I'd be inclined to try a heat treatment company, who will have the correct oil. In my apprenticeship days it was whale oil but I would guess that is difficult to obtain nowadays!

I would agree with Brian – after taking the effort to make it, I would be miffed if it bent or cracked when I tried treating it. The problem with sub con HT is the minimum charge they normally have (circa £50). Perhaps you could get it done by a local machine shop who get regular treating done and bung them a few beer tokens?

If you do try DIY then think about the best way to quench, I would guess it needs to go in bowed edge first with teeth at the top – on it's back so as to speak but certainly edge on, not flat side first.

Mark

All British gauge plate I've ever seen is oil hardening to minimise cracking /distortion. Quenching in water/brine is asking for trouble. Gauge plate is not a plain carbon steel & is an alloy steel formulated for oil quenching.

The D bit round stock mentioned is probably "silver steel" which is a plain carbon steel & is water /brine hardening. I've never oil quenched silver steel so cannot voice an opinion on this.

The more exotic "tool steels" have various additives to give high hardness/toughness/min distortion to allow for oil quenching.  

Edited By Dinosaur Engineer on 03/08/2015 02:14:15

Had good results with canola (rapeseed) oil from the grocers, preheated to about 35C in a slow cooker for quenching oil-hardening stock. It certainly smells better than old motor oil, and when it's cooled, just pour it back in the jug. The domestic authority knows that containers in the shop are not safe to put in the pantry.

You should weigh the cost of heat treatment firms against the cost of failure if the part breaks in use possibly damaging the car or possibly killing a bystander if it fails while parked on a slope.

Then professional heat treatment may be the better option.

Silver steel is an alloy tool steel. At one time or the other I have seen it mentioned for both water and oil quenching.

I have quenched items at work in oil – it was in something the size of dustbin and nearly full and plenty of room to wave the item about.

The main difference really is the cooling rates. Water is about 3 times faster than oil also boiling temperatures.

As an aside last time I handled one of these things it was pressed steel so why harden and temper it anyway? It's likely to be a lot stronger and more hard wearing than the original anyway. Heat treating the pawl would make mores sense as it has a much harder life but I feel that it would need tempering into the blue so also questionable really.

My driving instructor used to do his nut if I just pulled up the handbrake without pushing the button first. Just shows how quickly they can wear out.

John

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The oil water choice is down to cooling rates. Water is something like 3 times faster but spoiled by boiling to some extent which is why in both cases the parts need waving about. Taking an extreme HSS is likely to crack if quenched in water due to it's hardness and differential cooling through the section. Even more extreme stellite can crack due to quenching because it gets too hot while grinding it.

Where people at home get away with quenching oil hardening steels in water may just be down to none optimal conditions and simple sections. Relatively low amounts of water and space to wave it about etc.

People shouldn't forget over heating can cause problems as well.

John

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I stand corrected Silver steel is an alloy steel – normally contains Chromium and Manganese in addition to the carbon.

Gauge plate is similar in composition but contains further additions such as Vanadium & Tungsten to give improved properties.

The Mondeo auto-adjusting handbrake won't auto adjust if the push the button in!

Am I the only one impressed that a router bit will mill gauge plate? I thought the received wisdom is that one would chip if used like that.

Neil

"Reposted on the right thread.

Put this on Ground Flat Stock so it was really off topic. Sorry."

Going partially off topic the way I understand it is the faster the quench the more Martensite is produced respective to Austenite and Pearlite. Water quenches quicker than oil because the layer adjacent to the steel is flashed into steam and the energy required for the phase change cools the steel quickly. With proper agitation the bubbles that form are shaken off and the process repeats until the steel is fully quenched. Adding salt reduces the size of the bubbles that form before they break off which makes Brine a faster quench than plain water. Both water and brine are corrosive to hot steel which for tool production is undesireable. Oil has a higher boiling point than water so bubbles do not form and there is no phase change. Oil cools steel slower than water. Oil hardenable steels have been developed for just this reason. The requirements for the oil should logically then be high boiling point, no nasty additives and relatively clean. I would suggest lower viscosity would work better than thick stuff but that's just intuitive on my part.

I would add that this is just my basic understanding and would welcome any comments that elaborate on this as it's quite interesting.

regards Martin