Differences in steel...
 

What, if any, inherent differences are there btw reynolds 531/631 and 4130 cro-mo?

Material

AISI 4130 CrMo
- Modulus of Elasticity, E (GPa): 200
- Ultimate Tensile Strength, UTS (MPa): 1,425*
- Elongation at Failure (%): 12
- Fatigue Limit/UTS (5 x 10 8th power cycles): 0.5
- Density (Mg/m cubed) (specific gravity): 7.85

Reynolds 531
- Modulus of Elasticity, E (GPa): 200
- Ultimate Tensile Strength, UTS (MPa): 700-850**
- Elongation at Failure (%): >10
- Fatigue Limit/UTS (5 x 10 8th power cycles): 0.5?
- Density (Mg/m cubed) (specific gravity): 7.85

Reynolds 631/853
- Modulus of Elasticity, E (GPa): 200
- Ultimate Tensile Strength, UTS (MPa): 1,250-1,450**
- Elongation at Failure (%): >10
- Fatigue Limit/UTS (5 x 10 8th power cycles): 0.5?
- Density (Mg/m cubed) (specific gravity): 7.85

MPa = MegaPascal = approx. 1 ton force per square inch
GPa = GigaPascal = MPa to the third power

Source: Bicycling Science, 3rd Ed., David Gordon Wilson

* ASM Material Data Sheet lists the ultimate tensile strength of AISI 4130 as 670 MPa.

** Reynolds website says 531 has tensile strength of 700-900 MPa, 631 has tensile strength of 800-900 MPa, 725 has tensile strength of 1080-1280 MPa, 753 has a tensile strength of 1080-1280 MPa, 853 has a tensile strength of 1250-1450 MPa, and the new 953 has a tensile strength of 1750-2050 MPa (and has the added advantage of corrosion resistance).

In real, mechanical terms to you? Nothing.

Reynolds 531 is equivalent to the old UK BS En17/18 steel, used for most structural engineering work where hot rolled plate was insufficient and the structure was likely to be heat treated. It is substantially alloyed with manganese, to a level (1.7-1.8%) approximately 2.5 times that found as a residual in plain carbon steels, and has added 0.25-0.35% molybdenum. The molybdenum prevents temper embrittlement and acts as a general grain refiner and hardenability promoter.

4130 is an ASM standard steel, found throughout the welded tubular section aircraft engineering community and in sports equipment. It is alloyed with between 0.8 and 1.25% chromium and 0.15 and 0.35% molybdenum, for the same reason as in 531.

631 is the non-heat treated version of 853. 853 is a niobium-vanadium chromoly. Clever metallurgy is used to force the vanadium, that in vanadium chromolys usually balances with the molybdenum in solution and free as carbide and segregates to grain boundaries...etc, into solution, with most of the molybdenum. The steel is air-hardening and reaches higher strengths than 531 and 4130.

***Metallurgists digression:
Niobium, which has a very low solubilty in iron when carbon is present, tends to alter the total system solubility of vanadium, which forms less stable carbides and molybdenum, which in steel tends to segregate 2:1 to grain boundaries. Now, molybdenum isn't 'wasted' like this. While you may add x% to a steel and only 0.3x ends up dissolving in the steel grains and aiding the response to heat-treatment, the rest at the grain boundaries is massively strengthening them, and preventing segregation of tramp elemenst such as antimony and tin to prior austenite grain boundaries. That defeats the temper embrittlement that occurs because those tramp elements themselves normally segregate to those boundaries.***



All three steels will have identical, virtually, stiffnesses. All martensitic steels do.

All three will have similar strengths at low temperature tempers (high strength conditions), but 631 will retain strength to a higher temperature. It will also, as mentioned, air harden during welding.

One of the biggest fibs in bike metallurgy is that a heat-treated steel tube of 'x' composition is better than a non-treated tube of same. Any treatment will be destroyed by the welding at the tube joints. The HAZ will varyingly degrade the treatment. The point at which you need most strenth will be immediately hard and strong, then adjacent material will have a bizarre two step drop-off dependant ont he welder's skill.... Unles you re-heat-treat the whole damned thing, it's a bit of a waste of time. And then there's the whole cold-worked, then heat-treated one. The gain from cold work then heat treatment is almost negligible...


Toughness is an interesting one. Cheap 4130 is actually pretty poor. D-6 (aerospace grade, VIM-VARed) however probably has the highest toughness of the three. It's by far the cleanest, with most consistent assay, and the upper limits for alloying additions.

Edit; spelling fixes :)

Good work, it's nice to see some BS free advice,.

853 is quite a bit stronger than 631. It is definitely an upgrade. When 953 steel is more widely produced hopefully this will cause the price of an 853 frame to be lower.

But the likelihood of anyone ever seeing the strength limits of a frame rather than the toughness limit, or the fatigue limit is slim. I've never seen a frame fail in pure tension. I don't think many people on here will have.

To a rider, stiffness in profile section is probably the most important aspect. Only if they still plan to use that frame in ten years time does fatigue limit come into it...

I'm feeling better about the free straight 4130 tubes I scored for my touring project, and I'm feeling better about quality of discussion aorund here, a very competant sounding discussion.

One thing that wasn't mentioned above is that the HAZ from brazing at 1600 F is not much of an improvement over the haz from TIG. The critical temp for a lot of carbon steel is less than 1600, and the temp where all the desireable characteristic of a heat treated material are drawn out is in the 500-1000F range. The fact a steel is air hardening, means it hardens merely by being taken through the trans temp and left to cool at air temp, it does not mean the hardness thereby acheived is in the desitreable range it may in fact be worse than if the steel was not air hardening and merely normalized. The oxidation effect from TIG with a back purge may be better than what happens at lower temp with brazing, but no backpurge. The HAZ of TIG is smaller.

As far as I know that last para is all true, but it may not be true of the all bike specific steels. I'm pulling up a chair and hopeing to learn some more.

Any off those steels will ride the same, given the same tube diameters and wall thickness. Some weld easier making them suitable for low-cost high-production environments. A reasonable builder will pick a tube that he/she can build into a reliable frame.

High-strength steels do have the advantage of being harder to dent, for a given diameter and wall thickness. As a result, they can generally be drawn into larger diameter thinner walled tubing. The manufacturers are smart people and draw the different diameters and gauges that make sense for a given alloy. Aside from very extreme uses (Downhilling/Freeriding/Fully Loaded Touring), strength is not the issue - stiffness is. Most people, for most purposes, don't need the stiffest available tubes. Hence a lightweight tube set like S3 can work for most people in a racing setting.


High-strength steel is also harder on tools (saws, mills, cutters, etc.) and can take longer to complete machining operations. As a result, the frame cost typically goes up by more than the increase in the tubing cost for a custom hand-builder (who doesn't have access to automatic laser cutters and welders).

So, don't worry about the tubing sticker. Worry about whether you have a knowledgeable builder who understands you and your riding needs.

I should have added that the 1600 degree brazing temperature mentioned by PeterPan1 applies to "brass" brazing. A good silver-alloy filler will come in around 1000-1100 degrees.

Thanks catus! That's still way up there for drawing temper. Again that's for tool steels, simple carbon steels etc... They go through spring heat in and around 600 degrees, and of course the temp your solder melts at in the depest recesses of your joint may not be the maximum temperature you actually concentrate somewhere. I'm not trying to do the usual TIG vs. lug thing, though I have been capable of that kind of behaviour, I'm seriously interested what the real deal about the steel is. Whether it's the advocated air hardening steels for TIG or the low temperature solder, neither on the surface sounds all that wonderful unless either a) it's all good enough; or b) the tubes are more resiliant at tranformation hardness in the case of air hardening than normal, or the tubes have very high resistence to drawing temper in the case of the soldered steel. If you had a solder that worked at 600 it would still be a big bite into hardness. It just sounds as though the unhardened tubes are just fine and dandy, which has already been said.

I'm no metalurgist. Don't want to be one either. :) 4130 straight gauge is fine for tubing and its good to practice brazing on (although its mass makes it heat more slowly). For a first frame, it may be the right solution - especially if you're thinking of doing a second. So, don't be discouraged by the following.

The question is whether you can get it in a wall thickness appropriate for a bike frame. For full on touring that may or may not be so much of a challenge - but it is for any lighter purposes.

If the tubing is too stiff, the ride suffers. Also, the weight goes up fast because its straight gauge. I think a 31.7mm Deda ZeroTre tube with a .9/.6/.9mm profile might make a good downtube for you (depending on total bike/rider weight). When I look at Wicks aircraft, the closest straight gauge I can find is a 1.25" by 0.035" tube. That translates to a 31.7mm by .9mm tube. On the surface, this may sound like a good substitution, but the extra material (strength and weight) is where its not needed, making it excess material. How much excess? Well, you're going from .6 to .9mm over most of the tubes length, so that's probably a 40% weight gain.

Given the cost of basic bicycle tubing (not too much) it might be worth a call to Joe Bringheli (Deda) Kirk Pacenti (Columbus), Henry James (True Temper - they have BMX tubing offering thicker profiles in butted tubes), or Andy Newlands (Reynolds). Any of them can help you better decide your exact tubing needs, and provide you with a good set of tubes for a reasonable price.

Cheers,

Good points. I sure don't think it's optimum, unfortuanately they don't make moose sized touring tubes, so one option is to buy each tube which gets a little expensive, so I am happy with the 4130 main tubes, but there certainly are some better tubes out there. It's always a design spiral probably this frame will lead to yet more ideas. Eventually I hope the frame will be close enough to imortalize in the best materials, lugs, and paint.

Peterpan1
What do you mean "they don't make mosse sized touring tubes..."?
What do you mean "....one option is to buy each tube which gets a little expensive..."?

They don't sell tubing sets designed for all up loads (bike is extra) of 300-400 pounds. For instance on the Henry James list the maximum rider weight is 220, there can easily be a rider of that weight and another 50-100 pounds on a touring bike. There isn't a packaged set for heavy touring, least not that I have seen. So one just buys individual tubes, which is more expensive. The actual cost is not all that high but then the tubes are not all that refined to be paying 15 bucks a piece for.

Get a BOB trailer. Then you won't be loading up your frame and forks unnesessarily.

Falanx, you'll have to explain your understanding of 'air hardening' (thermophilic) alloys a bit better for us. Seems to me like you're saying that they're (853, Foco, Life etc) no better than the previous generation of steels because at the end of the day the advantages are lost through the HAZ, whereas I'm under the impression that they're better because their mechanical improperties actually improve at the HAZ due to the welding process.

Am I just believeing the literature or have we all been hoodwinked?

Hardening metals doesn't necesarilly improve them it just makes them harder, which is pretty much the same as more brittle in this case. I'm certainly willing to believe these air hardening tubes are an improvement, or it could be mostly marketing to couter the widespread inpression that TIG is some irresponsible process driven by those who find lugs too expensive. I raised some issues on the other forum:

"I probably just need to read the sales brochure or something to find out more about the air hardening tubes. As a general principle, heat treating is not a random process where any form of Hardening is just what the doctor ordered, It has to be carefully controlled. Given that a lot of modern tubing is designed with TIG in mind, and given the wide range of brazing alloys, and torches, what confidence should one actually have that air hardening steel is ending up heat treated to the desired range, has cycled through the transformation temperature at all, or hasn't in fact been embrittled, or that the end of the HAZ isn't just as pot luck as tubes that don't air harden at all.

There is going to be a point quite close to the joint where the metal didn't reach critical and a point fairly close to that where it wasn't significantly heated, can all these zones be just the perfect hardness?"

It would be interesting to know about other uses for these air hardeing tubes. In other fields where the industry accepts TIG, like aircraft and racecars, I haven't heard of these tubes, but then I only have a slight pnentration in those fields and probably wouldn't have heard much.

Good information here and points well made by all.

On the practical side of things we use what we can get and are limited to the processes at our disposal.

On the assembly line, the Heat Affected Zone produced by a programmed TIG welding arm is very small and uniform and is contained within the butted end of the tube. And there are only a few places in the world where this happens properly. (for bike frames)

The subtitle refinements in riding quality hoped for after brazening a one off frame can really only be achieved after years of experience both in riding and in fabrication.

In no way is this to be taken as an attempt to dissuade anyone from building his own frame. Only that it’s the baker’s skill that makes the pie not the brand of flower. And by golly you know how much we love our pie.

Having built a grand total of eight frames does not qualify me as an expert but I can say that tube selection makes a huge difference in the ride quality of the frame. I built two frames recently with identical geometery, but different tube sets, and one rides very firm, with a nice stiff bottom bracket, and the other rides smoother but has a little bit more wag when sprinting. Brazing/welding has no effect on how the bike rides but tube selection does. And yes, even a newbie like me can tell the difference.

Ed

Anyone who has built eight frames is no newbie but still I think you are misunderstanding me, or perhaps I am not being clear.

No one in their right mind, or at least any one that has ridden more than two bikes is going to say there is no ride difference between the different tube sets.

I am talking about the subtitle differences that can be achieved with different braising techniques like fillet and lugged styles or some of the stiffness or liveliness that can be lost by overheating and poor braising techniques.

And I beg to differ with you about the difference between welded and brazed frames. I have ridden prototypes that were fillet brazed from tubes for a tig production run and there is a subtle difference.

Perhaps the pie analogy was a poor choice but I couldn’t resist. Maybe I should have said the strength of the masons’ wall is more in the mortar and the way he places the bricks than in the bricks themselves.

With any TIG frame the HAZ should be well within any butted section, depending on trim. If you look at the tube and see the blue, that's 500F and up, but it may extend only a half an inch. Could be a lot less given the thickness in question.

If there are differences in feel relative to the method of joining, and that would be quite a trick to prove, though I am not the adverse to the idea, it should be a little worrying. If I sit in two otherwise identical chairs, and they "ride" differently due to the joinery, that's not a good sign. Really, think about it, what is happening to create the difference in feel? Now if some methods only allow certain geometries of the use of certain tubes that would be a big difference related to the method of assembly, but not the joinery itself.

Judging feel is by it's nature subjective. Golfers have a huge range of putters to choose from, and I think anyone trying a few out would notice a big difference in feel. There are big differences in look weight, flexibility of shaft, etc... Close analysis of similar putters that golfers experienced as having different feel due to "softer" materials etc... revealed that what golfers swore were different feels, was mostly attributable to differences in ball sound at impact. Not and easy area to judge subjectively. Even knowing about the sound, it still seems to be a feeling in the hands...

The joining method does not affect the ride quality; whether brazed w/lugs, fillet brazed, or TIG, the frame rides the same. Temper in the tubes may be slightly different in the HAZ, but that in itself does not effect ride either.

In short? Yes and no. Sorry I took so long to get back to you.

I never really liked the use of the work thermophilic. Much like 'paedophile', it conveys entirely the wrong meaning. But that's another thing.

Steel can't get any stiffer. Certainly not by the margin 8000 series Al alloys can get. Your only improvements in advanced steels is in the strength/toughness balance. You're all aware that as a material hardens and therefore gets stronger, it looses toughness. Well, in the case of metallic crystals, that's not actually true. Certainly not in steels, or any other metal that solidifies in the body-centred-cubic crystallography - tungsten, niobium, vanadium, ß-titanium, for example. The tougness and strength are both increased by grain refinement. Hence why the new bainites worked on by Cambridge university are so promising.

If you can drastically decrease grain size, the steels get both tougher and stronger. And that is what every new engineering steel tries to do better than before.

Until you melt them, or heat them up.

Progressively, from the weld zone, you have the fusion zone, partially melted zone, completely phase changed, transformed and (re-)heat-treated, normalised and annealled zones, each with different levels of strength and toughness. And no matter how advanced the steel, you still have these. In transformable (hardenable) steels, the degree, the length is due to the level of heat input and the actual composition. The more advanced they have got, the smaller, the zones are, but this is not always a good thing.

Pick a tubeset. It will take x amount of heat to melt the tubing to weld, and absorb and conduct y amount of heat along its length. At all points above 100 degrees you will alter the mechanical properties of the tube. Just a little to start with, but the shorter the zones of the HAZ, the more noticable, the more sever the strength and toughnes transitions. Obviously, thin walled, large diameter, ultra-high-strength, heat-treated tubes will suffer the worst because their strength is due to so many stages that you've just destroyed with the HAZ. And in tubes where the barrel section is a smaller proportion of the butt section - thinnest tubes - very sudden changes in mechanical properties can be catastrophic in high strain-rate situations, such as crashes because stress partitions to the weakest material as strain remains fixed.

Fastforward to specifically air hardening steels - 853, Foco etc. These materials, yes, do get harder in the immediate weld zone. But that area of HAZ that does not get hot enough to austentize is damaged. It recovers dislocation locking, and overages tempered carbides. When I posted about the issues I had with the overaging 953 in the weldzone, I said to utterly eliminate it, you would have to resolution the whole frame. Steels, unless they are air-hardening, end up distorting due to the ferocity of the required quench. Exactly the same for air-hardening steels.

Air hardeners have a shorter HAZ. But that is a double-edged sword. Sudden substantial changes in properties in thin sections balance vastly increased strength in every part that cools from over 600 degrees.

There's an awful amount of bull**** purported by manufacturers, in an attempt to sell these new tubesets. For example, Reynolds assertion that normal cromoly weakens after welding in the joint is rubbish. The surrounding HAZ is long and substantial annelled, yes, but the fuzed material is as strong and much thicker. Look at the as-welded strength minimums on the websites of the filler wire suppliers.

I will elaborate later, but now I'm off to bed.

Obviously nodoby is going to solution heat treat a steel frame. That would be insane. 6061 is bad enough, but who on earth would have the facilities to solution a steel frame effectively! Obviously that's a best case scenario, but let's leave that off the table for the time being as it's just completely unachievable.

Basically the only thing I've managed to glean from your comments are that there is a balancing act between the length of the HAZ (and therefore the length of the materials transition zones) and wall thickness. The reason we have thicker butts is to counter the fact that when we heat the joins during welding, we change the materials properties at various stages along the length of the tube.

That's fine, but what makes the proported 'air hardening' alloys any better than the previous generation of steels? You've mentioned that each generation of steel strives to improve grain structure and therefore improve the mechanical properties of the tube, but what is it specifically about the make-up of the proported 'air hardening' steels that makes them an improvement?

Each manufacturer proports a greater Yield Strength and UTS of the air-hardening alloys, so obviously they are better tubes, but the reason still remains.

Why?

Once this is assertained (let's say in 200 words or less! :) ), could you prehaps go on to how you believe 953 makes that next step forward (or doesn't, if that's what you believe)?

I've downloaded "Bainite in Steels" by H.Bhadeshia, so wish my Industrial Designer brain good luck with that one!

In some ways I think we're chasing our tails with this one. Increasing steels stiffness i think is the biggest issue in steel framebuilding, but currently I'm failing to see how increasing Yield Strength will effect that, unless increasing the strength of the tubes will allow for larger tubes of thinner wall section.
I did a calculation of a 953 frame in my size utilising the same diameter tubes as my current OX Platinum road frame. My Tephra SL is 1820g, the equivalent frame in 953 would be 1558g - a 262g weight saving, at (presumably) similar stiffness.

Not a huge amount, but considering a Ti frame would weigh the same and cost about the same yet be stiffer because you could use larger tubes of thicker wall thickness for the same weight, you can see where it starts to become a tough sell.

You might have the strongest steel frame ever built, but does it matter if it's not as stiff, light or corrosion resistant as a good Ti frame?

That's the battle I'm having with myself at the moment. (Poor Terry at Reynolds, he must hate my guts right about now)

God, I was tired last night. Just got back from Download.

Starting with the butts - I have an issue with pre-heat-treated frame tubes being considered 'better' because you can make a butt, even 40% thicker than the tube centre, weaker than that tube centre in parts after welding, due to the HAZ's behaviour. It's a waste of time. You need the strength in the join of a tube primarily. Yes, you can make them stronger, but I've said before, and people need ot remember this, what makes a tube dent resistant is not it's yield strength, it's it's sectional thickness:diameter ratio, because dents aren't governed by stress but strain.

Air-hardening steels are still a source of controversy, because of the combination of garbage that manufacturers puport about previous steels weakening at the joints, and because as I said, you get the over-tempering/over-aging/anneallign response in certain parts.

The strength levels that manufacturers claim are the as-treated tube, not the weld, because that would be variable based entirely on jointing method.

I tried to touch on why the 'air-hardening' steels are different a while back. They're basically doped 4130. they're doped with vanadium, to make more of the molybdenum, dissolve in the grains, rather than the grain boundaries - so, beware, they are subject to temper-embrittlement - and niobium to make sure the vanadium dissolves, too.

When you read through Steels, Thylacine, the most important bit relevant to this is the TTT diagrams. AH steels have a typically bainitic/martensitic diagram. They 'air-harden' (4130 itself will in thin enough sections) because that extra molybdenum dissolved in the grains, with vanadium, ******* reconstructive transformations - austenite to ferrite/pearlite/upper bainite etc - but not displacive ones, where the crystal shears - austenite to marteniste, lower bainite, ausferrite.

The temperature at which austenite transforms to martensite is lower in 853 than 4130, but the AC3 temp is higher, so there is more driving force for the hardening, and a greater hardening in the HAZ parts that harden. But then you have a 'damaged zone' right after it. They are only really an 'improvement' either side of it.

Really, I need to be able to sit you down and talk to you, with drawings. There's so much of this to explain, and it's difficult to cut it down for non metallurgists.