Case hardening questions

if you find a way to harden stainless let me know..... i design and make surgical instrumentsfor a living, if i want something to be reasonably hard i have to use a grade called 17/4 (precipitaion hardening) ..... if it needs to be a bit harder its carpenter 405 (expensive dosnt come close... £100/ft for 6mmØ) if you are looking for tool steel hardness you need a grade called 420, which, if hardend correctly (in a sianide bathe) can be hardened close to tool steel., but as you can imagine.... surgeons dont much like the idea of using an instrument that has been hardened in sianide.

Shouldnt that word be cyanide. Rotty

The instructions on my casenite say
heat to red heat, dip in powder, re-heat to red, then quench in water.
Obviously, this is for mild steel. It works, the gudgeon pins I made for Sweet Pea were so hard after this that they were brittle, and I broke one tapping it in.
AFAIK you can't harden stainless.

No Nigel, the Alzheimer's is kicking in again :-) What you describe is the tempering part of hardening and tempering. The powder type doesn't require tempering as it only puts an outside hard case on material that normally can't be hardened by flame. To use, heat to cherry red dip in and roll in compound [ the part that is, not you ] and allow to cool in the compound. Reheat to cherry again and quench into clean water. slender articles need to be done vertical to stop the shock warping the part. This will put about a 5 thou case on the part. Thicker cases need another repeat. When done correctly you should have a matt grey, mottled finish to the part.
Stainless can't be hardened this way but still try it as you have nothing to loose. If you can only convert part to a harder material it's got to be better.
Gudgeon pins are best fitted with a piece of tube, a leather patch to stop the tube scratching the piston and a length of thread rod to act as a puller. Washer and nut one end of the pin, small enough to pass through the piston. Tube and large washer the other side, tube large enough and long enough to accept the pin. Tighten the nut at the tube end and it will draw the pin out with no damage.
-- Regards,
John Stevenson Nottingham, England.

Case hardening only penetrates a few thou into the material, so it should have had no effect on the core of your pin. Could there have been some carbon in the steel that they were made from, as heating to cherry red and quenching would harden anything but mild steel. Case hardening certainly shouldn't make anything brittle.
Regards
Kevin

You are right - heating/quenching is a problem when you don't know what sort of steel you're working with. I remember case hardening the hammer on my .45 auto (a few years ago that!), first shot broke it in half. It wasn't the case that did that.
ChrisH

In article , John Stevenson writes Who are you? Is it time for my tea?
(Snip)
Cheers.
This is a factory "special tool" that I'm making for someone from drawings. It's probably not what I'd do, but there y'go.
Thanks again.

Perhaps it was the head-case holding the hammer?

"Airy R. Bean, village idiot" took a short break
Go back to sleep, the Job Centre's closed today. ...(_!_)...

Of course...... i had had 1 or 2 beer by the time i manged to post........ so didnt have my spelling head on...
typical lol......... but then.... i am an engineer.... i dont need to be able to spell lol

Why do you have to use cyanide to harden 420? If you use 420C or 440C, they are hardenable stainless alloys. Heat it and quench it. For best results, a reducing atmosphere, and careful heating per manf instructions.