Golden color after tig welding

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I was wondering what causes stainless steel to turn a golden color after welding. Thin materials usually don't do it, but sometimes the thicker stuff does. The welds usually look nice, but the heat affected area turns gold. I'm assuming that maybe i'm using a little too much amperage. Alot of times it's neccesary to get the proper penetration. Just wondering if i'm compromising the strength of the weld.
Reply:That is common with SS turning it a straw color. The darker the straw the more heat in the metal, when it gets purple its hot. There are color charts for tempering tool steels by the different colors, i know this dosen't pertain to this question but i thought i would add it...BobBob WrightSalem, Ohio  Birthplace of the Silver & Deming Drillhttp://groups.yahoo.com/group/southbend10k/http://groups.yahoo.com/group/sawking/1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun
Reply:The color is the result of non-inert gasses, mainly nitrogen and oxygen, reacting with the hot metal, forming compounds such as nitrides and oxides.When a weld is made, and allowed to cool, in a "totally" inert environment, such as in a controlled atmosphere glovebox, the weld and heat affected zone (HAZ) will remain entirely "silver/metallic" without any shades of color such as gold/blue/etc.When welding in open air, with inert shielding supplied through the torch nozzle, the completed weld and HAZ are exposed to air as the torch is moved forward, and if the temperature is still high enough, this material is discolored.  For critical applications, such at titanium welds, internal purging and trailing shields, or a glovebox , are/is used, to prevent reactive gas contamination.Titanium is severely embrittled when discolored beyond the light gold/straw range.  The corrosion resistance of stainless steels will eventually be affected at severe discoloration levels, not sure exactly what levels, but some blueing in normal and ok for open air TIG welds, although for high purity tubing in pharmaceutical/etc., light gold is probably the cut off for acceptance.The gas purity required to avoid any color has been studied for titanium, stainless, and the such.  The navy has color guidelines, and specifications for O2 and H2O limits in the gas when welding titanium.  The moisture in inert gas is often expressed in terms of dew point, the temperature at which moisture in the gas will condense.  Instruments are available to measure dew point, as well as H2O and O2 in parts per million (ppm).  High purity glovebox systems use equipment called a "dri-train" to remove O2 and H2O by circulating the glovebox atmosphere through a "dessicant" material bed.AWS D18.2 shows the internal surface color for a series of autogeneous orbital TIG welds on SS tubing and correlates the amount of oxygen in the argon purge gas to the color.  This study showed no color at 20 parts per million (ppm) O2, slight gold color at 50 ppm, and progressively darker blue/purple at increasing O2 levels.With regards to thick or thin material coloring different, it is all a matter of how cool or hot the metal is when exposed to air.  A small weld (low heat input) on thick material will be cooled rapidly by the large surrounding mass of metal and will be less discolored than the same weld on thinner material.
Reply:Great answer Pulsar. I was going to say that but my carpel tunnel from being on here and in the chat room was flaring up today.   Thanks for the excellent contribution.  John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com