Anyone use Cor-Ten steel??

For general topics and questions that do not fit into any of the other categories or forums.
Post Reply
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Anyone use Cor-Ten steel??

Post by davek0974 »

Hi all,

has anyone here used Cor-Ten or Corten steel?

I have an idea for a range of garden products that would look good with the type of natural rust finish that t his metal gives but have never used it before.

Anyone have any tips or hints for it?

Products would be plasma cut and hand welded, nothing seriously structural, its not railings or balustrades etc

Thanks
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

I use a fair bit of it in 1.6 and 3.0 mm.

Corten is a brand name originally adopted for the materials two main properties being "corrosion" and "tensile" in that ironically the fact that when it rusts, the rust on the surface builds a protective coating preventing it from rusting if that makes any sense and tensile in that it has a minimum yield strength of 350 Mpa and tensile of 450 Mpa.

In Australia it is largely marketed as weathering steel but most customers and architects ask for it as Corten.

As far as working it goes, it looks and plasma cuts like hot rolled but does have a slightly different glow to it when cutting (I'm told from the copper content) but as for drilling and guillotine cutting it is much harder and harder on your tools. It is also a lot less forgiving in the press brake in that it takes a lot more effort to bend and if you over bend it, it takes a bit more getting back. I mig weld it the same as I would hot rolled but it is a bit more proned to porosity in your welds if you weld it too hot. Even when you linish your welds they will take longer to rust than the parent material.

If the customer wants to see it rusty straight away a spray with diluted hydrochloric acid will start it rusting quicker but just wetting often with water will also make it rust fairly quickly.

The initial rust will be a powdery orange rust but becomes darker and firm to touch. Initial rust staining and leaching will happen as does with normal steel but once it has it's rust coating it basically stops. I find that by hitting it with some acid and spraying it liberally with water several times a day and letting it dry you can have this what they term "cured" or "aged" surface in as little as a week.

If it get graffiti'd just sandblast and it will as they term "self heal" as it did originally and the color will be the same fairly quickly.

Be careful, there is product which is being offered as Corten which definitely isn't, I have 27 sheets going back to a supplier tomorrow and they are crediting me for the one I have cut and used too.

These are my experiences with it and may vary from others, hope it helps.
Murray
beefy
4.5 Star Member
4.5 Star Member
Posts: 1504
Joined: Fri Jan 18, 2013 3:19 am

Re: Anyone use Cor-Ten steel??

Post by beefy »

This is very strange Murray, I was actually thinking today about asking you about "Corten" here in Australia.

What I was going to ask is do you know if there is a better final finish (completely rusted) with the original Corten than the "equivalents" we find here. Sites selling Corten screens, etc seem to show it off with such a wonderful coloured look, sometimes looks a bit purple, and/or with streaks and patterns. However, all I've ever seen in the real world with existing weathering steel (no idea what brand for most of them) is the equivalent of completely rusty metal, no fancy shades or colours. They all just look like...........well, rust LOL.

Keith.
2500 x 1500 water table
Powermax 1250 & Duramax torch (because of the new $$$$ync system, will buy Thermal Dynamics next)
LinuxCNC
Sheetcam
Alibre Design 3D solid modelling
Coreldraw 2019
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

Do you mean like the coloring in this one ?

Image

That was taken the day after it was cut, I'll try and take another pic of it tomorrow, it's a bit different now but will eventually end up just rusty brown unless I lock it off with clear. That won't stop it, just slow it down as the rusting will continue under the coating, just at a much slower rate as it's outside. If it's inside it seems to take a lot longer.

Some of the stuff I've seen advertised and sold through the garden centres and hardware chains as Corten is a painted on finish, bend it and it flakes off, similar to those wonderful suntans you see around Melbourne in winter ;)
Murray
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

Here's another one taken the day I cut it, wont look like that now though.

Image

and this one was done about 4 years ago but the photo is only about 6 months ago that I shot when going past.

Image

That's the color they eventually all end up, rust is rust.
Murray
User avatar
CNCCAJUN
4 Star Member
4 Star Member
Posts: 1108
Joined: Mon Dec 26, 2011 11:38 pm
Location: Baton Rouge, LA

Re: Anyone use Cor-Ten steel??

Post by CNCCAJUN »

Anyone here in the states using Cor-Ten?

Steve :D
Smiling Gator Metal Works, LLC
Dynatorch 4X4 XLS
PowerMAX 85
Baton Rouge, Louisiana
Shane Warnick
3.5 Star Member
3.5 Star Member
Posts: 563
Joined: Fri Jan 24, 2014 11:03 pm

Re: Anyone use Cor-Ten steel??

Post by Shane Warnick »

I have used it. I did some parts for a blacksmith friend of mine that was building some custom sign posts for a gated community down close to the coast. I cut all the sides for the posts (they were tapered octagonal steel posts that were 8 feet tall, he welded them up and ground the corners back to profile) and all the bases etc for them. He added some vines and grapes etc around them. I know it was damn expensive. I was puckered up afraid I was going to screw a sheet up, but managed not to have that happen. Last pictures I saw they were looking great, dark brown and, well, rusted. I do know that regular mild steel (A400) just basically delaminates and falls apart down there after 6 months or so if it's not kept painted. He asked me how to pre-rust them, I told him to use either pool acid (muriatic / hydrochloric) or, my preferred method, vinegar in a sprayer. He went with the vinegar, and after 4 or treatments over a 2 week period, they went from bright orange after the first treatment to a fairly dark brown. The quit bleeding after the second treatment, but I will say after the first one they looked almost fluorescent orange. Funny thing is, they scratched some of them pretty deep when they were transporting them and installing them, and the contractor actually called him and asked him to come fix it. He gave them a number and they said no problem. He basically got paid (very well) to drive down there, spray a super secret solution (vinegar one day, salt water the next, then wait 3 days and vinegar 2 more times) and drive home. He took a trailer with a small wash rig on it, and would wet the cement and then use a pump sprayer to spray the pole, then wait 10 min and wash the "bleeding" off the cement and down the gutter so as to keep it looking as pretty as he could. He waited until the last day and after he had sprayed all the poles, went back and acid washed the cement just to make it look like brand new, and the client couldn't have been happier. He had to let it "mature" for 3 days (insert he took an offshore fishing trip) in the middle, but was getting paid by the day plus expenses. I often wish I had lots of clients like that, but the ones I do have that are willing to just whip on something with their wallets, are a PITA and high maintenance.

Anyways, back to the original Corten question, yes I have cut it, cuts just like mild steel, yes it weathers nice, and it is retarded expensive. I think the lack of a local mill that produces it and the additional freight involved is what makes it so damn expensive. It's really dry here in the desert so I have never had the need to use it here.

Shane
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

Great stuff,

I have one price so far, it's costy but not that bad, less than 2x mild steel.

My stuff will be made to order so I'll need to explain how it weathers to the buyer, I can't make some of each design as there would likely be too many.
beefy
4.5 Star Member
4.5 Star Member
Posts: 1504
Joined: Fri Jan 18, 2013 3:19 am

Re: Anyone use Cor-Ten steel??

Post by beefy »

Thanks for the info Murray and Shane. Good to have that confirmed.

Loved that story by the way Shane.

I've seen lot of staining from weathering steel. Some guy had screens all around his back yard, set against a biege rendered wall. Rain + wind had caused a lot of water run off from the bottom of the "corten" and onto the wall, resulting in lots of brown streaks on the rendering.

From an arty BS prospective I'd love to give the item to a customer in its beginning "orange" condition, explaining that the "patina" (very posh word for dark brown solid rust covering) will take time to fully "mature", and reach its full "potential" :lol:

But I guess I'd also have to forewarn them about the "bleeding" that occurs until its full "maturity" is reached.

Must also find one of those silk scarves to put round my neck, plus dark sunglasses (which I'll still where in a dark room) and one of those French floppy hats that hangs to the side. Then walk with my head held high while sucking in my cheeks, waving my hands around and acting a bit mentally hyper.

Sorry guys, but being a metal man, rusty steel is just rusty steel to me :D I know many love it though.

Getting serious again, I've heard that when the rust coating is complete, it's self sealing, so no more rust occurs. I wonder if the bleeding completely stops soon after, or if it still occurs at least a little and will still stain things.

You can guess what's going to happen down the track if the customer wasn't forewarned about staining.

Keith.
2500 x 1500 water table
Powermax 1250 & Duramax torch (because of the new $$$$ync system, will buy Thermal Dynamics next)
LinuxCNC
Sheetcam
Alibre Design 3D solid modelling
Coreldraw 2019
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

As promised a picture of the same screen today, haven't had any rain since it went up and with mid 40 C (105 F) days there's not a lot of moisture in the air so hasn't darkened a whole lot but would if I watered it.

Image

As for early leaching, I use CLR to clean it off. Once it has aged or cured you don't get leaching, you can rub it with a white cloth and it wont come off.

To try and keep it looking like the picture above one of the artisans I do work for has told me to rub it with bees wax or grape seed oil, haven't tried it so I cant confirm.
Murray
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

Looks good.

I would definitely advise the buyer about staining, but i have a feeling it will not be much worse than the staining you get from normal powder coated garden work where the powder coat has cracked, as it always does, and the metal has blistered and rusted - you still get staining, but this stuff won't go through the ugly cracking blistering flaking stages.

I think it's a winner, hopefully.
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

Harder to get it to rust than I thought ;)

I stuck a test cut out in the garden two weeks ago, it's been damp, wet, dry, snowy, generally rotten but it still only has a patchy light rust.

Then I tried soaking the scale off the next test piece with vinegar, 24hrs shifts the scale and any dross from cutting, I washed it off and stuck it outside a week ago expecting flash rusting - practically nothing, a very very light discolouration.

Might have to invest in some hydrochloric maybe.
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

I'm wondering if you may have got some of the Indian stuff like I sent back.

I'm currently having a bit of a supply problem with it and it appears that the mill that it was coming from isn't rolling it in 1.6mm any longer due to the economic viability. As the steel merchant couldn't get me the right material I had to try and use some of this other Indian Corten to try and cut some orders.
This stuff they gave me, which they told me was out of India was totally different. In appearance it looked liked cold rolled/ pickled and oiled in that it had a shiny finish rather than the dark mill scale finish of Corten. It was also much easier to bend and drill than the normal Corten but was a real bitch to cut. The normal Corten I cut at pretty much book specs which gave an excellent cut with very minimal dross. With this Indian stuff I was having real cut quality issues and heaps of bottom side dross which was real hard, I tried faster and slower, higher and lower amps and ended up pretty close to stainless settings but it still had a very hard bottom side dross and wasn't as smooth in the cut. It is also different to weld, seems to sort of fizz with an orange glow.

The other issue was the rusting side of it.
Normal Corten I could cut it and give the customer a lightly rusted piece 30 minutes later or a fairly rusty piece the next day and with regular rinsing I could have the rusting process pretty much done so there was no leaching in about a week to 10 days. This other material isn't so easy. I had samples that I played around with and found the most successful results came from cleaning the sheet with thinners or acetone and then giving it a good scrub with a scotch brite pad and detergent. Once this was done the acid seemed to bite better but it still took days to rust up to what I would normally have in a few hours.

I am negotiating to try to get a coil of the usual Corten in 1.6 but at the moment I am having to use this other rubbish or 3mm where the customer wants Corten. I've tried to get material analysis data but they are telling me they cant get it on this imported product.
Murray
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

Hmm, going by your description, this stuff is the real deal - hard shiny mill scale, cuts beautifully and bends poorly.

That's one good thing at least.

I haven't tried solvent wipe yet, just pickle, wash and put out but it seems very slow to do anything, even slower than mild steel, I'll put a bit of that out for comparison.

Not sure what to try next, ideally I would like to supply with process under way, but in any case I need to know the timescale so I can answer questions.
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

Another one that some use to help speed up the rust is to add salt to the acid water mix and even spraying with a salt water mix for a few days. The more it is wet and dries again the more it rusts.
Murray
User avatar
tnbndr
4.5 Star Elite Contributing Member
4.5 Star Elite Contributing Member
Posts: 1669
Joined: Mon Jan 09, 2012 4:30 pm
Location: New Berlin, WI
Contact:

Re: Anyone use Cor-Ten steel??

Post by tnbndr »

Not sure what the temps are by you davek but one thing that speeds up the rusting process also is heat.
Can you put the piece in the garage or basement with a portable heater or infrared lamp aimed at it to raise the temperature while still keeping it wet and dry. Just an idea.
Dennis
LDR 4x8, Scribe, DTHCIV
Hypertherm PM45, Macair Dryer
DeVilbiss Air America 6.5HP, 80Gal., 175psi, Two Stage
16.9scfm@100psi, 16.0scfm@175psi
Miller 215 MultiMatic
RW 390E Slip Roll (Powered)
AutoCAD, SheetCAM, Mach 3
http://ikescreations.com
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

I can try that thanks,

Pity we don't have a greenhouse, nice and damp and warm.
muzza
4 Star Member
4 Star Member
Posts: 1472
Joined: Wed Feb 04, 2009 5:35 pm

Re: Anyone use Cor-Ten steel??

Post by muzza »

Here you go Dave, one I cut from 3mm Corten this morning about half an hour before this pic. It's washed with acid mix and rinsed with water and left to dry. Current temp is 26 C so about 79 F so dried reasonably quick.

It's going up right on the coast so it should rust up pretty quick, I'll try and get some follow up pics.
Murray

Image
Shane Warnick
3.5 Star Member
3.5 Star Member
Posts: 563
Joined: Fri Jan 24, 2014 11:03 pm

Re: Anyone use Cor-Ten steel??

Post by Shane Warnick »

muzza wrote:Another one that some use to help speed up the rust is to add salt to the acid water mix and even spraying with a salt water mix for a few days. The more it is wet and dries again the more it rusts.
Murray

Add salt water to the mix. Wet it with salt water, let it sit or even dry. Acid wash, and dry. Then re wet with salt water as often as you can remember. Plastic pump sprayer works awesome for this. Also try to use kosher or pickling salt, it works better / faster than iodized table salt. If the water and acid seem to sheet up and run off at first, give it a good wipe with mineral spirits or paint thinner to cut the oil off the mill scale, or rinse with a hot water / dish soap solution.

FWIW, I have "heard" that some places request their steel he sprayed with a sort of paraffin / wax coating instead of oil. If the steel is hot when it is applied it will absorb a little, and be hard to get off. Could be part of the issue. Again. I have never confirmed this from a mill, just some scuttlebutt from some old dude.

I do know I have used beeswax and also paraffin wax on hot steel, and once it cools it does inhibit rust really well. Started doing this blacksmithing and it worked so well I use it on tons of stuff. Even my table saw. Way better than paste wax. Cheaper too. Just a thought.

Shane
davek0974
4 Star Member
4 Star Member
Posts: 764
Joined: Wed Aug 13, 2014 8:30 am
Location: Hertfordshire, England
Contact:

Re: Anyone use Cor-Ten steel??

Post by davek0974 »

Thanks for the tips and picture.

I have a feeling I will have to go with pickling the scale off, washing, welding and dispatch. They will be sent with a note regarding keeping oil or grease off etc.

Most of my stuff is cut to order so buyers don't want to wait weeks while I pre rust it.

Dave
Post Reply

Return to “CNC Plasma Cutters General Forum”