Bending EN24t

[vintagengineerParticipant @vintagengineer]

I need to heat up and bend some en24t. What treatment does it need afterwards?

[DiogenesParticipant @diogenes]

Stress relieving, and then hardening and tempering to achieve the condition that you want – also I think you might be better to anneal the whole piece before the heating and bending, but will defer to those more knowledgeable..

Is it a safety-critical component?

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Good advice on this page:

https://www.steelexpress.co.uk/engineeringsteel/EN24T-properties.html

MichaelG.

.

Hardening EN24: Heat uniformly to 823/850°C until heated through. Quench in oil.

Tempering:  Heat uniformly and thoroughly at the selected tempering temperature, up to 660°C and hold at heat for two hours per inch of  total thickness.
Tempering between 250-375°C in not recommended as this can seriously reduce the steels impact value.

Stress Relieving: Heat slowly to 650-670°C, soak well. Cool the EN24 tool in a furnace or in air.

[vintagengineerParticipant @vintagengineer]

It’s a steering arm for a car.

[Clive FosterParticipant @clivefoster55965]

Steering arm is safety critical so you need to know exactly what material you have. Don’t consider anything that doesn’t come with proper certificate.

You really, really don’t want to use a material prone to fracture.

None of the EN steels have been made for donkeys years so what you get from a small quantity supplier will be some sort of nearest equivalent. Whether by properties or constitution. Equivalent by properties is generally pretty safe but constitution can be minefield. Just because the mix is within limits doesn’t mean the properties are the same.

Steel specifications are something of a minefield. There are so many! John Bradley quotes numbers from the later revised version of BS970 and says that any good supplier will recognise it. Euro harmonised numbers are of similar format but the steels aren’t always the same!

According to John Bradley the nearest modern BS970 equivalent to EN24T would be 817M40 which is not a material for amateur heat treating as it’s sensitive to imperfect methods and very likely to crack if things are done wrong. Bradley says it has been known to unexpectedly fracture even in T condition and been pronounced as “too brittle”. The major advantage of 817M40 is its large ruling section when heat treated to higher tensile ranges. 250 mm in T condition and 63 at V. More than double what the other two steels can manage. Not relevant for a steering arm tho’.

Bradley likes 605M36, a good equivalent EN16T, rather than 817M40 as it has excellent toughness and shock resistance whilst being much less susceptible to temper brittleness than the chromium based alloys. Doesn’t like low temperatures below -20° C though.

Another alternative is 709M40 (EN19 equivalent). More tolerant of low temperatures and much bigger ruling section than 605M36 if you want to heat treat it to higher tensile ranges.

In the normally supplied T condition tensile range there is very little difference in tensile strength between the three. 605M36 is the weakest and 817M40 strongest but specimen to specimen test variation ranges almost overlap.

Clive

[Keith BloorParticipant @keithbloor37728]

Sorry to infringe on your topic but cannot get around my question any other way. I am about to start making a pair of combination levers for a Don Youngs Horwich Crab. Will it be OK to use EN24t steel?.

[duncan webster 1Participant @duncanwebster1]

Why would you want to?

[Keith BloorParticipant @keithbloor37728]

Simple. I have made them out of EN3 and they are not strong enough. I have some EN24t on hand but not Gauge Plate has Don young suggests.

[Clive FosterParticipant @clivefoster55965]

£64,000 question is why isn’t the material you have been supplied as EN3 not strong enough?

Bradley reckons 070M20 is the most appropriate equivalent to EN3B. Comparing properties to 817M40 which he considers equivalent to EN24T its around half the strength with very similar elongation, surface hardness isn’t applicable because 070M20 can’t be hardened by heat treatment.

Tensile Strength   070M40   31 tons / sq inch minimum      817M40T  55/65   tons / sq inch

Yield Strength      070M40   23 tons / sq inch minimum      817M40T  44 tons / sq inch minimum

Elongation %       070M40   12 %   minimum                     817M40T  13 %   minimum

Objectively 070M20 is still pretty darn strong.

Far as I can see pretty much any decent steel will be strong enough for Model Engineering applications which generally aren’t highly stressed. Its the hardness needed for wear resistance et al that is most likely to make a difference in practice.

One potential problem when buying “EN3” or similar lower end commodity steels is that you are likely to actually get 080A15 supplied to analysis, (composition) not properties as the top end of the permitted mix overlaps the bottom end of 070M20.

Ideally you need a test certificate to verify what you actually have. Before discovering Bradleys books I once got 3 lengths of “EN3” from a small industrial supplier. Receipt said 080A15, which I queried and was told “Oh it’s the same stuff.”. The three bars machined quite differently and, whatever the composition analysis might have said were effectively different materials.

Clive

[Keith BloorParticipant @keithbloor37728]

Thanks for the reply Clive. The full story is that I first made them out of EN3, but when setting the valves everything seems OK but as the valve gear is fairly tight when I ran the chassis on air the left hand side lever bent, these levers as designed are quite fine. As I said Don young specifies Gauge Plate which I do not have but I do have some EN24T. Could you please compare these two for me, as you have done EN3 to EN24T.

[Clive FosterParticipant @clivefoster55965]

Keith

Assuming your gauge plate is ANSI O1 tool steel its much stronger than the aforementioned ones.

Around twice as strong as 817M40 so it should be much stiffer in a small section. Unfortunately I don’t have a handy quick reference but a quick look round the internet suggests :-

Tensile Strength   140 tons / sq inch minimum

Yield Strength      130 tons / sq inch

Elongation %       5 %   minimum

It’s not clear from the source I found what the heat treatment / temper state is for those figure but from the context I infer that the figures apply to the working hardness of around 60 HRC.

Please remember that although I’m a retired scientist / R&D Engineer I’m not a metallurgy guy. I just have some decent references.

For this sort of thing I like the data given by John Bradley in his book “The Racing Motorcycle, a guide for constructors” Volume 2 which covers materials as he has real practical experience of serious engineering using the Home Shop level resources where your choice of materials is seriously constrained by what you can actually get. If you are building your own racing motorcycle it’s advisable to ensure that it doesn’t fall apart and dump you on the road at umpteen MPH. I’ve met John and he absolutely knows what he is talking about.

Frankly given the effort involved in making the valve gear parts I’d get gauge plate and be sure the material is up to the job. Although the published designers at our level may not have done full blown engineering calculations they will have pretty shrewd idea st to what in practice works. As ever the general rule is :-

“If its stiff enough its strong enough”

Given the small sections involved in many model parts getting enough stiffness can be tricky.

I’m Home Shop guy working in 12″ to the foot scale so no practical experience.

Clive

[duncan webster 1Participant @duncanwebster1]

Confusion between stiffness and strength in the above post. Gauge plate is NOT more stiff then EN3 or any other steel. What section do you want, I have some stuff about 3/8 * 3/4 from memory, I’ll never use all of it, you’re welcome to a bit.

[Clive Brown 1Participant @clivebrown1]

The difference between materials lies in the yield strength, ( or proof strength ) which defines when permanent deformation will occur. That’s not the same as stiffness, which is defined by Young’s modulus.

[Keith BloorParticipant @keithbloor37728]

Many thanks Clive for the figures you gave me, Gauge Plate it is.

Duncan, many thanks for the offer. The size I require is .625″ x .500″ x 8.5″ long. This will make the pair end to end, which is the way I shall machine them.

[SillyOldDufferModerator @sillyoldduffer]

This stuff makes my head hurt, but here goes,

I don’t think stiffness helps much other than spring steel recovers when mild-steel stays bent.  Neither breaks!  Hardened O1 is springy.

Given that steels are all of much the same strength, this could be about arranging the section to resist bending.

A rod arranged to support a suspended load is much stronger than the same rod arranged as a column.   And short fat columns are stronger than long thin ones.  Combination levers take force repetitively in both tension and compression.  No problem in tension, but the lever will be much weaker in compression; when the cycle loads a lever as a column, it could kink and bend.

Not sure what the geometry of the valve gear allows, bu I suggest looking for ways to rib the combination levers to improve stiffness.  Ideally 𝐈,T, L, +, Z or ☐ section.  Or tube.

Dave

 

[duncan webster 1Participant @duncanwebster1]

Sorry SOD, but that is nowhere near right. Different steels have very different strengths, but the same stiffness.  All steel will break if you put enough stress on, some will stretch a long way before they do (ductile), others will snap with very little permanently distortion (brittle). Unless a column is long enough to suffer elastic collapse it will take more load in compression than in tension. Design codes typically allow about 30% higher stress in compression than in tension (from memory). Fully hardened gauge plate is brittle, there is a good reason why high strength steel is alloyed with expensive metals (EN19 et seq) rather than cheap carbon (silver steel and gauge plate). Having said that, as supplied gauge plate and silver steel are stronger than mild steel.

If Mr Bloor is sticking to true scale he doesn’t have much scope to change section, but I must admit I’m surprised he managed to break his combination lever

What I’m assuming is gauge plate wears out hacksaw blades and will harden by heat treatment. It is 1″*0.5″*18″. If you want it I can chop a bit off with the angle grinder. Yours for the postage. Unless you have a good supply of hacksaw blades I wouldn’t be tempted to saw it down the middle. Send me a pm with your email and we can sort it out.

 

[Julie AnnParticipant @julieann]

Surely a better approach would be to cure the fundamental problem, ie, a stiff valve gear, rather than adding a sticking plaster and hoping for the best.

Julie

[Nigel Graham 2Participant @nigelgraham2]

Dave –

The parts are very visible on the exterior of the locomotive, and of your suggested sections I would think only the I appropriate!

I managed to find a photograph of a full-size ‘Crab’ (immaculately turned-out 13065, but I don’t know where) showing the combination-lever and its associated parts seem not fluted but of rectangular cross-section, and it is not straight but cranked to align the top with the valve-spindle. So although fluting it might stiffen it, it might not be strictly right if high fidelity is needed (unless Keith’s example is based on a variant). Fluted on the back, perhaps? However, I am puzzled why there may be any twisting or sideways forces trying to bend it.

The OP though was about making steering parts for a car…. I’d be very wary of that, especially given the problems of sourcing the appropriate alloy, and of any necessary heat-treatment.

[Keith BloorParticipant @keithbloor37728]

Duncan,    Many thanks for the offer but a bit concerned about the cutting with an angle grinder as to hardening the edges. Have located a piece in Coventry which is not too far away, so going for a ride out. Again many thanks.

[Clive FosterParticipant @clivefoster55965]

Simplifying things from a practical viewpoint.

For our purposes:-

The stiffness of a piece of steel defines how hard it is to bend.

The tensile strength defines how hard it is to stretch.

If you bend a piece of steel the outside of the bend has to stretch to go round the corner. As a higher tensile strength steel is harder to stretch than a lower tensile strength one it will be harder to bend.

Something we have all noticed from practical experience. I’ve got some 1/8″ soft steel fence support wire that bends under finger pressure and some 1/8″ “piano wire” that is almost too stiff to bend by hand.

Although Youngs Modulus is essentially the same for all steels it has nothing to do with how stiff, as in resistance to bending, any given steel is. The mechanics of stretching round the outside of the bend are what is important in this case.

Clive

 

[duncan webster 1Participant @duncanwebster1]

Nope still not right. Stiffness is the ratio of stress over strain. A material which is difficult to stretch is also difficult to bend. You can have low stiffness and high strength in the same material, eg glass fibre.

[Clive Foster]

On Clive Foster Said:

 

Something we have all noticed from practical experience. I’ve got some 1/8″ soft steel fence support wire that bends under finger pressure and some 1/8″ “piano wire” that is almost too stiff to bend by hand.

That is to do with Yield stress – i.e. when the bending becomes permanent.

Stiffness of the 1/8″ wires prior to yield will be similar for both, but the soft wire will distort permanently at a lower stress.

Stiffness is proportional to the modulus, and (for equivalent sections) the cube of thickness.

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