Thylacine

Earth to Falanx.....come in Falanx.....

https://www.dedacciai.com/home_eng.html

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Falanx

Sorry, miles away. Specifically in Leeds, getting my frame taken in for a respray. Piccies to follow on the rebuild ;-)

Hmmm. Looks like a reworked version of their SAT14.5. The '18MCDV6' refers to its alloying family - (0.)18(% carbon), x%M(anaganese), y%C(hromium), z%(molyb)D(enum)*, (0.0)6%V(anadium)

*Don't ask me why they chose to denote metal like this

Anyways. It's an air-hardener, even at such a low carbon content with that much vanadium in. I imagine the base alloy is a >1%Cr, 1%Mn, 0.25%Mo steel. What is most likely is that they've juggled the coldworking and heat treatment cycles a little more than SAT14.5 to achieve greater strength - really just refined the production process, and altered the butting dimensions.

Nessism

Since when is 18MCDV6 "and air-hardener"? My understanding is that it's a fine grained steel alloy that retaines a great deal of it's strength after joining but does not harden like 853 or Platinum.

Falanx

Since most people have no idea what air-hardening actually is.

4130 is an air-hardening steel, whether or not the brochures wish you to believe so. Any chomium-molybdenum alloyed steel will air harden in bike tube sections and the addition of vanadium will only increase the effect. Vanadium tends to force half of the molybdenum retained at grain boundaries into solid solution, and as luck would have it, it increases the effect of molybdenum in lowering the risk of temper embrittlement, thus counteracting that deleterious behaviour.

You're right. It is fine grained. But any steel containing molybdenum already is. Solute drag on the advancing boundaries tends to promote substantial refinement of graisn anyway. I won't drag words like allotriomorphic and Widmanstätten into this.

I think what you were referring to was the presence of vanadium tends to promote profuse VC precipitation, which pins grain boundaries when the metal is heated up, thus maintaining a fine grain size in more of the HAZ than if it were not present.That's the common perception, but isn't a right as many people think. VC tends to dissolve at about 900°C in ferrite. A large portion of the HAZ is still well above that. Niobium and titanium are what you really need in the alloy if you want to stop grain growth right through the HAZ.

The 'retains a great deal of it's strength after joining' you've alluded to is wrong. Sorry. The fraction of strength supplied by pinned grain boundaries is much less than the greater volume fraction of martensite produced in the HAZ from greater hardenability, or from dislocation density from cold work.

Nessism

Well I guess you told me!
I bow down to the higher authority.

I will say this though, 853 and Platinum will harden significantly after exposure to the high heat of welding - 850+ degrees C as I recall. This hardening characteristic is important to manage, no welding of cable stops for example, since it will cause a stress consentration in the tube which can lead to tube failure. The alloy Dedacciai uses, 18MCDV6, may harden as you note but not to the degree as these other two alloys.

Falanx

That hardness difference is due to a much lower carbon content in the Italian alloy, over True Temper or Reynolds' alloys.

Thylacine

Lovely town, Leeds. Hopefully I'll get back there one day as I was 16 last time I was there. Kin are from West Yorks, ya see. Don't hold it against me.

So curiously, which high end steel bike tubeset do you feel gives the best uniform mechanical properties after welding with no post heat-treat?

What would be your reasoning behind this evaluation?


Man, I wish I remembered half the stuff from Materials class at University. That's the problem with being a frame designer. Nuff-nuffs expect you to be a metalurgist, psychologist, designer, baby-sitter, pro bike racer, paint expert, materials science expert, tool maker, marketer, philosopher and ****** all at the same time.

I swear it would be easier if I got a real job at a big Satanic bike company. Then I could specialise and not lie in bed at night imagining how changing a seat angle half a degree effects handing.

Falanx

You lie awake at night working over things like that? Okay. I can imagine impotence doing it, but not seat angles...



Now. For the tubing.
I will explain my selection process first.

All ferritic and martensitic steel alloys have the same Young modulus and bulk modulus, so we can assume rigidity, and stiffness (and this will be the one time they are synonymous) will be approximately identical. Their outer diameters and internal diameters will be effectively identical.

Which means two mechanical parameters remain: Strength - actual yield strength, not UTS, and KIC fracture toughness.

Now. The weld pool and the HAZ and the tube are three different regions and I will treat them as such;

Weldpool: Liquid metal so only niobium will help grain refinement in that zone. Even then, precipitates nucleated in the liquid will be coarse and sparse rather than fine and profuse. Will suffer highest thermal cycle, worst grain growth, most directional grain resolidification and the most impurity segregation.
REQUIRED: Niobium/titanium - grain control and hardenability*; molybdenum - temper embrittlement control, strength, toughness and hardenability*; carbon <0.3% - ensure transformations, strength, combining with Ti and Nb for grain control

HAZ: Various levels of heat will be experienced from the weldpool to the unaffected metal. Varying degrees of martensite, bainite, ferrite and retained austenite, plus coarsed carbides and precipitates. REQUIRED: Vanadium - grain control, precipitation hardening and hardenability*; molybdenum - temper embrittlement control, strength, toughness and hardenability*

Base tube: Requires a fine grain with retained coldwork texture along the length of the tube as well as any heat-treated microstructural phases. Precipitates need to be fine and within the grain as well as at the boundaries.
REQUIRED: Carbon - strength; molybdenum - temper embrittlement control, strength, toughness, and hardenability; chromium - enhanced workability

What does this mean? The ideal alloy contains niobium, titanium or aluminium (niobium for preference dues to precipitation sequence and solubility product in iron), vanadium, molybdenum, and chromium. Well, there's a surprise. Sounds like everything from Nivachrom to 853 (give or take the niobium and boron).

But it's not what, it's how much, and then what you do to it after you've concast the billets.

From my experience, we want an alloy with 0.05-0.10%Nb, 0.05-0.15%V, at least 0.15%Mo and ~1%Cr. The carbon content, as is usual shouldn't be above 0.3%, preferably closer to 0.25%. By default there'll be nearly 1%Mn in it, too. All steels contain Mn. Boron would be a great help, as it means you can lower the Cr content for the same effect, or double the effect of all the other elements. Boron does that. You need no more than 0.03%.

Finally, the most important part - the thermal and mechanical cycle that provides the as-supplied microstructure. The tubes need to be cold drawn to shape, butt profiles and all. But not all at once. If you do 50% cold deformation on a tube in a single pass and then heat it to half its melting point, niobium and vanadium or not, you'll have grains like a postage stamp. You have to do it a bit at a time, with inter-stage, little heat-treatments. That way you consistently refine the grain, develop stable dislocation substructures, etc.

Then the grain will be fine because the initial size was limited by NbCN from solidification, then further refined by NbC precipitation during controlled cooling, then further refined AND strengthened by VC precipitation during controlled thermomechanical treatments. The key is the control.

All of which leaves me with a problem. There isn't a single steel out there that matches what I'd be looking for. They either have the thermomechanical stability or the mechanical properties...

EG: Columbus' Niobium has the metallurgy I'd want but diabolical mechanical properties for what they could get out of it if they really tried... Then Dedacciai's EOM 16.5 has some excellent mechanical properties, but really needs some Nb or Ti in it...




The only answer is a compromise. 853.... (but I'd want it with Ti in, and given EOM's thermomechanical treatment....)

NoReg

"4130 is an air-hardening steel, whether or not the brochures wish you to believe so"

Without prejudice to what may be the correct nomenclature. I cycled this stuff, and got no increase in hardness. I couldn't tell if it was a few points harder on the Rockwell C, but it isn't percetably harder, not that any such claim was made. Now if I had smacked it in the super quench I could have easily made a 4130 chisel that cut through 4130. I'm guessing, but it works nicely with half the carbon, so it should work here, don't have the scrap to find out.

Falanx

Could you elaborate on what you mean by 'cycled'... give me a rough idea how long and how hot, as well as hot quickly it cooled from what you were doing at the time?

But you won't make an edged tool out of quenched xy30 steel that will readily cut annealed samples of itself. 'Hardening' and 'hardness are two different things....

NoReg

"But you won't make an edged tool out of quenched xy30 steel that will readily cut annealed samples of itself. 'Hardening' and 'hardness are two different things...."

You will get a blast out of this: https://www.cvbg.org/tips/superquench.PDF

I agree with you about there being a difference between hardening and hardness. That is basically the parameter of my test. It may be air hardening steel, but air hardening it isn't.

Falanx

There once existed a 'quench severity' list. It rated iced brine as 125% as severe as cold, clean water.

Anywayz... I like the home chemistry. Inventors in there own kitchens and sheds will always hold a special place in this engineer's heart, for they embody the true spirit of engineering. The idea's not new, but this seems the most refined I've seen so far.

I'll elaborate on my original example for clarification:

"What influences the hardness of a steel when quenched is the carbon content with respect to the eutectoid point of that particular composition. In a plain carbon steel, this is just under 0.8%C. In 41xx alloys, that's about 0.6% carbon (the alloy solutes, just like an other solution system lower each other's systematic solubility, so the eutectoid carbon content is usually lowered in alloy steels)."

That statement is usually simplified to; "Carbon is the only element that affects the hardness of martensite". And it's the most important part of ferrous metallurgy to remember.

No matter what you do, no matter how hard you quench, there's an absolute hardness you can reach with any given carbon content. At 0.3%C (in a 4130), it's about 55Rc. Most cases, even in thin section, you'll never get above 50. Now, how deep that hardness goes, before it starts to taper off from thermal effects is hardenability - how easy it is to harden and that is controlled solely be everything but carbon.

In short:

Carbon controls how hard
Alloying controls how deep

God, this sounds filthy ;-)


So, even in a superquench® you're limited to a certain hardness hard and to a certain depth. But it's still air hardening, and it does air harden. Just because it doesn't reach 60Rc....

NoReg

Interesting. Not here to argue the science. Depth hasn't been a problem. I know one guy who made anvils out of 1040 using superquench, but whether he succeeded in get the whole of the end of the a 6x6 billet of tank barrel hardened, or just the surface to a significant depth, I don't know. In cutting, tools, hammers, dies, etc... you get the same kind of useability as you would with a toll steel, it isn't just a surface hardening effect, but on larger objects I could see how there would be significant restrictions.

Even just the home heated tank barrell anvil hissed for 30 minutes after the initial banshee scream of the thing being dumped into the 50 gallons of SQ. Now where this might get interesting is with home processed 1020 DOs, or some similar part. Might be tough to come up with an example that wouldn't get anealed in use. But in the right situation one can save a little dough.

Thylacine

Hrm. Should I find some Niobium welding wire to give to my welder to try out?

You know, we could possibly make some things happen here in terms of a tubeset. Things are happenin' in the steel arena and a few companies are starting to realise that they're behind the 8-ball in a lot of areas.

Let me plant some seeds.......

Falanx

I'd like that. I'd be something to put on the resumé.

"Co-inventor of a world-reknowned bicycle tubeset alloy."

Warwick - Do you mean the recommended filler wire, or some raw Nb (O.O) wire? I know ESAB, if you request a certain weight of wire will melt a charge of requested composition to order (just mention Stanton And Stavely and John Bywater), but you have to know what you want in it and how much.

As I see it, we have a small number of steel manufacturers who are giving it some Cold-War style espionage tactics. One of them comes up with something 'new', which isn't really new, and is almost certainly an ASM approved composition before they do clever things with it, and the rest immediately have a counter because they knowwhat it's likely to be before they ever think to pinch an offcut and analyse it. There's no pressure to be innovative, or spec their own really custom alloys because steel is meant to be cheap. 953 is the closest we've ever got to exotic and new, and even that is a thirty-year old alloy in disguise.

As I said, I'm waiting for word from Edison welding institute on processes for these new high-carbon bainites. They will be the first really innovative thing in steel if we can expose them more... and we can find a satisfactorily easy fusion process....

Think about it. Add 1.5%Si (cheap), 1%Mn (cheap) and another 0.5%C (dirt cheap) to straight 4130 and you have all you need.

But as I've said, it's all about the dollar. You can't sell steel to people who doen't want steel. You have to make a sensible profit margin, and that's much easier to hide in an expensive tubeset. How many people go to a custom builder without some idea what material family the want? So your target market is pretty much fixed without some serious brochure horsepoo or extremely succinct and incisive technical reasoning accessible to the masses.

This will require a think....

Thylacine

I was thinking of a niobium doped welding wire.

What would be ****-hot would be a straight guage .5 mm super steel tubing that doesn't turn to *****e in the HAZ.

Then a 3lb indestructo steel frame would be a cakewalk.

Falanx

Get in touch with ESAB then. You look at their website and you don't get told they'll do custom heats. However, you are unlikely to be buying it in 150kg drums. Speak to them. The worst they can say is..."Sorry, that's just not commercially viable for us."

Most steels don't really turn to brown intellectual property in the HAZ. It's all a relative thing. Even vanilla 4130 is still much stronger than heat-treated 7005 after welding.

You remember what I said about post-weld heat treating heat-treating a whole, steel frame? That's a really your only route for such an outcome. I'll tell you now, it'd be pretty awesome. Before we had to pull out of our Robot Wars plans at Uni, we'd got a chassis made up in 531 square-section, TIGed with 2%MnMo welding wire, and heat-treated at a local place. 22mm square section, PG 1mm wall tubing. We couldn't drill it after we'd finished, and that was at a 350 degree temper and there was no distortion at all from a polymer quench. And the guys there did it for us for a minimal price - a tenner.

In fact, thinking about it.... That'd be the way to make it practical for you... Especially with these bainites I've been looking at. Do you have an places near yours that run heat-treatment facilities? You'd be surprised how amenable those kind of companies are to doing small, caerfully controlled batch work for locals, the prospect of regular work being in your favour.

Anywayz... I'm still doing some considering on the joining, H-T cycles etc of the new stuff. I'll be back to you as soon as I have more thoughts....