Hi, Chad. (and David)
From Metals And How To Weld Them (James F Lincoln Arc Welding Foundation,)
Chapter 15 (pp 233-254) is devoted entirely to Stainless Steels and
High-Chromium Alloys; I won't choose any selections from it unless there are
p. 152: (addressing carbide precipitation and the effect on the HAZ and
------------------- beginning of quoted material -------------------
Stainless steels of the nickel-chromium variety are austenitic by nature even
room temperatures. When such steels are heated, as by welding operations,
carbide precipitation is apt to occur. The carbides, or carbon compounds, are
chromium as well as iron. When chromium is used up in this way, in chemical
union with the precipitated carbon, the remaining austenite is deficient in the
chromium element. The result is a serious reduction int he corrosion-resisting
properties of the stainless steel.
When the carbides are precipitated in stainless steel, they appear mainly at
grain boundaries. If subjected to corrosion, ethe carbides along the grain
boundaries will be attacked readily. Severe corrosive conditions will cause
grains to lose there coherence and the steel to fail.
In making a weld on stainless, there will always be a region some distance back
from the weld where the base metal will be at the exact temperature of the
precipitation range: 800-1500 F (Fig. 9-3). Consequently the stainless
qualities of the structure will be lost unless steps are taken to prevent
Austenitic stainless steels may be stabilized against carbide precipitation by
the addition of elements known as stabilizers. Such elements are columbium and
titanium. These elements have a ready affinity for carbon; they will grab and
hold fast the carbon that might otherwise have been attracted to the chromium.
Moreover, both titanium and columbium carbide resemble stainless steel itself
having high resistance to corrosion. Stabilized stainless steels, therefore,
will not fail under the combination of heat and corrosive attack. Austenitic
stainless steels also are available in several grades with extra low carbon
(ELC). Since there is less carbon, the possibility of chromium migration to
grain boundaries is minimized.
It is well to remember that the stabilized and ELC austenitic steels will
carbide precipitation. If the welded stainless is to be subjected to corrosive
conditions, particularly at elevated temperatures, the base metal should be a
stabilized steel and it should be welded with electrodes or filler rods that
have also been stabilized.
---------------------- end of quoted material ----------------------
David Scheidt wrote:
> On Mon, Mar 3, 2008 at 9:31 PM, Chadwick E. Labno <email@example.com> wrote:
>> I need to gas weld a stainless steel exhaust system and I'm looking for
>> suggestions on the correct filler rod. I heard - read - stainless TIG
>> rods will work but the counter man at the welding supply tells
>> me that is a bad choice but could not offer an alternative. Unless I can
>> find some stainless coat hangers I'm at a loss. Ok, just joking about
>> the hangers but what I may end up doing is cutting strips off
>> the exhaust pipes and use that. Any ideas? Thanks in advance.
> I don't know much about welding stainless, but I know it can be done
> with a torch. It requires a flux, I think. What sort of filler is to
> be used depends on the alloy the parts are made of. Lots of
> stainlesses have problems with welding, because the alloy changes, so
> different fillers are required, or the welded joints are less
> corrosion resistant. Sorry I can't be more helpful.
> The tin man has a booklet about welding stainless, and sells a flux.
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