HSS - quench or not?

[JonF]

I've read that when sharpening/grinding turning tools you should regularly dip in water to keep them from overheating. However, I've now just read that with High Speed Steel this is not recommended and can cause fractures in the steel. Further with HSS any 'blueing' is just cosmetic and doesn't have any deleterious effect on the steel. Is this the case?

JonF

 

[jumps]

Tormek's sharpennig guide to turning tools has this to say

"Influence of heat on HSS steel
HSS steel can stand a much higher temperature than carbon steel without decreasing
the hardness. However, at the very tip of the edge, which is very thin, the temperature
can easily rise to a level which will affect the hardness. Therefore grind cautiously at the
tip of the edge and do not allow it to become blue. Overheating HSS steel can cause a
decrease in the hardness by as much as 4 HRC, which shortens the life of the edge. If
you cool it in water, do not cool abruptly from a high temperature, since this can cause
micro cracks invisible to the naked eye."

which is pretty consistent with what you have outlined -

1. you may soften an edge (short term) but you won't kill it.
2. not a whole lot to gain from quenching - and some risks associated.

 

[JonF]

Thanks for that, I'll remove my patented quenching platform (A yoghurt pot screwed to the wall of my shed).

JonF.

 

[NetBlindPaul]

JonF,
If you quench below the "critical" temp, thus keeping the tool tip well below any chance of damage then you'll be fine.
I don't mean critical in the technical sense, but just keep the thing well cool by grinding and cooling little & often.
Some grades of HSS can hold their hardness at up to and including red heat!
Oil is also a less severe quench than water, and stops the tool bits from rusting but it is a beggar if you get it on your workpieces!

 

[Steve Blackdog]

Tony Iles recommended to me regular dipping in water after every 'wipe' on the wheel. It will not damage it unless it is already too hot.

 

[NetBlindPaul]

Spot on Steve

 

[PsyMan]

I guess really that a quick dip now and again won't do any harm, whether necessary or not, I have always been one of those people that tends to over grind stuff or "reshape", big left grind on my big bowl gouge for instance then realise my lathe motor won't cope with the big cuts that grind would otherwise achieve, then have to grind it back to reality.

 

[NetBlindPaul]

The idea with quenching when dry grinding is to remove the heat energy from the tool prior to it reaching a level that can cause structural change to the material.
That is to keep its temperature as near to ambient as is physically possible.