What is stainless steel?

What is stainless steel?

In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable (inoxidizable), is a steel alloy with a minimum of 10.5% chromium content by mass.

Stainless steels are notable for their corrosion resistance, which increases with increasing chromium content. Additions of molybdenum increase corrosion resistance in reducing acids and against pitting attack in chloride solutions. Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure. Stainless steel’s resistance to corrosion and staining, low maintenance, and familiar lustre make it an ideal material for many applications where both the strength of steel and corrosion resistance are required.

Stainless steels are rolled into sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, surgical instruments, major appliances and as construction material in large buildings, such as the Chrysler Building. As well as, industrial equipment (for example, in paper mills, chemical plants, water treatment), and storage tanks and tankers for chemicals and food products (for example, chemical tankers and road tankers). Stainless steel’s corrosion resistance, the ease with which it can be steam cleaned and sterilized and no need for other surface coatings has also influenced its use in commercial kitchens and food processing plants.

The manufacture of stainless steel industrial products

The AISI defines the following ASTM A312 grades among others:

Also known as “marine grade” stainless steel due to its increased ability to resist saltwater corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants.

Design Features – Stainless Steel 304/304L

• Oxidation resistance up to 1650°F for continuous service and up to 1500°F where cyclic heating is involved.
• General purpose corrosion resistance.
• Non-hardenable except by cold working.
• Non-magnetic except when cold worked.
• May be susceptible to chloride stress corrosion cracking.
• Used where field working is employed.

Typical Applications – Stainless Steel 304/304L

• Sanitary
• Dairy and food processing
• Heat exchangers, evaporators
• Feedwater heaters

Tensile Requirements – Stainless Steel 304/304L

• Tensile Strength (KSI): 70
• Yield Strength (KSI): 25

Each alloy represents an excellent combination of corrosion resistance and fabricability. This combination of properties is the reason for the extensive use of these alloys which represent nearly one half of the total U.S. stainless steel production. The 18-8 stainless steels, principally Alloys 304, 304L, and 304H, are available in a wide range of product forms including sheet, strip, and plate. The alloys are covered by a variety of specifications and codes relating to, or regulating, construction or use of equipment manufactured from these alloys for specific conditions. Food and beverage, sanitary, cryogenic, and pressure-containing applications are examples.

Alloy 304 is the standard alloy since AOD technology has made lower carbon levels more easily attainable and economical. Alloy 304L is used for welded products which might be exposed to conditions which could cause intergranular corrosion in service.

Alloy 304H is a modification of Alloy 304 in which the carbon content is controlled to a range of 0.04-0.10 to provide improved high temperature strength to parts exposed to temperatures above 800°F.

316/316L Stainless Steel

Type 316/316L Stainless Steel is a molybdenum steel possessing improved resistance to pitting by solutions containing chlorides and other halides.
In addition, it provides excellent elevated temperature tensile, creep and stress-rupture strengths.

Chemcial Composition – 316/316L stainless steel tubing and pipe

Grade	316	316L
UNS Designation	S31600	S31603
Carbon (C) Max.	0.08	0.030*
Manganese (Mn) Max.	2.00	2.00
Phosphorous (P) Max.	0.045	0.045
Sulphur (S) Max.	0.030	0.030
Silicon (Si) Max.	1.00	1.00
Chromium (Cr)	16.0 – 18.0	16.0 – 18.0
Nickel (Ni)	10.0 – 14.0	10.0 – 14.0
Molybdenum (Mo)	2.0 – 3.0	2.0 – 3.0
Nitrogen (N)	—	—
Iron (Fe)	Bal.	Bal.
Other Elements	—	—

Typical Mechanical Properties- Stainless Steel 316/316L

Material	Form	Tensile Strength (ksi)	Yield Strength (ksi)	% Elongation	Hardness HB
Alloy 316L	316L Sheet AMS 5507	100 max	–	45	–
Alloy 316	316 Sheet AMS 5524	75 min	30	45	207 max

Design Features – 316/316L Stainless Steel

• Type 316 is more resistant to atmospheric and other mild environments than Type 304.  it is resistant to dilute solutions (i.e. 1-5%) of sulfuric acid up to 120°F.  However, in certain oxidizing acids, Type 316 is less resistant than Type 304.
• 316 is susceptible to carbide precipitation when exposed in the temperature range of 800° – 1500°F and therefore is susceptible to intergranular corrosion in the as-welded condition.  Annealing after welding will restore corrosion resistance.
• Type316L has the same composition as Type 316 except the carbon content is held below 0.03%.  Not unexpectedly, its general corrosion resistance and other properties closely correspond to those of Type 316.  However, it does provide immunity to intergranular attack in the as-welded condition or with short periods of exposure in the temperature range of 800° – 1500°F. The use of 316L is recommended when exposure in the carbide precipitation range is unavoidable and where annealing after welding is not practical.  However, prolonged exposure in this range may embrittle the material and make it susceptible to intergranular attack.
• The maximum temperature for scaling resistance in contnuous services is about 1650°F, and 1500°F for intermittent service.
• May be susceptible to chloride stress corrosion cracking.
• Non-hardenable; non-magnetic in the annealed condition, and slightly magnetic when cold worked.
• Improved corrosion resistance to chlorides.

Typical Applications – Stainless Steel 316/316L

• Nuclear
• Chemical Processing
• Rubber
• Plastics
• Pulp & Paper
• Pharmaceutical
• Textile
• Heat exchangers, condensers & evaporators

Tensile Requirements – Stainless Steel 316/316L

Tensile Strength (KSI): 70

Yield Strength (KSI): 25

KSI can be converted to MPA (Megapascals) by multiplying by 6.895.

310S Stainless Steel

310S Stainless Steel has excellent resistance to oxidation under constant temperatures to 2000°F.
Cyclic conditions reduce its oxidation resistance, and a maximum operating temperature of 1900°F is generally recommended if cycling is involved.
Having a lower coefficient of expansion than most 300 stainless steels, 310S may be used in operations involving moderately severe thermal cycling, such as rapid air cooling. It is not usually recommended for liquid quenching. Although 310S has less resistance to absorption of carbon and nitrogen than the higher alloys such as 330 and 333, it is widely used in moderately carburizing atmospheres such as encountered in petro-chem plants.
Because of ts high chromium and medium nickel contents, 310S may be used in atmospheres containng moderate amounts of sulfur.

Specifications – Stainless Steel 310S

• ASTM: A312, A403, A182
• ASME: SA312, SA403, SA182

Chemical Composition – Stainless Steel 310S

C	Cr	Mn	Mo	Ni	P	S	Si
Max		Max	Max		Max	Max	Max
0.08%	24% – 26%	2.0%	0.75%	19% – 22%	0.045%	0.03%	0.75%

Typical Mechanical Properties- Stainless Steel 310S

Alloy	Ultimate Tensile Strength (ksi)	Yield Strength (ksi)	Elongation %	Reduction of Area (%)	Hardness HRB
Type 310 Sheet (Sol Trtd) AMS 5521	75-100	30	40	–	95 max
Type 310  Bar (Sol Trtd) AMS 5651	–	–	–	–	187 max

Design Features – Stainless Steel 310S

• Austenitic stainless steel with excellent high temperature oxidation resistance.
• Good for continuous exposure to 2100°F, intermittent service to 1900°F.
• Better elevated temperature creep strength than the 18-8 grades.
• Good resistance to both carburizing and reducing environments.
• General corrosion resistance better than Types 304 and 309.
• May be susceptibe to chloride stress corrosion cracking. 
• Ease of fabrication.

Typical Applications – Stainless Steel 310S

• Sulfur bearing gas atmospheres
• Molten salt applications
• Heat exchangers
• Heat recuperator tubing

Tensile Requirements – Stainless Steel 310S

Tensile Strength (KSI): 75

Yield Strength (KSI): 30

317L Stainless Steel

317L is a molybdenum bearing austenitic chromium nickel steel similar to type 316, except the alloy content in 317L is somewhat higher.
It has a supperior corrosion resistance in special applications where it is desired to reduce contamination to a minimum. 317L was developed primarily to resist more effectively the attack of sulfurous acid compounds. Howerver, its proven ability to combat corrosion has widened its use considerably and is now being used for many other industrial applications.
The low carbon content of 317L provides immunity to intergranular corrosion in applications where heavy cross sections cannot be annealed after welding or where low temperature stress relieving treatments are desired.

Specifications – Stainless Steel 317L

• ASTM: A312, A403, A182
• ASME: SA312, SA403, SA182

Chemical Composition – Stainless Steel 317/317L

Grade	317	317L
UNS Designation	S31700	S31703
Carbon (C) Max.	0.08	0.035*
Manganese (Mn) Max.	2.00	2.00
Phosphorous (P) Max.	0.040	0.04
Sulphur (S) Max.	0.03	0.03
Silicon (Si) Max.	1.00	1.00
Chromium (Cr)	18.0–20.0	18.0–20.0
Nickel (Ni)	11.0–14.0	11.0–15.0
Molybdenum (Mo)	3.0–4.0	3.0–4.0
Nitrogen (N)	—	—
Iron (Fe)	Bal.	Bal.
Other Elements	—	—

Typical Mechanical Properties- Stainless Steel 317L

Material	Ultimate Tensile Strength (Mpa)	0.2 % Yield Strength (Mpa)	% Elongation in 2″	Rockwell B Hardness
Alloy 317	515	205	35	95
Alloy 317L	515	205	40	95
Minimum Mechanical Properties by ASTM A240 and ASME SA 240

Design Features – Stainless Steel 317L

• A molybdenum bearing austenitic chromium nickel steel with an alloy content somewhat higher than the 316 grades.
• Superior corrosion resistance in difficult environments.
• Higher creep, stress-to-rupture and tensile strengths than other stainless steels.
• Reduced intergranular precipitation of chromium carbides during welding and stress relieving as well as minimized possibility of corrosion failure from intergranular attack due to low carbon content.
• Resistance to pitting and crevice corrosion making 317L a successful life-cost product in a variety of highly corrosive environments.

Typical Applications – Stainless Steel 317L

• Flue gas desulfurization scrubber systems
• Chemical and petro-chemical processing equipment
• Pulp and paper plants
• Food processing equipment
• Textile equipment

Tensile Requirements – Stainless Steel 317L

Tensile Strength (KSI): 75

Yield Strength (KSI): 30

317L(1.4438) General Property

Alloy 317LMN and 317L are molybdenum-bearing austenitic stainless steel tube with greatly increased resistance to chemical attack as compared to the conventional chromium-nickel austenitic stainless steel pipe such as Alloy 304. In addition, 317LMN and 317L alloys offer higher creep, stress-to-rupture, and tensile strengths at elevated temperatures than conventional stainless steels. All are low carbon or “L” grades to provide resistance to sensitization during welding and other thermal processes.

The “M” and “N” designations indicate that the compositions contain increased levels of molybdenum and nitrogen respectively. The combination of molybdenum and nitrogen is particularly effective in enhancing resistance to pitting and crevice corrosion, especially in process streams containing acids, chlorides, and sulfur compounds at elevated temperatures. Nitrogen also serves to increase the strength of these alloys. Both alloys are intended for severe service conditions such as flue gas desulfurization (FGD) systems.

In addition to excellent corrosion resistance and strength properties, the Alloys 316, 316L, and 317L Cr-Ni-Mo alloys also provide the excellent fabricability and formability which are typical of the austenitic stainless steel tubing .

317L (1.4438) Heat Treatment

Annealing

The austenitic stainless steel pipe are provided in the mill annealed condition ready for use. Heat treatment may be necessary during or after fabrication to remove the effects of cold forming or to dissolve precipitated chromium carbides resulting from thermal exposures. For the Alloys 316 and 317L the solution anneal is accomplished by heating in the 1900 to 2150°F (1040 to 1175°C) temperature range followed by air cooling or a water quench, depending on section thickness. Cooling should be sufficiently rapid through the 1500 to 800°F (816 to 427°C) range to avoid reprecipitation of chromium carbides and provide optimum corrosion resistance. In every case, the metal should be cooled from the annealing temperature to black heat in less than three minutes.

Forging

The recommended initial temperature range is 2100-2200°F (1150-1205°C) with a finishing range of 1700-1750°F (927-955°C).

Annealing

317LMN and Alloy 317L stainless steels can be annealed in the temperature range 1975-2150°F (1080-1175°C) followed by an air cool or water quench, depending on thickness. Plates should be annealed between 2100°F (1150°C) and 2150°F (1175°C). The metal should be cooled from the annealing temperature (from red/white to black) in less than three minutes.

Hardenability

These grades are not hardenable by heat treatment. 
Alloys 316 and 317L stainless steel tube cannot be hardened by heat treatment.

321/321H Stainless Steel

Type 321 is basic type 304 modified by adding titanium in an amount at least 5 times the carbon plus nitrogen contents.
These titanium bearing stainless steels are stabilized against carbide precipitation and designed for eperation within the damaging temperature range where carbide precipitation develops. In this type of steel, the carbon combines preferentially with titanium to form a harmless titanium carbide, leaving the chromium in solution ot maintain full corrosion resistance.

Specifications -321/321H Stainless Steel

• ASTM:A312, A403, A182
• ASME: SA312, SA403, SA182

Chemical Composition – 321/321H Stainless steel

Grade	321	321H
UNS Designation	S210000	S32109
Carbon (C) Max.	0.08	0.04 – 0.10
Manganese (Mn) Max.	2.00	2.00
Phosphorous (P) Max.	0.040	0.040
Sulphur (S) Max.	0.030	0.030
Silicon (Si) Max.	0.75	0.75
Chromium (Cr)	17.0 – 20.0	17.0 – 20..0
Nickel (Ni)	9.0 – 12.0	9.0 – 12.0
Molybdenum (Mo)	—	—
Nitrogen (N)	0.1 Max.	0.1 Max.
Iron (Fe)	Bal.	Bal.
Other Elements	Ti=5(C) to 0.70%	Ti=5(C) to 0.60%

*The titanium content shall not be less than 5 times the carbon content and not more than 0.60%.  321H requires the titanium content to be not less than 4 times the carbon content and not more than 0.60%.

Typical Mechanical Properties

Material	Tensile Strength Rm, N/mm²	Yield Strength Rp 0.2, N/mm²	% Elongation
Alloy 321 Tube	500-730	200	35

Design Features – 321/321H Stainless Steel

• Immune to intergranular corrosion when heated within the carbide precipitation range.
• Titanium addition eliminates the formation of chromium carbides at the grain boundaries by tying up the carbon and nitrogen as titanium carbides or nitrides.
• Better high temperature properties than 304 or 304L.  Generally used for parts which are intermittently heated up to 1500°F. For continuous service the alloy is good to 1650°F.
• May be susceptible to chloride stress cracking.
• Excellent weldability in field.
• Type 321H has high carbon (.04 to .10) for better high temperature creep properties.

Typical Applications – 321/321H Stainless Steel

• High temperature chemical process heat exchanger tubes
• Refineries
• High temperature steam service

Tensile Requirements – 321/321H Stainless Steel

• Tensile Strength (KSI): 75
• Yield Strength (KSI): 30

410 Stainless Steel

Type 410 is a martensitic stainless steel which is magnetic, resists corrosion in mild environents and has fairly good ductility.
410 pipe is used where abrasion and wear resistance is needed, combined with fair resistance to general corrosion and oxidation.

Specifications – Stainless Steel 410

• ASTM: A268, A815, A182

Chemical Composition – Stainless Steel 410

C	Cr	Mn	Ni	P	S	Si
Max		Max		Max	Max	Max
0.15%	11.5% – 13.5%	1.0%	0.5%	0.04%	0.03%	0.75%

Design Features – Stainless Steel 410

• Martensitic stainless steel with high mechanical properties.
• Ferromagnetic in the annealed or hardened condition.
• Contains minimum amount of chromium to impart stainless steel properties.
• Resists oxidation and scaling up to 1200°F.
• Resists abrasion and wear better than most 300 series stainless steels.
• Good sulphide stress corrosion cracking resistance.
• Hardness is one of Type 410’s best features.

Typical Mechanical Properties- Stainless Steel 410

Material	Tempering Temp °C (°F)	0.2 % Yield Strength (Mpa)	Ultimate Tensile Strength (Mpa)	% Elongation in 2″	% Reduction of Area	Charpy V Notch Impact Strength (J)	Hardness Brinell
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	260 (500)	1089	1331	17	62	76	401
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	317 (700)	1069	1296	17	60	66	401
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	482 (900)	1014	1303	18	58	38	401
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	538 (1000)	917	965	19	62	33	285
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	593 (1100)	724	827	20	63	52	248
Alloy 410 Bar Hardened 1850°F (1010°C) 30 mins, oil quench, tempered 4 Hrs	649 (1200)	634	731	21	65	119	223

Typical Applications – Stainless Steel 410

• Pipelines transporting fluids mixed with solids like coal, sand or gravel.

Tensile Requirements – Stainless Steel 410

Tensile Strength (KSI): 60

Yield Strength (KSI): 30

Duplex 2205 (UNS S31803)

Duplex 2205 (UNS S31803), or Avesta Sheffield 2205 is a ferritic-austenitic stainless steel.
The high amounts of molybdenum and chromium content in 2205 offer strength, improved pitting and consistent stress corrosion cracking resistance. 2205 integrates the best features of austenitic and ferritic steels (as well as nearly equal amounts of austenite and ferrite) and can be welded with common stainless steel welding techniques – its uniform composition minimizes localized corrosion.

Specifications – Duplex 2205

• ASTM: A790, A815, A182
• ASME: SA790, SA815, SA182

Chemical Composition – Duplex 2205 

C	Cr	Fe	Mn	Mo	N	Ni	P	S	Si
Max			Max				Max	Max	Max
.03%	22%-23%	BAL	2.0%	3.0% -3.5%	.14% – .2%	4.5%-6.5%	.03%	.02%	1%

Design Features – Duplex 2205

• High Strength
• Exceptional uniform corrosion resistance
• Better heat conductivity and lower thermal expansion than austenitic steels
• Resistance to stress corrosion cracking
• Resistance to erosion
• Resistance to corrosion fatigue
• Resistance to pitting
• Resistance to crevace corrosion
• Resistance to sulfide stress corrosion cracking

Typical Applications – Duplex 2205

• Heat exchangers, tubes and pipe for production and handling of gas and oil
• Heat exchangers and pipes in desalination plants
• Pressure vessels, pipes, tanks and heat exchangers for processing and transport of various chemicals
• Pressure vessels, tanks and pipes in process industries handling chlorides
• Rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized
• Cargo tanks, piping and welding consumables for chemical tankers

Tensile Requirements – Duplex 2205

Tensile Strength (KSI): 65

Yield Strength (KSI): 90

Stainless steels are also classified by their crystalline structure:

• Austenitic stainless steels comprise 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 is 18% chromium and 10% nickel, commonly known as 18/10 stainless is often used in flatware. Similarly 18/0 and 18/8 is also available. ¨Superaustenitic〃 stainless steels, such as alloy AL-6XN and 254SMO, exhibit great resistance to chloride pitting and crevice corrosion due to high Molybdenum contents (>6%) and nitrogen additions and the higher nickel content ensures better resistance to stress-corrosion cracking over the 300 series. The higher alloy content of “Superaustenitic” steels means they are fearsomely expensive and similar performance can usually be achieved using duplex steels at much lower cost.
• Ferritic stainless steels are highly corrosion resistant, but far lessdurable than austenitic grades and cannot be hardened by heat treatment. They contain between 10.5% and 27% chromium and very little nickel, if any. Most compositions include molybdenum; some, aluminium or titanium. Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni.
• 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%), no nickel, and about 0.1-1% carbon (giving it more hardness but making the material a bit more brittle). It is quenched and magnetic. It is also known as “series-00” steel.
• 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 60:40. Duplex steel 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 and lower nickel contents than austenitic stainless steels.

Stainless standard

Standards for stainless steel seamless tube & pipe:

• Hydraulic
• Instrumentation
• Heat exchangers
• Pipe ASME / ANSI
• ISO & metric
• High Temperature

Our Stainless Steel Pipes meets mainly the following standards:

Stainless steel of tube number comparision between china and international

Stainless steel pipe is one of the more standardized materials in the building and engineering industries.

Standard:

• ASTM Standards: ASTM A312, ASTM A213, ASTM A269, ASTM A376
• European Standards: DIN 17456, DIN 17458, EN 10216, EN 10297
• Japanese Standards: JIS G 3459, JIS GS3463, GS3467, JIS G3448
• Russian Standards: GOST 9940, GOST 9941

Grades:

• ASTM Standards: 304/L/H, 316/L/H, 321/H, 317/L, 347/H, 310S, 2205, 2507, 904L, etc.
• European Standards: 1.4301, 1.4307, 1.4307, 1.4401, 1.4404, 1.4541, 1.4550, 1.4438, 1.4845, etc.
• Japanese Standards: SUS304, SUS304H, SUS304L, SUS309S, SUS310S, SUS316, SUS316L, SUS317, SUS317L, SUS321, SUS347
• Russian Standards: 08X18B10, 03X18H11, 08X17H12M2T, 03X17H12M2, 08X17H15M3T, 03X16H15M3, 08X18H10T, 12X18H20T, 08X18H12B, 10X17H13M2T

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

Please notice that you might be interested in the other technical articles we’ve published:

  • CHEMICAL COMPOSITIONS FOR COMMON STAINLESS STEELS

  • Stainless Steel Chemical Composition and Mechanical Properties

  • The History of Stainless Steel

References:

• https://en.wikipedia.org/wiki/Stainless_steel
• https://www.yaang.com/what-is-stainless-steel.html