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5160 heat treat


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I understand that double hardening can increase the hardening for 5160.  My question is: do you then also do two rounds of tempering?  Or just two hardening steps and then temper?  
What I am really after is optimal sequencing for 5160 steel.  I am making mocotaugans.  Is there any 5160 fans out there with advice for me?

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Are you talking about quenching in oil, heating it back up to critical temperature and quenching it again? I've heard of people doing this, but I don't see the point personally. I quench once and always temper 2 or 3 times.

I don't have a smartphone, but I think there is an app called Heat Treatment Guide (or something like that). That will give you the optimal normalize, harden, temper sequence.

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Yes Frazer!  I quench in oil.  I have usually just quenched once and tempered once.  I know that some smiths do a double heat and quench.  I understand the concept of double tempering too.  I’m just wondering about whether to redo the whole quench and temper cycle twice or to skip the temper cycle between the double quenches?  I’ll look for a heat treatment guide… but info from a practical smith working often with the material… seems more useful to me.

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Thank you Irondragon!  I actually have that on my iPad.  I just looked at it though and it doesn’t seem to address my interest in the double quench treatment.  
Obviously I am using this steel outside of its normal commercial parameters.  The hardness values look good for my purposes though!  Perhaps I will just skip the double quenching?  Around 60 Rockwell seems pretty good for carving woods.

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I've never even seen reference to double quenching other than on youtube videos and social media inspired urban myth. 

Whatever the first heat treatment WILL be erased when the stock is heated up again through tempering to critical temp. The very idea shows a lack of understanding of how hardening and tempering actually works. 

Frosty The Lucky.

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Yes, multiple heat quench cycles are used by "some" knife makers. Some claim its a gimmick to sell knives.. Some claim that each cycle puts more carbon into solution. I'd be interested  in the science but until a metallurgy report that supports such cycling comes out I'll  stick with Irondragons method. Worked fine for me for over 6 years. 

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Bigfootnampa. Sorry got sidetracked. I do 3 grain refining cycles at approximately 1550f. Then one heat to nonmagnetic or when I see decalescence. Quench, and into tempering for 3 two hour cycles. Tempering temperatures vary as to blades end use. 

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OK, I am not a metallugist and I don't make a lot of knives but is there any empirical data that , or how much, multiple heat treating improves the characteristics of a blade over a single quench and temper?  For example, that a blade is that much harder or tougher or will bend further without breaking.  I guess what I'm asking is whether the amount of improvement, if any, is worth the extra effort.

If we don't know why or how much a process does it just becomes ritual and magic.

"By hammer and hand all arts do stand."

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Besides ritual and magic you must also include folks trying to differentiate their product  from other people.  *Why* you should spend a pile of cash buying their item instead of another.  I think a lot of "myths" come in through that route.  After all urine is probably a better quench medium than blood!

The University isn't in session yet; but I'll try to visit a Metallurgy Prof I'm friends with and ask him about how much of a difference multiple cycles makes for hardening.  (Didn't find anything in my 8th edition of the ASM; they had noted an explosion of information on heat treating; the 7th edition only being 7% of the number of pages in the 8th and they are WAY beyond that in more recent editions.)

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Bigfootnampa. Could you define you use of hardness. What qualities are you looking to achieve with  multiple quenches. Are you looking  Impact resistance,  blade wear,  or actual blade hardness on a Rockwell scale

Thomas. I look forward to what the Profs have to say. Metallurgy terminology like hardness versus toughness get intermixed in knife makers world. I've read where multiple quenches refines grain size and that improves  toughness. Could hardness be construed in layman's terms as toughness. Thanks for consulting with profs 

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Hardness and toughness are just opposite ends of the same beast. The same as hot and cold.

There are a few tool steels that the specs indicate tempering twice. I don't believe any state temper thrice.

Hardening more than once does nothing except take time and burn fuel.

Normalizing is the step in heat treating where you deal with grain growth.

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I've sent an email to my friend the metallurgist and  Chairman of the MatSci department.  May take a few days to get a reply what with the fuss getting the University up and running for the spring semester during this age of Covid-19.

One of the aspects of heat treat "transformations" is that they are statistical in nature; eg: it's not a 100% change from Austenite to Martensite  when you quench.  Some alloys have more retained Austenite than others---which is why cryo quenching works; but  it's like half lives; the percentage left goes down with every cycle and soon diminishing returns sets in---especially in a commercial setting where time is money!

As a hobbyist I have to remember that most of what I'm reading is based on commercial research and not on "what's the absolute best?"  (I mean when was the last time you thought about making a platinum flux tray for your gasser?)

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I'll have to see if I can find this article I read a few years ago.  In it they were discussing/exploring the concept of multiple quenches.  They used the same stock and did single, double, and triple quenches on different pieces.  After that they broke the pieces and took pictures of the resulting grain structure.  There was a noticeable reduction of grain size for the multiple quenched pieces.  However, I do not recall if they did multiple normalizations before the first quench or in between quenches.

Personally I think that a single quench after 3 normalization cycles and then followed by at least one temper cycle of 2 hours is going to get most of the possible benefit out of a simple alloy steel.  For me the added stress on the steel and increased potential risk for catastrophic failure of the piece with subsequent quenches is not worth whatever minor benefit that they might provide.

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Wow!  I guess I piqued some interest!  Thanks to all for thinking and discussing this topic!  We used to have a smith on here that made a lot of large chopping blades and sold quite a few to military operators.  He noted the double quench if my memory is correct.  He used 5160 for most of his blades.  I can’t quite remember his name though.  I asked about it at the time and was explained that it apparently converted more carbon to austenite.  Or… something like that.  I expect that I’ll probably get good results by single quenching and tempering, though.  I want to make a form of hook knife known as a mocotaugan and to use it carve some pretty hard woods!  I might also make some shallow curved hook knives designed primarily for finishing cuts on carved spoons.  
 

velegski: I am mostly interested in getting a good hardness with an eye to edge retention.  I expect that 5160 will be inherently tough enough for my uses… carving hard woods.  What worries me a little is that I might not get my blades to be as durably sharp as I would prefer.  It is time consuming to produce a razor sharp polished edge on a shape like a hook knife that cannot be fully worked with power equipment!  I mean I insist on extreme sharpness and I disdain softer woods… so I guess that makes me one of those fussy old curmudgeons?

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stormccrow is a member of I.F.I.. he has not visited for a while. His name is Helms (I forget his first name).

He lives in San Antonio Texas. a search on this site, (using the name stormcrow will find his page.

Or you may wish to search http:/helmforge.blogspot.com will also get you good results.

His old net name was rainy raven. You may wish to search, using that moniker on this forum and also the old "keenjunk" site archived in the www.way back site.

Happy hunting!

SLAG.

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Bigfootnampa. The one and only carving knife I made I  used 1095. The user likes its edge retention, durability and ease of sharpening. You might try looking for a local woodcarving association and webb site. My friend was astonished  at how carvers make, sharpen and use their tools.

As far as multiple quenches and metallurgy in general I've found a website called Research gate has some very interesting  discussions.  Metallurgy specialists, person with dictoratesand from all the world  engage in questions concerning

Sorry .. fat fingers sent before i was done. Meant to include  persons employed for major steel manufacturers engage in interesting metallurgy conversations. Just be aware that they sometime talk and write at doctorate levels. 

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Still no explanation of why or how triple quenching benefits 5160 steel.

Similarly, I am somewhat confused by multiple tempering cycles.  It seems to me that multiple cycles in an oven means that you will end up with a blade that is uniform in temper.  With single edged blades I have always tried to temper the back of the blade to be "springy" (blue) while keeping the edge harder (yellowish).

"By hammer and hand all arts do stand."

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You guys are the GREATEST!  Storm Crow… that’s him!  
Velegski, I have some 1090. Yes it’s a good steel for me.  I once made a carving knife from an old hollow ground circular saw blade that was stunningly durable!  Not forged just ground but I did heat treat it.  I tempered it with a tiny flame on a propane torch and incredible PATIENCE!  I got a blue temper at the spine and straw at the edge!  That blade would cut for days before needing sharpened!  
Thank you Irondragon! 
What a crew!

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22 minutes ago, George N. M. said:

I am somewhat confused by multiple tempering cycles

I have read from multiple sources that there is sometimes retained untempered martensite after a single tempering cycle. Additional cycles at the same -- or sometimes slightly lower -- temperatures can improve the "completeness" of the initial temper. I'm not sure how this would interact with a differential temper that comes with drawing back the spine.

Note: I'm not a metallurgist/bladesmith.

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I suppose that what it really amounts to is how any crystallographic/metallurgical change or condition will translate into physical characteristics of the blade.  If, say, more austenite equals tougher or harder or more martensite equals more brittle then the question becomes how much mechanical change there is for each process.  If there is 20% greater toughness then the process is certainly justified.  If the improvement is 2% maybe not so much.

"By hammer and hand all arts do stand."

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