Hardening the knives.

[Titus]

This is what the knives looked like last Thursday night.

The knives are heated to 1080C and then quenched in special oil at 70C to harden them to 66RC. Then they are cryogenically frozen for more than 12 hrs and then tempered 3 times at 200C for an hour to give them flex and memory. These knives will flex to just over and angle of 30deg. :thumbsup:

 

[Titus]

Quenching in oil. Note the flash at contact. :grin:

 

[jbullard1]

Looking good so far Titus

 

[LRB]

Sounds good, but what steel?

 

[Titus]

Sounds good, but what steel?

Wick, that one is 4mm 12C27 stainless, which I prefer, but I also work with N690 and D2 :grin:

 

[bwhoffman]

sounds like you know what you are doing! :thumbsup:
Those are going to come out nice. Be sure to put up pics of the finished goods!

 

[flaming canvas]

What is the oil, if it isn't a trade secret?

 

[Titus]

not a trade secret. I'll try and get the name for you. its a special quenching oil for steel. any other oil causes the steel to warp or bend.

Brett, sure will post the pics as I progress. :grin:

 

[50cal.cliff]

Looking good Titus! :thumbsup:

 

[paope]

What does cryogenic freezing do for the blade? Liquid nitrogen I presume.

 

[LRB]

It causes more of the retained austenite to convert to martensite after the quench. Simply put, it makes the steel even harder than before. This is usually only done with alloy steel, and has little effect on the simple steels. It is especially beneficial to the stainless types.

 

[paulvallandigham]

They say the cryogenic treatment actually causes the molecules to compact more, making the steel tougher, but not so brittle. The tempering relieves the stresses that make steel brittle. Chrome-moly steels, used in modern gun barrels, but NOT in MLers, benefit from the cryo treatment. So do many knife steels.

 

[Titus]

What Wick and Paul said. :hatsoff:

 

[LRB]

Paul, I am a little surprised at you. There are no molecules in metals. metals are a crytaline structure. Groups of atoms make crystals, groups of crystals make grain, groups of grain make metal, in this case. Just picken at cha, don't take it the wrong way.
One note not mentioned, is that after being cryogenic treated, the extra martensite needs to be tempered, in most cases involving knife steels. Untempered martensite, is unwanted stress.

 

[paulvallandigham]

Okayk, Wicke, you got me! I used the wrong terms. What I am seeing is granules, and not crystals. All I know is that the grain has shiny facets to it before it is tempered, and that most of that disappears when it is tempered. At least we are looking at the same process.

Most MLers don't know that the steel used in our barrels is about as soft as steels come, to make them easier to cut with cutters, as opposed to using a button to rifle, or a mandrell and hammers set up. Because the steel is so soft, cryogenic treating of these barrels doesn't have much effect. With modern steel barrels using harder alloys, cryogenic treatment has a remarkable effect on the rifle's accuracy potential. Even small barrel making companies either have their own freezers on site, or are sending their barrels out to be treated before sale.

 

[flaming canvas]

I've tried making a couple of knives out of L6 from an old sawmill blade. The big bowie I took to a shop and they clamped it before heat treat and it came out great. 58 Rockwell, if I remember right. Tried to treat a french pattern knife my self with a mixture of vegetable oil and transmission fluid. It came out with a slight bend in the middle. Tried to force it gently with the shop press and wound up with a couple of good strikers.

 

[LRB]

Flaming, next time try this. The following is Bill Morans method, and it works. This is done AFTER the tempering is completed. Determine the area of warp. Polish so that you can see heat color on the steel. Put an inch or so of the point in a vise. Apply heat on the spine in the warp area, until it turns straw color, being very careful to not allow the edge to get any hotter than straw color. Over flex the blade a bit, hold it there, and pour water over the heated area until cooled off. With some steels, it may take more than one go at it, but it will straighten out. The best time to straighten is right out of the quench while it is still too hot to hold bare handed. At this time you have about five minutes that you can straighten by hand pressure, or other means, without damage to the blade. If it does a re-warp in the tempering, then do the first method mentioned.

 

[J.D.]

And be ready for the steel to feel like it comes to life.

I have had knives that felt like I was holding a snake while straightening them. It doesn't happen very often, and I don't know what causes it, but flexing seems to occur most often with large knives.

 

[chipper]

I've found that knife warpage can be caused from a bunch of reasons.....

Banging on one side of the knife more than the other when shaping it..

Not normalizing properly is probably the biggest culprit though...

Heating one side and not the other during the hardening processes...

Allowing the knife to touch the side of the forge during heating pryor to quench (bending it).

At least, those are all the reasons I've seen during the making of a knife.
A statement was made earlier that the knife done in the cryogenic quench will flex up to 30 degrees. I've worked with W1, 5160 and O1 pretty much exclusively. I Use a clay coating during the quench becuase I like the control. Every knife I've treated will flex 30 degrees pretty easily in a 3 point set up I use in my vise. I simply use a charcoal forge and cooking oil for my quench. I currently use an oven to temper but I'm slowly changing over to oil base tempering.

Those are just my two cents.

Regard
Loyd Shindelbower
Loveland Colorado