ 0.01 8.5~9.5 0.3~0.6 B0.001 0.006 ≤ 0.4 0.15~0.25 ≤ 0.015 1.5~2.0 0.04~0.09 0.03~0.07
 

Application:For tubular heat exchangers,condensers and similar heat transfer apparatus.

Production Standard, Steel Grade:
ASTM A179
GB6479 10, 20, 16Mn, 15MnV, Cr5Mo, 1.25Cr0.5Mo, 12CrMo, 15CrMo, 12Cr2Mo, 12SiMoVNb

Delivery Conditions:Annealed, Normalized, Normalized and Tempered

Inspection and Test:
Chemical Composition Inspection, Mechanical Properties Test(Tensile Strength,Yield Strength, Elongation, Flaring, Flattening, Hardness, Impact Test), Surface and Dimension Test,No-destructive Test, Hydrostatic Test.

Surface treatment:Oil-dip, Varnish, Passivation, Phosphating, Shot Blasting.

 
high-temperature alloy steel pipe
 
The structure of the kinds of power machinery, boiler and steam turbine thermal power stations, aviation and naval vessels with gas turbine and nuclear reactor project
Many of the structural member is to work in a high temperature state. Hand affect the the steel chemical stability; operating temperature increases, on the other hand reduce
The strength of the steel. To this end, the requirements steel under high temperature should have
(1) The creep resistance, thermal relaxation and thermal fatigue performance and antioxidant capacity;
(2) corrosion resistance capabilities in a certain medium, as well as adequate toughness;
(3) having a good processing performance and welding inspection;
(4) In accordance with the different uses reasonable stability of the organization.
Heat resistant steel refers to work at high temperatures and corrosion resistance of the steel species having a certain strength and oxidation resistance, heat-resistant steel comprising a thermally stable steel and hot
Steel. Thermally stable steel is anti-oxidation at high temperature or the execution high temperature medium the corrosion without destroying steels, such as the furnace floor grate. They work when
The main failure mode of a high-temperature oxidation. Bear the load per unit area is not large. Heat resistant steel at high temperatures antioxidant capacity
And having adequate strength without causing large deformation or fracture types of steel, such as high temperature bolts, the turbine blade. They work required to bear a greater
The main reason for the load failure is high temperature strength is not enough to lead to instability, failure.
A steel thermal stability and thermal stability steel
Steel oxidation resistance and Ways to Improve
The workpiece and the high-temperature air, steam or gas contact surface to high temperature oxidation or corrosion damage. Therefore, the requirements of the workpiece must have compared
Good thermal stability. In addition to the added alloying element method, surface alloying methods, such as infiltration Cr infiltration Al or infiltration of Si to improve steel
The antioxidant properties.
Second, heat stabilized steel
The thermal stability of steel (also known as anti-oxidation steel) are widely used in industrial boilers components, furnace floor, muffle furnace, radiant tube, this uses heat
The stable steel ferrite (F) thermal stability steel and austenitic (A)-type heat stable steel two categories.
F-type heat stabilizers steel F stainless steel, based on the oxidation resistant alloy and formed steels, having a single phase F substrate surface easily be
Have a continuous protective oxide film. Cr13 type steel, Cr18 steel Cr25 steel, can be divided according to temperature. Thermal stability of F-type steel and F
Stainless steels, because no phase change, so coarse grain, low toughness, but a strong antioxidant activity.
Thermally stable steel of type A is further on the basis of the A-type stainless steel is formed by Si, Al Antioxidant alloying steels. Type A thermally stable steel
Better process performance and thermal strength than the F-type thermal stability steel. However, this type of steel consume a lot of Cr, Ni resources research from the 1950s
Study of Fe-Al-Mn system and the thermal stability of the Cr-Mn-N system steel instead, and have made some progress.
2 hot strength of the metal
High temperature mechanical properties of metallic materials characteristics
At room temperature, regardless of the mechanical properties of steel and the load times, but the strength of steel at high temperatures and the amount of deformation is not only time-related, and with
The temperature, which is heat-resistant steel, the so-called thermal strength. Resistance to plastic deformation and breaking heat intensity refers to heat-resistant steel in high temperature and load together
Bad capacity. This shows that in the assessment of the mechanical properties of materials under high temperature conditions must be assessed by the intensity of heat. Hot strength material at high temperature
The instantaneous performance under the conditions, and long-time performance.
The transient performance is often present Test of mechanical properties as measured by performance in high temperature conditions. Such as high-temperature tensile, high temperature shock and high
Temperature hardness. Which is characterized by high-temperature, short-term load Generally instantaneous performance steel hot strength of one side surface, the measured performance of a
Like not as design specifications, but as a reference index of select high-temperature materials.
Long performance refers to the measured performance of the material in common for a long time under the action of high temperatures and loads, a common performance indicators are: creep limit,
Lasting strength, stress relaxation high temperature fatigue strength and hot and cold fatigue.
Hot strength table and Ways to Improve
1. Strong factors affect the heat-resistant steel heat
As the temperature increases, the heat-resistant steel continue to lower the resistance to plastic deformation and fracture, which is mainly caused by the following two factors:
(1) the influence factors of the softening of the heat-resistant steel. As the temperature increases, the steel between atoms binding force reduced atomic diffusion coefficient increases, thereby guide
Organizations to steel by metastable transition to a steady-state, multiphase alloy composition changes, such as the second phase of aggregation grew up, the sub-structure of alienation and occurred
Recrystallization and the like, these factors lead to a softening of the steel.
(2) deformation change of fracture mode. The deformation of a metallic material at low temperatures are generally to slipping method, but as the temperature increases, the carrier
The Dutch role longer, this time not only slip deformation and grain boundary sliding and migration, but also the proliferation of. The diffusion deformation is in the metal
Deformed but not see the slip line. This deformation mechanism at high temperatures increased thermal motion of atoms in the metal, resulting atom hair
HEALTH move, but under no external force movement of atoms is non-directional, so the macroscopic deformation does not occur; when an external force, the atom moves pole
Prone and directionality, thus promoting the deformation. Grain boundary can also occur when the temperature rises, under the external force, sliding and migration, the higher the temperature,
The load time is longer and more obvious, grain boundary sliding and migration.
Room temperature fracture of the metal in normal circumstances are generally transgranular fracture, which is due to the large degree of lattice distortion of the grain boundary region, the intragranular strength
Below due to the grain boundary strength. With the elevated temperature zone, the degree of lattice distortion due to the grain boundary area is small, so that atomic diffusion rate of increase in the grain boundary strength less
Weak. The higher the temperature, the load time is longer, then the metal fracture mode more rendered as intergranular fracture.
2. Improve the hot strength steel ways
Based on the above analysis, the main way to improve the hot strength of steel three areas: strengthening the matrix and the second phase strengthening, grain boundary strengthening.
(1) strengthening the matrix. The main starting point is to improve the matrix metal atom binding force, reducing the diffusion process of the solid solution. Studies have shown that
The chemical composition of the steel, any high melting point, since the diffusion coefficient is small, can increase the recrystallization temperature of the steel of the alloying elements dissolved in the matrix after they have
Improve hot strength steel. Such as Mo, W, Co and Cr. From the lattice of the solid solution type, austenitic group than ferrite substrate thermal strength
High. This is due to the The austenite matrix arrangement is compact, the diffusion process is not easy compared with the ferritic. If the iron-based alloy, Fe, C, Mo, etc. Element
Elements in A diffusion coefficient was significantly lower than in F diffusion coefficient, which makes the recovery and recrystallization process slows down, the slow-down in a second phase of aggregation speed,
So that the steel is not easy to soften in the hot state.
(2) In the second phase strengthening. The main point of departure is to request a second phase stability, not easy to gather grew up fine and uniform dispersion of long-term high temperature
State, so there are certain requirements on the composition and structure of the second phase particles. Most of the heat-resistant steel with refractory alloy carbides for strengthening phase, such as MC
M23C6, M6C. Higher heat resistance, and can be used with higher thermal stability intermetallic compound. Such as Ni3 (TiAl), Ni3Ti, Ni3Al
As strengthening of the matrix phase.
(3) grain boundary strengthening, to reduce the sliding of the grain boundary in the high temperature state, the following ways:
① reduce the grain boundaries, the need to appropriately control the grain size of the steel. Grains too fine grain boundary, although hindered intragranular slip, but the amount of deformation of the grain boundary sliding
Increases, reducing plastic deformation resistance. Grain is too large, the increased brittleness of the steel, it should be appropriate to control the grain size of the heat-resistant steel, usually 2 to 4 crystal
The granularity can get better high temperature performance.
(2) clean grain boundaries. The steel in the low-melting impurities such as S and P Yi in the grain boundary segregation, and easy to form low melting eutectic iron, thus weakening
Grain boundary strength steel heat intensity decreased. B and other rare earth elements can be added in the steel to form a stable compound of the high melting point, in the crystallization process
As nuclei, so that the fusible impurities transferred from the grain boundary to the grain interior, so that the grain boundary to be purified, and strengthen the grain boundary.
③ to fill the grain boundaries, vacancies, grain boundaries vacancy more diffusion easily performed, is the crack easily expandable by adding B, Ti, Zr,
Other surface activation elements, can be filled with grain boundary vacancies, hinder the grain boundary diffusion of atoms to improve the creep resistance.
④ grain boundary precipitation strengthening. If not continuous reinforcing precipitated at the grain boundary phase, will allow the plastic deformation along the grain boundary sliding and crack along
The grain boundary extension disruption improve hot strength steel. For example, the secondary solution heat treatment method can be precipitated at the grain boundary chain Cr23C6 compound
To improve the hot strength of steel.
In addition, can also be used thermomechanical treatment method to change the shape of the grain boundaries as the the jagged grain boundary and intragranular cause multilateral subgrain boundary into
Further improve the hot strength of steel.
3 a-Fe-based heat resistant steel
a-Fe-based heat resistant steel containing pearlitic heat resistant steel and heat resistant steel, martensitic steel in these two types of heating and cooling a-γ transition occurs,
Therefore, to further increase the use temperature is restricted. Such steel temperature, good heat resistance, thermal stability and process performance, the coefficient of linear expansion
Small number of lower aggregate amount of carbon, low prices, is suitable in 600 ~ 650 ℃ temperature zone of heat resistant steel, widely used in manufacturing boilers
Turbine and oil refining equipment.
Pearlitic heat resistant steel
Pearlitic heat resistant steel according to the aggregate amount of carbon and application characteristics of low-carbon pearlitic heat resistant steel can be divided into two categories in carbon pearlitic heat resistant steel, the former mainly
To the production of boiler tube, which is mainly used for the production of turbine and other heat-resistant fasteners, turbine rotor (including shaft, impeller), pearlitic heat resistant steel
Working temperature is not high, but because of long working hours, coupled by the corrosive effect of the surrounding medium, in the course of their work may produce the following
Organizational changes and performance changes.
1 pearlite spheroidization and carbide gathered. Pearlitic heat resistant steel, sheet carbide in the long-term high temperature into a ball,
The dispersed fine carbides aggregation carbides of larger particles. This organizational change will cause strong steel transformation, leading to creep limit, lasting
The reducing of the strength, the yield limit. This transition is a transition from the unbalanced state to the balanced state spontaneous process, is through a carbon of the original
Diffusion promoter.
The impact of carbide ball and gathered the main factor is the temperature, time, and chemical composition. Carbon steel ball, most likely to an aggregate amount of carbon increase will accelerate
The spheroidized process. Dissolved in solid solution in the composition of the steel and to reduce speed and increase of the diffusion of carbon atom bonded carbide force element such as Cr, an MO,
V, Ti can hinder or delay the ball, and aggregation process.
2 steel graphitization
Steel parts in the working temperature and stress the long-term effect, make carbide decomposed into free graphite, this process is spontaneous, said
Pearlitic heat resistant steel of the graphitization process, which not only eliminate the role of the carbides, and the graphite to the equivalent of small cracks in the steel, the steel
Significantly reduce the strength and ductility of steel caused brittle fracture. This is a very dangerous process of transformation.
Added to Cr to steel, Ti, Nb, and other alloying elements, can prevent the graphitization process; Further, in the smelting can not be used to promote the graphitization of
Al deoxidation; annealing or tempering treatment can also reduce the tendency of the graphitization.
3 the redistribution of alloying elements
Long-term heat-resistant steel, the alloying elements will occur reallocate the phenomenon, i.e. the carbide forming elements Cr, Mo to carbide diffusion,
Enrichment caused by solid solution alloying elements depleted, resulting in heat intensity decreased. Add strong carbon was often used in the production forming elements V, Ti, Nb,
Etc. thereby preventing the re-distribution of the alloying element diffusion aggregation, improve the hot strength of steel.
4 hot brittleness
May occur when the long-term work of pearlitic stainless steel at a temperature dropped significantly impact toughness, sudden brittle fracture present
Elephant. Such brittleness known as hot shortness. It is with some new phase precipitated at this temperature. Take the following measures, anti-heat brittle steel
Long-term working temperature to avoid brittle zone temperature; smelting minimize S, P content: adding the right amount of W, Mo and other alloying elements, thermal
Brittle steel, rapid cooling can be used in high temperature of 600 ~ 650 ℃ tempered be eliminated.
Pearlitic heat strong heat treatment of steel, generally obtained by the process of normalizing (Ac3 + 50 ℃) organization is unstable, in order to ensure the use of
Organizational performance stable temperature is generally higher than the temperature of 100 ℃ tempered.
Martensitic heat resistant steel
This type of steel is mainly used in the manufacture of turbine blades and turbine or diesel engine exhaust valve.
First applied Cr13 steel, it is a martensitic stainless steel. High mechanical properties can be obtained after heat treatment, and good resistance to
Heat.
Type martensite efficiency Crl3 strong steel heat treatment process usually 1000 ~ 1150 ℃ oil quenching from 650 to 750 ℃ ​​high temperature tempering tempering troostite
Body and tempered the sorbite organizations, to ensure that in use temperatures organizations and performance stability. They are used in the manufacture of the like the temperature is below 588 ° C steamships
The machine and the blades of the gas turbine.
4 γ-Fe-based heat resistant steel
Pearlite, the general temperature of the martensitic heat resistant steel, can not apply to a higher use temperature is below 650 ℃ The reason is that, regardless of the
Pearlite matrix or heat resistant steel of martensitic matrix, the matrix phase are ferrite body, that is congenitally deficient. It is necessary to replace the base for the organization, with the Austrian
's Body. The reason why the austenite-based steel higher than the Fe-based steel having a heat resistance, the reason is that: the binding force between the γ-Fe lattice atoms than α-
The bonding force between the atoms of Fe lattice; γ-Fe diffusion coefficient is small; high γ-Fe the re-crystallization temperature (α-Fe recrystallization temperature of 450 to 600
℃, and γ-Fe recrystallization temperature greater than 800 ° C).
γ-Fe-based heat resistant steel has good weldability, oxidation resistance, high ductility and impact toughness. This kind of steel also has some disadvantages, such as the chamber
The low temperature yield strength, pressure processing and cutting poor, poor thermal conductivity, and from time to time changes in temperature effect force and therefore the thermal fatigue resistance is poor.
However, due to the high intensity of heat, so the full development and a wide range of applications.

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