EN24 Heat Treatment

Hi Modellers,

I am sorry to post on this excellent forum but it seemed to be the only useful one!

I want to make some U shaped bolts for a bicycle project I am doing. I was originally advised to make them from S155 Stainless Steel, then I thought they might be strong enough in a high alloyed steel like EN24 or EN26, initially in the annealed condition for turning, rolling threads on, and bending, then heat treated to the Z specification.

Do you think this should be cheaper than S155 too?

Some of your model stuff is very impressive.

You will need to give the guys some details

How thick is the bar? 3mm? 12mm? are you making the nuts?

Basically, whats it for?

S155 is not a stainless steel - it is an aerospace spec alloy steel, offering very high strength.

EN 24 & EN26 are not high alloy steels - they are low alloy steels.

BS S series steel are typically expensive because of the tighter production specification and extra testing demanded for aerospace certification. S155 is vacuum re-melted (extra cost), I'm not familiar with the specific grade - the high Silicon content is rather unusual. At least some S series steels are based upon steels from BS970, so there may be a less expensive alternative for non-critical applications. Perhaps another member is aware of any close equivalent grade.

When considering such high strength levels, you should also look at toughness & fatigue properties of any alternative considered.

Edited By David Jupp on 15/07/2015 07:49:42

No need to apologise!

For a bike project, I'd have thought stainless was much preferred to avoid rusting? How much load will these take, does it need high tensile strength or even heat treatment? Stainless U bolts are available ready made - look at marine suppliers for example, you may find some to fit your needs or be able to adjust your design. In marine service they may for example take the load of a shroud holding up a mast so need to be strong.

To answer the question, using data obtained from 'Mechanical & Physical properties of the BS EN Steels' by Woolman and Mottram, 1968.

EN 24: To obtain the Z condition, the limiting ruling section is 1.125" (28mm) max. Harden by heating to 820-850C, and oil quench. Temper to 180-250C and air cool.

The Z condition is very strong and relatively brittle - Izod impact energy 16ft-lb compared to about 50 ft-lb for a 550C temper (condition T). Typical Z condition strength = 1850 N/mm^2, 0.5% proof = 1544 N/mm^2. I must admit I rarely deal with anything above 1200 N/mm^2 as it becomes brittle at low temps - the glass transition temp for the Z condition is +100C, compared to -25C for condition T (800N/mm^2 UTS).

Hope this helps.

Regards,

Richard.

Edited to say: all this also applies to EN26, just forgot to mention it. However the limiting ruling section is 4" (100mm approx.)

Edited By richardandtracy on 15/07/2015 15:26:37

Edited By richardandtracy on 15/07/2015 15:27:57

Thanks for the information about the steels.

How does this sound:

I will check for marine U-bolts again, I have already checked but it is to go around the seat stays of my mountain bike to fit some stabilisers, they need to be a particular size to replace the ones that broke before I applied hardly any torque. The original set were very weak.

The U-bolts are 6mm diameter.

I was going to use EN24 or EN26 and get them Parco-luberized so they are coated black, they will be rubber coated black over the contact section.

I may try making them from EN24, with no heat treatment to minimise cost.

I can see if I can tighten this up without it breaking, using off the shelf nyloc nuts,

Or can I make this from EN24T. What is this like to bend? The U-bolts are about 35mm wide and 75mm high.

If you're applying the load to these bolts via nylock nuts, then the thread in the nut is going to strip long before EN24 breaks. To make life easy can you make up two saddles with long bolts through them then just use HT bolts?

Commercially available stabilisers are intended for small children's bicycles, the bolts supplied were likely adequate for the application.

If you want stabilisers for an adult size bike then you will need the whole lot made from scratch, not just the attachments. Any system using U-bolts is unlikely to be suitable for an adult bike, the frame will be damaged before sufficient clamping loads can be achieved.

If you seek a stable cycling platform, stabilisers are not the answer, you need a tricycle.

I suspect that any know spec of steel will be good enough for your application, try getting some long 6mm HT steel bolts cut off the head and heat up the centre section to bend it round a mandrel, then thread the other end.

Steve

If you're going to make your own U-bolts it's always best to do the thread cutting before the bending..... just saying.

If you want to go the stainless route, then **LINK** do a range of 316 U bolts - most of them are designed to go through a deck so have backing plates etc that you won't want - you may have to make some split collars to go round your tube to avoid crushing it. As John says above, when used as intended for holding up a mast they carry enormous loads, to the extent that they can cause the deck-to-hull joint to fail or even to pull the backing plate through the deck in extremis., rather than the thread stripping.

Just an observation , but zinc plated mild steel 'u' bolts 8mm diameter are available in sizes from about 30mm up around 100mm as ' Exhaust U Bolts' from a Motor Factors for literally pennies each. Or even the popular online auction site , such as **LINK**