Not tempering 5160

[PedroS]

Hi all , greetings from Argentina.  I been doing some knives with 5160 and notice they're not able to hold a good edge. I believe it is because it's not a really hard steel , plus I have been tempering to straw yellow (I temper by color) .

So the thing is I will be quenching a kitchen knife for my father tomorrow and I want to try not to temper (the edge at least) . The question is I'm I loosing some mechanical benefit besides toughness? 

[Latticino]

5160 will hold an edge very well, if correctly heat treated.  It isn't D2, or one of the exotic crucible steels, but it should be fine for most purposes.  You are most likely tempering too hot, not getting good hardness from your quench, or working the steel so long you have a major amount of decarb.  I would certainly not skip tempering a kitchen knife altogether.  Provided your edge tests out hard after the quench cools it completely, you could do a light "snap temper" in an oven of the whole blade at a relatively low 350 deg. F, then carefully torch or plate temper the spine (keeping the edge cool in wet sand), but if you skip the temper altogether you are giving your father a time bomb IMHO.

5160 is pretty easy to heat treat, you shouldn't have trouble with it if you are moderately careful.  Normalize correctly, stress relieve, prep your quench oil, heat to just over decalescence and quench.

Color is not appropriate measure for tempering blades, use it for chisels and hammer heads, if you must, but temper blades with an oven if at all possible.  A cheap solution is either a garage sale toaster oven or an electric kitchen oven.  In either case I would recommend cleaning off all quench oil, burying the blade in a metal tray filled with dry sand, and use of an inexpensive oven thermometer:

Of course there are more expensive alternatives.

[Frosty]

Welcome aboard Pedro, glad to have you. What is your source of 5160? If it's spring steel off vehicles there's almost no telling what alloy it is. Did you file test after hardening to confirm hardness? A file should skate on hardened 5160.

So, not knowing if what you have actually IS 5160 make a test coupon, heat to non magnetic quench in warm oil, file test and if it skates put it in a vise, cover with a rag and hit it with a hammer to see if it breaks. If it snaps check the break you want to see a fine gray grain, without sparkles. Repeat to hard, file test with another coupon from the same stock and temper to pale straw, repeat the break test. When you find the tempering heat that produces a tough result is time to try it on a blade.

Latticino is correct in his method, my only real contribution is you NOT being able to be sure you have 5160 to work with UNLESS you buy it as new stock and it is available. 

Frosty The Lucky.

[ThomasPowers]

I had one of my students go to the American Bladesmith Society school in Texarkana fairly recently.  They used 5160, bought new from a reputable dealer and the Instructors told them they could forge and heat treat it and pass the ABS Journeyman cutting tests with a knife made from 5160.  You may want to read what those tests consist of.

One extra thing: it is possible to decarburize steel by leaving it hot too long in contact with air.  People starting out are more prone to this as they tend to work slower and take more heats.

[CheechWizard]

ive found 5160 to be one of the easier steels to harden, and it gets quite hard, i sometimes temper it a couple times, like they said throw its right in the oven and get it to light straw, then do some differential tempering as needed. as far as a kitchen blade goes, the edge geometry is so narrow if you were to not realize the hardness you would chip that bad boy the moment it makes contact with something other then a tomato, probably even just by sharpening it

[Frosty]

A metal supermarket opened in Anchorage a while back so it's easy to find new 5160, I used to hit spring shops and ask to buy their drops. 

Over heating and holding it too long is a pretty common beginner's thing. Been there done that. 

Frosty The Lucky.

[Nobody Special]

I don't have a lot to add to what's above.  The main mechanical benefit that you surrender if not tempered, is that if you've hardened it properly, or even improperly, you are at serious risk of the edge chipping or the knife breaking. They sometimes even break on their own with no use if you don't temper after hardening.  This can be especially dangerous in a kitchen knife.