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Re: stainless conductivities



A couple respondents have pointed out that the electrical conductivity
of stainless steel is, in fact, not real high. I will corroborate this
with one more piece of information.

The typical "resistance wire" we use in wire-wound resistors and in
heaters is nichrome wire. The name, of course, indicates it is an
alloy with nickel and chromium content.

From chemistry.csudh.edu/oliver/chemdata/alloys.htm: Nichrome is an alloy with
the approximate composition of 60% Ni, 25% Fe, and 15% Cr.

That pretty much makes it
stainless steel. As has been pointed out, there are many formulations
for stainless steel; i.e. the term is fairly generic and covers a broad
range of steels formulated mostly with iron, nickel, and chromium.
Therefore, calling nichrome wire "stainless steel" is not
inappropriate.

I suspect that a metallurgist would disagree with you. For example, nothing in
the table of alloys given in the Web site above which has "steel" in its name
is less than 75% Fe. But of course that is just a matter of nomenclature.

Wires made of any of the stainless steels (such as 304 or 316) have a
lot higher resistance than similar-sized wires made of copper.


Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270

I think I may have lost the point of this thread. Are we discussing why
different metals have different conductivities? Or are we saying that stainless
steels have an anomalously low conductivity?

That metals have different resistivities is (like the mechanism of
ferromagnetism discussed in another thread) not usually covered in undergrad
courses because it is so complex. Conductivity depends on intrinsic metal
properties like density of states at the Fermi surface, but also such
processing dependent parameters as the level of impurities and presence and
size of crystal impurfections.

If we are saying that SS has an anomalously low conductivity, then we need to
say what the standard is. A deviation from the Weidermann-Franz realtion might
be taken as evidence of anomalous transport. Here is some data taken from the
CRC:

Substance: thermal electrical product
conductivity resistivity

(J/s-cm-K) (microohm-cm) (yucky units)

Ingot iron 0.73 9 6.6
Plain carbon steel 0.52 10 5.2
SS 304 0.17 72 12
Aluminium 3003 1.56 4 6.2
Copper 3.89 1.7 6.6
Yellow brass 1.19 7 8.3
Cupronickel 30% 0.29 35 10
Red brass 0.73 11 8.0
Solder 50-50 0.30 15 4.5
Constantan 0.22 49 11
Titanium 0.17 80 14
Zinc 1.07 6 6.4
Zirconium 0.17 41 7.0

So stainless does seem to be on the extremes both of resistivity and the
Weidermann-Franz ratio, though it isn't exactly alone. Interesting that it
shares the extreme with (commercial) titanium, since one usually thinks of
alloys as having the higher resistance.

Tim Sullivan
sullivan@kenyon.edu