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Austenitic heat-resistant steel
Introduction:
Ⅰ. Low carbon: Mostly above 0.1%, and can reach 0.4%. Carbon is used to form carbides to maintain high thermal strength.
Ⅱ. Add a large amount of chromium and nickel. The total amount is generally above 25%. Cr mainly improves the thermochemical stability and thermal strength, while Ni ensures the acquisition of stable austenite.
III. Adding tungsten, molybdenum, etc. increases the recrystallization temperature and precipitates more stable carbides to improve thermal strength.
IV. Add vanadium, titanium, aluminum, etc. to form a stable second phase to improve thermal strength. The second phase includes carbides (such as VC, etc.) and intermetallic compounds [such as Ni (Ti, Al), etc.], and the latter has a better strengthening effect.
Classification
According to the alloy element composition, it can be divided into different series such as chromium-nickel, chromium-nickel-nitrogen, chromium-manganese-nickel-nitrogen, chromium-manganese-nitrogen, iron-manganese-aluminum, etc.:
1.Chromium-nickel system.It is the most widely used and most widely used series of steels. With its different chromium and nickel content ratios, it meets the needs of different temperature grades. As the chromium and nickel content increases, the oxidation resistance and high-temperature strength increase accordingly. Solid solution strengthening elements (tungsten, molybdenum), carbide-forming elements (vanadium, niobium, titanium) and trace elements (boron, zirconium, magnesium, rare earth, etc.) are added to the steel as needed to further improve the thermal strength of the steel.
The most typical grade is 1crl8Ni9. On this basis, 0Crl8NillTi, 0Cr18NillNb, Cr17Nil2Mo2, etc. can be used for 600-650℃ boiler tubes, various plate and tube materials for petrochemical industry with a certain stress of about 850℃, such as heating furnace tubes, heat exchanger tubes, combustion chamber cylinders, furnace hoods, etc. Appropriately increasing the chromium and nickel content forms Cr23Nil3 steel, which is used for heat-resistant components of furnaces at about 1000℃. 1cr25Ni20 (Si2) is a heat-resistant steel grade commonly used in countries around the world in the range of 1000-1200℃. In order to improve the carburization resistance and thermal strength of heat-resistant steel, Cr21Ni32AlTi (Incoloy800) has been developed abroad for use in petrochemical and nuclear energy industries. More strengthening elements tungsten and molybdenum are added to steels such as Cr14N|14W2Mo, OCrl5Ni-25Ti2MoAlVB, 1Cr22Ni20Co20Mo3W3NbN to improve thermal strength. The former is used for exhaust valve materials with higher loads, and the latter two grades are used for high-temperature turbine rotors, bolts, blades, etc. at 700-750℃.
2.Chromium-nickel-nitrogen system.In order to save nickel and improve the high-temperature strength of steel, nitrogen is added to the steel. China has developed grades such as 3Crl9Ni4N and 3Cr-24Ni7SiN (RE). The former can replace 1crl8Ni9, and the latter can replace lCr23Nil3, lCr25Ni20 and HK40 (4Cr25Ni20). 3cr24Ni7SiN (RE) has been included in the Chinese national standard and is widely used. 2Cr22Nil2N is an introduced steel type used for gasoline and diesel engine exhaust valves.
3.Chromium-manganese-nickel-nitrogen and chromium-manganese-nitrogen systems.At the same time, adding manganese and nitrogen to steel can save a lot of nickel. Many grades have been developed both at home and abroad. For example, 5Cr21Mn9Ni4N is a typical valve steel, which is widely used in gasoline and diesel engine exhaust valves that are mainly subjected to high temperature strength. On this basis, adding tungsten, molybdenum, vanadium, and niobium can further improve the high temperature strength and be used for exhaust valves that withstand greater loads, such as China's Cr21Mn9WNbN, Cr21Mn-10MoVNbN, etc. 2Cr20Mn9Ni2Si2N and 3Crl8Mnl2Si2N are steel grades developed by China itself. They have good high temperature strength, good oxidation resistance and carburization resistance. They can be used as hanging brackets, carburizing furnace internals, heating furnace conveyor belts, trays, etc. The former is better at oxidation resistance than the latter, and can also be used as salt bath crucibles and other furnace materials. Compared with chromium-nickel steel, chromium-manganese-nitrogen and chromium-manganese-nickel-nitrogen steels have higher strength, but because more manganese is added to the steel, it has an adverse effect on high temperature oxidation resistance, and the oxidation resistance is not as good as chromium-nickel heat-resistant steel.
4.Iron-manganese-aluminum system.This type of steel does not contain any chromium or nickel at all, and forms an austenite matrix with manganese and carbon, relying on aluminum to solve the problem of high-temperature oxidation resistance. As early as 1934, Germany first published the iron-manganese-aluminum iron angle phase diagram. After discovering that there is a stable austenite phase in the carbon-containing iron-manganese-aluminum system, the research on iron-manganese-aluminum austenitic heat-resistant steel has gradually received attention. In order to save nickel and chromium, China began to study iron-manganese-aluminum heat-resistant steel. Drawing on foreign experience, it developed Mn30A19 type heat-resistant steel for furnace components at 700-950℃. In order to save alloy elements, according to the requirements of furnace heat-resistant steel below 950℃, 6Mnl8A15 type heat-resistant steel with better performance than Mn30A19 type was developed, saving 40% of alloy elements and improving process performance.Chinese brand 6Mnl8A15Si2Ti is furnace steel, 6Mnl8A15SiMoTi and 6Mnl8A15SiMoV are valve steel. 2Mnl8A15SiMoTi (2Mnl8A15Si2Ti) is a dual-phase steel that can be used to produce steel pipes to replace 1Crl8Ni9. When producing iron-manganese-aluminum steel deformation products, electroslag remelting is required to ensure quality and yield rate.
Stainless steel grade correspondence table:
|
Commonly used austenitic stainless steel, heat-resistant steel and austenitic-ferritic stainless steel grades and their chemical compositions |
|||||||||||||
|
No. |
Chinese Brand GB/T20878-2007 |
Main chemical components |
|||||||||||
|
Unified digital code |
Old brand |
New grades |
Ni |
Cr |
C |
Si |
Mn |
P |
S |
Mo |
N |
Ti |
|
|
1 |
304 |
0Cr18Ni9 |
8.00-11.00 |
17.00-19.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
08Cr19Ni10 |
8.00-11.00 |
18.00-20.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.045 |
≤0.03 |
-- |
-- |
-- |
|||
|
2 |
309s |
0Cr23Ni13 |
12.00-15.00 |
22.00-24.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
06Cr23Ni13 |
12.00-15,00 |
22.00-24.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.045 |
≤0.03 |
-- |
-- |
-- |
|||
|
3 |
310s |
0Cr25Ni20 |
19.00-22.00 |
24.00-26.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
06Cr25Ni20 |
19.00-22.00 |
24.00-28.00 |
≤0.08 |
≤1.50 |
≤2.00 |
≤0.045 |
≤0.03 |
-- |
-- |
-- |
|||
|
4 |
316L |
00Cr17Ni14Mo2 |
12.00-15.00 |
16.00-18.00 |
≤0.03 |
≤1.00 |
≤2.00 |
≤0.035 |
≤0.03 |
2.00-3.00 |
-- |
-- |
|
|
022Cr17Ni12Mo2 |
10.00-14.00 |
18.00-18.00 |
≤0.03 |
≤1.00 |
≤2.00 |
≤0.045 |
≤0.03 |
2.00-3.00 |
-- |
-- |
|||
|
5 |
321 |
1Cr1BNi9Ti |
8.00-11.00 |
17.00-19.00 |
≤0.12 |
≤1.00 |
≤2.00 |
≤0.035 |
≤0.03 |
-- |
-- |
Ti≥5(C％-0.02) |
|
|
08Cr18Ni11Ti |
9.00-12.00 |
17.00-19.00 |
≤0.08 |
≤1.00 |
≤2.00 |
≤0.045 |
≤0.03 |
-- |
-- |
Ti≥5(C％-0.02) |
|||
|
6 |
2205 |
022Cr23Ni5Mo3N |
4.50-6.50 |
22.00-23.00 |
≤0.03 |
≤1.00 |
≤2.00 |
≤0.03 |
≤0.02 |
3.00-3.50 |
0.14-0.20 |
-- |
|
|
Table of commonly used martensitic steel grades and their chemical compositions |
|||||||||||||
|
No. |
Chinese Brand GB/T20878-2007 |
Main chemical components |
|||||||||||
|
Unified digital code |
Old brand |
New grades |
Ni |
Cr |
C |
Si |
Mn |
P |
S |
Mo |
N |
Ti |
|
|
1 |
0Cr13 |
0Cr13 |
-- |
11.50-13.00 |
≤0.08 |
≤1.00 |
≤1.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
08Cr13 |
0.6 |
11.50-13.50 |
≤0.08 |
≤1.00 |
≤1.00 |
≤0.04 |
≤0.03 |
-- |
-- |
-- |
|||
|
2 |
1Cr13 |
1Cr13 |
-- |
11.50-13.50 |
≤0.15 |
≤1.00 |
≤1.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
12Cr13 |
0.6 |
12.00-14.00 |
≤0.15 |
≤1.00 |
≤1.00 |
≤0.04 |
≤0.03 |
-- |
-- |
-- |
|||
|
3 |
2Cr13 |
2Cr13 |
-- |
2.00-14.00 |
0.16-0.25 |
≤1.00 |
≤1.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
20Cr13 |
0.6 |
12.00-14.00 |
0.15-0.25 |
≤1.00 |
≤1.00 |
≤0.04 |
≤0.03 |
-- |
-- |
-- |
|||
|
4 |
3Cr13 |
3Cr13 |
-- |
12.00-14.00 |
0.26-0.35 |
≤1.00 |
≤1.00 |
≤0.035 |
≤0.03 |
-- |
-- |
-- |
|
|
30Cr13 |
0.6 |
12.00-14.00 |
0.25-0.35 |
≤1.00 |
≤1.00 |
≤0.04 |
≤0.03 |
-- |
-- |
-- |
|||
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