5160 Help Needed


Well-Known Member
Hello all,
I'm in need of some advice on 5160. I'm ready to pull my hair out! I've been making knives for 15 yrs. Always stainless. I have decided to move to carbon and start with 5160. Not having much luck. Best a can get is 50C. Here's my process:
1525 soak for 10 min.
P50 @ 120 degree quench
This is done with an even heat kiln and tested on a grizzly hardness tester. Calibration block are right on. I have tired AAA and P50. Changed the thermocouple on the oven. When quenched in water I get 60C. What am I doing wrong!?
What condition is the steel in when you start out?

My first thought is that your steel may be heavily spheroidized and need normalized.
To expound on what tkroenlein said. If you've only done stainless you might not know that carbon steels will often need to be heat cycled of some sort (annealing, normalizing, thermal cycles, etc.) before hardening, even if you haven't forged them, which is stuff I never do with SS (discounting equalizing of course, but you know that, and probably more than I do). Hope that helps.
Also, I've heard that walking any sort of distance to your quench will bring you perhaps below critical temp, which could be causing your problems. That is not as much of a problem with air cooling steels as they need to be hardened slower, I think as a general rule.
Can't give much advise in regards to 5160 as I haven't really used it. However, Parks 50's operating temperature range is 50 F to 120 F. If you are heating it to 120, you are putting it at the edge of it's working temperatures. AAA must be heated, but 50 is normally a room temperature quench oil.

I do know that 5160 also does better with a soak due to the chromium content. I've heard some people doing as much as a 25 minute soak, but I can't verify that.

I also believe that 5160 is a medium quenching speed steel, so AAA would be optimum.
Thanks for the help everyone. I should have stated this heat treat will be on stock removal blades and not forged blades. Do I still need to do the thermocycling for this? And I was not aware that the P50 should be room temp. So far I'm only testing on small 3/4 ×3/4 samples. And with not much luck.. lol This steel is bar stock from Tracy.
Where did you get your 5160? Also, you have been given some good directions to go but my advice would be change one thing at a time so you can know what the problem was.
I can rule out the quench, Parks #50 is much too fast for an alloy steel, although 5160 is one most likely to survive it. I would first look to proper solution. 1525°F is spot on for this steel. My standard soak for an alloy is 10 minutes, but that is with faster heating equipment than an oven. To trouble shoot solution issues, first increase time, that is your "fine tuning". If you get out to 25 minutes, time is not enough, then you move to bumping up temperature, that is your more powerful "coarse tuning."

Carbon steels should not need normalizing and other treatments to achieve good solution, and alloy steels shouldn't any more than stainless. But sometimes chromium bearing alloy steels will be deeply annealed for free machining and a quick soak at the normal temperatures may not be enough. Carbon in solution = a reinforced matrix, and at room temperature this means steel that is harder to machine. Carbon out of solution = a soft ferritic matrix, which means soft, ductile metal. But where the carbon goes when not in solution is into carbide. The deeper the anneal, the larger and more widely spaced carbides, so when it comes time to put that carbon back into solution it takes more effort to strip it off the carbide and spread it through the iron. With carbon steels, this is not a problem, iron carbide (Fe3C) starts to dissolve at 1335°F. But alloy steel will include much more stubborn carbides and the alloying elements presence will slow the speed at which the carbon moves. So I have never seen a piece of 10XX that was 'carbon locked" but I have seen a few bars of steel that got that way with rather modest additions of Cr.

Also, from reading your post where it includes the water test, gives some other clues. Be aware the the maximum you should expect from this steel is 62 HRC ( it makes great choppers but disappointing hunters and other fine edged knives), but all the same, you should have gotten to around 62.5 or even 63 with a water quench. So there is still something going on. As has been mentioned, you do want your quench tank right next to your heat source, but the timer doesn't really start until you hit the oil. Yes you can take too long to get to the quench, if the blade recalesces (goes dark and then begins to glow unevenly) you will not get proper hardening, but it takes a surprisingly long time for that to happen in air.

You want your AAA, and that is what 5160 wants, to be at round 130°F, get the 1525°F blade entirely below the surface without too much delay, and AGITATE! Move the blade in the oil in a cutting an stabbing motion; just holding it still in the quench is a common source of warping or lower HRC readings. Keep it in the oil until you can comfortably hold it in your hand, above 200°F you are not done quenching with most steels but 5160 should be, but...

Clean up the surface to be Rockwelled with a 220X and then a 400X belt and take you test. The 220X will insure the removal of scale and decarburization, and the 400X is necessary for a truly accurate HRC reading. Less than a 400X finish can give you lower readings.

I can't tell you how much heat treatment troubleshooting I do for other makers and industrial clients and the the two most common causes of lower HRC issues are - decarb and improper solution (and in that order).
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Kevin, Thank you very much for your help. It's VERY MUCH appreciated. My quench tank is very close to my oven. Quench happens in 3 to 5 sec. after opening the oven door. I have extended the soak time to 15 min. In AAA with no change in hardness. Always 50C. Scale is removed before testing with a 400 grit belt. My Grizzly tester is with .2 of the calibration blocks. I will try a 20 and 25 min soak tonight if I get a chance or first thing tomorrow. Im a weekend knife maker and welding engineer by day. When increasing temp from 1525 what is your suggestion? 50 degree increments? 100? One thing might add is this is a 110v even heat oven and it does take a bit to get to 1525.
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if your drillbit started chattering halfway through the bar of steel, and your drilling technique is good, you probably have course carbides in the centre... where i am from, about half my sources supplies chattery steel... so i am not fond of it... so i normalise at 1600 and grain refine and harden and put some preliminary grinding in... we dont have sources for the faster oils, so with all of that, i max out at 62,5 after quenching on thinner sections... in oil, it makes a good enough cheap competition cutter then... after temper it will be 60 -61... 80crv2 responds much better, and i daresay it is not less tough as far as i can tell... even at 62 rc it wobbles a competition cutter edge, rather than chip, on a resinny knot in the pine... I think Kevin's hunch is better, but that is seriously low hardness... I also have most of my thicker knives in the oven for at least 25min... from time it is inserted in hot oven. the steel takes a while to get up to heat... the oven bounces back... you know nothing is ideal...