TIG shielding questions; bluish area and dark line

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What causes the bluish area and dark line in the following photo?  Is this a bad sign for weld quality?From this photo can you give me any advice?  I am using a #7 gas lens with 15 cfh using a miller 150 STH in pulse mode with 1/16" RED tungsten and .035 filler rod.Last edited by febikes; 09-19-2011 at 08:42 AM.
Reply:That weld looks great to me.
Reply:Hey febikes,The bluish coloration you see is simply the metal responding to heat. The color is a defining way to estimate the level of temperature induced into the steel. Each color, ie.; blue/straw is a change in temperature that should be monitored as the area is your HAZ & you don't want to soften the surrounding area excessively. Here's a good chart to show you heat/color & affects on steel.Dennyhttp://members.optusnet.com.au/terry...rChartEtc.htmlComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:If you are talking about the cone shaped line that widens out as it goes to the right, I believe that is an effect of the shielding gas and post flow. I get similar effects, especially if I weld a thicker material without changing the post flow settings I had for something thinner. I think (though I am not sure) that it is an effect of the metal cooling or being above a certain temperature while in contact with oxygen, while the area that is still blanketed in your inert gas has no color change.Experiment on some scrap with different post flow times, or simply pull the torch away at the end of the weld and you will see what I mean.Dane
Reply:Originally Posted by ticnIf you are talking about the cone shaped line that widens out as it goes to the right, I believe that is an effect of the shielding gas and post flow. I get similar effects, especially if I weld a thicker material without changing the post flow settings I had for something thinner. I think (though I am not sure) that it is an effect of the metal cooling or being above a certain temperature while in contact with oxygen, while the area that is still blanketed in your inert gas has no color change.Experiment on some scrap with different post flow times, or simply pull the torch away at the end of the weld and you will see what I mean.Dane
Reply:Originally Posted by papaharley03I believe it's the Nitrogen in the atmosphere that turns the steel blue when it's hot enough to react with it.
Reply:I agree with the previous responses.  The lack of discoloration in the perfectly shiny silver length of weld shows that this area was totally protected from the surrounding air by the inert shielding gas while the metal was still hot enough to react with oxygen and nitrogen.  The area at the end of the weld which has discolored to blue color was exposed to air while still hot enough to react and form oxide/nitride.  The weld was very well shielded, except at the end.  Shielding at the end of the weld requires adequate post flow time of the shielding gas, the torch must be held in position long enough to shield the hot metal, and this all depends on how much heat was put into the weld and how quickly it cools.  Heavy sections of base metal with a small weld cool quicky and do not require prolonged shielding like a big fat weld on thinner material.  Nice weld, excellent shielding, that small amout of blue would not be an issue on steel or stainless steel welds, but would be very detrimental on critical titanium welds or other very reactive metals.
Reply:Thanks pulser; that is great information.Thanks to everyone else as well.I have been learning welding and really enjoy it.  The machine I have does not have an adjustment for post flow but someday when I upgrade I plan to get a machine with better features.  I am building steel bike frames right now, thin tubes and not too much heat so I think the lack of post flow is something I can live with.  Titanium is on my five year plan but it is not something I need in my bag of tricks yet.
Reply:Originally Posted by febikesThe machine I have does not have an adjustment for post flow