American Welding Society Forum
Gentlemen, long time no see. I hope all is well. I have run into something that is outside my general experience, and I thought I'd pick some of the finest brains I know.
I am working with a load of A572-60 steel sheet on my laser cutter. The steel is hot rolled, but there's no mill scale on it. It has a reddish-brown color on the surface. The only thing I can remember in my life like this was HY80 and HY100 sheets that looked the same. Is this an oxide layer of some sort? How is it produced? Inquiring minds want to know...
High strength, low alloy steels like A572-60 will produce a natural "weathering" or "patina" of a sort. This coating will protect it from further oxidization. This is used on applications where no painting is required. If you have ever seen bridges or towers etc that have a "rust" colored appearance, it is this natural coating. Like you stated, I have also seen HY-80 with this. Depending on application and needs, it can easily be cleaned off. What is interesting, is after cutting/grinding/welding, the coating will naturally "heal" itself.
Obviously, I haven't seen your sheet so it could be something else lol but it sounds like this to me.
Last I checked, A572 is NOT a weathering steel. It is a Low Alloy High strength steel.
A572 Steel Composition
Grade 42 Grade 50 Grade 60 Grade 65
Carbon 0.21% 0.23% 0.26% 0.23-0.26%
Manganese 1.35% 1.35% 1.35% 1.35-1.65%
Phosphorus 0.03% 0.03% 0.03% 0.03%
Sulfur 0.03% 0.03% 0.03% 0.03%
Silicon 0.15-0.4% 0.15-0.4% 0.4% 0.4%
A588, A709-50W, A847 are examples of atmospheric corrosion resistant steels.
You are correct. A588 is what I was thinking of. Thank you for clarifying!
So this (as mentioned by OP) is most likely just normal oxidation, one would assume?
We use A572 Gr. 60 plate for all of our products (to comply with European design criteria), over $1M per year. This appearance you speak of is quite common from what I've seen, although when you get up around 1-1/2" and thicker I think you may see a more traditional mill scale on it.
We machine/weld a significant amount of A572 Grade 50 which has mill scale, although the only time I have seen the reddish brown color is when it is exposed to moisture, humidity, etc. Which then creates surface rust, especially on the areas that are machined, sheared, plasma cut, etc. You might be seeing surface rust??
Generally speaking Hot Rolled Steels all have some Mill Scale.
They use a lot of water when rolling steel to reduce the amount of mill scale that forms on the surface while it is hot. The amount of mill scale can be controlled to a certain extent during the rolling process by flooding the surface of the steel with water. The resulting steam protects the hot steel surface from the oxidation effects of air. Subsequent heat treatment such as normalizing can expose the hot steel to air and in the absence of a protective barrier, thicker oxides (mill scale) can form.
So I bet the laser does not like it? Or your concerned it won't? Is it temperpass?
I could usually get less then perfect looking 572 across the laser without objection. If the color is very uniform it will probably cut ok, with a tweak to speed or heat. If it rubs off with your finger you may have some issues. "sick of the tariff bs"
If you are having cutting issues with it....start tracking some metrics on your MTR's by grade (content, supplier, mill) and reconcile with issues in production. This helped me identify an unreliable source once.
Have a great day man.
Steam! Yes, I should have known that!
The laser doesn't mind this stuff as much as lower quality HR finishes, like A36. Of course, the manufacturer tells us to run only CRS, but that's $$$ we don't want to spend if we don't have to. We are just now getting our first delivery of a mill run, and quality seems pretty consistent. My initial concern was that the mill wouldn't be able to provide a consistently clean surface. We're much more used to dealing with HR bars, which come to us with a very heavy (5+ mils) scale; however those are sent through the stamping presses.
Thanks to all you guys for the inputs.
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