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Advanced Degrees in Steel Science and TechnologyAdvanced Degrees in Steel Science and Technology

Stainless Steel

GIFT 672

Lecture 4


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Classification of stainless steels

1. Ferritic stainless steels2. Austenitic stainless steels3. Martensitic stainless steels4. Duplex stainless steels

5. Precipitation-hardened stainless steels


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Microstructure of stainless steels

Review of the properties of alloying elements in stainless steels

Chromium: Corrosion protection, ferrite stabilizer, carbide former (M23C6), nitride former (Cr2N)

Nickel: austenite stabilizer, toughness improving element in ferrite-martensite

Manganese: always present in steels (1-2% in stainless steels), austenite stabilizer, sulfide former(MnS), increases N-solubility in austenite

Silicon: always present in steels (0.3-0.6% in stainless steels, de-oxidation of steel), improves heat

resistance (4-5%)

Molybdenum: improves corrosion resistance, high temperature strength

Nb, Ti, V: MC carbide forming elements

Al, Ti, Cu: promote precipitation hardening by Ni3Ti, Ni3Al, or Cu precipitates

C: solid solution strengthening, austenite stabilizer, critical in martensitic grades

N: solid solution strengthening, austenite stabilizer, increases corrosion resistance


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Classification of stainless steels

Schaeffler diagram: stainless steel grades composition ranges

ASM International

Austenitic steels

Duplex steels

Ferritic steels

Martensitic steels


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Classification of stainless steels according to AISI and UNS(AISI: American Iron and Steel Institute)

(UNS: Universal Numbering System)

1. Type 400: Ferritic stainless steels2. Type 300: Austenitic stainless steels

3. Type 200: Austenitic stainless steels with Mn4. Type 400: Martensitic stainless steels5. UNS: Duplex stainless steels6. UNS: Precipitation-hardened stainless steels


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AISI stainless steel classification scheme.

302: 18Cr-8Ni303: free-machining 18Cr-8Ni, with min 0.07% Se, P or S304: 18Cr-10Ni (C


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Classification of stainless steels according to AISI and UNSMost Important Types of Stainless Steels

0% Mo2% Mo0% Mo

304

301316

301

304L

321347

316L

316Ti

9% Ni

430Ti409

430434410

0% Ni

17%Cr12% Cr


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Classification of stainless steels according to EN(EN: European EN Classification)

1. Ferritic stainless steels

2. Austenitic stainless steels3. Austenitic stainless steels with Mn4. Martensitic stainless steels5. Duplex stainless steels6. Precipitation-hardened stainless steels


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EN10088 stainless steel classification scheme.

General notation:

XNNNLLLN-N-N

X: the prefix X refers to an alloyed steel withmore than 5% in weight of any element.

NNN: Mass-%C times 100

LLL : Main elements

N-N-N : Mass-% of the element

Examples:

X2CrTi12X10CrNi18-8

X2CrNiMoN17-13-5X2CrNiMoN22-5-3

Steels:

1.XXXX

Stainless steels:

1.4XXXFerritic and martensitic grades:

1.40XX: 2.5%Ni, with Mo, no Ti, Nb1.45XX: with additions of Ti or Nb

Common use of type numbersEN Numbering system


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Composition

AISI 321

EN 10088 1.

X6CrNiTi18-11

Microstructure

Steel

0 4 8 12 16 20 24 28 32 36 400

8

16

24

32

40

100% F

0% F

F+M

A+M

MartensiteFerrite

Austenite

Ni-equivalent

Cr-equivalent

1.2%0.3%0.4%9.5%18%0.06%

MnSiTiNiCrC

x100

Special Ti additions

Stainless steel

4541

Example classification scheme.


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