Stick welding color

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Welding with 7018, doing horizontal Tee joints at Tech School... with 3/32 rod I didn't notice it so much. But with 1/8 rod I notice it more... Sometimes the metal takes on a purple color- teacher said he didn't know! Other teacher joked and said "You're going blind"! Educate me please. Thank You.
Reply:On mild steel, I guess? With stick, the only time I notice any "color" is when I've skimped on cleaning. Maybe didn't grind through all the mill scale.. rust and/or dirt being picked up by the weld pool makes the bead darker, or more dull, I suppose.
Reply:You can get strange colors if you knock the slag off before it cools.  Excessive heat input will cause strange colors.Welding oily steel will cause strange colors."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Google "heat treating steel".  Those colors are the same used when tempering steel after hardening.
Reply:I'm chipping the slag off too soon then?? Why does it do this??? You'd think the instructors would know this.
Reply:some metals change color with heat. Don't sweat it, just keep on practicing.
Reply:Little brother, I wouldn't be to concerned about the color that the metal takes on as you weld on it, but it is a fascinating thing to study and keep an eye on.  Why don't you on the next piece you weld on watch the metal change colors as you weld more rods- more heat is put in and more molecular change takes place in the parent (base metal).  Get back to us on you observations- results of your study.  You can never remove slag to soon.  What I mean by the time you finish your weld, put your stinker down and pick up your chipping hammer it is about ready to come off.  You won't get it off till it cools.  You can try but it is not coming off until it cools a bit.  Let it cool and see that it comes off easier (generally speaking) when it has had a chance to cool.  I'm not talking minutes, hour or days here.  It will cool, depending on the type/size of rod and metal thickness and how much heat is stored up in the piece(s) you are welding on.  It is kind of the opposite to ice in a glass of water.  Which will melt first, one cube of ice in a glass of water or a whole glass full of ice cubes in water.  The glass with lots of ice cubes will of course take longer to melt because all the cubes keep each other cold longer.  Stored cold opposite of sored heat in welding.  With welding, your first weld bead slag will cool fast and come off easier, but by the time you have welded on you plate (metal) for hours you have a lot of heat built up and the weld will cool slower because of all the heat build up.I think another important thing for you to watch is your weld bead appearance.  It has been my experience when I make a "good" weld (with certain welding rods such as 7018, 7024, etc.) the slag comes off easily and will peel off with no or little chipping hammer involved.  On the other hand, if I make a weld that is defective and has slag inclusion (junk in the weld), I can beat on it all day long and the slag is not coming off/out.  Hope this helps.By the way, I do know of a one on one welding school, but it is in Tenneesee, quite a ways from you.Some kind of Big Blue constant current welding machineAnother smaller yet, Blue machine (it's got wire in it)
Reply:Coming back to this, I'm reminded of welding carbon steel with tig.It's usually just a regular silvery color... but sometimes, when you're going hot and fast and everything is kicking as$, it'll come out looking gold tinted.Either that or it's just contaminated. I'm not a metallurgist.
Reply:It's just a thin layer of oxidization, like others said. It formed because the weld was still hot enough when the slag removal exposed it to the atmosphere. You can get the same colors if you take a wire wheel to a weld while it's still quite hot, the entire surface will turn purpleish blue.Give me fuel, give me fire, give me that which I desire.
Reply:Originally Posted by Trucker2WelderI'm chipping the slag off too soon then?? Why does it do this??? You'd think the instructors would know this.