I am using 8670 and trying to do differential quenching. I am trying to just hardned the edge only. I am quenching in water and when I do the blades break. I might try oil but am not sure. I dont want to break more blades. I also did one with firebrick clay and it broke also. Help

Ni-Chrome alloy and want differential harding?  use a different 10xx or W series steel until you have more time under yer belt. thsese alloys, even as low as that 8670 are hard to see any Hamon even if you do get it right, and it does not need it,  with the chrome it is going to want to fully harden anyway, Keep trying, one trick is to use the lowest possable hardening temp as you can. 

 

PS  Water is never very good for  NI Chrome.

Thanks for the help. I was just trying to not harden the whole blade so it would have some bend to it. Maybe I will hardnen the whole blade then try to draw the spine back with a torch. What do you think?

Why are you using this steel ? I am not saying its a bad steel, I do use it myself.  Read up on the steel, even L6 the "big brother" to 8670 will flex at a through hardening.  It does not make sense to me why you choose this steel then try a diferential temper for it ???   if you want,  try a differential temper, but even at RhC 50 it will have great flex and a good edge.  there are issues with differential hardening at teh transition betweeen the martinsote of the hadened portions meating the non harden sections,  read up also on why the japanese use (and needed to use) Ashi when using the clay
 
FYI did you realize that most if not all regulatory comittiees ban the use of differential harden blades in  competitions?  more to read up on  to understand why :)

The problem is using water, never quench in water.  As far as the defferential quench goes, you will not get any temper line.  I use this method on most of my L-6 blades and never get any indication this was done other than from a file test.  For small blades it's not really necissary, but if you need a 8" Bowie that can rip a 65lb vice off the work bench, chop through a 2x4 3 times and still make a single slice through a piece of rope then use it. 

The problem is using water, never quench in water.  As far as the defferential quench goes, you will not get any temper line.  I use this method on most of my L-6 blades and never get any indication this was done other than from a file test.  For small blades it's not really necissary, but if you need a 8" Bowie that can rip a 65lb vice off the work bench, chop through a 2x4 3 times and still make a single slice through a piece of rope then use it. 

 

I suggest people start with a simple steel like 1084 and learn that before worring about alloy steels, and a differential quench for a beginner is asking for troubles.  If I need to rip a vise off the bench I would not use any knife I would choose a pry bar.

Wouldn't it be easier to unbolt the vice????? :) :) :) :)

Just to jump in here and offer one other thought: In lumber mills the big band saw blades are made of either L 6 or 15N20. I am not sure wot the RC test is on the blades but they are hard enough to maintain a cutting edge for an eight hour shift...soft enough for them to be resharpend, and then  run over wheels top and botton so are constantly being bent and straightened.

Car springs, both leaf and coil are expected to flex and bend through out a really long life span. Lots of decades long.

I am not sure if the saw blades are differentially heat treated but the springs are not.

Steels like 1084,1095, L6 15N20 or 5160 heat treated all the way through work wonderfully for a knife. you can perform flex. and cutting tests, and see for yourself.

Ummmm. Brine comes to mind.....not just water straight out of the tap....

I suggest people start with a simple steel like 1084 and learn that before worring about alloy steels, and a differential quench for a beginner is asking for troubles.  If I need to rip a vise off the bench I would not use any knife I would choose a pry bar.

lol, I was acually trying to get the blade to fail (brake) instead the lag bolts holding the vice down failed.  I love L-6, it is very forgiving, easy to work with and makes a most excellent working knife.  I've found it much easier to deal with than simple carbon steels.  But yeah, the differential quench is tricky and takes a little practice.  I tried it once as an experiment with 1080 in water, for some odd reason the blade cracked from the back.  Won't ever do that again.

If you read my papers in heat treating you would have tried oil first.... water is last resort. water aint good for blades.

I used motor oil today and had good luck. I will have to test it tomorrow at work for rc hardness but it seems real hard so I put it into the oven at 350 for 2 hours to draw it back it a little. But it looks good no breaks that I can tell and I did not hear the big snap I was before lol. I did fully harden this blade. Thanks for helping!!

lol, I was acually trying to get the blade to fail (brake) instead the lag bolts holding the vice down failed.  I love L-6, it is very forgiving, easy to work with and makes a most excellent working knife.  I've found it much easier to deal with than simple carbon steels.  But yeah, the differential quench is tricky and takes a little practice.  I tried it once as an experiment with 1080 in water, for some odd reason the blade cracked from the back.  Won't ever do that again.

I had some crack on the spine also. Most on the edge.

lol, I was acually trying to get the blade to fail (brake) instead the lag bolts holding the vice down failed.

Time to make some lag bolts from the L6. :lol:

i use L6 a lot heat the cuting edeg cherry red  quench in warm oil. even use it in damascus

i used to use motor oil it works good. but i started using peanut oil for hardening, it works good and it smells alot better then burnt motor oil

Ya well i tried the motor oil and the knife did not harden. So i used a real light oil i found at work and it worked. Weird thing is i decided to just fully harden the blade so i just fully quenched it. Well long story short my crappy forge if thats what u want to call it (made from a turkey deep fryer n some firebrick) did not make the whole blade uniform in heat. The edge was hotter than the spine. The whole thing was non magnetic but the spine did not harden like the edge did. So by dumb luck it came out differencial treated. I did do one at work in the oven and it hardened fully but my ones at home have all been differencial treated.

It is not  unusual at all for a lot of us to answer questions in these little boxes when we simply have not been given enouigh information about wot is really going on.

Blacksmithing and the sub section of blade making needs to be done in a logical progression and done in steps.

This is a little bit like like trying to play sone ZZ Top guitar riffs with a broken guitar with three strings. Step back and look at the big picture and learn the basics. It will actually take yoiu less time in the end.

What competitions? What committees? You made me curious about this, but I will never find the litterature unless I know what it is.

Here's one: http://www.bladesports.org/ but it is not one of the ones Steve was talking about. They have no restriction against differential hardening. Perhaps Steve will be kind enough to name the organization(s) he was referring to.

Many Asian matrial arts orgs will not allow,  Olympic and sport fencing not only refuses to allow them , but also insists the maker also have their groups certifications for manufacture. Too many poeple trying to Dif-HT without knowing the physics behind what is going on leaving fragile blades at the division line of the HT.  I was warned about this from one of my teachers, Dr JPHrisoulas. He has the details, I have a warning I am sharing from my training.

I believe the Olympic and sport fencing outside of the U.S. (FIE standards) require maraged blades.  I don't know about others.

 

ron