I heat-treated new leaf-springs of fairly similar size, for a 7.25"g loco, by quenching them in oil from cherry-red, then lead-tempering them. The owner of a 2" – inch scale steam-wagon told me he'd used the same method for its springs.

These were springs tempered to a temperature corresponding to blue, which is slightly below the melting-point of lead; but too hot for the domestic oven.

Melt some scrap lead in a suitable container – I used a cleaned-out food tin – then soak the polished springs (tied onto wire for retrieving them) for a few minutes while keeping the lead just on melting-point. You can observe a slight pasty stage in it, as it cools, and that's where it wants to be.

I noticed that the steel would turn blue, or nearly purple, only where exposed to the air. That submerged, stayed bright.

The advantage of liquid tempering is that provided you can control the temperature reasonably closely, as by watching for the crystallising to start, it allows the steel to soak evenly. I have not experimented further but alloying the lead with soft-solder may reduce the melting-point for less tempering.

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You can also temper small items like leaf-springs on a piece of fairly thick steel plate or a shallow sand-bath heated from below, and there were recent references on this forum to using a bath of brass-filings. That was new to me, but I did note the caution that the filings need be clean, not contaminated with oil. (It didn't say how you wash filings…)

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(Tempering in lead copies in a small back-garden scale, the industrial practice of using various molten salts.)

Hi Bob, did you mean the steel is Annealed or Hardened? If annealed it can be bent to shape rather easily, if hardened it will have to be heated red to bend it. However in both cases the shaped spring will have to hardened by quenching, probably in oil, before finishing by tempering.

Dave

Bob, I have made several springs like this. Yes you need to heat them red hot to make the bend. You may need to heat it several times to get the 180 deg. bend tight so that there is no hinge type movement at the bend. the power in the spring should come from the spring leaves, not the bend. Do your bending and shaping in a fully annealed state. To temper the spring, heat it until red (non-magnetic) and quench, usually in oil. Then reheat to desired stiffness. I usually shoot for 500-600 deg F. If too soft, reheat, quench and re-temper to a lower temp, or to a higher temp if too hard. There are numerous temp tables on the internet.. Good luck. Rick

I would definitely bend that spring at red heat to avoid it cracking .Colin

You need to talk to one of the leaf spring manufacturers. I know they can temper a spring to many different tolerances using the same spring, so there must be a bit of tech in it. IE initial temp & then plunge time & medium used.

Years ago i worked with a performance shop, getting the spring rates for my Calibra turbo which we were lowering. The same springs were re treated several times before we got them right.

Steve.

Edited By Steviegtr on 09/04/2021 15:26:04

Sod, I have some proper common as muck spring steel 1/16" thick x 6 1/2" wide, about 4 pieces 4ft long, I will never use all this so if anyone wants a piece, FOC but pay the postage, send me a PM.

Chris Gunn

Bob, don't waste your time with Gauge plate, completely the wrong material, get some EN45 Spring steel, you defiantly must forge the spring when red hot, you need to keep a small gap, say 0.010" at the heal of the bend. File to shape and ensure the two legs have an even taper. Harden from red heat in oil and temper to a little over 300*C I usually go for 320*C

Good luck John

I would soak at cherry red for a longer time than usual – to anneal out any stresses caused by the bending, then your oil quench.

Finally, temper way past straw colours, you need to be past dark blue for a spring.

Neil

Hi Bob clearly too hard ! Going just blue will be around 300* C you need to be above that at around 310 or 320*C even up to 340*C look a Neil’s colour chart. I temper my springs in a muffle furnace, another point why quench in water after tempering ? The wrong medium use oil. Also do you know for sure what the material is ? rather than spring steel, it make a considerable difference, you need EN45 or EN47 45 is best and traditionally used for gun springs. See you PM’s

John