CTI claims to have an adhesive that will work (link below) Also, your idea of adhering cork to the metal and then the wood to the cork is good thinking, as the cork can help dampen the movement between the two dissimilar materials.

If I were specifying the job it would be a good urethane adhesive, such as Stauf's PUM-950 Power Grab, PUM-955 Ultra Nail or similar products...and I would glue the cork to the metal and then the wood to the cork. Or, I would use the CTI adhesive.

For technical information about Stauf adhesives simply go to their website.

Here is a link that might be useful: CTI adhesives

glennsfc: I am so glad you answered as I've seen your help to others and admire your knowledge! I DID happen to run across the CT1 adhesive in my web search and that actual link! When I did I was SO happy...then found it only in Ireland and UK & didn't persue, assuming no sales were in the US (may be wrong though). Do you know if there's a US source?

Your mention of Stauf is one I did not find & appreciate that tip. Are you saying you'd spec it for both the cork to the steel AND the flooring to the cork? I couldn't tell for sure from the website if the two products you listed worked on "steel/metal" specifically. The Power Grab DID say "Excellent Bond to virtually any surface" so I am HOPING it includes steel because the company is in TN!

I'm finding the Steel part is the hard part ...
Have YOU ever glued anything to steel or know of anyone who has? We're having these two steps fabricated special due to our circumstances and steel is the coolest option. I am so hoping we can stick with this idea!

The technical folks at Stauf ought to be able to help you further.

I have adhered flooring to steel with multipurpose latex flooring adhesive and one with flammable contact adhesive. I believe there are lots of adhesives that will bond with steel. Most flooring adhesives are very difficult to remove from steel trowels, for example. Come to think of it...I can usually peel urethane flooring adhesive from steel trowels, so perhaps that is not a good choice. I don't know. Give Stauf a call and see what they tell you. They might even recommend a polymer based adhesive for your project.

Glad to know you've been faced with a steel application before, at least we know it's possible! We'll call Stauf tomorrow.

(Either one could work so) Wondering if you would recommend cork or plywood if it isn't smart to glue flooring directly onto the steel?

Cork.

For anyone who is also needing the answer to my question. Here's what I found:

Called Stauf...nothing for steel.
Called Bostik, poor customer service, just wanted me off the phone.
Called several other manufacturers of adhesives and fasteners and you name it...no luck.

Finally found 3M on a websearch and called. Great customer service and recommendation for the 3M� Hi-Strength 90 Spray Adhesive (another 3M choice they gave was their Fast Bond 30-NF contact adhesive).

Found rolls of 2.4mm cork at a local Ben Franklin craft store (less $$ and the amount we needed vs. a boat load!) and tried a square of the cork using the 3M 90 spray on a piece of scrap steel. It sticks like GLUE! haha Super strong! Mystery solved, hooooray!

We're going to use this product to adhere the cork to the steel steps and then use a flooring recommended adhesive to install the flooring on the cork. Hoping all goes well!

Thanks to those who tried to help!

Here is a link that might be useful: 3M Hi-Strength 90 Spray Adhesive

Good to know! High Strength laminating contact adhesive in a spray can! Very good.

Here is a link that might be useful: 3M youtube demo of Hi-Strength 90

Hey! loved that video! Looked up the 3M 30NF on youtube too and picked up a hint how to use a roller after placing our cork down (probably to get air bubbles out and smooth it as best as possible). Thanks a heap for passing that on!

Update:
Installed our steps and it turned out great. Adhesive was super strong & held the cork perfectly!

One change we made in our process is the cheap rolled cork we originally purchased from Ben Franklin (hobby shop) was too thin and brittle. We found a much better application by laying some 8 x 12" sheets of cork we found at a fabric/craft store and it was much easier to manage the size in relation to being able to lay it on the adhesive accurately before it stuck down too quick.

The 8 x 12" sheets of cork (the thickness of coaster material) was about $3.00 per sheet. Our steps are 12" wide so we didn't have to trim the width at all, just laid it end to end! It turned out less $ for us to do it this way than to have to buy the huge quantity sold in home improvement or carpet stores (we only had 4 steps to do).

Just a FYI to anyone in the future.
Peace

Sika T-55 remains elastic, like rubber, after curing.
www.sikaconstruction.com will advise about steel.