Carbon steel vs. 4130 alloy steel

[titan354]

Both frames are made of 1.5 inch square tubes.
One is .120 inch thick 4130 steel alloy.
The other is .188 inch thick carbon steel.

Which type will create the stronger frame?

 

[zcp]

Frames for what? If just in general, going with the larger tube size will often give larger weld sizes. But weight might be a factor (of course it could make things better or worse). Do you have any more information....application, fabrication method, etc.?

ZCP

http://www.phoenix-engineer.com

 

[titan354]

The frame will be for automotive usage. Weight will not be a factor, due to relatively small quantity used.

The dimensions of each frame will be identical, except for the wall thickness. There is no choice, it's either 0.188 carbon steel or 0.120 4130 alloy.

I don't know if 4130 alloy can either match or outperform carbon steel, considering it will be thinner.

 

[PSlem]

CM SFy = .283 x 115,000 = 32,600
MS Sfy = .388 x 36,000 = 14,000
So 4130 looks to be over twice as strong and 64% of the weight but has to be tig welded and is more $

 

[EddyC]

Other things to consider are the flexibility of the frame if it is made of lighter construction. In addition, when racecars were just beginning to be made from Chrome Moly, there were brittle failures caused by the lack of heat treating and stress relieving.

 

[titan354]

CM SFy = .283 x 115,000 = 32,600
MS Sfy = .388 x 36,000 = 14,000

I'm lost. Sorry.

 

[PSlem]

The difference is what I was shooting for. S is a member's resistance to bending based on it's size. Fy is the yield strength of the steel. We would reduce this to .6 fy to be safe. Multipiled together they give the moment the member can resist. Moment is the bending force on the member.

 

[titan354]

Thanks for the input.

 

[rb1957]

titan354,

which heat treat ... 4130 can be heat treated for Ftu from 125ksi up to 180 ksi ?

what's important to you ... the 4130 frame will be more flexible than the carbon steel, 'cause I will be smaller (and E the same). and 4130 will have a lower natural frequency, maybe important to a car design ? then, as other posters noted, there are different manufacturing considerations (which may not be an issue for a limited production run)

 

[titan354]

... Yes, other considerations ...

The price of 4130 was not the expected 25% more than carbon steel, as one source indicated. There aren't many 4130 small-order retailers, so competition is limited. That resulted in 270% price increase over the thicker carbon steel.

To me it seems that 4130 is no more economic to use than Titanium alloy, which is exactly what 4130 was not supposed to be.

 

[PSlem]

It's not just the small orders. If you look at rollcage prices from the big builders, 4130 is 2.5 times the cost of steel.

 

[EddyC]

It all depends upon how much you need to cut down the weight. Also keep in mind that it is harder to weld the 4130 than the mild steel.

 

[titan354]

I thought about the ease of welding too. Titanium 811 for example was said to have different ease of welding depending on who I talked to.

Just for the sake of price comparison, I could not find any small order suppliers of Titanium 811, or any Titanium alloy for that matter.