Austenitic Stainless Steels
Physical Properties and Specifications
The physical properties of the austenitic stainless steels are different than those of iron and steel in that the elastic moduli are slightly lower and the thermal conductivity is substantially lower, while the thermal expansivity and electrical resistivity are significantly higher.
The austenitic stainless steels are also nonmagnetic in the annealed condition if they contain no delta ferrite. Small amounts of delta ferrite that result from welding, or martensite produced by cold work, will produce a small amount of ferromagnetism.
Some typical physical property values are listed in Table 4.6.
Table 4.6 Physical Properties
|
UNS No. |
Type or Alloy |
Density lb/in.3 |
Modulus of Elasticity 106 psi |
Linear Expansion 68-212°F x 10-6/°F |
Thermal Conductivity Btu/ft·hr·°F |
Heat Capacity Btu/lb·°F |
Electrical Resistivity mW·in. |
|
S20100 |
201 |
0.28 |
29 |
9.2 |
9.4 |
0.12 |
27.2 |
|
S20200 |
202 |
0.28 |
29 |
9.4 |
9.4 |
0.12 |
27.2 |
|
S20400 |
Nitronic 30 |
0.28 |
28 |
9.4 |
--- |
--- |
--- |
|
S30100 |
301 |
0.29 |
29 |
9.4 |
9.4 |
0.12 |
28.3 |
|
S30200 |
302 |
0.29 |
29 |
9.4 |
9.4 |
0.12 |
28.3 |
|
S30430 |
302HQ |
0.29 |
28 |
9.4 |
9.4 |
0.12 |
28.3 |
|
S30400 |
304 |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
27.6 |
|
S30403 |
304L |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
27.6 |
|
S30451 |
304N |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
27.6 |
|
S30500 |
305 |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
29.8 |
|
S31600 |
316 |
0.29 |
29 |
9.2 |
7.8 |
0.12 |
29.5 |
|
S31603 |
316L |
0.29 |
29 |
9.2 |
7.8 |
0.12 |
29.5 |
|
S31703 |
317L |
0.29 |
29 |
8.9 |
7.8 |
0.12 |
29.5 |
|
S31726 |
317LMN |
0.29 |
29 |
8.9 |
7.8 |
0.12 |
33.5 |
|
S21800 |
Nitronic 60 |
0.28 |
26.2 |
8.8 |
--- |
0.12 |
--- |
|
S20161 |
Gall-Tough |
0.28 |
24.8 |
9.6 |
7.1 |
0.12 |
28.2 |
|
S30300 |
303 |
0.28 |
--- |
10.4 |
--- |
0.12 |
28.3 |
|
S30323 |
303Se |
0.28 |
--- |
10.4 |
--- |
0.12 |
28.3 |
|
S30800 |
308 |
0.29 |
29 |
9.6 |
8.8 |
0.12 |
28.3 |
|
S30883 |
308L |
0.29 |
29 |
9.6 |
8.8 |
0.12 |
28.3 |
|
S30409 |
304H |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
27.6 |
|
S32100 |
321 |
0.29 |
29 |
9.4 |
8.7 |
0.12 |
27.6 |
|
S34700 |
347 |
0.29 |
28 |
10.4 |
--- |
0.12 |
28.3 |
|
S31609 |
316H |
0.29 |
29 |
9.2 |
7.8 |
0.12 |
29.5 |
|
S30815 |
253MA |
0.28 |
29 |
9.4 |
8.7 |
0.12 |
33.5 |
Table 4.6 Physical Properties (continued)
|
UNS No. |
Type or Alloy |
Density lb/in.3 |
Modulus of Elasticity 106 psi |
Linear Expansion 68-212°F x 10-6/°F |
Thermal Conductivity Btu/ft·hr·°F |
Heat Capacity Btu/lb·°F |
Electrical Resistivity mW·in. |
|
S30908 |
309S |
0.29 |
29 |
10 |
--- |
0.12 |
30.7 |
|
S30909 |
309H |
0.29 |
29 |
10 |
--- |
0.12 |
30.7 |
|
S31008 |
310S |
0.29 |
29 |
8.6 |
7.0 |
0.12 |
31.5 |
|
S31009 |
310H |
0.29 |
29 |
8.6 |
7.0 |
0.12 |
31.5 |
Austenitic Stainless Steel vs. Carbon Steel Physical Properties
Physical properties of stainless steels vary between their categories which have a significant effect on their applications (e.g., weldability). For example, the difference in thermal expansivity between carbon steel and these stainless steels is great enough to require that this be taken into account when designing structures containing both metals for elevated temperature service.
A comparison of physical properties between carbon steel and austenitic stainless is shown in the following Connecting-the-Codes© Example.
|
Connecting-the-Codes© Example: Comparison of Physical Properties |
|||
|
Physical Property |
UNS S30400 (Type 304) |
Carbon Steel |
Welding Remarks |
|
melting point |
2550-2650°F 1400-1450°C |
2800°F 1540°C |
UNS S30400 (Type 304) requires less heat to produce fusion, which means faster welding for the same heat or less heat for the same speed. |
|
magnetic response |
non-magnetic all temperatures |
magnetic to over 1300°F 705°C |
Duplex stainless steels are magnetic. |
|
rate of heat conductivity (% at 212°F) (100°C) (% at 1200°F) (650°C) |
28% 66% |
100% 100% |
UNS S30400 (Type 304) conducts heat much more slowly than carbon steel, thus promoting sharper heat gradients. This accelerates warping, especially in combination with higher expansion rates. Slower diffusion of heat expansion through the base metal means weld zones remain hot longer; one result of which may be longer dwell times in the carbide precipitation range unless excess heat is artificially removed (e.g. chill bars, etc.). |
|
electrical resistance (annealed) (microhm-cm approx.) At 68°F (20°C) At 1625°F (885°C) |
72 126 |
12.5 125 |
This is of importance in electrical fusion methods. The higher electrical resistance of UNS S30400 (Type 304) results in the generation of more heat for the same current or the same heat with lower current, as compared with carbon steel. This, together with its low rate of heat conductivity, accounts for the effectiveness of resistance welding methods on UNS S30400 (Type 304). |
|
thermal expansion over range indicated in./in./F x 10-6 in./in./C x 10-6 |
9.8 (68-932°F) 17.6 (20-500°C) |
6.5 (68-1162°F) 11.7 (20-628°C) |
UNS S30400 (Type 304) expands and contracts at a faster rate than carbon steel, which means that increased expansion and contraction must be allowed to control warping and the development of thermal stresses upon cooling. For example, more tack welds are used for stainless steel than for carbon steel. |