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The main elements in stainless steel

Stainless steel or corrosion-resistant steel is a kind of metallic alloy that is found in a variety of forms. It serves our practical needs so well that it is difficult to find any sphere of our life, where we do not use this type of steel. The major components of stainless steel are: iron, chromium, carbon, nickel, molybdenum and small quantities of other metals.

Chromium and Nickel:
Chromium is the element that makes stainless steel stainless. It is essential in forming the passive film. Other elements can influence the effectiveness of chromium in forming or maintaining the film, but no other element by itself can create the properties of stainless steel.
At about 10.5% chromium, a weak film is formed and will provide mild atmospheric protection. By increasing the chromium to 17-20%, which is typical in the type-300 series of austenitic stainless steels, the stability of the passive film is increased. Further increases in the chromium content will provide additional protection.

Symbol

Element 

 Al  Aluminum
 C  Carbon
 Cr  Chromium
 Cu  Copper
 Fe  Iron
 Mo  Molybdenum
 Mn  Manganese
 N  Nitrogen
 Ni  Nickel
 P  Phosphorous
 S  Sulfur
 Se  Selenium
 Ta  Tantalum
 Ti  Titanium
Nickel will stabilize the austenitic structure (the grain or crystal structure) of the stainless steel and enhance the mechanical properties and fabrication characteristics. A nickel content of 8-10% and above will decrease the tendency of the metal to crack due to stress corrosion. Nickel also promotes repassivation in case the film is damaged.
Manganese:
Manganese, in association with nickel, performs many of the functions attributed to nickel. It will also interact with the sulfur in stainless steel to form manganese sulfites, which increases the resistance to pitting corrosion. By substituting manganese for nickel, and then combining it with nitrogen, strength is also increased.
Molybdenum:
Molybdenum, in combination with chromium, is very effective in stabilizing the passive film in the presence of chlorides. It is effective in preventing crevice or pitting corrosion. Molybdenum, next to chromium, provides the largest increase in corrosion resistance in stainless steel. Edstrom Industries uses 316 stainless because it contains 2-3% molybdenum, which gives protection when chlorine is added to the water.
Carbon:
Carbon is used to increase strength. In the martensitic grade, the addition of carbon facilitates hardening through heat-treating.
Nitrogen:
Nitrogen is used to stabilize the austenitic structure of stainless steel, which enhances its resistance to pitting corrosion and strengthens the steel. Using nitrogen makes it possible to increase the molybdenum content up to 6%, which improves corrosion resistance in chloride environments.
Titanium and Miobium:
Titanium and Miobium are used to reduce the sensitization of stainless steel. When stainless steel is sensitized, intergranular corrosion can occur. This is caused by the precipitation of chrome carbides during the cooling phase when parts are welded. This depletes the weld area of chromium. Without the chromium, the passive film cannot form. Titanium and Niobium interact with carbon to form carbides, leaving the chromium in solution so a passive film can form.
Copper and Aluminum:
Copper and Aluminum, along with Titanium, can be added to stainless steel to precipitate its hardening. Hardening is achieved by soaking at a temperature of 900 to 1150F. These elements form a hard intermetallic microstructure during the soaking process at the elevated temperature.
Sulfur and Selenium:
Sulfur and Selenium are added to 304 stainless to make it machine freely. This becomes 303 or 303SE stainless steel, which is used by Edstrom Industries to make hog valves, nuts, and parts that are not exposed to drinking water.
Related stainless steel products
Austenitic stainless steel
Steel No. Standard No. Type Chemical composition Other
C Si S P Mn Cr Ni Mo Other ób ós δ5 HB
00Cr17Ni14Mo2 GB1220 Bar 0.03 1 0.03 0.035 2 16-18 12-15 2-3 480 177 40 187 ψ%:60
00Cr17Ni14Mo2 GB4237 Plate 0.03 1 0.03 0.035 2 16-18 12-15 2-3 480 177 40 187
00Cr17Ni14Mo2 GB/T14976 Pipe 0.03 1 0.03 0.035 2 16-18 12-15 2-3 480 175 35
00Cr19Ni10 GB1220 Bar 0.03 1 0.03 0.035 2 18-20 8-12 480 177 40 187 ψ%:60
00Cr19Ni10 GB4237 Plate 0.03 1 0.03 0.035 2 18-20 8-12 480 177 40 187
00Cr19Ni10 GB/T14976 Pipe 0.03 1 0.03 0.035 2 18-20 8-12 480 175 35
0Cr17Ni12Mo2 GB1220 Bar 0.8 1 0.03 0.035 2 16-18.5 10-14 2-3 520 205 40 187 ψ%:60
0Cr17Ni12Mo2 GB4237 Plate 0.8 1 0.03 0.035 2 16-18 10-14 2-3 520 205 40 187
0Cr17Ni12Mo2 GB/T14976 Pipe 0.8 1 0.03 0.035 2 16-18.5 10-14 2-3 520 205 35
0Cr18Ni9 GB1220 Bar 0.7 1 0.03 0.035 2 17-19 8-11 520 205 40 187 ψ%:60
0Cr18Ni9 GB4237 Plate 0.7 1 0.03 0.035 2 17-19 8-11 520 205 40 187
0Cr18Ni9 GB/T14976 Pipe 0.7 1 0.03 0.035 2 17-19 8-11 520 205 35
0Cr18Ni10Ti GB1220 Bar 0.8 1 0.03 0.035 2 17-19 9-12 Ti:5C 520 205 40 187 ψ%:50
0Cr18Ni10Ti GB4237 Plate 0.8 1 0.03 0.035 2 17-19 9-12 Ti:5C 520 205 40 187
0Cr18Ni10Ti GB/T14976 Pipe 0.8 1 0.03 0.035 2 17-19 9-12 Ti:5C 520 205 35
0Cr18Ni12Mo2Ti GB1220 Bar 0.8 1 0.03 0.035 2 16-19 11-14 1.8-2.5 Ti:5C-0.7 530 205 40 187 ψ%:55
0Cr18Ni12Mo2Ti GB4237 Plate 0.8 1 0.03 0.035 2 16-19 11-14 1.8-2.5 Ti:5C-0.7 530 205 37 187
0Cr18Ni12Mo2Ti GB/T14976 Pipe 0.8 1 0.03 0.035 2 16-19 11-14 1.8-2.5 Ti:5C-0.7 530 205 35
1Cr18Ni9 GB4237 Plate 0.15 1 0.03 0.035 2 17-19 8-10 520 205 40 187
1Cr18Ni9 GB5310 Pipe 0.15 1 0.03 0.035 2 17-19 8-10 Cu:0.2 520 205 35
0Cr25Ni20 GB1220 Bar 0.08 1 0.03 0.035 2 24-26 19-22 520 206 40 187
ASTM A312/A312M
Steel No. Type Chemical composition
C Si S P Mn Cr Ni Mo Other ób ós δ5 HB
TP304 0.08 0.75 0.03 0.04 2 18-20 8-11 515 205 35
TP304H 0.04-0.1 0.75 0.03 0.04 2 18-20 8-11 515 205 35
TP304L 0.035 0.75 0.03 0.04 2 18-20 8-13 485 170 35
TP316L 0.035 0.75 0.03 0.04 2 16-18 10-15 2-3 485 170 35
TP321 0.08 0.75 0.03 0.04 2 17-20 9-13 Ti:5C%-0.7 515 205 35
ASTM A312 Mechanical Property:
Steel Grade Heat Treatment Temperure Min. º F(º C) Tensile Strength Ksi (MPa), Min. Yield Strength Ksi (MPa), Min. Elongation %, Min
TP304 Solution 1900 (1040) 75(515) 30(205) 35
TP304L Solution 1900 (1040) 70(485) 25(170) 35
TP304H Solution 1900 (1040) 75(515) 30(205) 35
TP310S Solution 1900 (1040) 75(515) 30(205) 35
TP316 Solution 1900(1040) 75(515) 30(205) 35
TP316L Solution 1900(1040) 70(485) 25(170) 35
TP316H Solution 1900(1040) 75(515) 30(205) 35
TP316Ti Solution 1900(1040) 75(515) 30(205) 35
TP321 Solution 1900(1040) 75(515) 30(205) 35
TP321H Solution Cold: 2000(1100) Hot: 1925(1050) 75(515) 30(205) 35
TP347 Solution 1900(1040) 75(515) 30(205) 35
TP347H Solution Cold: 2000(1100) Hot: 1925(1050) 75(515) 30(205)
ASTM A312 Equivalent steel grade:
ASTM A312 JIS G3459 DIN 17440 BS NF
TP304 SUS 304 TP X5CrNi 18 9 304S18 A 49-230
TP304H SUS 304 HTP 304S59 A 49-214
TP310 304 LTP X2 CrNi 19 9 304S14 A 49-230
TP316 SUS 304L TP
TP316H 310STP X5 CrNiMo 18 10 316S18 A 35-573
TP316L SUS 316 TP 316S59 A 49-230
TP321 SUS 316 LTP X2 CrNiMo 18 10 316S14 A 49-230
TP347 316 HTP x10 CrNiTi 18 9 321S18 A 49-230
TP347H SUS 316 LTP X5 CrNiNb 18 9 347S18 A 35-573
Nominal wall thickness for ASTM A312(Seamless and straight seame welded steel pipes)
NPS ASTM A312  WT Tolerance, %
+
1/8-2 1 /2 20.0 12.5
3~18, t/D≤ 5% 22.5 12.5
3~18, t/D> 5% 15.0 12.5
≥ 20, welded 17.5 12.5
≥ 20, seamless, t/D≤ 5% 22.5 12.5
≥ 20, seamless, t/D> 5% 15.0 12.5
ASTM A312 Stainless Steel Pipes OD Tolerance
NPS ASTM A312  OD Tolerance
+
inch mm inch mm
1/8~1 1 /2 > 1 1 /2~4 > 4~8 > 8~18 > 18~26 > 26~34 > 34~48 1/64(0.015) 1/32(0.031) 1/16(0.062) 3/32(0.093) 1/8(0.125) 5/32(0.156) 3/16(0.187) 0.4 0.8 1.6 2.4 3.2 4.0 4.8 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 0.8 0.8 0.8 0.8 0.8 0.8 0.8


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