Heat treating 5160

[autosolutions]

I am new to this passion. I am reading and trying to understand the artice on Mr. Caffrey's site about heat treating a 5160 blade. My questions are two fold.
1. when normalizing, annealing or hardening, Once the steel has reached critical and is no longer magnetic, is there any advantage or downside in keeping it at this temperature for an extended period of time?
2. When heat treating, It apppears to me that Mr. Caffrey recommends hardening the edge only. Am i undertanding correctly that only the edge (1/2 the blade width) needs to be brought to non magnetic then quenched? If so wouldn't the rest of the blade remain in an annealed state and therefore remain soft and unable to spring back in place when bent?
I would have thought that the whole blade would need to be brought past non magnetic then the edge quenched then the remainder of the blade cooled in the quenching oil.
Would appreciate a comment
thank you

[jonwelder]

I believe Ed could explain this much better than I,, but I will try. Also, it would be much easier to understand after you "did" it a time or 2! Please remember, just heating the edge to non mag, will also heat the rest of the knife to "near" critical, and hardening the edge for the required amount of time, then totally immersing the rest of the blade (as Ed describes in his J.S. tutorial) till cool, will give the rest of the blade a certain amount of "spring",,, it will not be "dead soft" as you might think. After you do this to a knife blade,, (harden and temper) do some cutting and bending tests,, you will be amazed!! Check out my pictures of "my" J.S. performance test on my web site. All heat treatments were done according to Ed's tutorials!!----Jon

[Ed Caffrey]

Thanks for helping out on that Jon! I haven't been at the computer all day, so I didn't get to this thread until now.

Auto.... Welcome to the forums! Lots of very good people around here, and lots of great knowledge!

I'll try to answer your questions specifically...

1. when normalizing, annealing or hardening, Once the steel has reached critical and is no longer magnetic, is there any advantage or downside in keeping it at this temperature for an extended period of time?

Answer: Yes, a very major problem occurs when blade steels are held above the critical temp...namely grain growth. This occurs in steel at a exponential rate when the steel is anywhere above it's critical temp. Grain growth weakens the steel overall. There are some steels that will benefit from "soaking" but those are usually the higher alloy steels that require more time at critical to allow everything to go into "solution" before quenching. The temp, and duration at temp must be monitored closely to ensure its not taken too far and the grain growth issue occurs.

2. When heat treating, It apppears to me that Mr. Caffrey recommends hardening the edge only. Am i undertanding correctly that only the edge (1/2 the blade width) needs to be brought to non magnetic then quenched? If so wouldn't the rest of the blade remain in an annealed state and therefore remain soft and unable to spring back in place when bent?

Answer: Jon explained this portion very well! In my opinion, edge hardening gives you so much more latitude to create a blade with just the characteristic you want, I encourage it. The very same thing CAN be achieve by fully hardening a blade, and then doing what is known as a "soft back draw" IF the soft back draw is done correctly. With this method the thing you must keep in mind is that TIME AND TEMP have everything to do with the end results. By that I mean that for changes to occur within the steel's matrix, it requires a specific temp, for a specific amount of time. (each depends on the specific steel type) All too often I have see soft back drawn blades fail because the maker did not take the time to do it correctly, and only achieved a tempered "skin" of about .010-.015 on the outside of the blade, while the core still remained too hard.
OK, now back to the edge quench. You can control how difficult or how easy it is to bend a blade, by the ratio of hard to soft area you create with the edge quench. The deeper you quench the edge, the more difficult the blade will be to bend, whereas the shallower you quench the edge, the easier the blade will bend. I have quenched blades to within 1/4" of the spine, and still they would bend to 90 degrees without breaking. Mind you they were really difficult to get that far, but it proved to me that it can and does work.
This brings up a point of contention among some makers. The argument goes that some would rather have their blades break than bend, while others (including myself), think its better to have a blade that will bend rather than break. To my way of thinking, if a blade breaks, then all I have is two or more pieces of steel....if the blade bends, I can always try to straighten it out and still have something I can use as needed.

The very best thing you can do is to experiment, and keep notes of ALL the specifics. That way you will find what works the best for you, and if its written down, then its very likely that you can repeat the results when you discover something you like.

[jonwelder]

The first time I tried to bend and break a knife blade I had made, I was so surprised to find the hard cutting edge cracked cleanly right up to the quench line, then bent. This was no easy task just to get it to bend that far! Ed, your tutorial made a believer out of me!!! I use this process on all my knives now, close attention really paid off on my J.S. knife! ---Jon

[autosolutions]

Thank you gentlemen. I really appreciate your help. Your answers were super instructive and on point. Thank you Jonwelder for the link to your site.
I would like get a little more details regarding the heat soak. Especially regarding the lenght of time that is required for the grain to start growing. Mr. Caffrey , if I recall correctly, mentioned that the grain growth was exponential. Is there an amount of time in seconds or minutes or hours that is not particularly harmfull?
I have experimented with a piece of 5160 and find that in order to get the whole piece to reach non magnetic, it may take several minutes and that a portion of the stock reaches the critical temp earlier than the rest of the material. Therefore a portion of the stock is heat soaking around or above critical while the rest is slowly comming up to temp. Is that something avoidable? Obviously the corrolary of the question is how to re-shrink that grain growth? Is that even possible through normalizing cycles or should the stock be scrapped and the process started anew?
Finally, the obvious thing to me is that I need to read more and learn! Any suggestions on a book or other media that can get me up to speed so I do not have to keep asking basic questions and waste your time?

Thank you

[jonwelder]

This is how I do my "heat treat",, (per Ed's tutorial) Please remember, we are talking about heat treating a "wedge" shaped blade, not a rectangular bar. Also I use an old magnet from a lawn mower flywheel. It has lots of "pull" but it will not fail like a ceramic will. Heat kills ceramic magnets!
I use a torch to heat the blade, running the torch along the sides of the blade next to the cutting edge, but not trying to concentrate it, that it would heat too fast. Doing this has another merit, I keep blade warp to a minimum by NOT HEATING THE WHOLE BLADE TO CRITICAL. (I think this will answer another question you had) As the heat just behind the cutting edge increases, I'm moving the blade length ways and flipping it over to heat the other side, avoiding hot spots. I start testing with the magnet against the edge,, this is really weird, because one minute it will stick, the next it will not, I am still moving the blade, heating it up equally. When all the edge I want to harden is non-magnetic I quench it in pre-heated mineral oil, and even then, I just dip the cutting edge first for a few seconds, watching the color leave the metal, then quench the whole blade till cool (oil temp 130-160) This gives a hard edge and a "softer" spine.

Of course there are other methods, like heating the whole blade and quenching the whole blade making the whole thing hard as a rock, then going back and trying to re-heat the spine back to 400 degrees with a torch, then quenching to stop the "softening" in water,, but this is tricky, and you run the risk of blade warp as I said before.
Also,, if you do a search here on "grain growth", I think you will find more info. As I understand it, grain growth comes as the steel cools in "still air" before the heat treat is done. The steel is heated to orange and allowed to cool in still air, this can be done several times. Long metal "grain" is stronger than "short", so it is desirable in a knife blade.
There are books, but where else can you get help on a "personal" level except here.
6 years ago, I printed out Ed.s "tutorial" on how to make a blade to pass the ABS "journeyman" knife performance test, and I refer to it VERY often!! --Jon

[jonwelder]

One more thing,, there is more heat on the edge than the spine, as I am heating from the edge in toward the spine, so there is "no heat soaking" as you asked about. The cutting edge is the hottest part, and it is "only" non magnetic,... no hotter,, well, maybe just a little, but you get the idea!! I hope this helps..... Jon

[Doug Lester]

Grain growth is a product of both heat and time with heat being the most significant. What that means in practical terms is that you can soak a blade longer in a 1600 degree forge longer than you can in a 2300 degree forge without causing undue grain growth, everything else being equal. This illustrates why one should tune their forge(s) to run at the temperature needed to do a given job.

Doug Lester

[LRB]

5160 requires a soak of around 10 minutes in the heat range of 1500?, give, or take a tad, in order to reach a good solution. Simply bringing to non magnetic, 1423?, if I remember correctly, will not give 5160 enough heat to do this. Due to the amount of chrome in 5160, grain growth is not a great concern at heats under 1525?, if you did a proper normalizing proceedure first. Chrome retards grain growth, and promotes hardness, but requires soak time to reach full solution with the carbon, or you end up with areas harder, or softer than others, and a less than ideal heat treat.

[jonwelder]

The question "autosolutions" had posted was a question about heat treating a "BLADE" per Ed's instructions on his site.. it was not a question on metallurgy, or how metal changes during extended soaks. The question was about "a blade" ..
Following Ed's instructions will help you make a "blade" that WILL PASS THE ABS-JS test!!!

[LRB]

Well, excuse me. You are correct, but I thought the idea of knifemaking, mean't that one makes the best blade one can, rather than try and suit some criteria that is totally off base with reallity. I would never intentionally try to muddy the water with facts. Sorry, but ABS standards do not impress me in the least. They lost my interest, over twenty five years ago, when they were pushing forged being superior to stock removal.

[Ed Caffrey]

Easy fellas. No need for anyone to get offended. We all have ways of doing things based on our experiences and equipment. What works for one, is not necessarily how everyone does it. I'll let anyone state their opinions and methodologies, but lets keep things civil.

[LRB]

You are right Ed, will do.

[jonwelder]

----"Ditto!"

[Wade Holloway]

Dang it was just starting to get interesting Ed.