DIY hardening of centerpunches?

[e9999]

I have a bunch of centerpunches (regular tapered point, not the transfer kind) that I use for (trying, often pathetically unsuccessfully) to start more accurately my drilled holes. Many of them are generic Cr-V steel made in Taiwan (if that matters) centerpunches.

Even though I used them mostly on mild steel, it seems like the points flatten out very fast, as in after just a few -as in 5- smacks. Evidently, that stuff is not very hard. (Some of my flat ended punches also tend to bend at times...)

So, I make a new point on a grinder, trying to keep them cool by dipping frequently in water. And have to do it again before too long...

I'm sure the means of hardening the steel are critically dependent on the exact composition of the steel, which I don't know of course. And the little bit of Metallurgy I was compelled to memorize in school has thankfully be long forgotten, but I was wondering:

What if after putting on a new point, I would heat them up with a torch and then quench them in water or oil? I realize a metallurgist would cringe at the vague question, but is it more likely than not that this would result in longer-living points? Hoping for first-hand experience feedback. And, yes, I could probably buy centerpunches made of diamond or something but what's the fun in that?

 

[Pin_Head]

You can be reasonably sure that it is carbon alloy tool steel. Do the grind test to look for forked end sparks.
Hardening tools steels like chisels and punches is easy: Heat 3-4 inches at the end to cherry red. Quench the end 1.5 inch in water for 5-10 seconds but leave the steel behind the quench spot red hot. Remove the tool and quickly file off any discoloration from the point of the tool with a file so that it is shiney. Watch the colors change in the bright spot and when gets to a straw color, then plunge the whole tool into the water.

 

[e9999]

thanks.
I was afraid somebody would mention red hot... I don't have an oxyacetylene torch, just MAPP. But that might be enough for a fine point. I'll try.

 

[Pin_Head]

MAPP will do the job on something small, like a punch, but it needs to be red hot to harden. The heating time after the first quench is to draw or temper the hardened tip so it is not too brittle. Not enough tempering and it will crack like glass the first time you hit it.

 

[e9999]

what do you mean by heating after the quench? Reheat with torch or just let the tip draw heat from the non-quenched body?

 

[Pin_Head]

This:

 

[Rifleman]

Your biggest problem is most of those tools from Harbor freight use crap steel to begin with. Best bet would be to buy a quality center punch made in the USA. Oh one more thing don't even waste your time or money on any of those drill bits made overseas. Spend your money on a good set of jobber length HSS or Cobalt bits made in the USA.

 

[e9999]

well, I started out with the simplest experiment.

Tried an unknown generic punch after making a nice point on a grinder, cooling frequently. Got flattened noticeably in a couple of smacks on some fairly mild steel (I think, it files fine).
Tried a fancy looking made in the USA new-looking and probably actually new punch. Same thing. Disappointing. Goes to show you...
Another US made one held fine, though.

So I repointed the 2 weak ones on a grinder and then heated them both to dark orange (LP worked fine) and quenched in water. No tempering.

Tried again. They seem just fine now, the points stay sharp and make very nice divots still after quite a few good smacks.

So, maybe there is hope for the ultra simple hardening technique eh? I half thought they might shatter since I didn't temper them, but no. If that's all it takes, I'm good with that.

 

[Pin_Head]

They are probably not as hard as they could be because they weren't hot enough before the quench or they don't have enough carbon to harden.
If you heat carbon alloy tool steel, like 1050 or 4140 about 1200 C (bright yellow) and rapidly quench in water, it would be very brittle. Above 1200C it is in the austinitic phase and rapidly quenching converts it to martensite which is hard and brittle. The post quenching temperature reduces the amount of martensite. The higher the tempering temperature, the less martensite.

 

[e9999]

since I don't want brittle, just hard, maybe the dark orange and no tempering is good enough. A compromise of sorts maybe. Simple enough at least.