Help With L6

[MarlinSpike]

Hello all. I'm new here and I find this site fascinating. I am very new to knife making and haven't done much more than think about it.

I recently aquired some nice L6 tool steel about the right size for a couple blades. I would love to give this a shot. I have access to a Lucifer RD8-KHE24 furnace. The upper chamber has a max temp of 2250F and the lower has a max temp of 1200F. After reading in the ASM handbook (Vol 4), I've come up with the following process for heat treating.

Normalize at 1600F to 1650F and cool in still air
Anneal at 1400F to 1450F for 2 hrs
Cool at 40F/h until 1200F then cool in air

Stress relieve (if necessary) at 1150F to 1200F for 15 min then cool

Austenitize at 1450F to 1500F hold for 10-30 min
Quench in Oil to 125F (can be handled with hands)
Double Temper at 250F (2 1/2 Hr + 2 1/2 Hr)

I would appreciate any suggestions from those who have experience with this about this process. Any input would be quite useful. Thanks.

 

[mete]

That temper is not correct . It should be 350 F to 1000 F. Typically for knives 400 F giving you about HRc 60. L6 is a very tough steel and is best in applications where the knife is used for chopping -it really shines there ! If the search function is working you should find lots of comments about L6....Welcome to the forum.For heat treating [and other knife making functions] it's best to first read all the tutorials you can find .You'll find mine and others at Dan Gray's site ,www.knivesby.com/robert-cella-1.html

 

[MarlinSpike]

Thanks for the suggestion. The ASM book says that the low-alloy steels should be tempered at a minimum of 250F. I figured the lower temperature I used the harder the blade while still retaining reasonable toughness of the L6. This is exactly the kind of feedback I was hoping for. The book is great but no substitute for real experience!

 

[Stacy E. Apelt - Bladesmith]

Good thought ,but bad metallurgy.The minimum might be fine for an engine block,but a knife blade would likely snap in use if tempered at 250F.For an L-6 chopper I'd use 400F.
A great book is "Metallurgy,Theory and Practice",by Allen. Lots of tutorials and HT info at www.knifehow.com .
Welcome - Stacy

 

[Kevin R. Cashen]

...Anneal at 1400F to 1450F for 2 hrs
Cool at 40F/h until 1200F then cool in air...

heat to 1350-1375F. for 1 hour and then cool no faster than 40-50F./hour.

...Austenitize at 1450F to 1500F hold for 10-30 min
...

Austenitize starting at 1500F, 1450F would be too low.

...Double Temper at 250F (2 1/2 Hr + 2 1/2 Hr)...

I like the double temper part, I myself ussually end up with three tempers, but it needs to start at 400F, and may go as high as 450F depending on where you want your hardness and your as-quenched condition. If you get any drop in HRC before 375F. the austenitizing and quenching was probably a little off.

 

[MarlinSpike]

Thanks for the input. I have made the suggested changes to my process and I'll let you know how it turns out.

One more question, should I be able to use an end mill to machine when in the annealed condition. The way I've got it figured, there's no reason I shouldn't be able to machine this if I kept it flooded with coolant... right.

Thanks for the help.

 

[Kevin R. Cashen]

L6 will laugh at most attempts to machine it unless it is thoroughly spheriodized annealed. Which is the anneal I touched upon in my previous post. I always spheroidize, and how I do it is to soak at 1375F for an hour and then cool no faster than 50F per hour to below 900F. In this condition you should be able to mill it even without coolant (although coolant is always better). Short of spheroidizing L6 will form varying degrees of bainite and even some martensite with almost any other heat treatment.