Straightening a blade during HT/Quench?

[kvehikite]

The following is a quote from a post by Kevin Cashen refering to HT of 1095---
"I quench into #50 heated to 130F and keep the blade moving length wise for a count of seven and then interrupt the quench, on a good day this should be about 450F… is that nonscientific enough for you . I put on my gloves and eyeball things straight and tweak it if I need to. I do not stop the cooling or reheat it in any way while the martensite is forming, for fear of stabilizing austenite."

Question I have is, dose this seven second quench and then straighten apply to other carbon steels or if this time fram isolated to 1095 only? Too early = poor heat treat? Too late = broken blade?

 

[stezann]

It does apply to all steels, but i need to clarify.
When you quench, you need to quick surpass the pearlite "nose" (tipically when the steel become black again) and continue cooling to the Ms (martensite forming starting temperature) and to the Mf (martensite finish transformation). You can bend anything above Ms, but....
Due to different steel makeups, those temperatures (Ms-Mf) may differ. Usually the high carbon steels have a lower Ms (around 400F) then the low carbon steels that can have the Ms temperature higher then the usual tempering temperatures (i.e. you don't want to temper 1070 at 540F)
During cooling the steel is very ductile (it is still austenite) until you hit the Ms, and that gives you a good window to straighten your blade by hands or with a notched wood in the vise.
With low carbon steels though this windows is narrower, at an higher temperature and that can increase the auto tempering effect of the newly forming martensite.
When you starighten the blade above the Ms you will find it is very collaborative, then it starts to stiffen, that is the time you had reached Ms and it is better quit messing do your first tempering cycle and finish straighten the blade at 400F...at that temperature the Young modulus is modified and the straightening could take place better than at room temperature...repeat as needed.
Anyway, as a starting point look the cct graph for Your steel...under the pearlite nose it indicates the time/temperature available before Ms.
Have fun and pratice with a scrap knife shaped object to get a feel and thus be prepared when it does matter

Stefano

 

[kvehikite]

Thank you Stefano. Not to oversimplify all this, but if I understand you correctly once you get past the pearlite noise and the steel is then black, that is your window to tweak/straighten the blade. Once the blade starts to feel less pliable you stop. At this point you can make further adjustments between tempering cycles (at 400 degrees). If this is correct, I will do some experimenting.
Again, thank you.
Ken

 

[Pumpiron]

On a somewhat related note, I'd like to put minor bends in carving tools such as gouges in CPM 3V before sending them off for HT. Can this be done at room temperature without causing trouble? If not, what temperature and time would be required, and would that process mess up the fine grain structure? Would austenization, perhaps with a good equalization soak on the ramp up, be sufficient to relieve the cold work stress and achieve the standard response without breakage? Thanks for your advice.

 

[Stacy E. Apelt - Bladesmith]

It would be simplest to do such minor bends at sub-critical. Heat to 1000-1200°F and bend as desired. Re-heat to 1200°F for 10 minutes and the blade will be stress free and ready for HT.