What will be stronger?

Leu Custom

Leu Custom

Joined
Jun 2, 2007
Messages
1,354
Lets pretend I have heat treated 2 knife blanks the same exact way as far as the austenizing temperatures and soak times and preheats, etc. Now my question is, what blade will be stronger and last longer? The blade I have tempered at 400' degrees for 2 hours twice or the blade I have tempered at 500' degrees for two hours twice. Both would be A2 tool steel and vary from 1/8" to 1/4" thick. Any advice would be awesome! Thanks!
 
The idea behind tempering is to lessen brittleness, and increase toughness. The higher the temper, the less brittle, and the tougher it will be. But it still needs to hold an edge reasonably well. You have to find the middle ground.
 
Stronger, as in ultimate tensile or compressive yield strength, is generally closely correlated to hardness. The harder, the stronger. If memory serves me, A2 at HRC 61 is around 315,000 PSI. That's pretty strong... But if it is subjected to a strong shock that would dent or bend a softer temper it would instead fail catastrophically.
 
According to Crucible, the charpy c notch test shows 400F to be 31ftlbs while 500 is 41. So if this is your definition of stronger then 500f is were you should go. If you went to 600 then it would drop to 37ftlbs. So at 500f you should have a 60RC just about were you need to be.
 
Are you making a prybar or a knife? If it's a knife, you need a balance of qualities.

A2 is one of those steels that has a narrow band for maximum toughness, after which both toughness and harness taper off. A C Richards is right. 500 degree tempers should give you the sweet spot.

Crucible doesn't call for it, but someone told me A2 is one of those steels that will benefit by a third temper cycle. I've been doing that because it may help and won't hurt.

Rob!
 
Right! P.H. does three temper cycles! But at what temperature is the mystery! Then again, there's his complete heat treat to begin with which is also quite a mystery!

Stronger meaning edge retention and um tensile strength and um well like someone said, the sweet spot.

I am making a knife, not a prybar. =) I'm guessing a prybar wouldn't be too hard to figure out. I am however grinding to zero/infinity with no secondary bevel. If that helps.
 
There is your fine line. Are you flat grinding or convex grinding?? Flat gives a very weak edge on zero grind applications while convex provides a bit of meat behind the edge. You may need to adjust the HT to allow for the zero edge.
 
A C Richards said:
There is your fine line. Are you flat grinding or convex grinding?? Flat gives a very weak edge on zero grind applications while convex provides a bit of meat behind the edge. You may need to adjust the HT to allow for the zero edge.
Click to expand...

ummm neither? A lot of the blades are just either chisel ground at say 15-20 degrees zero grind or a zero V grind with 12.5 or so degrees per side totalling 25 degrees or so. No flat or convex grinding here!
 
So do you guys do your final tempers in an actual kiln or in a toaster oven? How bad can toaster ovens actually vary in temperature?

Lets say I cut into a 2 x 4 made of i think pine and the edge is severly damaged, does that mean possibly that the edge is too hard which is causing it to chip out or because it's too soft? The 2 x 4 is being destroyed pretty well in the process though.
 
If the edge is chipping away badly when chopping a 2X4, it is one of several problems:
The edge is too brittle - improper HT or too low temper.
The edge geometry is too thin - thicker,rounder edge.
The method used in chopping is breaking the edge (Twisting motion?)

I would take a serious look at the edge and try to see why it is breaking so badly. If it is thin, regrind thicker and try again. If it still chips out, then re-do the ht and use a higher temper.
Stacy
 
As has been covered- the 400F will be stronger, the 500F will be tougher (unless of course you suffer some tempering embrittlement in that range)
 
Leu, you are describing flat grinding, just at a steeper angel. P.H. grinds his in a chisel grind. Stacy pointed out the areas to look at if you are having chip out problem. Also I have seen my toaster oven vary as much as +- 25f. I put a layer of heavy brick into my garage oven (not a toaster oven) and it varies much less +- 10f.
 
I think I tempered that particular blade at 350' degrees? to see what it would do. I guess I have my answer? Does the strength of the edge change that much adding 150 degrees? (probably so!.)

Lets juts say that one would use a toaster oven for the first time to make sure to take the stress of the blade after austenizing. Say I tempered it at 350 or 400 degrees. Then I waited till the next day to temper it again in the actual kiln that hopefully isn't going to vary that much at 500' degrees. and then the 3rd day I tempered it again in the kiln at 500' degrees. Would that work?

so basically all of you are saying that the higher the tempering temperature, the more shock the blade can take correct? cutting a 2 x 4 for instance and the lower the tempering temperature, the longer the edge will last as far as maybe push cutting instead of using a chopping motion.
 
bladsmth said:
If the edge is chipping away badly when chopping a 2X4, it is one of several problems:
The edge is too brittle - improper HT or too low temper.
The edge geometry is too thin - thicker,rounder edge.
The method used in chopping is breaking the edge (Twisting motion?)

I would take a serious look at the edge and try to see why it is breaking so badly. If it is thin, regrind thicker and try again. If it still chips out, then re-do the ht and use a higher temper.
Stacy
Click to expand...

It's kinda of funny. I'm trying to make a blade that will shave hair with ease and cut with practically no drag, but at the same time be a chopper!

Thanks for the replies guys. I do appreciate it very much. :D
 
Leu Custom said:
It's kinda of funny. I'm trying to make a blade that will shave hair with ease and cut with practically no drag, but at the same time be a chopper!

Thanks for the replies guys. I do appreciate it very much. :D
Click to expand...

Join the club!;)
 
I think I just checked the toaster oven I used on that particular knife! It varied by like 100 degrees!
 
Leu Custom said:
I think I just checked the toaster oven I used on that particular knife! It varied by like 100 degrees!
Click to expand...

I had one like that, too. It has a cooking tray about 1/2" deep and I filled it with coarse sand/fine gravel (about 3/8" depth). The extra mass of the gravel flattens out the hi/low curve very well... nearly imperceptable movement on the temp. gauge used for calibrating the toaster oven dial. Takes longer to get up to heat, though.

Tried using a hard, half thick (1"), fire brick but that was too much mass and it took too long to come to heat and stabilize.

Mike
 
You must log in or register to reply here.
Back
Top