Heat treatment problems on punch head

[blackleafforge]

Hi, Im having more problems with my chisels after moving from EN9 to 01 tool steel. Initially i got fractures at the business end that I was subsequently told due to the enlarged grain structure it was probably caused by me over heating during forging. So I forged a new set of punches and kept them at a lower heat and that seemed to solve the problem, but I now get large bits flaking off on the striking end. No enlarged grain structure and I had brought it up to critical, oil quenched the tip, let the temper run then re quenched the tip again and let the punch cool naturally under the forge ash. Have I missed something? 

I really like the toughness of 01 vs EN9 that I had to re forge every week but it seems much more temperamental, Is this the best steel to be using or am I just using it wrong?

Thanks!

[Jackdawg]

Doesn't look like you tempered the striking end at all?

[stockmaker]

I have to agree with jackdawg, what color did you let the color run to in the very end of the punch?  I would think blue would be what to use, but others may have more experience than I on O1. I think if I was doing it I would not heat treat it at all I see how it holds up to use.  Only treat after I saw too much mushrooming to live with. 

[blackleafforge]

I let it temper to a light straw, It did stand up to a few uses before breaking so I have lost the tempering colours on the end. 

[Alan Evans]

There is a clue to the appropriate hardness or otherwise of cold chisels when you see how many of the old well-used but badly-maintained ones are mushroomed. 

It is better and much safer to have the struck-end soft enough to upset/spread (which should be dressed back before mushrooming occurs) than to have it shatter.

For hot work punches you do not need anything like the struck-end hardness shown in your illustration for the tool to do its job.

As a caveat...most of my experience with hot work punches are the ones I have made from Ø50mm (Ø2") Progen for the hydraulic press.  I heat treat those so they will bend before shattering...and have done when someone has kept their foot on the pedal too long.. They stand up to punching and drifting mild and stainless steel fine.

For the same safety reason most of the tooling I make for hot work, power hammer tools etc. are from mild steel. It stands up to hot work fine. I only use the added toughness of the Progen for focussed energy things like hot sets and punches.

Alan

[basher]

O1 would not be my first choice for a punch I would mach ratherr use en9 eny time. The reason I would not want O1 is its tendancy to air harden.  the potential that It may do that if the end gets too hot and cools rapidly, with the risk of shattering.

 I have found that all hot tools need some reworking, somtimes every heat (when punching deep holes with a thin punch).

 H13 is a good steel but needs specialist HT. I also Like En45 as its quite red hard and has a high hardening temp (900C) so is less likly to harden on you when cooling the punch off.

 I then to draw the temper on  the struck end y striking tools to a dull (visible in a darkned room) red , more of a sub critical anneal. I repeat this when ever I have to dress them to prevent work hardening.

I have hersd good things about the s series steels that farriers use for punches but have no personal experience with them.

 

 

[Frank Turley]

Quote

Yes, 01 will air harden from critical, but it is an unstable hardness, so it is not done. Therefore, you can't normalize. After forging, 01 should be annealed before hardening and tempering. 01 is designed to be used on cold work.

 

[Steve Sells]

be aware when you say I prefer not ti HT the struck end, that you may have already HT it while forging ir could have hardened on its own,  but you just throwing the dies by leaving it as it wants to turn out is not a good idea.  harden then sub crit anneal is only way to know.