American Welding Society Forum
A stupid question:
What does it mean when the surface of the metal surrounding a weld turns blue?
Using a Hobart Handler 175 MIG with 0.030 solid wire and AR/CO2 shieding gas. The color is only on the surface and it is quickly removed with brillo pad. A friend of mine claims that the metal has undergone a transformation and is now brittle, but the color is only on the surface.
Also, he said that the little hobby welders like this are crappy toys and cannot put out enough energy for safe structural welds. Is that true?
Thank you much!
There are no stupid questions, if you don't know or are not sure, then ask. You shouldn't get flamed for asking questions on this board.
Next to the toes of the weld there is an area that is called the "HAZ" (Heat Affected Zone). Yes, heat input does affect the base metal. There are welding procedures written that limit heat input to minimize this affect. In AWS D1.1(Structural code for buildings) they have Min. Preheat and Max. Interpass temp. charts for various grades and thicknesses of steels. You may be running the wire speed alittle fast or your travel speed may be alittle slow, inputting more heat than is necessary in that thin material. Usually the wire mfg's have recommended current/wire speeds and voltages along with travel speeds that are listed in "ranges" to suit the wire. If you are not confident in your ability then sub out the work that is critical. Don't want any rear axles running out from under any racecars. What type of joint is the "critical" weld that you are referring to? Joint prep is critical to making all this come out right.
Hope to help,
The wire (ER70S-6) should be OK for what you are using it for. It is used to weld mild steel in structural buildings all the time.
As Mr. Wright indicated. No stupid questions exist here. I may occasionally give a stupid answer but people here are kind enough to not never say so :)
The blue color is oxidation that is the result of the temperature the base metal reaches during welding.
Changes do occur to the base metal and heat affected zone but they are typically of no concern to mild carbon steel.
Some steel alloys have a tendency to become brittle at certain temperatures/cooling rates. This is usually related to the amount of carbon or other alloys present and is not of concern for most around the house type welding.
Thank you all for your help.
The critical joint is a bracket that holds a front lower control arm pivot shaft to the frame. The lower control arm in turn holds the front wheel in place, so this is about as critical as you can find on a car frame. I think that I will farm that one out but do the rest myself. On the other hand, the bracket is held with slot welds in the center and I can add fillet welds all around, so I think that it should be hard to screw it up so bad that it would not hold...
For prep is removing all rust and paint with a sandblaster (or wirewheel) and wiping off oil with laquer thinner adequate?
For a good butt weld in 10 gauge mild steel, should the gap between the two panels be about the width of the welding wire (.030") or closer to panel thickness?
For a correct lap weld in any thinkness, should you bee able to see a darker "heat effected area" on the bottom side of the lower piece to confirm proper "penetration"?
Thank you much!
When you said control arm I immediately thought of the rear suspension "truck arms" on rear coil spring cars. I completely forgot about the "A frames" up front. I hope you now have enough information to calm your fears about the color you are seeing in all that thin material around the welds. Good luck with your project. What kind of car are you working on? Bowtie I hope, (just fooling with DGXL and his blue ovals)
Have a great day
"Also, he said that the little hobby welders like this are crappy toys and cannot put out enough energy for safe structural welds. Is that true?"
Well, the Hobart Handler 175 is actually manufactured by Miller for Hobart, and Miller's one of the two most recognized brands here in the US. In fact, if you look on Miller's web-site, you'll find a model with the exact same specs as the Hobart (sorry don't remember the model #). Not sure how much of a "toy" this thing is...for home hobby use, I'd say you probably picked a pretty good machine. (Not everyone can afford or justify industrial quality tools for home hobbys!) The difference between this one and the next step up is not only it's power output, but it's duty cycle (the 175 is something like 15-20%, whereas the next step up is something like 200 amps @ 40% duty cycle, but of course it costs twice as much!)
A neighbor of mine is building a rail buggy with a 90 amp 110V MIG, and he seems to be doing just fine with it! I think folks here would tell you that you could probably do just about anything with anything, if you have the time, patience, and skill. I'm sure you could weld 1" thick plate sections together with your machine, you'd just have to prep the edges into a V-groove, then make many passes to fill in the gap (and take a smoke break between passes to let the machine cool!).
Where there's a will, there's a way!
I have a stupid question:
Is the blue area on the weld itself or in a location adjacent to the weld?
The blue area was adjacent to the weld surrounding it. it extended at least an inch away from the weld maybe 2 inches. This was on some scrap pieces I was practicing on. Mild steel, thickness probably over .060", but less than .100". (Possibly with too high a voltage setting, but I'm not sure.) The blue appeared to be only on the very surface of the metal. A quick wipe with a brillo pad caused it to disappear without any visible signs that it used to be there.
The 2 "stupid" questions result in one simple answer:
What you are seeing visually is perfectly normal for a plate that thin that is welded on continuously and/or intermittently.
There were some blue marks in the area around most of the GTAW welds I left on one of my best friends Mustang shock mounts, steering box mounts, steering shaft brackets, etc. which was in the form of a kit. There is some really thin stuff up there on the factory Ford chassis. I am not at all concerned about his safety. Some areas got a little hotter, his car kicks a*!. Come to think about it, there were blue marks on the Cobra chassis I used to weld.
Don't worry about the blue.
I think I would be more worried about NOT having any coloration of the metal around your weld bead. This would mean to me that you have a "cold" weld and lack heat input and weld penetration.
I try to look for coloration on all sides of objects I weld to give me an indication of how much, or how little heat/penetration is there after welding.
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