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What is the "4130" in "4130 Chromoly"?

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Q. I am taking fab/weld here at Lane Community College in Eugene, OR, USA, and I need to know (because of a friendly debate on a message board, and for general knowledge) what do the numbers stand for in "4130 Chromoly". I have been riding BMX bikes (yeah, the "little kids' bikes") for a few years, but the kind I ride are super expensive hehe. Now, go to K-Mart or Wal-Mart, and most of the BMX bikes there are made of 1020 high tensile steel (which is what most of us use here in the shop). But, you purchase the good stuff, the stuff you can actually use and abuse hehe you will find that most of the stuff is made of 4130 chromoly steel, so in other words, when it comes to BMX, 1020 is bad, and 4130 is good.

Now I know that both materials are derivatives of steel, and "chromoly" is chromium, molybdenum, and the rest is steel, correct? SO, the thing that I want to know, and it helps in the discussion on the message board, is what do the numbers "4130" stand for? And really, the main question on the message board, is what is the difference between "100% Chromoly" and "4130 Chromoly"?

Jimmy Spoor
Student - Eugene, Oregon


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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 [link is to spec at TechStreet] "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 [link is to spec at TechStreet] "Chemical Compositions of SAE Carbon Steels".

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

Toby Padfield
Automotive module supplier - Michigan


Second of two simultaneous responses -- ++++

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 "chromoly"). 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.

Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia

It is this website's profoundly sad
duty to relate the news that Bill
passed away on Jan. 29, 2010.



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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
Sulphur 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, please leave me a message and I will try to answer you -- a bored Tool and Die / Toolmaker that has worked with many different materials and applications over the years.

Jack Demcovich
- Webster, New York


February 19, 2009

thumbsup2I 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.

Michael Harmon
project engineer - Franklin, Tennessee



May 9, 2009

Q. Wow! You guys are amazing! Great information Mr. Demcovich. Some guys here are debating whether or not powder coating will effect the steel on a bicycle. They claim a frame broke after being powder coated. Can we powder coat a 4130 chromoly bicycle frame without the oven temperature (350° F to 400° F for 10 min to 30 min) adversely affecting the steel? What about a cheaper brand bike with 1020 steel? I see the tempering process is twice the temperature as the powder coating oven, but could it have any ill affect? My guess is, No. A manufacturer doesn't re-temper a frame after it is welded do they? Certainly the welding would affect the steel's strength before the oven. I think, simply, their paint cracked and not the steel. Maybe I'm wrong. Please advise.

Steve Seagraves
commercial painter - Buildings - Douglasville, Georgia


May 11, 2009

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

Dan Neelands
- Olympia Washington

Lugged Bicycle Frame Construction



November 5, 2009

Q. Can anyone suggest which Reynolds cycle tubing would be the closest equivalent to 4130? Or are they all? I read somewhere that Reynolds 531 is the same, but my understanding is that Reynolds 531 was always used in lugged tubing only and could not be welded.

Thanks,

Stephen Lord
- London, UK



December 9, 2010

Q. How about blasting the 4130 to remove paint? What type of medium is best? Will steel shot damage the 4130 tubing?

Jason Doscher
- Benson Minnesota USA


sidebar
June 19, 2011

Q. As long as we're on the 4130 topic ... I have been considering making a knife. It seems to me that 4130, an old friend, would be a good choice, yet none of the knife makers I've read about use it. Any thoughts on why?
I have already formed a blade and I'm ready to harden and temper it. Additionally, any thoughts on that in the context of a knife blade would also be greatly appreciated.
Thanks.
thumbsup2PS great post Dan! Hope you're still around!

George Harding
- Eugene, Oregon, USA


Hi, George.

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 truly 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,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


March 26, 2012

Q. Hello, I would like to know if Steel 4130 and 4140 could be affected by Alkaline cleaners.

Thank you,

Martine Morel
Bita - Montreal, Quebec, Canada


March 27, 2012

A. Hi Martine.

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

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


June 13, 2012

Q. Hallo,
Another question regarding 4130. I am bending 1 3/8" .065" wall tubing into a long bend with about a 25" radius, over about a 5' length, and this I am doing cold.
There is a fair bit of stress as only one end is fixed, and the curved piece does flex. So my question is as follows:

Should I do some sort of heat treatment, post bending, to retain the strength to ensure it always returns to my initial radius? Or is it better to just leave as is as I did, bend it cold? I have been advised to heat it up to red heat and then let it air cool, but I would like more opinions.
Many thanks,
Jonathan

Jonathan Summerfield
- London, England

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