What sort of steel are building I beams made of?

drizler · Aug 6, 2014

I fabed up a couple of squares of bracing the other day using a piece of scrap steel from an old structural I beam. I/4" by 4" across. I put that in my chop saw and had one **** of a time cutting it. In the end it got the gas axe treatment which was good enough for the task. It welded and cut just fine though. The only thing I could figure was that the saw blade which happens to speak Chinese just wasn't doing the deed. It was worn down some so I must have been using it before successfully and I have used the Chinese disks for years with no problem.
When I cut that steel it cut a bit then the spark spray died to that same tiny orangish fine spray and it pretty much stopped cutting. The only time I have ever had this happen was when I had glazed the disk or when once in a while hit a particularly hard spot in a piece. The other thing I noticed with this scrap was that when I left it out in the rain after i cleaned it was that instead of rusty color it got a very thin gold glaze. So what in the world is this stuff?

Gary Fowler · Aug 6, 2014

Most structural steel is ASTM A-36 material which is plain vanilla carbon steel. There are some varieties that are rust resistant, Cor-Ten for instance but normally any cut-ability is not noticed. You may have run into a hard spot due to some variation in the carbon content or heat treatment that made it hard to cut.

Arc weld · Aug 7, 2014

Were did the beam come from? When I was in school, they had a 2' section of a large I beam in the material testing lab. The beam was defective as the last foot of it was the only part still in one piece. They were using it to make an oilfield skid and when they cut the end to bend the flange up, it split down the middle when they hit it with a sledge hammer. They figured it was just a bad batch of steel with too much carbon but definitely one of those, need to see to believe kind of things.

Reverser · Aug 7, 2014

I have a couple short pieces of scrap I-beam that were used on a railroad bridge, so I think it would be some pretty hard stuff. I have thought about using it for a project some day.
I'm just guessing here, but I think it's somewhere around 12 to 14 inches high & wide and 5/8 to 3/4 inches thick. I would be cutting it with a torch, but have never welded heavy I-beam.

I figured it best to use low hydrogen rod, but I don't know about pre-heat though. What would be the right process for this?
Would a 6010 root pass be preferred, or 7018 only?
I think Shield arc used to weld this heavy type I-beam all the time.

Shield Arc · Aug 7, 2014

There is nothing in the world wrong with using 6010 for the root when splicing beams. 6010 works best for open root. If you go with a backing bar 7018 is fine for the complete weld.
Here is a few joint details for you to consider using.

Gary Fowler · Aug 7, 2014

7018 is the preferred rod to use for welding structural steel. I don't recall AWS allowing use of 60xx rods for welding steel buildings/bridges. Anything 3/4" or less only requires 50F preheat. Above 3/4" requires 200F preheat and a double V bevel to prevent distortion.
To my knowledge almost all structural steel shapes are made from A-36 grade steel. The loading and span is governed by the weight of the steel member.
There are some structural steel beams that are low temp grade of carbon steel for use where weather temperatures get below -40F to prevent brittle fracture because of the extreme cold. These welds are usually PWHT after welding. Most folks in the USA don't have to deal with that though.