Intro to Heat Treating

[Eventlessbox]

On 12/23/2015 at 3:41 PM, GIJosh said:

As for myself, I could have never forged that last set of dragon scale armor of impending sarcasm nor my +5 mithril longsword of unavoidable mockery without doing some homework first.

This just made my day. 

[Emmitsfixitall]

Ok I read it and am still a little confused, forgive my stupidity please. Do I temper the knife then harden? I had the idea somehow that I would harden the blade sharpen and then temper.

[Steve Sells]

harden, temper then sharpen

[ThomasPowers]

Part of the problem may be in how we use the language.  In the outside world "temper" is often misused to cover almost all aspects of heat treating.  In bladesmithing we carefully use specific terms for each step so when discussing things we all know exactly what other smiths mean by "annealing, normalizing , heating to critical, soaking, quenching, tempering, cryo cycling, etc" and so can ask specific questions like "How long and at what temp should I soak a 154CM blade before quenching?" and get meaningful answers.

Yes it's Jargon and serves jargon's purpose in allowing people to make careful differentiation when talking about a subject---besides confusing folks who don't know their winkle fork from their asparagus tongs!

[LennyD]

 

So, during the final quench, to harden the blade, do you let it cool to room temp before tempering in an oven? Or just dip it in, and pull it out within a second or two and straight to the preheated oven?

[ThomasPowers]

Usually you want to bring it down near ambient before going to tempering.  However there is also austempering and marquenching for specific alloys and wanted end states.

[LennyD]

1 hour ago, JHCC said:

Welcome to IFI, LennyD! If you haven't yet, please READ THIS FIRST!!!

Thanks. And FYI, i tried my hardest for the best part of an hour to find an answer to my question already posted somewhere, but could not  

[ThomasPowers]

I need to add another caveat; if you are using heated oil; it needs to come down to the temperature of the oil and not ambient temperature. 

[LennyD]

Ah, yes of course

 

[Need Iron]

Very clear intro to HT

[120ace]

Hello there,  For some time now I have been under the impression that normalizing was all that was needed before quenching, 
But I have recently been watching videos of Japanese Smiths, And have realized that allot of them do not do the standard normalize and quench routine,
Instead they:

1. Normalize the blade 2-3 times
2. Then proceed to Anneal the blade by heating it to a "low temp", And then placing it in a container of ash("Straw Ash") for upwards of 3 hours,
3. Then some of them, Not all,  Even proceed to Cold Work(Forge?) the blade,  Which from some other information I have been reading says that it can improve the structure of the steel even after normalizing it.

I have also seen a few videos from a Russian Smith/Crafter who says to always Anneal a blade before quenching it,  He accomplishes this by heating it in a a small gas forge,  Then turning off the gas and sealing the forge for upwards of 6 hours,  Or until room temperature.

In asking this question I am hoping to get more information on annealing before quenching, And more hopefully on annealing after normalizing,  And on cold working(forging?) before quenching.

As these Smiths only speak Japanese( Most are them are actually silent for the whole video, Such that i cannot even use youtube with translated subtitles), So I have limited information to run on,  Hence why i am asking here.

On a side note I picked up a neat trick from the Russian, That you can take a blade after quenching, And tempering,  You tie the tang to a piece of string and give the blade a good tap with something metal, If it rings clearly then you know that it has no internal cracking.

To those of you answering this question, Thank you for taking the time out to help Me,  I am a novice smith and appreciate the help.

Thank you.
 

[Steve Sells]

What part of this post was confusing to you?

[Latticino]

Definitions of the normalizing cycle vary, depending on who writes them.  Also different steel compositions work better with different heat treatment cycles.  Personally when I use the term normalizing I am typically referring to a three step cycle that precedes the hardening quench.  The normalizing cycle works for both grain refinement and stress relief.  The first step is just above austenizing temperature (and holding just long enough for the phase change) then air cooling to return to magnetic.  The second step is a little  below austenizing then again air cooling to magnetic.  The third step is mostly for stress relief.  This is also called sub-critical annealing.  The stock is brought up to around 1200 deg F (just barely glowing in a shadowed viewing) and slow cooled down to ambient.  I'm not certain if there is an advantage to cooling it in an insulated chamber, but it can't hurt.  Most likely will help with softening the steel further and allow easier grinding, filing, drilling...  This third step can also be repeated after grinding and before hardening to remove any residual stress put into the billet during the grinding process.

As regards cold forging after this process:  "You pays your money and takes your chances".  In my opinion you are putting stress back into the steel that was removed by the normalizing cycle.  I personally would limit it to the minimum required to straighten the blade.  I am not aware of any science behind the assertion that it improves the structure of the steel to cold forge it (it could work harden the steel, but that is likely eclipsed by the hardening process).  In my experience it works better for laminated steel blades, and I have heard it works for steel consolidated from tamagani or blister steel as well, but I have no direct experience there.

[ThomasPowers]

Cold forging was a method used for grain refinement before modern steels were around.  Introduce more dislocations into the steel's structure that result in renucleation of grains when heated.  I would expect it's use with "old fashioned" type of steels and as a hold over---do you also plan a Shinto religious rite before forging like traditional Japanese smiths do?

As for testing of cracks; "ringing the anvil" has been used extensively as a method for hunting for hidden cracks. Also when looking at pottery/glassware; flicking it to see if it's free of cracks is a common test. Folks have not realized it also applies to blades before now?

Some alloys do NOT profit from normalization, S-1 as I recall is one of these.  ANY time you discuss heat treat processes you have to mention alloys they apply to!  This is so common a lapse it's not surprising to see a new smith expect to harden true mild steel by quenching in water or even worse, quench a HC blade that requires an oil or air quench in water and then be upset that it shattered in water!

[anvil]

I tend to follow the specs of the steel. Most follow what your Russian and Japanese Smith's do.

1: forge

2: normalize

3: anneal

4: harden

5: temper

6: cold work( final filing etc)

[Steve Sells]

annealing after the normalizing un-does any grain reduction of the normalizing cycles, FYI

[ThomasPowers]

Who is this "most"?  I don't know any professional knife makers that anneal after normalization.

[Steve Sells]

I already explained annealing is to work the blade.  In the pinned post I also explained we normalize after working then we harden, but does anyone listen?  lol

[Frosty]

That's the problem right there Steve, they ARE listening to . . .  written TEXT.

Frosty The Lucky.

[Buzzkill]

Not to be obnoxious here, but I don't think most bladesmiths consider Kevin Cashen to be in the "to be ignored" crowd.

For 1095, for instance, he lists this:

Forging:  heat to 2100°F (1150°C) . Do not forge below 1500°F (815°C). 

Normalizing: Heat to 1575°F (855°C). Cool in still air. 

Annealing: Heat to 1475°F (800°C). Furnace cool to 1200°F (650°C) at a rate not exceeding 50°F (28°C) per hour. 

Grinding or Machining

Hardening: Austenitize- Heat to 1475°F (800°C). In thicker sections can be quenched in water or brine with extreme care but can also be oil quenched in sections under 1/4 in. (6.35 mm) thick as the preferred method.

Tempering:  As-quenched hardness of approximately 66 HRC. Hardness can be adjusted downward by proper tempering.

Polish

Now, we can see that his listed annealing temperature is below the normalizing temperature and would therefore not undo the effects of the normalizing.  However, due to the terms used, this can be confusing to people trying to sort all of this out.

 

[Steve Sells]

Annealing temp is not less than normalizing temps. it clearly says cools to 1200 but you still had to take it to 1475. Also this is a list of actions,  not a baking recipe it gives all the needed  information except the cooling rate needed to harden, IIRC is <0.8 sec

 I always normalize after working to relieve stress.  Rather than tell us we are wrong, why dont you ask Kevin why its listed that way and what he meant

[Buzzkill]

I'm not following you.  I've always been under the impression that 1575°F (his listed normalizing target) was hotter than 1475°F (his listed target for beginning annealing).  What am I missing?

The title of that web page is "Recommended Working Sequence for 1095."

His Recommended Working Sequence for 52100 also shows normalizing before annealing.

The point is if I'm finding the details of this confusing based on information provided by 2 different trusted sources, one of them being this site, then I'm guessing others find it confusing as well.

I never said you were wrong.  I'm saying there appears to be conflicting information, and I was hoping you could provide some insight, explanation, or clarification as to the apparent discrepancies.  I'm trying to understand this topic better for myself, but also highlight why others might question the sequence given here since it seems to be different than they may have seen in other places that are also trusted places for getting information.  I can ask there too of course.

[Steve Sells]

I am reading cross eyed,  I screwed up,  you're right it did say 1575 I wonder why so high hmm, either way both are above Austenizing temp so it reforms the steel grains

My Habit: I always normalize after forging to reduce stress form the working of the metal and I always normalize before doing the hardening quench

My Habit:  I anneal  before cold working the steel to make it easier to work

Perhaps its these two habits combining to give that other method? I dont know but I have to admit it wont hurt anything to do it that other way just uses more fuel

[Steve Sells]

I can understand normalizing after the annealing to reduce grain size, the other way around confuses me,  we need to invite Kevin Cashen to join us here for this conversation

[velegski]

Always hate these discussions since each maker seems to have an opinion. However it seems that when I research several sites that normalizing is often done before annealing during the manufacturing process. It also make sense in that in his process the annealing helps in the stock removal and molecular structure.  Since you dont go back above in temps the grain structure doesnt grow. All in all its if  make sense from his perspective  and analysis.  and since it works extremely well for him .. great.