W1 hardening issue

[Obi_wan]

Gday everyone, previously a lurker but first post! Have tried to search for the answer but couldn't find anything so apologies if this has been covered previously.

Long story short, I'm in the process of making my first (unsupervised) knife out of totally the wrong bit of metal. It's a section of W1 in 1/4in. Yep, that thick. Why use it? Because in NZ a 2x72 grinder is unheard of and I found one for insanely cheap to get into the hobby. The guy threw in the W1 and I decided to grind it anyway.

Things are moving along smoothly, profiled, holes drilled for the handle pins, decided I didnt like the handle design and reground it differently. Since it's a big ol slab of steel I wanted to lighten it up by drilling out the handle a bit. The pin holes were fine, but now 5 mins of solid drilling with multiple sized bits barely put a scratch in it?!?! So the question is, would the heat buildup from grinding with cooling in the slag bucket harden the steel that much?

Cheers

 

[Stacy E. Apelt - Bladesmith]

Welcome Obi_wan.

The drill bit work harden the steel …. and the work hardened steel dulls the bit. You need to sharpen your drill bits, and drill slower with a good drilling coolant. The grinding also work hardens the steel, but to a much less degree than drilling. Carbide bits also solve the problem.

You can do a sub-critical anneal to soften the steel by putting the blade in a HT oven at 1250F/675C and holding for 2 hours.
You can do a slow anneal by heating the blade to 1500F/800C (medium red) and putting in a bucket of dry ashes or vermiculite overnight. You can heat the blade with a torch if you don't have a HT oven or forge. It needs to get about 100F/40C hotter than non-magnetic.

BTW, here in the USA the bucket you dunk the steel in to cool it is called a slack bucket. The term means to let the steel rest and cool off in water. I see it called a slag bucket from time to time in error.
A slag bucket is a type of bulldozer bucket used in steel mills and foundries.
They may use a different term in NZ.

 

[P.Brewster]

When I encounter this kind of question, the first thing that comes to mind is a counter-question: how much experience do you have drilling mild steel at the same diameter? Are you minding your RPMs?

 

[mete]

It's not heat build up from drilling it's work hardening ! That will happen to some extent to all metals ! Once you get it try carbide bits or anneal and start over. Sharp drills , food feed [don't baby it ]

 

[Obi_wan]

Thanks to you both for your input, I didnt think it would be hardening due to heat buildup as I've been grinding barehanded and only occasionally had to pull away when it got a bit warm.

P.Brewster, I've been stuck behind a desk for the last decade or so which is why I've gotten into knifemaking (miss working with metal) but have a reasonable level of experience with basic metalwork ( I'm definitely no pro!) I do adjust rpm based on drill size but am yet to throw money at a drill press so a bit difficult with a hand drill.

Mete, I considered that also but aside from some mill scale removal on the platen hadn't really touched the area I was attempting to drill. No forge... yet.. but have a mate who's a farrier so will try annealing in his forge.

 

[Obi_wan]

Welcome Obi_wan.

The drill bit work harden the steel …. and the work hardened steel dulls the bit. You need to sharpen your drill bits, and drill slower with a good drilling coolant. The grinding also work hardens the steel, but to a much less degree than drilling. Carbide bits also solve the problem.

You can do a sub-critical anneal to soften the steel by putting the blade in a HT oven at 1250F/675C and holding for 2 hours.
You can do a slow anneal by heating the blade to 1500F/800C (medium red) and putting in a bucket of dry ashes or vermiculite overnight. You can heat the blade with a torch if you don't have a HT oven or forge. It needs to get about 100F/40C hotter than non-magnetic.

BTW, here in the USA the bucket you dunk the steel in to cool it is called a slack bucket. The term means to let the steel rest and cool off in water. I see it called a slag bucket from time to time in error.
A slag bucket is a type of bulldozer bucket used in steel mills and foundries.
They may use a different term in NZ.

Hi Stacy, thanks very much for your time, it sounds like work hardening is exactly what's happened. It just struck me as odd that there was such a significant difference in drilling the handle pin holes vs another hole 10mm away. Will attempt an anneal and make sure the drills are sharp before retrying.

Also slack, not slag, got it! I have a neighbour who is an ex-engineer and picked the term up from him, although hes an old bugger and does a lot of mumbling.

Appreciate the help and welcome from everyone, I'm taking pictures as I go so will post some once I'm done and throw myself at your hopefully gentle criticism

 

[Natlek]

The pin holes were fine, but now 5 mins of solid drilling with multiple sized bits barely put a scratch in it?!?! So the question is, would the heat buildup from grinding with cooling in the slag bucket harden the steel that much?

Cheers

Buy ceramic tile drill bits and drill that holes no need to annealing . You can try this...start drill with ceramic tile bits , drill little just to pass hardened part /if that was issue /, then use drill bits you have and if they start to drill . . . ......That way you will know that steel hardened when you drill with your drill bits ?

 

[Obi_wan]

Buy ceramic tile drill bits and drill that holes no need to annealing . You can try this...start drill with ceramic tile bits , drill little just to pass hardened part /if that was issue /, then use drill bits you have and if they start to drill . . . ......That way you will know that steel hardened when you drill with your drill bits ?

Hi Natlek, that's a very interesting idea, I'd never have considered it. You dont think it will cause the hole to be uneven due to the hard steel chipping rather than "peeling" swarf away like a typical twist drill would? Probably not an issue for these hidden holes though.

 

[Tom Lewis]

The other day I had trouble drilling a hole in some steel. I finally used a masonry bit. It drilled right through.

 

[Obi_wan]

The other day I had trouble drilling a hole in some steel. I finally used a masonry bit. It drilled right through.

Sounds like masonry bits are gonna be handy to have. Thanks for confirming how well they work, time to spend some money! Cheers Tom

 

[Natlek]

Hi Natlek, that's a very interesting idea, I'd never have considered it. You dont think it will cause the hole to be uneven due to the hard steel chipping rather than "peeling" swarf away like a typical twist drill would? Probably not an issue for these hidden holes though.

Just buy them and do not worry , they drill easy in any steel ......this is 3mm hardened HSS steel