Millscale

[zapster]

Many times we are asked "What is Millscale?"

Millscale is the crappy finish that comes standard on HOT ROLLED steel...
Don't matter if it's plate..round stock..flat stock..or angle..
If it is hot rolled it has Millscale.
And if you are going to TIG weld it...IT MUST GO!!!

Below are two plates that are hot rolled and have the standard Millscale on them..





In pic 1 there is the grinder with a hard disc on it...
After grinding the surface it looks like this..


You can remove it with the hard disc and what I like to do is hit it with a flap wheel after..


When all said and done your parts should be nice and shiney like this..


One quick wipe with acetone on a clean rag after grinding and you are good to go..

You don't need to grind the whole surface but you do have to GRIND WHERE THE WELD IS GOING!!!!

(I only ground the plates because they will be painted after assy...That's for another thread in projects and pictures....Kinda killed two birds with one stone..)

So GRIND OFF THE MILLSCALE especially before TIG welding!!!

...zap!

[Gamble]

Millscale is the crappy finish that comes standard on HOT ROLLED steel...

What about cold rolled? How can you tell the difference between hot and cold?

[zapster]

What about cold rolled? How can you tell the difference between hot and cold?

Cold rolled has no millscale on it..

It may be a tad rusty from the elements but for the most part CRS comes covered in oil so it don't rust.
It looks like it's ready to go without grinding...Comes "Shiney" right out of the box.

...zap!

[Welderskelter]

Zapster. I hate to argue with the moderator but this mill scale thing is really scaring me. You make me think after almost 40 years under the hood I done it all wrong. I cant go back and do it over because I dont think I will live that long. I never have cleaned the millscale off before welding. Worked in some shops that shot the gray primer on tanks that you had to grind before being able to weld on them. Even with the wire welders I havent ground off millscale. I hate wire welders.
Millscale comes off when hit with heat. Be it with a torch or a welder. I have burnt some off to be able to make a good solid mark with a soapstone for cutting . Sorry I have to disagree with you but its what makes this a free country. I hope you come back on this and not just delete it. Thanks Harold

[Gamble]

I would like to know why I get better looking welds with mill scale on and when grinded off my welds don't look at good.

[zapster]

Zapster. I hate to argue with the moderator but this mill scale thing is really scaring me. You make me think after almost 40 years under the hood I done it all wrong. I cant go back and do it over because I dont think I will live that long. I never have cleaned the millscale off before welding. Worked in some shops that shot the gray primer on tanks that you had to grind before being able to weld on them. Even with the wire welders I havent ground off millscale. I hate wire welders.
Millscale comes off when hit with heat. Be it with a torch or a welder. I have burnt some off to be able to make a good solid mark with a soapstone for cutting . Sorry I have to disagree with you but its what makes this a free country. I hope you come back on this and not just delete it. Thanks Harold

If you re read the post I stated it MUST come off when TIG welding..

Yes it does.

Any other process you can leave it or get rid of it.

I choose to get rid of it whenever possible no matter the process..

...zap!

[zapster]

I would like to know why I get better looking welds with mill scale on and when grinded off my welds don't look at good.

Yeah I would too.

...zap!

[Gamble]

Well if you don't know I'll never figure it out. I thought it was just me, but I guess not.

[Welderskelter]

Zapster. I stand corrected. I apologize. I did miss that part. I would have to agree. Harold

[zapster]

Zapster. I stand corrected. I apologize. I did miss that part. I would have to agree. Harold

Ahhhhhh no biggie..

I don't read half the stuff I should either...

...zap!

[rockland]

So what are other differences between HRS and CRS?

Strength?

Cost?

Warppage?

Good thread Zap. Love to learn.

[fredschrom]

Wow and all this time I thought it was something my dentist said I had.

Seriously though even with stick welding I clean scale of when using 7018, not really necessary with 6010 but beads look better if you do.

On scale removal Crest works ( Opps ) I mean disks work betterr than flaps and hitting it with the grinder first then lightly flapping saves on flap disks.
And boy sometimes you can run into scale that is just tough and nasty and thick, 7-9 inch grinder time I got some 3/4 plate outside like that.

[turk]

one more thing to throw in there is that wire wheels are in no acceptable to remove scale, they only polish the scale.

[Gamble]

Will a flap disc by itself remove mill or just polish it?

[Welderskelter]

You can wear a ditch in a piece of iron quickly with a flap disc.

[Sandy]

Will a flap disc by itself remove mill or just polish it?

Those come in many grits so it's sort of up to you. From 60 grit and larger they can get pretty dern aggressive. A 40 grit can move some metal quick like. Be careful.

[aevald]

Hello Zap, I can maybe add a few other items that might give some credence when you are "allowed" to remove mill scale before welding. Mill scale is a form of oxide, it requires more energy to melt it and consume it in the welding arc than the "pure" metal that is presented to the arc/weld metal. When you weld on cleanly ground metal, especially hot rolled plates or other shapes, the aesthetics and often the mechanics of the weld will be of higher quality. The toes of some welds will exhibit undercut, lack of fusion, and microscopic deficiencies when welds are done without scale removal. Out-of-position welds will especially show effects of not removing scale more so than other weld positions. Run just about any weld joint in the vertical position with SMAW, FCAW, GMAW and the joint that has been ground will turnout looking better and will generally be easier to control and yield a higher quality weld. Even these very small or large deficiencies (if it's deep and long undercut) can cause stress risers and similar problems that could result in weld failures. Amount and thickness of mill scale will vary widely with plate thickness, manufacturing process, and many other variables. Industry, application, process (in this case GTAW) and sometimes fabricator/welder craftsmanship could be the determining factor as to whether scale is removed or not. In some cases, referring to industry, removal of scale, rust, oxidation (from thermal cutting processes) galvanizing or similar surface applications, and other foreign materials, is absolutely required before welding can be done. I believe many items welded for military applications definitely require removal, at least the ones that I was associated with did, and a lot of the other governmental agencies requiring metal fabrication had similar requirements. Removal of mill scale will ensure better quality when applied to welding. With my comments here I don't say that all welds require scale removal to be "correct" or of quality, I simply say that a few minutes with a grinder will certainly be appreciated when you get to the welding end of things and possibly the look of the bead afterwards. Economics along with a number of other requirements will likely dictate in an industrial context whether you will or won't. Best regards, Allan

[tanglediver]

I tried my toothpaste but it didn't work. Does it have to be CREST brand?

What about Tabasco? I think that works on pennies.

[Steelwill]

Many times we are asked "What is Millscale?"

Millscale is the crappy finish that comes standard on HOT ROLLED steel...
Don't matter if it's plate..round stock..flat stock..or angle..
If it is hot rolled it has Millscale.
And if you are going to TIG weld it...IT MUST GO!!!

Below are two plates that are hot rolled and have the standard Millscale on them..





In pic 1 there is the grinder with a hard disc on it...
After grinding the surface it looks like this..


You can remove it with the hard disc and what I like to do is hit it with a flap wheel after..


When all said and done your parts should be nice and shiney like this..


One quick wipe with acetone on a clean rag after grinding and you are good to go..

You don't need to grind the whole surface but you do have to GRIND WHERE THE WELD IS GOING!!!!

(I only ground the plates because they will be painted after assy...That's for another thread in projects and pictures....Kinda killed two birds with one stone..)

So GRIND OFF THE MILLSCALE especially before TIG welding!!!

...zap!

Thanks for the thorough explanation.

[Steelwill]

So zap I take it that the orange haze that was around my practice beads were from the mill scale on the metal.

[StickWeldor87]

Hello Zap, I can maybe add a few other items that might give some credence when you are "allowed" to remove mill scale before welding. Mill scale is a form of oxide, it requires more energy to melt it and consume it in the welding arc than the "pure" metal that is presented to the arc/weld metal. When you weld on cleanly ground metal, especially hot rolled plates or other shapes, the aesthetics and often the mechanics of the weld will be of higher quality. The toes of some welds will exhibit undercut, lack of fusion, and microscopic deficiencies when welds are done without scale removal. Out-of-position welds will especially show effects of not removing scale more so than other weld positions. Run just about any weld joint in the vertical position with SMAW, FCAW, GMAW and the joint that has been ground will turnout looking better and will generally be easier to control and yield a higher quality weld. Even these very small or large deficiencies (if it's deep and long undercut) can cause stress risers and similar problems that could result in weld failures. Amount and thickness of mill scale will vary widely with plate thickness, manufacturing process, and many other variables. Industry, application, process (in this case GTAW) and sometimes fabricator/welder craftsmanship could be the determining factor as to whether scale is removed or not. In some cases, referring to industry, removal of scale, rust, oxidation (from thermal cutting processes) galvanizing or similar surface applications, and other foreign materials, is absolutely required before welding can be done. I believe many items welded for military applications definitely require removal, at least the ones that I was associated with did, and a lot of the other governmental agencies requiring metal fabrication had similar requirements. Removal of mill scale will ensure better quality when applied to welding. With my comments here I don't say that all welds require scale removal to be "correct" or of quality, I simply say that a few minutes with a grinder will certainly be appreciated when you get to the welding end of things and possibly the look of the bead afterwards. Economics along with a number of other requirements will likely dictate in an industrial context whether you will or won't. Best regards, Allan

^^^^^ What he said. ^^^^^^

[Matt_Maguire]

So zap I take it that the orange haze that was around my practice beads were from the mill scale on the metal.

If you TIG or spray MIG all the junk in the scale makes for strange looking soots next to the weld.

So what are other differences between HRS and CRS?

Strength?

Cost?

Warppage?

Good thread Zap. Love to learn.

HRS is at a temp where it's very soft and even though water and brine will pop some of the scale off between roll stands a lot of it just stays stuck. For machining purpose HRS has less internal stress and stays more stable.

CRS goes through a cooler draw below temps where the material can de-carb, the steel is also much stronger at these temps. CRS has uniform size and is stable until the highly worked surface is disturbed. When welding you can expect a bit more warping. For machining, milling CRS will result in more warping, for turning there is usually no problem.

In testing raw stock CRS, will have higher mechanical properties, it varies from a little (1018) to a lot (1144 hard worked = Stressproof).

Matt

[scudzuki]

So what are other differences between HRS and CRS?

Strength?

Cost?

Warppage?

Good thread Zap. Love to learn.

CRS is more expensive.
The cold rolling creates a skin and resulting stresses in the material. Removing the skin from one side results in the material bowing in the opposite direction.
Good CRS is very close to size, often within a few thousandths of an inch of nominal, flat, with square sides and relatively sharp corners.

Rule of thumb, use HRS unless your aaplication requires CRS.

Joe

Joe

[Darth Velder]

CRS is more expensive.

It took me a minute to remember what that stands for. I thought you were talking about my medical condition, Can't Remember . . . Stuff. It can be expensive when you forget an anniversary or something.

On a more serious note, are "Hot Rolled" and "Hot Worked" the same thing?

[philmicrackin]

Wow thats alot of interchange about millscale, one thing that will remove it is Apple Cider Vinegar, the thicker the millscale the longer the soak time, Muratic acid will do it faster but is very hard to be around, burns the nose and rusts everything around