Difference between austenitic and ferritic stainless steel

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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