4130 Chromoly -- what are its properties (and meaning)?

A. Hi Rob. Chromoly should polish just fine (even plain carbon steel polishes fine). But Chromoly is not stainless steel, it's just a low alloy higher strength carbon steel, which means it is not much better at resisting corrosion and rust than plain steel.

It's probably not going to be well maintained, so I'd strongly consider lacquering or clearcoating it.

Luck & Regards,

A. Richard, remember that 4130 is a chromium-molybdenum steel. Roughly 1% Cr, and 0.2% Mo. So if you look in Matweb or Efunda under "steels" or search under "4130 steel", your efforts will likely be more fruitful.

Enjoy!

A. Properties of 4130 vary according to their process routine; the method by which the item was produced. If it is tubing you are referring to the typical properties I can provide you: they are easily obtained by looking at ASTM A519 - Seamless Mechanical Steel Tubing (American Society for Testing and Materials)

A. 4130 is a designation for a steel alloy that contains chromium and molybdenum among other elements. The exact composition range is defined in the standard SAE J404 "Chemical Compositions of SAE Alloy Steels".

1020 is another steel alloy, but since it does not contain appreciable amounts of alloying elements other than carbon, silicon, & manganese, it is called a carbon steel, not an alloy steel, and its composition range is defined in the standard SAE J403 "Chemical Compositions of SAE Carbon Steels".

So, to answer your question, there is no difference between "100% " and "4130 " except that one description refers to an industry standard and the other one is pretty much meaningless.

A. The 4130 is a code of the American Iron & Steel Institute and defines the approximate chemical composition of the steel.

The "41" denotes a low alloy steel containing nominally 1 percent chromium and 0.2 percent molybdenum (hence the nickname ""). The "30" denotes a carbon content of 0.30 percent. In addition, as normal constituents of plain carbon and low alloy steels, there will be around 0.2-0.5 percent silicon, 0.5-1.0 percent manganese, and well under 0.1 percent of each of a dozen or so other elements whose presence is unavoidable, in a few cases deliberate, and generally not harmful. The remaining 97-98 percent is iron (Fe).

There are many tens, perhaps hundreds, of different steels defined by that AISI 4-digit code system. The code does not specify any particular mechanical properties, only approximate chemical composition. For any particular grade (composition) (AISI number) of steel, the mechanical properties depend on what heat treatment has been applied, and what (if any) cold work has subsequently been done.

A. The chromium content is approximately 0.8-1.1%. The carbon content is nominally 0.30% and with this relatively low carbon content the alloy is excellent from the fusion carbon content the alloy is excellent from the fusion heat treatment. The actual breakdown of 4130 alloy steel is as follows:
Carbon 0.28 - 0.33
Chromium 0.8 - 1.1
Manganese 0.7 - 0.9
Molybdenum 0.15 - 0.25
Phosphorus 0.035 max
Silicon 0.15 - 0.35
sulfur 0.04 max

Some other facts regarding this material:

Applications
Typical applications for 4130 low alloy steel include structural use such as aircraft engine mounts and welded tubing applications.

Machinability
This alloy is readily machined by conventional methods.
Machinability is best with the alloy in the normalized and tempered condition. Although the alloy may be machined in the fully heat treated condition, machinability becomes more difficult with increasing strength (hardness) of the alloy.

Forming
Formability is best in the annealed condition for which the ductility is very good, Bend radii of 1t on annealed sheet material may be made.

Corrosion Resistance
4130 is a steel and as such is not corrosion resistant. In corrosive environment the alloy should be given a protective coating.

Welding
4130 alloy is noted for its weldability by all of the commercial methods.

Heat Treatment
Heating at 1600 °F followed by an oil quench will harden the 4130 alloy. For best results a normalizing pre-hardening heat treatment may be used at 1650 to 1700 °F followed by the 1600 °F soak and oil quench.

Forging
Forge at 2200 °F maximum down to 1750 °F.

Hot Working
4130 in the annealed condition has excellent ductility.
Thus it is usually not necessary to do hot working to form parts. If hot working is needed it can be done in the range of 2000 °F to 1500 °F.

Cold Working
Cold working by conventional methods is readily accomplished on this alloy.

Annealing
4130 (and most of the other low alloy steels) may be annealed at 1550 °F for a time long enough to allow through heating of the section size. It should then be cooled in the furnace at a rate of less than 50 °F per hour down to 900 °F, followed by air cooling from 900 °F.

Tempering
Tempering is done to restore some of the ductility that may be lost after the hardening heat treatment and quench. Alloy 4130 is tempered at between 750 °F and 1050 °F, depending upon the strength level desired. The lower the tempering temperature the greater the strength.

Other Comments
The 4130 alloy is a through hardening alloy and should not be case hardened.

If you have any other questions or comments regarding steels of any type, I will try to answer you -- a bored Tool and Die / Toolmaker that has worked with many different materials and applications over the years.

I just want to respond to the reply from Jack Demcovich. That was a very excellent answer. Thanks.
The tensile strengths, annealed, quenched, and tempered would be nice to know. Otherwise, I think you covered it all.

A. They powder coat 4130 aircraft fuselages with no other heat treatment so I'd have to say "yes".
Dan

A. Hello Abraham,
In my opinion you absolutely need a consultant in steel fabrication, heat treatment, automated welding, etc. This forum is basically dedicated to finishing questions. Should you have any problems later on when painting your bicycles, post them here. [The] Mostly Metallurgy [category on the index] is for specific and rather simple questions.

A. Hi, George.

A. Please search our site for "knife making" for several very interesting threads which include great info about what makes for a good knife blade. If you are not finding any info about making blades from 4130 (we have none here), I suspect that it is because it doesn't make a great blade, rather than that no one ever tried it. Some pretty special properties are required of great knife blades -- like a combination of hardness (to hold a good edge), and toughness (to bend and not snap), and most metals lack that combination.

Regards,

A. Hi Martine.

That's pretty vague, so you probably won't get definitive answers. But I'd say that in general alkaline cleaners have very little effect on low alloy steels like 4130.

Regards,

A. Hi Jonathan.

Steels are elastic up to a point. So if you try to bend them a little while cold, they spring back. But if you exceed the "elastic limit", they stay deformed. It can be tricky to exceed the elastic limit (or yield point) without exceeding the ultimate strength and causing any breakage/cracking though. But you are not going to be able to get it to take this "set", cold, without a "fair bit of stress" (exceeding the yield point). Typical figures for annealed 4130 are probably about 52,000 PSI yield strength, 28% elongation (meaning it will definitely break before it stretches that much), 81,000 PSI ultimate strength. You are probably okay with your 25" radius if you are using a proper tubing bender that discourages kinks on the inside of the bend ... but I have no actual experience in this and have done no calculations; it just "sounds" okay. Note that you haven't told us what you are doing! It's one thing to say "it'll probably be okay" if you're using it as as a handle for your own lawn mower, but it's quite another thing if it's a vital aircraft component :-)

If you bend it hot, it will not spring back at all. But you should probably research the annealing of 4130 to make sure you are following the right protocol, which involves slow cooling in still air, and no quenching.

The third approach is to cold bend it, then heat it and anneal it. This probably leads to a somewhat safer component because it will now be able to bend, i.e., it will now have the cold working stresses relieved and some ductility restored. But my experience is in finishing, not in bending and heat treatment, so take this as an intro to theory, not as an expert opinion on your design :-)

Regards,

A. Hi Evone. I read "In Search of Excellence" so many years ago that my memory has distilled it down almost to what I considered it's most important single lesson, which ran something like this: "If your restaurant wants to offer good salads while meeting a low price point, search for the crispest lettuce, not for the cheapest artichokes". The relevance is that a science project that is within his educational level can turn out great even if it seems a bity trivial at first, because we can always go deeper on any aspect that we find interesting. But a project which is beyond what he has the engineering background to tackle might turn out more like a child's review of rickshaws than a science-based project. Unfortunately he's not ready to size that tubing for the 1000 lb. loading, and won't be before completing more years of high school and then the first 2 years of engineering college :-(

The required calculations are too far beyond his skills, so all you could do instead is look at similar devices like other rickshaws and try to duplicate their elements. But a large diameter but thin walled tube, like Jonathan's 1-3/8" dia. x .06" wall tubing will give a great "strength-to-weight ratio", which is what you'll want for a human powered rickshaw.

Please look at my recently updated response to Jonathan, above, for an explanation of how you bend something that strong: you either heat it red hot so that it's soft, or you impose very high stresses on it that exceed the yield point of the steel. Sorry that I don't have easy answers.

Best of luck, and please tell us more about the rickshaw project if you stick with it!

Regards,

A. Hi Jeff. Bicycle frames are not made either of chrome nor molybdenum. They are made out of steel with various but small amounts of chrome and/or molybdenum and other alloying ingredients (although they can also be made of aluminum, carbon fibre, or titanium instead). We appended your inquiry to a thread about Chromoly to give you a basic understanding of it, but the strongest steel will not be the most flexible, and it's very difficult to figure which of two materials is best by starting from the sales pap offered by a bicycle manufacturer :-(

Spend a few paragraphs explaining in some detail what is on your mind, and your actual situation, and we can probably help. Good luck.

Regards,

Q. I wanted to understand how .01 of chrome and .002 of molybdenum could make such a difference in the way the bike rides.
My hunch is that it has something to do with the flexibility not the weight. Do they use 4130 for railroads?

My main question is which metal will give me the propulsion for my pedal power.

A. Hi again Jeff. Small amounts of alloying material can make a big difference. Low carbon steel (<0.2%) isn't hardenable, but add a smidgen more and you have hardenable medium carbon high strength steels because the whole crystal structure can be different. Yes, chromium and molybdenum allow some properties of flexibility and toughness that probably can't be obtained from a carbon steel, and I do believe that railroad tracks sometimes are chromoly or similar steels, but there are literally thousands of carbon and low alloy steels.

Although I'm neither a metallurgist nor a mountain biker, I probably can't agree with you that those small amounts of chrome and molybdenum are the main parameter controlling the flexibility of the bike though. It probably has more to do with the thickness of the tubing, the heat treatment regimen, whether the frame is constructed of tubing mitered and welded together vs. with tube & lug design, etc. I think the actual situation is more like this:

Renoir and Van Gogh were so skilled that they probably could have done impressive art by drawing with crayons on brown paper lunch bags, but they chose instead to use the best materials available to them. Similarly, bike designers could probably make a pretty competitive bike with carbon steel instead of tubing but they don't because they want to make the best bike they can within the cost range.

I think the way to pick a good frame material is to pick a respected brand bike with lots of good reviews, and trust that their engineers will pick materials well. It would be difficult for an expert metallurgist to predict what frame material would perform better. If you read a couple of books about bike frames, a couple about steel metallurgy, and acquire a lot of trail miles, you might try to figure out what steels are good from first principles -- although I don't think it will work. Trying to pick a frame material based on the manufacturer's sales pap ... impossible. Best of luck.

Regards,

A. For 4130 Steel, I think you could check this link: www.astmsteel.com/product/4130-steel-aisi-25crmo4-7218-scm430/, you have detailed 4130 alloy steel's properties. And you could also refer to ASTM A29 standard, which 4130 steel belongs to.

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Ed. note October 2020: Jeremy's link is now broken.