
What is the difference between austenitic and ferritic stainless steel?
Out of the four main classes of stainless steels, both austenitic and ferritic stainless steels are amongst the widely used ones. The classifications of said classes are based on their crystalline microstructure. Austenitic classes have a face-centered cubic crystal structure, whereas, in the case of ferritic stainless steels, their crystal structure is that of a body-centered cubic one. The dissimilarity in their microstructure is on account of their chemical composition. Unlike austenitic stainless steels, ferritic alloys tend to exhibit magnetic nature.
Whenever you buy from any austenitic stainless steel suppliers, do not forget to take a test certificate to ensure the material quality.
Why ferritic and austenitic stainless steels are not heat treatable?
The main reason why both classes are not heat treatable is that they possess the same microstructure at all temperatures. This means that the crystallinity of their microstructure, whether austenitic or ferritic remains a constant from temperatures ranging between as low as cryogenic settings to as high as the melting point of alloys belonging to either stainless steel classes. In the case of austenitic stainless steel classes, the inclusion of adequate nickel and/or manganese along with nitrogen is sufficient to stabilize the austenite microstructure in their alloys. On the other hand, ferritic stainless steels contain chromium content ranging between 10.5% to 27% with the inclusion of either very little or no nickel. This chemistry aids the crystalline microstructure of ferritic classes to remain the same.
Many ferritic stainless steel suppliers recommends post-heat treatment at 750- 850 degree celsius while preheat to 200 degree celsius.
Austenitic and austenitic-ferritic stainless steel forgings
Austenitic stainless steel forgings, though non-magnetic tend to exhibit superior levels of resistance to both corrosion and heat. Ferritic steels also tend to be resistant to corrosion. However, similar to austenitic classes, these forgings are neither hardenable by heat treatment, nor are they durable as compared to other steel classes. Stainless steels that fall under the duplex category, or as known as austenitic-ferritic stainless steel, exhibit properties such as high formability, superior tensile strength, and ductility. Their forgings achieve such remarkable properties because the alloys are heated above their recrystallization temperature, following which they are forged by the application of external force.
Annealing of austenitic and ferritic steels
All stainless steels that belong to the Ferritic class are treated by the use of process annealing. In this process, the alloys are heated in the ferrite temperature range, or the alloys are fully annealed by the use of heat above the crucial temperature in the austenite range. For alloys that belong to the austenitic stainless steel classes, annealing is done by the use of heat treatment for the precipitation-hardening of the alloy. Annealing alloys tend to improve their mechanical properties.
Irradiated austenitic and ferritic steels
Irradiation or radiation of steel is similar across all classes of stainless steel. When stainless steels are irradiated, they become hard, and there is an increase in strength. This means that the fracture toughness of these stainless steel alloys is reduced.
Austenitic and ferritic microstructure
As discussed previously, the microstructure of ferritic steels consists of a body-centered cubic type. In this kind of microstructure, the unit cell structure consists of atoms arrayed in a cube. In this setting, each corner of the cube will share an atom, such that a single atom is positioned at the center. In the BCC microstructure arrangement, the atoms will not be packed as closely, as seen in the case of other arrangements - for instance, the face-centered cubic or as known in short as FCC. Due to this kind of an arrangement, it is very hard for the atoms to slip past each other. This characteristic is what makes BCC containing microstructures such as ferritic stainless steels harder and less malleable, especially if compared to materials that have a closely packed microstructure. These properties are considered to be vital, in particular when materials are to be selected for specific applications.
The microstructure of austenitic class stainless steels is a face-centered cubic type. This means a single unit cell within its microstructure will consist of atoms that have been arranged in a cube. In every single corner of the cube is a fraction of an atom, which in turn has six additional full atoms located at the core of each cube face. This type of packing arrangement makes FCC metals softer and more ductile. In comparison to their BCC counterparts, they have excellent ductility and malleability. Similar to BCC microstructure containing alloys, their ductility is an influential factor when electing substances for a given application.
Austenitic stainless steel material composition
Euronorm (EN) / werkstoff number | EN designation | AISI / SS | Mo | C | Cr | Ni | Others |
---|---|---|---|---|---|---|---|
1.4310 | X10CrNi18-8 | 301 | NS | 0.10 | 17.5 | 8 | NS |
1.4301 | X5CrNi18-10 | 304 | NS | < 0.07 | 18.5 | 9 | NS |
1.4307 | X2CrNi18-9 | 304L | NS | < 0.030 | 18.5 | 9 | NS |
1.4305 | X8CrNiS18-9 e | 303 | NS | < 0.10 | 18 | 9 | 0.3 |
1.4541 | X6CrNiTi18-10 | 321 | NS | < 0.08 | 18 | 10.5 | Ti: 5×C ≤ 0.70 |
1.4401 | X5CrNiMo17-12-2 | 316 | 2.2 | < 0.07 | 17.5 | 11.5 | NS |
1.4404 | X2CrNiMo17-12-2 | 316L | 2.25 | < 0.030 | 17.5 | 11.5 | NS |
1.4571 | X6CrNiMoTi17-12-2 | 316Ti | 2.25 | < 0.08 | 17.5 | 12 | Ti: 5×C ≤ 0.70 |
Austenitic stainless steel grade table
- 301
- 304
- 304L
- 303
- 321
- 316
- 316L
- 316Ti
Austenitic stainless steel standard specification
- SAE (also AISI, USA)
- UNS (USA)
- British Standards/ UK (BS)
- International Standards Organisation (ISO)
- European Standards (EN)
- Japan Industrial Standards (JIS)
- Germany Standard (DIN)
- GB (China)
Ferritic Stainless Steel grades
- 405
- 409L
- 410L
- 430
- 439
- 430Ti
- 441
- 434
- 436
- 444
- 447
Ferritic stainless steel composition
Grade | EN | Weight % | |
---|---|---|---|
Cr | Other elements | ||
405 | 1.4000 | 12.0 - 14.0 | - |
409L | 1.4512 | 10.5 - 12.5 | 6(C+N)<Ti<0.65 |
410L | 1.4003 | 10.5 - 12.5 | 0.3<Ni<1.0 |
430 | 1.4016 | 16.0 - 18.0 | - |
439 | 1.4510 | 16.0 - 18.0 | 0.15+4(C+N)<Ti<0.8 |
430Ti | 1.4511 | 16.0 -18.0 | Ti: 0.6 |
441 | 1.4509 | 17.5 - 18.5 | 0.1<Ti<0.6
0.3+3C<Nb<1.0 |
434 | 1.4113 | 16.0 - 18.0 | 0.9<Mo<1.4 |
436 | 1.4513 | 16.0 - 18.0 | 0.9<Mo<1.4
0.3<Ti<0.6 |
444 | 1.4521 | 17.0 - 20.0 | 1.8<Mo<2.5
0.15+4(C+N)<Ti+Nb<0.8 |
447 | 1.4592 | 28 - 30.0 | 3.5<Mo<4.5
0.15+4(C+N)<Ti<0.8 |
Ferritic stainless steel mechanical properties
EN Grade | ASTM Grade | UNS | Austenitic (A) or Ferritic (F) Stainless Steel | Rp 0.2 | Rp 1.0 | Rm | Elongation A | Elongation A80 | Hardness | Hardness |
---|---|---|---|---|---|---|---|---|---|---|
MPa | MPa | MPa | % | % | HR | HB | ||||
1.4000 | TYPE 410S | S41008 | F | > 240 | 400 - 600 | > 19 | > 19 | |||
1.4003 | S40977 | F | > 280 | 450 - 650 | > 20 | > 20 | ||||
1.4016 | TYPE 430 | S43000 | F | > 260 | 430 - 600 | > 20 | > 20 | |||
1.4510 | TYPE 439 | S43035 | F | |||||||
1.4512 | TYPE 409 | S40900 | F | > 220 | 380 - 560 | > 25 | > 25 | |||
1.4520 | F | |||||||||
1.4589 | F | |||||||||
A | ||||||||||
1.4301 | TYPE 304 | S30400 | A | > 230 | > 260 | 540 - 750 | > 45 | > 45 | ||
1.4303 | TYPE 305 | S30500 | A | > 220 | > 250 | 500 - 650 | ||||
1.4306 | TYPE 304L | A | > 220 | > 250 | 520 - 700 | > 45 | > 45 | |||
1.4307 | TYPE 304L | S30403 | A | > 220 | > 250 | 520 - 700 | > 45 | > 45 | ||
1.4310 | TYPE 301 | S30100 | A | > 250 | > 280 | 600 - 950 | > 40 | > 40 | ||
1.4318 | TYPE 301LN | S30153 | A | > 350 | > 380 | 650 - 850 | > 40 | > 35 | ||
1.4372 | TYPE 201 | S20100 | A | > 350 | > 380 | 680 - 880 | > 45 | > 45 | ||
1.4509 | S43940 | F | > 230 | 430 - 630 | > 18 | > 18 | ||||
1.4513 | F | |||||||||
1.4541 | TYPE 321 | S32100 | A | > 220 | > 250 | 520 - 720 | > 40 | > 40 | ||
1.4550 | TYPE 347H | S34709 | A | |||||||
1.4622 | S44330 | F | > 300 | 430 - 630 | > 22 | |||||
1.4401 | TYPE 316H | S31609 | A | > 240 | > 270 | 530 - 680 | > 40 | > 40 | ||
1.4404 | TYPE 316L | S31603 | A | > 240 | > 270 | 530 - 680 | > 40 | > 40 | ||
1.4420 | S31655 | A | > 350 | > 380 | 650 - 850 | > 35 | ||||
1.4432 | TYPE 316L | A | > 240 | > 270 | 550 - 700 | > 40 | > 40 | |||
1.4435 | TYPE 316L | A | > 240 | > 270 | 550 - 700 | > 40 | > 40 | |||
1.4436 | TYPE 316 | A | > 240 | > 270 | 550 - 700 | > 40 | > 40 | |||
1.4521 | TYPE 444 | S44400 | F | > 300 | 420 - 640 | > 20 | > 20 | |||
1.4571 | TYPE 316Ti | S31635 | A | > 240 | > 270 | 540 - 690 | > 40 | > 40 | ||
1.4462 | S32205 | D | > 500 | 700 - 950 | > 20 | > 20 | ||||
1.4362 | S32304 | D | > 450 | 650 - 850 | > 20 | > 20 | ||||
1.4410 | S32750 | D | > 550 | 750 - 1000 | > 20 | > 20 | ||||
1.4016 | TYPE 430 | S43000 | F | > 260 | 430 - 600 | > 20 | > 20 | |||
1.4301 | TYPE 304 | S30400 | A | > 230 | > 260 | 540 - 750 | > 45 | > 45 | ||
1.4307 | TYPE 304L | S30403 | A | > 220 | > 250 | 520 - 700 | > 45 | > 45 | ||
1.4310 | TYPE 301 | S30100 | A | > 250 | > 280 | 600 - 950 | > 40 | > 40 | ||
1.4318 | TYPE 301LN | S30153 | A | > 350 | > 380 | 650 - 850 | > 40 | > 35 | ||
1.4376 | A | > 400 | > 420 | 600 - 900 | > 40 | > 40 | ||||
1.4401 | TYPE 316H | S31609 | A | > 240 | > 270 | 530 - 680 | > 40 | > 40 | ||
1.4404 | TYPE 316L | S31603 | A | > 240 | > 270 | 530 - 680 | > 40 | > 40 | ||
1.4420 | S31655 | A | > 350 | > 380 | 650 - 850 | > 35 | ||||
1.4501 | S32760 | D | ||||||||
1.4571 | TYPE 316Ti | S31635 | A | > 240 | > 270 | 540 - 690 | > 40 | > 40 | ||
FDX 27 | S82031 | D | ||||||||
1.4162 | S32101 | D | > 530 | 700 - 900 | > 30 | > 20 | ||||
1.4662 | S82441 | D | > 550 | 750 - 900 | > 25 | > 20 | ||||
1.4547 | S31254 | A | > 320 | > 350 | 650 - 850 | > 35 | > 35 | |||
1.4438 | TYPE 317L | S31703 | A | |||||||
1.4529 | N08926 | A | ||||||||
1.4652 | S32654 | A | > 430 | > 470 | 750 - 1000 | > 40 | > 40 | |||
1.4466 | S31050 | A | ||||||||
1.4539 | N08904 | A | > 240 | > 270 | 530 - 730 | > 35 | > 35 | |||
A | ||||||||||
1.4006 | TYPE 410 | S41000 | M | < 600 | > 20 | > 20 | ||||
1.4021 | TYPE 420 | M | < 700 | > 15 | ||||||
1.4024 | M | < 650 | > 20 | > 20 | ||||||
1.4031 | M | < 760 | > 12 | > 12 | ||||||
1.4034 | M | < 780 | > 12 | > 12 | ||||||
1.4110 | M | < 850 | > 12 | > 12 | ||||||
1.4116 | M | < 850 | > 12 | > 12 | ||||||
1.4122 | M | < 900 | > 12 | > 12 | ||||||
PH | < 1275 | > 5 | > 5 | |||||||
1.4568 | TYPE 631 | PH | < 1030 | > 19 | > 19 | |||||
1.4835 | S30815 | A | > 310 | > 350 | 650 - 850 | > 40 | > 37 | |||
1.4724 | F | |||||||||
1.4828 | A | > 230 | > 270 | 550 - 750 | > 30 | > 28 | ||||
1.4833 | TYPE 309S | S30908 | A | > 210 | > 250 | 500 - 700 | > 35 | > 33 | ||
1.4841 | TYPE 314 | A | ||||||||
1.4845 | TYPE 310S | S31008 | A | > 210 | > 250 | 500 - 700 | > 33 | |||
1.4948 | TYPE 304H | S30409 | A | > 230 | > 260 | 530 - 740 | > 45 | > 45 | ||
1.4305 | TYPE 303 | A | ||||||||
1.4307 | TYPE 304L | S30403 | A | > 220 | > 250 | 520 - 700 | > 45 | > 45 | ||
1.4404 | TYPE 316L | S31603 | A | > 240 | > 270 | 530 - 680 | > 40 | > 40 | ||
PH | < 1275 | > 5 | > 5 |
How to weld ferritic stainless steel?
- Shielded metal arc welding (MMA, SMAW)
- Plasma arc welding (PAW)
- High frequency welding (HF)
- Gas metal arc welding (MIG, MAG, GMAW)
- Gas tungsten arc welding (GTAW, TIG)
- Resistance welding
- Laser welding
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