Using mild steel, will the frame collapse and kill me?
 

Is mild steel an acceptable material to use over 4130 steel? It seems that the alloy steel has numerous advantages but how much better is it than mild steel? Will the steel bend or deform if I go over a pothole?

It seems that older bikes used mild steel with no problem at all. Being strapped for cash, it would be a great advantage to use mild steel which is about 7x less expensive than the aircraft grade steel.

Any thoughts?

those mild steel frames are correspondingly heavy. As long as you don't make a weight-weenie mild steel frame, you should be ok

"Mild" steel is already used in many high end bikes. Bridges, braze ons, lugs, shells, crowns and drop outs can all be found made of such. Andy.

Straight gage 4130 for industrial use in lengths that will fit on a Truck, being stronger, allows thinner tube walls to be used ..

Specially made butted tube sets for Bike frames cost a Lot more per foot.

What's your source for mild steel tubing? Aircraft spruce's 0.035"-walled 4130 tubing is about $5/foot and $7/foot for tubing under and over 1" diameter, respectively. You can get a full kit of butted/tapered tubes for about $100 at Nova.

Look at Shapiro in St. Louis.

https://www.shapirosupply.com/

I'm not a materials expert but I think it's more the butting rather than the alloying that raises the price of steel for bicycle use. Nonprecious metals are exactly that: nonprecious –i.e., relatively cheap. About the only nonprecious metal that isn't cheap is titanium and its relatively high cost for bicycle use comes more from the work it takes to make flawless tubes with it and not the cost of the materials.

or the cheapest True Temper at Henry James. Bike tubing is one of the biggest bargains around

Everything can be made "rare" by controlling the supply and demand.

Chromoly is a couple of times more expensive than high tensile carbon steel. Obviously the butting and other machining is expensive too.

I was looking at square aluminum, and the 6063 was about half the cost and half the strength of the 6061 :(

I seem to have overestimated the cost of 4130 tubes as I only looked at two websites which happened to have extortionate prices. Thanks for the websites which I will use as a last resort but has anyone had dealings with any suppliers based in the UK? (which is where I live)

edit: After browsing some websites it seems that the price in the UK is around £7/foot ($11/foot) while I could get all the mild steel needed for a mere £15, so the question still stands regarding the use of mild steel.

My 1967 Peugeot UO-8 frame was of steel close to mild. That bike needed realignment after every spill, even very minor ones. I usually didn't and the wheels operated in planes not remotely related to each other. Still, that frame went 19,000 miles before the right chainstay broke. (A failure that was perfectly safe and left the bike still rideable.) So, in answer to the OP's question, yes, mild steel is perfectly safe as a bike frame material as long as you stay with tubes with appropriate wall thicknesses, ie weight.

Ben

What are you building?

The mild steel (high carbon) is unlikely to catastrophically collapse. However, it probably should be 2x or 3x as thick as the 4130, and thus you will end up with a heavier frame.

Heat treating and tempering?

I will say that my cargo bike has quite a bit of mystery scrap metal in it, and the rack is the least of my concerns for strength.

Thanks for the replies. The planned usage will be for commuting but also occasional rides along the uneven river tow path. Ben, after what you described, it seems unwise to use a steel which is inferior to the one used in the Peugeot (high carbon steel vs the low carbon content of mild steel).

The simple answer lies in the physical property of the material called Yield Strength.

Mild steel (plain carbon steel) like AISI 1010 has a yield strength of ~305 MPa depending on temper, while AISI 4130 chromoly has a yield strength of ~760 MPa.

In order for a frame or other structure made of mild steel to have the same resistance to permanently bending that chromoly has, the wall thickness of the tubing has to be thicker, and therefore heavier.

Considering the labor to build a frame, the cost difference between 1010 and 4130 is insignificant.

I don't know what you mean by "mild steel. Bikes have been built for a century using non-alloy carbon steels like 1020, or comparable. These aren't as strong, so would use thicker walls to compensate, hence making them heavier than a comparably strong high strength steel frame might be.

Also, because the flex property of steel is similar for all grades, the heavier frames tend to be unduly stiff, and ride like trucks.

If you figure the total costs of building, I can't imagine that using a 1020 steel saves enough over a 4130 (the most common tubing alloy) to bother. Yes you can go that route, but why would you?

Are you thinking about something like the old 40s and 50s roadsters with 28" tires (635)? A lot of different 26" and 28" frames where made until the late 1980s. At that time high quality steel was still common (carbon steel and welding are not the same). They are very durable, the most cost effective frame often comes from a used bike.

Thank you so much for all the replies. I think in light of all this I will invest in the 4130 steel to save weight. What kind of thickness do you guys recommend when using 4130? I was thinking 0.889mm for top and seat tube with 1.245mm for the bottom.

How heavy are you? What size frame? A 1.245mm wall thickness might be overkill for the down tube depending on your weight. It could make the ride uncomfortably stiff if you're a light weight.

90kg (200lbs) with a planned frame size of about 22" maybe 24". However, I got these thicknesses from a video about bike frames which were using mild steel. If your interested, here's the link www.youtube.com/watch?v=fL25BYkA6Xw

You'd be fine using 0.9mm walls (or in your case, 0.889mm) straight gauge for everything. Ordering butted tubing from Nova would save a little weight, but probably not enough that you'd notice.

Thank you, I will keep all this in mind and hopefully post the finished product on here in the (probably distant) future!

Regarding the costs... Are you planing on building a frame? If so I would expect greater expenses arising from the needed equipment and skill learning.

Yes I'm planing on building it. Luckily I see this as a hobby and an exciting opportunity so I'm not really worried about the man hours required but I don't underestimate the time and effort this will require. I also have a wide but basic selection of tools available.

Framebuilding Bicycles. Tubing, Parts, and Tools is in the U.K. They used to sell everything you needed to build a lugged bike for a very reasonable price

...and then, there's:

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