Thread: Burnt HSS turning tools

Generally speaking, no... they'll probably be fine to use with a quick sharpen. HSS is much more forgiving of bluing than Carbon Steel. This is not to say that it can't ruin the tip; HSS will be fine where CS isn't, but there is a point where too much is too much.

Me, I'd sharpen & use 'em normally, with luck the blue is just visual and with normal usage will eventually be ground away.

If the edge has turned brittle & starts chipping then I'd sharpen a bit more aggressively, but not so far as to remove all the discolouration. There'll still be good steel in there and tool steel isn't cheap...

I very much doubt that there is a grinder in the world that can create enough heat to "burn" HSS. You would need to get it to 500°C before it is affected!

The blueing represents heat, but it is superficial colouring. Ignore it. Sharpen and go ..

Regards from Perth

Derek

Originally Posted by derekcohen

I very much doubt that there is a grinder in the world that can create enough heat to "burn" HSS. You would need to get it to 500°C before it is affected!

This is technically true. However not all steel stamped as HSS is created equal; I've had a couple of sections that became extremely brittle and prone to spalling on the edge until I've ground past it, hence my caveat.

Nevertheless, it is uncommon.

Here is the typical temper curve for M2 (HSS).



M2 won't drop below HRC 61 even up tp 1100ºC which is more than hard enough for turning tools.

More importantly, (unlike O1) the tempering temperatures have to be held for significantly longer than it takes to grind a chisel to reduce the hardness, so the chances are that the temper has not changed.

No big deal to blue it, just don't qwench it in water while it is hot.

Originally Posted by Cliff Rogers

No big deal to blue it, just don't qwench it in water while it is hot.

Dumb question? What will that do?

It can cause micro cracking.

Regards from Perth

Derek

At what heat/quench temp would cracking occur? When I was making my little skew chisels from the M2 plane blade cutouts I was continually dunking the blades during hand shaping on the 6" grinder to keep them at a comfortable holding temperature. The blades never got to really red hot but did get hot to hold and did go through many hot/dunk cycles. I've only used the fishtail to any extent sofar and haven't noticed any problem......yet.

I've never taken a detailed interest in the whole heat/quench to temper relationship. Probably about time I added it to my reading list.

Originally Posted by Fuzzie

At what heat/quench temp would cracking occur? When I was making my little skew chisels from the M2 plane blade cutouts I was continually dunking the blades during hand shaping on the 6" grinder to keep them at a comfortable holding temperature. The blades never got to really red hot but did get hot to hold and did go through many hot/dunk cycles. I've only used the fishtail to any extent sofar and haven't noticed any problem......yet.

I've never taken a detailed interest in the whole heat/quench to temper relationship. Probably about time I added it to my reading list.

Generally speaking, if you can hold the steel without burning yourself it will be fine to dunk it in water without harm.

ron

One of the local members here put me onto an article about the hardening and annealing cycles of HSS. The crux of the info was the cycle times were very long (hrs) and at very specific high temperatures to anneal m2 HSS. A few mins on a grinder turning blue will hardly effect it's working hardness on a lathe.

When I have cooked a bit while turning, the most it's done is dull the cutter (poor form from a novice!) I just tip it up with a small diamond hone and keep going.

Ages ago, Cliff put me onto not quenching the cutters! He is on the money with that. I just grind as normal, a quick hone and it's back to work.

The blue will not impact on the strength of the HSS steel, but remember to get that extent of blueing it was very likely red hot at the tip, and that does damage it.

As for dipping HSS in water, just don't do it Micro-cracking is just plain dangerous

Originally Posted by dai sensei

The blue will not impact on the strength of the HSS steel, but remember to get that extent of blueing it was very likely red hot at the tip, and that does damage it.

The blue colour on steel resulting from heating is indicative of a temperature of around 300ºC which is well below any visible "red heat" which starts at around 750ºC.
For a Colour temp chart see http://www.engineeringtoolbox.com/te...el-d_1530.html
So there will be no damage if the steel is a quality product.

At one point or other most of my rough metal working drill HSS bit set (a set of P&Ns I bought in 1968) have had blue tips and some that have been let get too blunt have been briefly even been to visible red heat. Following a touchup sharpen there has not been any discernible degradation in performance even in metal.

A good quality HSS can be repeated heated to a medium yellow (~ 1000ºC) for short periods without affecting its wood working properties - but as Skewy says not all HSS is quality HSS .

Originally Posted by BobL

The blue colour on steel resulting from heating is indicative of a temperature of around 300ºC which is well below any visible "red heat" which starts at around 750ºC. .. .

Using a grinder the heat is not uniform and hottest at the edge being ground. If you look at the steel edge against the grinder, it would have been well over the 1000C required to damage the temper, to get the blueing exhibited is what I was saying. At lower than damaging heat, the bluing exhibited is only few mm from the edge. My rule of thumb is that if the bluing is >5mm you have damaged the immediate edge. Given the extent of bluing in the above photograph I would say at least 5mm is damaged.