What exactly is chromoly?

good question OWS!

I have just had a chromolly hub put in my MUni (thanks
Mike!!) Seems strong... Roger says it is stronger than a
Suzue.

Someone please tell us....

Joe,

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Chromoly is a high carbon steel. Meaning yes it is stronger
and you can design stronger/lighter components with it. It
is brazable and weldable commonly used in aircraft and
solar cars.

🙂

Check out the construction of the solar car in action! Yeah,
I got to hold the torch half of the time.

Zia

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From the name, I believe it is an alloy of steel or a
coating containing both chromium and molybednium (sp?) for
extra protection against the elements.

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oregonguy
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It's an steel alloy containing chromium and molybdenum,
hence the name.

Check out this website for more info 'Metallurgy for
Cyclists' (63xc.comsteel.htmOpen ↗)

Paul

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Cool, thanks. So can it be welded to regular steel? Or can
only regular steel be welded to regular steel etc? How
expensive and hard to get is it? Also how strong/stiff etc
is it in comparison to other unicycle related
metals/materials (ie carbon fibre)?

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one wheeled stallion - Guerilla Unicyclist

OWS
"It's all in the mind, not the behind" -MikeFule
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OK, you asked for it...

Yes, basically, chromoly is strengthen steel.

At first, steel is a blend of iron with other elements. The
composition of different steel and aluminium can be very
complicated, like those NASA-areospatial-secret-alloy...

There is some basic standard classification for steels. The
AISI-SAE standard is the most used in the USA. Those are 4
numbers designations, that tell the composition of the
alloy. (f.e. the number you see on KH frames: 4130)

There is a serie for each type of steel or alloy: -10xx,
11xx, 12xx, 15xx = Carbon steels -13xx = Manganese steels
-etc. -41xx = Chromium-Molybdenum steels

The most common steels named ''chromoly'' are the 4130 and
the 1045. Note - their properties change if a heat treatment
is done on the part.

Some mechanical properties:

Tensile Strenght (the point where it breaks): -low carbon
steel, as rolled = 61 000 lb/in2 -1045, as rolled = 90 000
lb/in2 -4130, normalized = 97 000 lb/in2

Composition of the 4130: -0.28-0.33% Carbon -0.40-0.60%
Manganese -0.035%max Phosphorus -0.040%max Sulfure -0.15-
0.35% Silicon -0.80-1.10% Chromium -0.15-0.25% Molybdenum
-small quantities of certain elements are also present.

My answer is too much resumed to be clear, so feel free to
ask if you want more informations.:p

Vincent

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vincelemay - Quebec unicyclist
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oh what really sucks is that the army has taken preatty much
all the chromoly steel, so the guy who is building my trials
uni cant finish it because of the stupid army.

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dubmuni2004 said:

*oh what really sucks is that the army has taken preatty
much all the chromoly steel, so the guy who is building my
trials uni cant finish it because of the stupid army. *

You can't be serious...

Chromoly is readily available in the U.S from a number of
suppliers. I'd even bet that there's enough chromoly
scraps laying around some machine shop in Denver to make a
trials frame.

I don't know who fed you the excuse of chromoly not being
available because of the U.S. Army, but I'd get a second
opinion. Further, you probably wouldn't be enjoying the
lifestyle you do now if it wasn't for our armed forces.

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George C. Barnes IV
GB4 Manufacturing, L.L.C.
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Wow that was a lot of detail! Thanks! So.... can it be
welded to regular steel? Or can only regular steel be welded
to regular steel etc? How expensive and hard to get is it?
Also how strong/stiff etc is it in comparison to other
unicycle related metals/materials (ie carbon fibre)?

--
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OWS
"It's all in the mind, not the behind" -MikeFule
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Chromolly is steel with chromium and molybdenum in the
mixture. ("Steel" is any of a number of alloys of iron and
other metals.)

When I was a bicyclist in the 1970s/80s, the big thing
was Reynolds tubing. Reynolds 531 was the thing to have.
Then they brought out Reynolds 753, 453, 501 and 500
(amongst others).

Very roughly, the 3 digits referred to the proportions of
three of the various elements included in the alloy (e.g.
Reynolds 531 included those three elements in a ratio of
5:3:1 to each other.)

Also very roughly, it happened that the higher the
number, the "better" the alloy. So 753 was better than
531, and so on.

Some time in the mid - late 80s, I noticed the term
"Chromolly" being used more often. I got the impression that
this was a blurring of the distinction between the various
grades, so that a basic chromolly alloy could be sold as
"the same as" a better one - in much the same way as they
used to sell mediocre bikes on the basis of the number of
gears (rather than the range of those gears), and they now
sell mediocre bikes on the basis of front and rear
suspension (rather than the quality of the suspension).

The Pashley MUni has Reynolds tubing, but I note that the
stickers only say "Reynolds Tubing" rather than 531, etc.

Thing is, chromolly is stronger than normal steel, weight
for weight, and is typically used to make bikes lighter
rather than stronger. That means they use less of the steel
so the strength is the same but the weight is reduced.
However, the stiffness of the steel is approximately the
same, so, with less of it to be stiff, the chromolly bike
frame ends up more flexible than the standard steel one.

--
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So many pedestrians tell me I've lost a wheel.
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dubmuni2004 said:

*stupid army. *

Hmm. They probably need it to protect themselves against
stupid bullets. Which is where I'd rather see it go until
those boys can get home. But like someone else already
mentioned, any shortage of chromoly is most likely a local
or temporary one, specific to the supplier your builder
works with.

Thanks for the great info on chromoly!

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John Foss, the Uni-Cyclone
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In the US 4130 tubing seems to be easy to buy in multiples
of 1 foot lengths. I easily found a few websites which
stocked suitably dimensioned material.

In the UK however it seems harder to buy, you can easily get
~5m lengths but nobody seems to sell short bits. It is cold
drawn from a large lump, I believe each drawn bit comes out
around 5-7m when the required wall thickness is achieved.

T45 is another suitable tube, which is nearly identical to
4130 but is based on a British standard. Race cars,
Dragsters and proper go karts are all made of 4130, as you
live in Oxford there my be a suitable local fabricator to
buy off-cuts from (although a lot of their tubing would be
too thick).

You shouldn't overheat the tubes so, apparently, brazing is
best. However race cars are TIG welded (very expensive
equipment) rather than the cheaper MIG.

Personally I want to learn how to make my own frames so am
planning to take an evening class this September on Oxy-
Accetelene welding/brazing.

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keg
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WOW! Thanks very much everyone!

All you need to know about Chromoly in ONE thread -
cool! 😎

Keg, I also want to learn to weld. Not sure which type (not
even sure if there is types, just you said you were going to
learn oxy- Accetelene welding/brazing.) I dont know anything
about welding at all yet.

I know this is slightly off topic to 'What is chromoly', but
what is the different to welding and brazing, and what
different types is there, like Keg said.

Cheers,

Joe,

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but to show them what can be done on a unicycle' - Sofa

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