need tempering suggestions

[GreyWhiskers]

A buddy helped me pound out a blade with his forge. I took it home and drilled some holes in the tang and finished shaping it with a file.

The metal was cut from an old concrete saw blade. What should I do to harden/temper it? GW

 

[Joe Yanta]

I would think the simplest way of heat treating your blade would be to either heat your blade with a rosebud on a welding torch or fire up your charcoal grill and with the use an air source such as a hair dryer for a bellows. Heat your blade up until it just becomes non-magnetic. You could normalize it by letting cool to room temperature at this point or go ahead and quench it in oil. If you normalize it you'll have to heat it back up to non-magnetic for the quench. Have your kitchen oven warmed up to about 450 degrees and temper your blade a couple of times for about 45 minutes to one hour. The cooler your oven is the harder your blade will be, the hotter your oven, the softer your blade will be. That should be a simple heat treatment that will work.

Joe

 

The hard part about making stuff from unknown scrap like that is that each steel requires different treatment for hardening and tempering. To get hardness in the mid 50's on the Rockwell scale, for example, 1075 tempers at about 450. However 1095 requires about 600-650. It gets more complex for many of the alloys. My feeling is that I would do what Joe is suggesting and see if you can cut it with a file after tempering at 450. If not re-temper at a higher temperature and try it again. I'd let it soak for 2-3 hours at that temp and don't trust the thermostat on your kitchen oven. Go buy a cheap oven thermometer at walmart that you can hang on the rack. You won't need to anneal and reharden each time unless you go too far and get it too soft.

Sean

 

[LRB]

450° would be about max on temper. Even if 1095. 1095 tempered at 650° would be a spring temper, and not a knife edge temper. A quench heat of just at non-magnetic will not bring steel to solution. You will need to go what you think is around 75° higher, and hold it there if possible, for a few minutes. Non-magnetic is only around 1414°, to 1420°. I don't know of any steel that will go into a good solution much below 1475°, and 1500° is more ideal. In most cases that is going to be in a color range of bright red-orange in dim light. Of couse, most everyone sees light colors a tad different, but that should be pretty close. Pre-heat your quench oil to around 125° in order to lessen the vapor jacket that will form around the blade in the quench, and move the blade fore, and aft, as soon as it is in the oil. Never sideways though. For your circumstances, I would recommend ATF as your quench oil, or canola oil. That's about as good as quench oils get unless using real quench oil, which in your case would not be practical as far as cost. Normalize with three heats before quench, starting at around 1500°for the first heat, then at about a good red heat, then just at non-magnetic. Let the blade cool between each heat, until no heat colors are showing. This will lessen warp, and reduce the grain size, making the blade stronger after the HT is done. Good luck. Let us know how it turns out.

 

[J.D.]

What Wick said. And to add a bit more. That blade is probably an alloy containing chrome, vanadium, and no telling what else. After cleaning off anyoil and scale, try tempering at 350 for 2 hours. Let it cool and 24 hours later, temper again at 350. Repeat for a third time and you should have a decent knife...provided you get the hardening temp right.

Triple tempering alloy steels seems to improve performance. Some even recommend double or triple tempering plain carbon steels, but I question that rational.

 

[J.D.]

One last thought. If you use a charcoal grill to heat your knife, do NOT use charcoal briquettes. Briquettes contain clay and binders that will do a number on your knife blade.

Use lump charcoal instead. Lump charcoal is pure charcoal without the binders. It heats hotter and faster than briquettes, so ya gotta watch your heat.

 

Wick,

You're a way better smith than I will likely ever be and you're right. 650 may be a bit high. The charts I have for 1095 (which his steel probably isn't) say that 400 degrees would put it at Rc62, which I personally think is too hard and is way harder than period knives. But according to those charts 600 should end up about Rc55 which is more reasonable. My point was just that he'll have to monkey with it. I've done some broadheads out of circular saw blades and found that tempering at 450 resulted in stuff so hard I couldn't cut it with a file.

Grey Whiskers, you can search online for tempering charts for a different steels to give you some ideas of where to start. Here's an example for carbon steels:
http://www.admiralsteel.com/reference/heattrt.html

Sean

 

[LRB]

Temper range on the 1095 chart does concur with what you said, however that is based on a water quench reaching 66 Rc, which is it's max hardness. When oil quenching, chances are 1095 is not going to quite reach 66 rc. Even if it did, 1095 does a better job as a cutting tool at around 58 to 62 Rc. I would shoot for maybe 58/60 Rc, to make sharpening easier. To each his own on PC, but I can't see trying to duplicate the hardness of original early steels. We are using modern steel to make PC looking knives in this hobby, which is a far cry from blister, or shear steel. Why waste the inherant potential of the steel, in order to be more PC, by making an inferior blade on purpose? One would end up having to sharpen more often, and the blade wears away faster. Most all of us accept modern steel gun barrels which last much longer, and are stronger than the originals. What's the dif?

 

[GreyWhiskers]

Guys, thanks for all the detailed info. :thumbsup: I think my best bet is to take the blade back to the forge for quenching. Then I can put it in the oven at home. Will send pic when I get a handle on it. GW

 

Temper range on the 1095 chart does concur with what you said, however that is based on a water quench reaching 66 Rc, which is it's max hardness. When oil quenching, chances are 1095 is not going to quite reach 66 rc. Even if it did, 1095 does a better job as a cutting tool at around 58 to 62 Rc. I would shoot for maybe 58/60 Rc, to make sharpening easier. To each his own on PC, but I can't see trying to duplicate the hardness of original early steels. We are using modern steel to make PC looking knives in this hobby, which is a far cry from blister, or shear steel. Why waste the inherant potential of the steel, in order to be more PC, by making an inferior blade on purpose? One would end up having to sharpen more often, and the blade wears away faster. Most all of us accept modern steel gun barrels which last much longer, and are stronger than the originals. What's the dif?

Wick, I didn't mean we need to make soft knives to be pc. I just hate sharpening the really hard ones. I sent you an e-mail asking some questions about your response above.

Sean

 

[vikingsword]

Very good information by all! I'd like to add that if you do normalize several times just before going through the hardening process, be sure to visually check blade straightness and correct if needed as you don't want to be hardening a warped blade into a permanently warped blade( though there is a way take the warp out if this does happen). Sometimes if a blade has pent up stresses from being worked before heat treating the heating up of the blade can cause warping. One other thing is do not forget to clean the quenching oils off the blade before putting the blade in a tempering oven,(ecspecially the family cooking oven), sounds like common sense, I know, but it's real easy to overlook that little detail when your in the groove. I usually wash mine with dawn dish soap several times. Wes

 

[LRB]

A very good point. Normalizing reduces warp as well as reducing grain size, and is especially important if the blade is forged. Even stock removal blades will have stresses that normalizing will reduce, and if a blade has to be straightened before quench, normalize again after straightening. It is best to straighten while red hot also. Straightening can be done in a cool state, but the blade will often re-warp when heated. To beat this, straighten, and heat until it no longer returns to the warp, then give it one, or two more low red heats before moving on to the quench heat, or repeat the entire normalzing process if you want.

 

[chipper]

I don't know about you guys but that's allot of information to swallow in one setting. I learned from Wick but I had to write it all down, memorize it and walk through the steps one at a time before I got it right. Hardening is the most important time of the knife making process and learning it correctly is difficult.
I personally have a whole bunch of broken blades to show for it.
Oil temperature and normalizing are very important steps.
I personally would write everything down in a book and use it for next time. It helped me dramatically.
Regards
Loyd Shindelbower
Loveland Colorado

 

[rich pierce]

Most important thing is making stuff and learning from it. The mistakes teach us the best, so don't be afraid of them, but avoid them if you can. Just don't avoid making stuff! In my experience it is easy to fix a blade that is a little soft (spring temper) but not a broken one. To make really good knives takes a lot more knowledge and experience and new raw materials. But many of us get a lot of enjoyment out of something functional we made ourselves.

 

The mistakes teach us the best

Man... then I should be one of the smartest guys in the world. :wink:

Sean

 

[GreyWhiskers]

I don't know about you guys but that's allot of information to swallow in one setting.

I personally would write everything down in a book and use it for next time. It helped me dramatically.

Don't worry. I printed this entire thread and also forwarded it to my blacksmithin' buddy. Gonna be busy for a few weeks but will try to straighten and temper the blade as per instructions. It may look like a monkey pounded it out but it should be the right hardness. GW