Tempering a file knife

[Stringman]

I've made several now and I'm starting to get a feel for the overall process, but I'm trying to better understand the tempering aspect.



I heated this file to 400 then did my stock removal. In a simple build I would anneal the tang to allow me to cut lightening and pin holes, but does anyone have an explanation for putting this file thru a temper cycle to get a little better performance out of the steel? Or is that too complicated and not enough info about the metal in the file? Keep in mind I don't have a forge or any smithing equipment.

[Aaron H]

After you quench a blade it is very hard, and therefore very brittle and susceptible to breaking.  Tempering reduces the likelihood of breaking by softening the blade somewhat and making it less brittle

[Stringman]

Yea, I understand the concept, but the more I read and the more videos I watch, everyone has a different technique and some of them are stupid complex! Just trying to consolidate some info here from minds I trust. If I'm over thinking it, then I'll just keep it simple.

[osage outlaw]

Thanks for posting this Scott.  I have the same questions on a file knife.  I was hoping to get mine done by the Classic but that's not looking to likely.

[BOWMAN53]

Tempering releases the stress in steel from quenching. After quenching, the steel is so brittle it can be broken by hand, tempering gives it its toughness back.

[KHalverson]

as quenched if done properly you have created an austenite (very hard and brittle) state in the steel
tempering this properly changes this to Martensite which is  tougher and less brittle .
further tempering @ too high of temp or too long reverts the steel back to pearlite which is soft.
at least that's the technical jargon.
when doing these home home builds  it is better to use simple alloy steels and use the K.i.s.s method
this has been preached to me by a.b.s master and journeyman smiths alike
another thing to take into account is that edge geometry plays a large part in having a good performing knife.
many a knife has been made from files with no further tempering of the blade being done.
now would I take a as hard file and put a full scandi (flat ) grind and expect the edge to hold up under heavy use   NO.
the edge is very likely to chip of worse yet snap the blade.
now take the same file and use an apple seed grind and the edge longevity will be a lot better .
but still susceptible to breakage an be  hard to sharpen.
I prefer a flat grind but leave enough meat at the edge for a slight convex grind
I also would prefer a knife that is soft enough to sharpen relatively easy.
if the edge rolls slightly under heavy use  I can use a steel and strop to bring it back to shaving

[Stringman]

Tempering releases the stress in steel from quenching. After quenching, the steel is so brittle it can be broken by hand, tempering gives it its toughness back.

Yep, got it... Now, how do I apply that to my project. More importantly, is there a specific recipe I can follow - first quench, then temper at ___• for 3 cycles allowing blade to cool slowly overnight between each temper...

I don't have a thermometer so in the past I have relied on metal color to decide when to remove from heat. What's some thoughts from the metal heads.

[Stringman]

Thanks Kevan, a post on FB mimics your advise and said,

"If it was never heated past 400°F, you may not want to do anything else to it. That's around the low range of tempering for the types of steel Nicholson used."

So maybe KISS is the right approach with these.

[KHalverson]

I get ya now

most files from what I have been told are very close to 1095.
if your quench produces a full hard steel  temper @400 f for 2  2hour cycles that should produce an Rockwell of 58-60 ish which is ideal
I use a grilling thermometer they are pretty cheap @ wally world.
if your unsure of the type of steel that ya have  start @ about the 350 range and temper for 2 hours if the edge is still harder than ya like  up the temp by 25 degrees and retemper  till a sharp file will cut it but not easily
not all steels temper out at the same temp or duration.

[BOWMAN53]

Quench in oil, high carbon steels don't really like water. Ruined a few blades recently. Used oil on my current project and got great results.

[Stringman]

Perfect! Thanks guys. I'm gonna copy this and tack it up in my workshop now. 

[nclonghunter]

By no means do I claim any skill or knowledge here.....I have read a lot on it also.

Get very, completely dry sand in a can. Heat your metal to red and stick it into the sand. Any moisture will harden the steel, so it must be bone dry. The slow cooling metal will soften it. You can grind, drill and shape your knife when soft.

Once shaped you heat to red and put it in water. It is then brittle hard and will break. Polish the steel and get into a dim light area and begin heating the metal again to a straw or yellow color. Begin slowly inserting the knife into oil and try to get a dark line moving above the oil line all the way to the handle and then sink it into the metal cooling it. Stopping the heat at a straw color is a "temper" good for knives. Not too hard and not too soft. Polish again and put handles on it.

Different metals require different colors for the perfect "temper". The speed that you push the metal into the oil makes a difference on the "temper". The type of oil you use makes a difference on "temper".

Best I can explain what little I know...Good Luck