Composition of Typical Stainless Steels
(ASTM A270)
|
|
304 |
304L |
316 |
316L |
|
|
*UNS: S30400 |
UNS: S30403 |
UNS: S31600 |
UNS: S31603 |
|
Element |
**Composition, % |
|||
|
Carbon, max |
0.08 |
0.035 |
0.08 |
0.035 |
|
Manganese, max |
2.00 |
2.00 |
2.00 |
2.00 |
|
Phosphorus, max |
0.040 |
0.040 |
0.040 |
0.040 |
|
Sulfur, max |
0.030 |
0.030 |
0.030 |
0.030 |
|
Silcon, max |
0.75 |
0.75 |
0.030 |
0.030 |
|
Nickel |
8.00 - 11.00 |
8.00 - 13.00 |
10.00 - 14.00 |
10.00 - 15.00 |
|
Chromium |
18.00 - 20.00 |
18.00 - 20.00 |
16.00 - 18.00 |
16.00 - 18.00 |
|
Molybdenum |
none |
none |
2.00 - 3.00 |
2.00 - 3.00 |
* United Numbering System
** Balance of composition is iron.
Notes: 1. Steel is any alloy of iron and carbon that contains less than 2% carbon. 304 and 316 stainless steels are classified as austenitic (contains nonmagnetic austenitic grains) stainless steels. They are non-magnetic materials with a basic composition of 18% chromium and 8% nickel: the term "18/8 stainless" refers to this composition. Adding more chromium and nickel increases corrosion resistance. Small amounts of molybdenum greatly increase corrosion resistance. 304 and 306 are designations of the American Iron and Steel Institute (AISI). 2. 304L and 316L are low carbon alloys developed to minimize carbide precipitation during welding which may lead to corrosion problems. 3. Passivation refers to the formation of an oxide film (Fe O· Cr2O3 in the case of stainless steel) that serves as an impervious protective layer on the surface of the metal.
Typical Properties of 304 and 316
Stainless Steels
Density Range: 7861 to 8082 kg m-3
Thermal Conductivity (at 100° C): 16.3 W m-1 °C-1
Specific Heat (0°
C to 100° C): 0.46 kJ kg-1 °C-1
Coefficient of Thermal Expansion (20°C to 500°C): 17 x 10-6 m/m per °C
Finishes for Stainless Steel (ASTM
A270)
|
Finish Number |
Finish |
|
80 |
A ground finish produced by grinding a tube with an abrasive belt impregnated with No. 80 grit. |
|
120 |
A ground finish produced by grinding a tube with an abrasive belt impregnated with No. 120 grit. |
|
180 |
A ground finish produced by grinding a tube with an abrasive belt impregnated with No. 180 grit. |
Grit and Roughness Average
|
Grit Number |
Roughness Average (micro inches) |
|
150 |
27-32 |
|
180 |
16-23 |
|
240 |
14-18 |
|
320 |
8-10 |
3A standards specify a highly polished surface finish (150 grit) for stainless steel.
Joining Stainless Steel Tubing
Manual Connections: Clamp, John Perry, Bevel Seat
Butt Welds: Stainless steel tubing (including fittings, etc) may be joined with butt welds using a process known as gas tungsten-arc welding (GTAC). It is also called TIG (tungsten inert gas) welding. Heating is caused by an arc between the surface of the steel and a tungsten electrode. The electrode is not consumed during the process, so filling metal may be needed depending on the weld. An inert gas (such as agron) is used as a shielding gas to prevent atmospheric contamination of the weld. TIG welding requires a high degree of skill. It can produce high quality welds on many materials in addition to stainless steel: aluminum, magnesium, carbon steel, copper, nickel, and titanium.
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