1018 steel question

[Mike Switzer]

Several older sources I have seen (Including my copy of the Ryerson Engineering Data manual from the 60s) list the yield strength of 1018 cold drawn steel as 70,000 psi, which is nearly as high as 4130.

Current data from the top manufacturers & the better engineering texts list it as 54,000 psi.

(The advertised properties for hot rolled 1018 have stayed the same over the years)

I was just wondering if anyone had an explanation for the difference? My first thoughts are either manufacturing processes have changed or it is CYA by the manufacturers?

[Dana]

Could be the prevalence of recycled steel these days; they're less certain of what's in it? Or could be differences between cold drawn seamless vs. welded and cold drawn over mandrel (DOM) tubing?

[Matt Gonitzke]

When I was in school, one of my professors that has been in the aerospace industry for 35+ years mentioned that allowables in general have been getting more and more conservative over the years, so I'm guessing the manufacturers are trying to cover themselves.

At any rate I would still use the current data.

[Dana]

At any rate I would still use the current data.

Me, I'll just use 4130...

[Matt Gonitzke]

Yeah, me too.

[Mike Switzer]

Me, I'll just use 4130...

I would too, but I was considering using a tube spar as a fuel tank (similar to the cheetah/tiger), you cant get 4130 in those sizes, it is all 1018, 1020, 1026 or ASTM 500 or 513

Plus there is a huge price difference between 4130 & the structural steels commonly used in industry.

[Dana]

Big tube spars like that are nearly always aluminum, no? That'd be pretty heavy in steel...

[Mike Switzer]

Some sizes are available with a pretty thin wall. For the strength needed steel & aluminum are pretty close in weight if you can get the steel tube with a thin enough wall.