Temperature for tempering a knife blade

[Robert Egler]

I made my first knife blade the other day. (Well, the first one that ended up actually looking like a knife, anyway).

I used a (new) file as the steel, heated it to orange (as seen in a darkened, but not totally dark, garage), and let it cool slowly. After this it was soft enough that I could work with it using other files and a saw blade. Smoothed all the file ridges off, got the profile I wanted, and heated it enough to add some hammer marks to look sort of rough, village-blacksmith-made. Then I heated it until it was yellow-orange, and quenched in water (about 70 degrees). Got a VERY slight warp to the left, about 1/16 inch total, and got a VERY hard blade. Other files now just skittered off without making a mark.

Now I didn't want the blade to be that hard, because first it would be brittle, and second that there was no way to sharpen it, a sharpening stone didn't do much of anything.

So I did a cheap (very cheap) tempering job by putting it in the oven suspended from the middle rack and turning the oven to 500. I let the oven heat up, and kept the blade in the over at 500 for 1 hour, then turned the oven off and let the oven and blade cool down without opening the oven door.

The blade was quite a pretty color of bright blue, sort of bright royal blue rather than the usual darker metal blue, I'd never seen that color on metal before (but I'm not that experienced in metal work) which came off with a single pass of 400 grit sandpaper.

The knife took a good sharp edge, and I can use the back to get sparks from a flint piece.

After that long-winded explanation :yakyak: :snore: my question is: is 500 degrees for an hour a reasonable tempering time/temperature for a knife blade, about 1/8 inch thick? Or is the fact that the blade is hard enough to use for flint and steel an indication that the blade is still too hard? Or is the blue color an indication I overheated it?

It seems to work as a knife pretty well and holds it's edge well. It is a little hard to sharpen, but not terribly hard.

Any observations or suggestions would be appreciated!

 

[Nifeman]

Squirrel Tail, I ususally do an edge quench (or differential quench). Take your knife up to a nonmagnetic state in your forge (cherry red or 1400 degrees, test with a magnet. If it won't stick you're ready ), hold it there for about 20-30 seconds, then quickly put just the cutting edge into your quench leaving the back (spine sticking above the quench). When the back loses color, but still retains heat, take it out and let it cool on your forge or a fire brick. The ambient heat will run towards the edge and temper your blade. This is the way man did for thousands of years. It won't make a high tech job, but it will servicable for most everyday applications :thumbsup: .
I use a semi solid quench of Crisco and bacon grease(50/50) and this has served me well for years with no complaints. I hardened one for my son this way and it has skinned 4 deer with no sharpening other than touching it up with a ceramic stick.
Hope this helps a little...Nifeman

 

[rich pierce]

Bright blue on a file-made blade is usually a little softer than I like for the blade edge. Should be safe to not snap. if it holds an edge for you, go with it.

 

[Robert Egler]

Thanks to both of you! I appreciate the advice.

 

[Elnathan]

Usually you want a straw or bronze color, which would indicate that it was around 60 Rw. The blue color would indicate that you overheated it. According to this graph, however, it would seem that you didn't heat it enough.
Maybe it isn't W-1 (the usual through-hardening steel in files)? I guess if it holds its edge and isn't too hard to sharpen its OK.

 

[Robert Egler]

Ahh heck!! Back to step one! There's that old saying that "Perfect is the deadly enemy of good enough."

It seed ok, but I decided it was likely a bit too soft, so I took it up to non-magnetic and quenched in water again. It had a little bit of a corkscrew warp, but only in the tang, so I thought I could make a small adjustment with a few hammer taps before I tempered it, and the thing snapped. :cursing: Well, tomorrow I buy a new file and try again. This time with a better idea of what I'm doing, thanks to all the advice.

 

[LRB]

1400o is not enough heat for quenching. Non magnetic is not your quench heat. You went closer to being right the first quench, except never use water. You are very lucky it did not crack. There are very few steels that get the quench they need under 1475o, to 1525. Next time use ATF if you are not using real quench oil. Your temper heat was probably fine since your blade did not crack in the quench, but 450o would have given you a good balance between strength and edge hold. You would have been better off with what you had.
This business of quenching as soon as the steel is non magnetic is pretty much limited to the 10xx series, and even those benefit from another 75o, to 100o. W1 is not just another simple steel, and benefits even more with a 5 minute soak at real quench temp. Steels such as 5160, and 01, require a 12 minute, and 20 minute soak respectively, if you want a good heat treat. The magnet only tells you that the steel is going into austenite. It takes more heat to make a good solution, and a little time. When I say solution, that means that the carbon, and iron, and alloys, become homogenized. Evenly, and thoroughly mixed. Then you have a properly heat treated blade, assuming you are useing a quench oil that meets the needs for that particular steel. Bacon grease, and crisco, just don't cut it. Pun intended, and 1400o is not going to properly quench harden any steel that I know of. The file test is limited to what it really can tell you. A file can skip right off a piece of steel, and that steel may still have scattered soft areas that the file just rode right over, and, or undigested carbon. There is no way to tell without a high powered microscope. W1, needs a very fast cool down in the quench. It is classed as a water quench steel, but not with thin steel as in a knife blade. You need a thin oil that will drop the temp from 1500o, to below 900o, in a couple of seconds in order to get it really right, but not water, unless you are a gambler. You also need the quench oil heated to at least 125o, to 135o. Believe it or not, that will drop the heat in the steel faster.
You also need to heat the steel red hot, and let it cool to no color three times before you heat it to quench heat. This is called normalizing. This makes the grain smaller, and reduces warpage by relieveing stresses. Edge quenching works only OK. You get a better result by full quenching, then softening the spine, if that is what you want. You will get less warpage, and better quality in the steel, although it is not a critical thing, either way. If you want the real story on PROPER heat treat, email, or PM me. If you just want to stumble around in the dark, get yourself a magnet, and a bucket full of bacon grease and crisco. You could call it, "Bagrisco". never do any research on the matter, and be happy as a pig rolling in this stuff. Take care, and good luck in your endeavors.

 

[Nifeman]

OUCH!!! All I know is that it works for me...Bud

 

[LRB]

Bud, I must apologize for that post. You have every right to be angry, upset, ect. I should not have said what I did, and I apologize for it. As long as you, and your customers are happy with what you produce, that is what matters. Again, I offer my sincere apologies. Wick Ellerbe

 

[Robert Egler]

Many thanks! :bow: I'm going to print this out and keep it. After I get a trade knife made (which is what I'm working on), I don't have any plans to make another knife, but I may in the future at some point.

I usually never make 2 of anything. I do both wood working (tables, chairs, etc), and wood carving (duck, boats, people...)and often someone will ask me to make them one like this or that thing. I have only very rarely ever made another ("rarely", as in about twice in the last 30 years). To me, the fun part is figuring out how to get it done, and after that, it is not too interesting to me. People have said I should sell my carvings, but I have no interest in doing the same thing over again.

So I really appreciate the advice, and I know it will help with my third attempt at this trade knife, but after I get this done I don't have plans for another knife.

 

[Elnathan]

Cab I make a suggestion? Buy a piece of tool steel instead of a file. That way you actually know what the steel is, and how to heat-treat it. Well worth the cost, in my opinion.

 

[LRB]

I will second that suggestion, with one exception, Nicholson file steel is very good steel, and if he is home heat treating it is pretty forgiving to work with. Some of the tool steels may require more than he is capable of doing in order to get a really good HT.

 

[LFC]

For those interested in knives, tomahawks, and the making of either or both, there's[url] www.bladeforums.com[/url], which has all sorts of detailed information on those subjects.

 

[Nifeman]

Mr Wicke, I graciously accept the apology. I know it was not meant to be malicious. However as a fellow knifemaker I'm sure you're aware that there's "more than one way to skin a cat" so to speak. At any rate being gentlemen, we'll let bygones be bygones.
PS...kinda liked the nickname you gave my concoction :thumbsup:
Bud

 

[LRB]

Thankyou Bud. I am in complete disagreement with your methods, but I had no right to say what I did, or in that manner. You are a good man for accepting my apology, thanks again. Your friend, Wick