Hey all, I could use some help.I forged two blades on two different days, using 1084 from Aldo. I normalized 3 times. I gently - slowly, heated the edge with a torch - James Crowell style, and quenched in canola oil.
Both knives cracked in about the same place, in the same way. The first crack has a real pretty curve to it - looks like a smiley face <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />. They did not crack in the quench. They cracked later. One in the oven tempering, the other while sanding, after tempering twice at 425f.
Do these look like stress riser cracks? I had sanding lines running from blade edge straight to spine. Do you all sand the length of the blade before heat treat? What grit should I end on before I heat treat? Do you de-burr/sand the cutting edge edges round before quench?
Any help would be appreciated and thanks for looking.
-Jim
Here is the second knife right out of the quench.
Jim,
Give us a little more info. 1) How are you determining temperature? 2) How thick was your cutting edge at H/T? 3) Did you preheat the quench oil?
Gary
Additional to what Gary asked..... are those hammer marks/fire scale on the blade in the pic right after quench? Did you forge too cool? Maybe overheated the blade during austenitizing?
Hey guys,
Thanks for looking at this. To answer your questions:
I determined temp by color and when blade went non-magnetic.
Cutting edge was thicker than a dime, thinner than a nickel. I did not pre-heat the canola.
Those are not hammer marks or fire scale - it is burnt canola oil - smelled good, kinda like french fries 
Jim,
If you normalized & quenched at or slightly past non-magnetic then the problem may well have been the forging
temperature(s).
Bend the blades until they crack in two and look at the grain size. That will tell you a lot.
Gary
Thanks for replying Gary. I will snap them off and look at them.
Ok, snapped it at the tip (grain looks tiny and good - don't know how well it shows in the pic)
Snapped it off at the crack into three pieces:
To me - the grain looks great right above where the crack is but terrible in the crack itself.
I think that it is kinda cool that you can see the third type of grain in this last pic - you can see where the hardening stops and the soft back steel tore more than broke off. Neato chemistry!
Jim,
Next time heat your canola oil to about 130°. Also make sure not to overheat the choil area. It's real easy to create a stress riser by over heating that area and not having your oil heated.
When I try Jim's method,I like to do it in the dark, so I can see the color better. I've cracked several myself. Takes practice to get it right.
Best of Luck,
Bob
could just be the photo, but the grain in the first pic looks a little large to me. in that last pic the black in the crack makes me tend to think it did cracked in the hardening, just did not show up until later. as to what caused it I would guess over heating, but that would just be a guess.
you asked about stress risers. I ether go length wise in my grinding if at all possible with the design or go to 220 before heat treat, I always run my grind marks length wise along the spine and edge, and I break all of the edges lightly.
MP
Matthew,
Thanks for replying. I will try changing grind direction, going to 220, and heating my oil like you and Gary mentioned.
Matthew - I think the first pic is bad - I only have my phone to take the pics and couldn't get it to focus well up close. To me, the grain at the tip looks great - it is very small, tight, and shiny grey.
I will try your suggestions on my next blade.
Thanks again - it is really nice to have experts like you guys help me with my knives.
-Jim
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could just be the photo, but the grain in the first pic looks a little large to me. in that last pic the black in the crack makes me tend to think it did cracked in the hardening, just did not show up until later. as to what caused it I would guess over heating, but that would just be a guess.
you asked about stress risers. I ether go length wise in my grinding if at all possible with the design or go to 220 before heat treat, I always run my grind marks length wise along the spine and edge, and I break all of the edges lightly.
MP
Hey Jim...I agree totally with all of this^^^.
The grain on the edge does look a little large. It would seem to suggest overheating....somewhere along the the line.
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...the grain at the tip looks great - it is very small, tight, and shiny grey.
Hi Jim. Just saw this and wanted to comment. The grain should appear very smooth and a dull flat gray in color. Really you don't want to see any texture at all. I know all of the adjectives are subjective but any grain that I would ever describe as 'shiny' is large grain.
After looking at the pics, my instincts tell me too hot, for too long. The telltale signs for me are the enlarged grain size, and the burnt on oil......neither usually happens with 1080/84 unless the temp and duration are excessive.
I have to ask....was there any "soaking" involved? I ask because these days I keep hearing and reading about folks "soaking" plain carbon steels, and others recommending soaking, some posts I've seen on other forums recommend soaking for up to 10 mins! Thats a reciepe for disaster wtih plain carbon steels.
Ed Caffrey, ABS MS
"The Montana Bladesmith"
www.CaffreyKnives.net
Ed is correct, attempting to soak with a torch is a recipe for disaster. Grain growth being a product of temperature infinitely more than time, soaking with a torch is practically a contradiction in terms. With tight temperature controls that eliminate overheating possibilities soaking can be done for hours with no concerns for grain growth, even simple carbon steel have particles from the killing process that help keep things in order. However each steel has a grain coarsening temperature at which all the particles keeping grain boundaries in place will be dissolved and grain growth will commence very rapidly. An O/A torch is capable of a 6,000F flame, this is more than enough to exceed the coarsening temperature of even the most complex alloys in the blink of an eye. The bottom two photos tell the story quite clearly, the edge portion that saw the heating is dark and quite coarse in grain size, this indicates that the steel cracked during the hardening and opened up wide enough to see later as the stresses manifested later. This was not the quenchant, forging, tempering or finishing, the edge was overheated.
A few years back I tried many experiments with 1084 to see if it could be more deeply hardened in low temp salts, I extended the soaks out to 30 minutes to and hour to get complete solution at 1450F and 1500F and could not get the depth of hardening I wanted, but the grain size was quite fine and unchanged. At 1525F I suddenly got deeper hardening, but with a marked increase in grain size, I had found the grain coarsening temperature for that batch of steel. I have also soaked higher carbon steels for hours with no increase in grain size until the coarsening temperature was reached, but in this case the results were lower hardness for both overheating and over-soaking due to increasing levels of retained austenite.
"One test is worth 1000 'expert' opinions" Riehle Testing Machines Co.
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Jim,
Next time heat your canola oil to about 130°. Also make sure not to overheat the choil area. It's real easy to create a stress riser by over heating that area and not having your oil heated.
When I try Jim's method,I like to do it in the dark, so I can see the color better. I've cracked several myself. Takes practice to get it right.
Best of Luck,
Bob
Thanks Bob
