Stainless Steel Ferritic Martensitic Precipitation-hardening Martensitic Duplex

Types of stainless steel

There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels non-magnetic and less brittle at low temperatures. For greater hardness and strength, more carbon is added. When subjected to adequate heat treatment, these steels are used as razor blades, cutlery, tools, etc.

Significant quantities of manganese have been used in many stainless steel tubing compositions. Manganese preserves an austenitic structure in the steel as does nickel, but at a lower cost.

Stainless steels are also classified by their crystalline structure:

Austenitic, or 300 series, stainless steels make up over 70% of total stainless steel production. They contain a maximum of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy. A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless steel, is often used in flatware. Similarly, 18/0 and 18/8 are also available. Superaustenitic stainless steel， such as alloy AL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion due to high molybdenum content (>6%) and nitrogen additions, and the higher nickel content ensures better resistance to stress-corrosion cracking versus the 300 series. The higher alloy content of superaustenitic steels makes them more expensive. Other steels can offer similar performance at lower cost and are preferred in certain applications

The low carbon version of the Austenitic Stainless Steel, for example 316L or 304L, are used to avoid corrosion problem caused by welding. The "L" means that the carbon content of the Stainless Steel is below 0.03%, this will reduce thesensitization effect, precipitation of Chromium Carbides at grain boundaries, due to the high temperature produced by welding operation.

Ferritic stainless steels are highly corrosion-resistant, but less durable than austenitic grades. They contain between 10.5% and 27% chromium and very little nickel, if any, but some types can contain lead. Most compositions include molybdenum; some, aluminium or titanium. Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. These alloys can be degraded by the presence of σ chromium, an intermetallic phase which can precipitate upon welding.

Martensitic stainless steels are not as corrosion-resistant as the other two classes but are extremely strong and tough, as well as highly machineable, and can be hardened by heat treatment. Martensitic stainless steel contains chromium(12-14%), molybdenum(0.2-1%), nickel(0-<2%), and carbon(about 0.1-1%) (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic.

Precipitation-hardening martensitic stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades. The most common, 17-4PH, uses about 17% chromium and 4% nickel. There is a rising trend in defense budgets to opt for an ultra-high-strength stainless steel when possible in new projects, as it is estimated that 2% of the US GDP is spent dealing with corrosion. The Lockheed-Martin Joint Strike Fighter is the first aircraft to use a precipitation-hardenable stainless steel Carpenter Custom 465—in its airframe.

Duplex stainless steels have a mixed microstructure of austenite and ferrite, the aim being to produce a 50/50 mix, although in commercial alloys, the mix may be 40/60 respectively. Duplex stainlss steel pipe have improved strength over austenitic stainless steels and also improved resistance to localised corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. They are characterised by high chromium (19–28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. The most used Duplex Stainless Steel pipe are the 2205 (22% Chromium, 5% Nickel) and 2507 (25% Chromium, 7% Nickel); the 2507 is also known as "SuperDuplex" due to its higher corrosion resistance. Duplex stainless steel pipe properties are achieved with an overall lower alloy content than similar performing super austenitic grades making their selection and use cost effective for many applications.

Comparison of standardized steels

EN-standard Steel no. k.h.s DIN	EN-standard Steel name	SAE grade	UNS
		440A	S44002
1.4112		440B	S44003
1.4125		440C	S44004
		440F	S44020
1.4016	X6Cr17	430	S43000
1.4512	X6CrTi12	409	S40900
		410	S41000
1.4310	X10CrNi18-8	301	S30100
1.4318	X2CrNiN18-7	301LN	N/A
1.4307	X2CrNi18-9	304L	S30403
1.4306	X2CrNi19-11	304L	S30403
1.4311	X2CrNiN18-10	304LN	S30453
1.4301	X5CrNi18-10	304	S30400
1.4948	X6CrNi18-11	304H	S30409
1.4303	X5CrNi18-12	305	S30500
	X5CrNi30-9	312
1.4541	X6CrNiTi18-10	321	S32100
1.4878	X12CrNiTi18-9	321H	S32109
1.4404	X2CrNiMo17-12-2	316L	S31603
1.4401	X5CrNiMo17-12-2	316	S31600
1.4406	X2CrNiMoN17-12-2	316LN	S31653
1.4432	X2CrNiMo17-12-3	316L	S31603
1.4435	X2CrNiMo18-14-3	316L	S31603
1.4436	X3CrNiMo17-13-3	316	S31600
1.4571	X6CrNiMoTi17-12-2	316Ti	S31635
1.4429	X2CrNiMoN17-13-3	316LN	S31653
1.4438	X2CrNiMo18-15-4	317L	S31703
1.4539	X1NiCrMoCu25-20-5	904L	N08904
1.4547	X1CrNiMoCuN20-18-7	N/A	S31254

Stainless Steel grades

The SAE steel grades are the most commonly used grading system in the US for stainless steel seamless pipe . Other steel grades include the UNS grades.

100 Series—austenitic chromium-nickel-manganese alloys

Type 101—austenitic that is hardenable through cold working for furniture
Type 102—austenitic general purpose stainless steel working for furniture

200 Series—austenitic chromium-nickel-manganese alloys

Type 201—austenitic that is hardenable through cold working
Type 202—austenitic general purpose stainless steel

300 Series—austenitic chromium-nickel alloys

Type 301—highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
Type 302—same corrosion resistance as 304, with slightly higher strength due to additional carbon.
Type 303—free machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with ISO 3506.
Type 304—the most common grade; the classic 18/8 stainless steel. Also referred to as "A2" in accordance with ISO 3506.<
Type 304L— same as the 304 grade but contains less carbon to increase weldability. Is slightly weaker than 304.
Type 304LN—same as 304L, but also nitrogen is added to obtain a much higher yield and tensile strength than 304L.
Type 308—used as the filler metal when welding 304
Type 309—better temperature resistance than 304, also sometimes used as filler metal when welding dissimilar steels, along with inconel
Type 316—the second most common grade (after 304); for food and surgical stainless steel uses; alloy addition of molybdenum prevents specific forms of corrosion. It is also known as marine grade stainless steel due to its increased resistance to chloride corrosion compared to type 304. 316 is often used for building nuclear reprocessing plants.
Type 316L—extra low carbon grade of 316, generally used in stainless steel watches and marine applications due to its high resistance to corrosion. Also referred to as "A4" in accordance with ISO 3506.
Type 316Ti—includes titanium for heat resistance, therefore it is used in flexible chimney liners.
Type 321—similar to 304 but lower risk of weld decay due to addition of titanium. See also 347 with addition of niobium for desensitization during welding.

400 Series—ferritic and martensitic chromium alloys

Type 405— ferritic for welding applications
Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
Type 410—martensitic (high-strength iron/chromium). Wear-resistant, but less corrosion-resistant.
Type 416—easy to machine due to additional sulfur
Type 420—Cutlery Grade martensitic; similar to the Brearley's original rustless steel. Excellent polishability.
Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
Type 439—ferritic grade, a higher grade version of 409 used for catalytic converter exhaust sections. Increased chromium for improved high temperature corrosion/oxidation resistance.
Type 440—a higher grade of cutlery steel, with more carbon, allowing for much better edge retention when properly heat-treated. It can be hardened to above Rockwell 55 hardness,[citation needed] making it one of the hardest stainless steels. Due to its hardness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless.Available in four grades: 440A, 440B, 440C, and the uncommon 440F (free machinable). 440A, having the least amount of carbon in it, is the most stain-resistant; 440C, having the most, is the strongest and is usually considered more desirable in knifemaking than 440A, except for diving or other salt-water applications.
Type 446—For elevated temperature service

500 Series—heat-resisting chromium alloys

600 Series—martensitic precipitation hardening alloys

601 through 604: Martensitic low-alloy steels.
610 through 613: Martensitic secondary hardening steels.
614 through 619: Martensitic chromium steels.
630 through 635: Semiaustenitic and martensitic precipitation-hardening stainless steels.
- Type 630 is most common PH stainless, better known as 17-4; 17% chromium, 4% nickel.
650 through 653: Austenitic steels strengthened by hot/cold work.
660 through 665: Austenitic superalloys; all grades except alloy 661 are strengthened by second-phase precipitation.

Type 2205— the most widely used duplex (ferritic/austenitic) stainless steel grade. It has both excellent corrosion resistance and high strength.

Stainless Steel Designation

SAE

UNS

% Cr

% Ni

% C

% Mn

% Si

% P

% S

% N

Other

Austenitic

201

S20100

16–18

3.5–5.5

0.15

5.5
-7.5

0.75

0.06

0.03

0.25

202

S20200

17–19

4–6

0.15

7.5
-10.0

0.75

0.06

0.03

0.25

205

S20500

16.5–18

1–1.75

0.12–0.25

14
-15.5

0.75

0.06

0.03

0.32
-0.40

301

S30100

16–18

6–8

0.15

0.75

0.045

0.03

302

S30200

17–19

8–10

0.15

0.75

0.045

0.03

0.1

302B

S30215

17–19

8–10

0.15

2.0
-3.0

0.045

0.03

303

S30300

17–19

8–10

0.15

0.2

0.15 min

Mo 0.60 (optional)

303Se

S30323

17–19

8–10

0.15

0.2

0.06

0.15 Se min

304

S30400

18–20

8–10.50

0.08

0.75

0.045

0.03

0.1

304L

S30403

18–20

8–12

0.03

0.75

0.045

0.03

0.1

304Cu

S30430

17–19

8–10

0.08

0.75

0.045

0.03

3–4 Cu

304N

S30451

18–20

8–10.50

0.08

0.75

0.045

0.03

0.10–0.16

305

S30500

17–19

10.50–13

0.12

0.75

0.045

0.03

308

S30800

19–21

10–12

0.08

0.045

0.03

309

S30900

22–24

12–15

0.2

0.045

0.03

309S

S30908

22–24

12–15

0.08

0.045

0.03

310

S31000

24–26

19–22

0.25

1.5

0.045

0.03

310S

S31008

24–26

19–22

0.08

1.5

0.045

0.03

314

S31400

23–26

19–22

0.25

1.5
-3.0

0.045

0.03

316

S31600

16–18

10–14

0.08

0.75

0.045

0.03

0.10

2.0–3.0 Mo

316L

S31603

16–18

10–14

0.03

0.75

0.045

0.03

0.10

2.0–3.0 Mo

316F

S31620

16–18

10–14

0.08

0.2

0.10 min

1.75–2.50 Mo

316N

S31651

16–18

10–14

0.08

0.75

0.045

0.03

0.10
-0.16

2.0–3.0 Mo

317

S31700

18–20

11–15

0.08

0.75

0.045

0.03

0.10 max

3.0–4.0 Mo

317L

S31703

18–20

11–15

0.03

0.75

0.045

0.03

0.10 max

3.0–4.0 Mo

321

S32100

17–19

9–12

0.08

0.75

0.045

0.03

0.10 max

Ti 5(C+N) min, 0.70 max

329

S32900

23–28

2.5–5

0.08

0.75

0.04

0.03

1–2 Mo

330

N08330

17–20

34–37

0.08

0.75
-1.50

0.04

0.03

347

S34700

17–19

9–13

0.08

0.75

0.045

0.030

Nb + Ta, 10 x C min, 1 max

348

S34800

17–19

9–13

0.08

0.75

0.045

0.030

Nb + Ta, 10 x C min, 1 max, but 0.10 Ta max; 0.20 Ca

384

S38400

15–17

17–19

0.08

0.045

0.03

904L

19-23

23-28

0.02

0.045

0.035

Mo 4-5, Cu 1-2

Ferritic

405

S40500

11.5–14.5

0.08

0.04

0.03

0.1–0.3 Al, 0.60 max

409

S40900

10.5–11.75

0.05

0.08

0.045

0.03

Ti 6 x C, but 0.75 max

429

S42900

14–16

0.75

0.12

0.04

0.03

430

S43000

16–18

0.75

0.12

0.04

0.03

430F

S43020

16–18

0.12

1.25

0.06

0.15 min

0.60 Mo (optional)

430FSe

S43023

16–18

0.12

1.25

0.06

0.15 Se min

434

S43400

16–18

0.12

0.04

0.03

0.75–1.25 Mo

436

S43600

16–18

0.12

0.04

0.03

0.75–1.25 Mo; Nb+Ta 5 x C min, 0.70 max

442

S44200

18–23

0.2

0.04

0.03

446

S44600

23–27

0.25

0.2

1.5

0.04

0.03

Martensitic

403

S40300

11.5–13.0

0.60

0.15

0.5

0.04

0.03

410

S41000

11.5–13.5

0.75

0.15

0.04

0.03

414

S41400

11.5–13.5

1.25–2.50

0.15

0.04

0.03

416

S41600

12–14

0.15

1.25

0.06

0.15 min

0.060 Mo (optional)

416Se

S41623

12–14

0.15

1.25

0.06

0.15 Se min

420

S42000

12–14

0.15 min

0.04

0.03

420F

S42020

12–14

0.15 min

1.25

0.06

0.15 min

0.60 Mo max (optional)

422

S42200

11.0–12.5

0.50–1.0

0.20–0.25

0.5
-1.0

0.5

0.025

0.90–1.25 Mo; 0.20–0.30 V; 0.90–1.25 W

431

S41623

15–17

1.25–2.50

0.2

0.04

0.03

440A

S44002

16–18

0.60–0.75

0.04

0.03

0.75 Mo

440B

S44003

16–18

0.75–0.95

0.04

0.03

0.75 Mo

440C

S44004

16–18

0.95–1.20

0.04

0.03

0.75 Mo

Heat resisting

501

S50100

4–6

0.10 min

0.04

0.03

0.40–0.65 Mo

502

S50200

4–6

0.1

0.04

0.03

0.40–0.65 Mo

Martensitic precipitation hardening

630

S17400

15-17

3-5

0.07

0.04

0.03

Cu 3-5, Ta 0.15-0.45