high strength + high toughness blade

[BluntCut MetalWorks]

I seek high strength + high toughness (together, not either or) for fully hardened(martensite matrix) steels.

3.5" blade, 0.095" spine thickness (near handle), FFG, distal taper, 14-15dps (28-30 degrees inclusive), 0.01" behind edge thickness, hardness 63rc
Satin Burl with Ebony handle.

Thanks for watching & comments.

Whittled: oak, pork rib bone, gabon ebony, lignum vitae arg, aluminum rod, hardened mild steel rod.
http://youtu.be/pr5ocZ9RUsM

Heheh - it sure wasn't easy to whittle hardened steel rod. The biggest microchip is around 0.12mm / 0.0048" deep. Hence thickness at damaged shoulder ~ 0.0028" / 0.07mm.

 

[mycough]

Luong, you gave that later one heck of a workout! I was cringing a lot during your video. Is that 52100 or W2? Amazing what a knife can take when the heat treat is well done. Thanks for posting this, Russ

 

[HeavyHanded]

That is some rough stuff, well done!

 

[atavist]

Nice video, nice knife.

Though to be pedantic I don't think the word "tough" applies to.this knife... tough is generally synonymous with ductility... at 63rc she is definitely hard (strong) but not ductile.

 

[BluntCut MetalWorks]

Russ, That is a 52100 knife ht for nano grain size with almost uniform distribution of tiny cementite/iron-carbide size. Yesterday, I also tested CruforgeV blades, much higher wear resistant but suffered carbide tear out when whittle hardened mild steel rod.

Luong, you gave that later one heck of a workout! I was cringing a lot during your video. Is that 52100 or W2? Amazing what a knife can take when the heat treat is well done. Thanks for posting this, Russ

Thanks Martin. Will you show off your new sharpeners and possibly WashBoard V2, soon? My Bday is coming up - hmmm seem to be a yearly thingy....

That is some rough stuff, well done!

 

[BluntCut MetalWorks]

Thanks. You are right, this video doesn't directly shows toughness.

I conducted many tests, especially focusing plasticity (which overlaps with ductility) because that was the area of my prev ht weakness revealed from BackScatter Electron Diffraction imaging (50K and 100K magnification). So, could consider ductility as a super set, where plastic is a starting point where lattice dislocation permits small displacement/movement limited to low curvature in direction. High strength from well align grain boundaries (low mis-align angles) will resists/disallow displacement with rotation component (ductility movement) - a true classic case compromise between strength vs toughness.

Edge of blade in video will minor bend & dent at 63rc, chip taken place displacement exceeded plasticity.

Here is additional info (in a response in yt) about this blade:

Nano grain size 52100. Yep, I corrected the toughness & plastic issues. Carbide size (~100-200nm) & distribution around 90+% perfect. Grain size (I am guessing but will BackScatter Electron Diffraction imaging after another around of ht) probably varying from 750nm to 40nm, where 90+% around 60nm.
​

Nice video, nice knife.

Though to be pedantic I don't think the word "tough" applies to.this knife... tough is generally synonymous with ductility... at 63rc she is definitely hard (strong) but not ductile.

 

[NJBillK]

With this finally being pinned down to a sufficient amount of toughness and strength for your demands, what are you planning on making? Competition choppers, edc blades, thin kitchen knives with no worries of accidental chipping?

 

[BluntCut MetalWorks]

Yesterday, I ht-ed with increased in toughness while retain same strength. At similar hardness these blades exhibits higher edge rolling ability, extended plastic curve and added some ductility (I projected 0.5% additional stabilized RA). A test blade 10dps, 0.005" thick paring edge rippled & bend when whittle African Blackwood (no problem whittle Lignum Vitae Argentine). Probably good EDC spec. Will add a tad more toughness for choppers.

8-10dps; 0.002-0.004" edge thickness, 65rc for general kitchen
3-5dps; 0.005" edge thickness, 65+rc for speciality single bevel blades
Straight razor
so on...

Keep in mind with extra strength, thin cross section will be more rigid than less strength. e.g. a 10" gyuto with 0.015" spine thick 1.5-2.0" away from tip is actually quite stiff (low flex). Fun to julienne those small vegies/herbs...

With this finally being pinned down to a sufficient amount of toughness and strength for your demands, what are you planning on making? Competition choppers, edc blades, thin kitchen knives with no worries of accidental chipping?

 

[BluntCut MetalWorks]

For a Few Dollars More (1965) ... Monco: Ten thousand... twelve ... Thought I was having trouble with my adding...​

Exactly, Thought I was having trouble with whittling... While testing today, I file the steel rod near whittle area. File skidded, it was work hardened greater than a 60hrc file. So I cut off the work-hardened area and filed clean a new test whittle area.

Here is a rematch - this time using 3 blades (2x 52100 and a CruforgeV) against the steel rod. No chips, just a minor roll from 1000 grit finished ~15dps edge.

Thanks for watching & comments.
http://youtu.be/OwubcKmtAvg

 

[Chris "Anagarika"]

Paring knife with utility toughness ... Scary
:thumbup:

 

[BluntCut MetalWorks]

Thanks Chris!

Paring knife with utility toughness ... Scary
:thumbup:

Here is a macro shot of the knife edge after whittled non-work-hardened steel rod

While previous edge after whittled work-hardened steel rod

 

[BluntCut MetalWorks]

Here is trivia about tensile strength - just pointing out what's possible, that's all ...

http://en.wikipedia.org/wiki/Ultimate_tensile_strength
Steel, Micro-Melt 10 Tough Treated Tool (AISI A11) 5205 MPa
Carbon fiber (Toray T1000G)[19] (the strongest man-made fibres) 6370 MPa
Carbon nanotube (see note below) 11000-63000 MPa
on market - Industrial hardened 52100 (~15um grain diameter) ~2000 MPa

In theory - http://en.wikipedia.org/wiki/Grain_boundary_strengthening
http://www.bladeforums.com/forums/s...ffects-yield-strength?p=14631930#post14631930

Key formula (sigma_y = sigma_zero + Ky / sqrt(grain diameter)), where sigma_y = yield strength
Yield Strength of 52100 with flawless microstructure 60nm martensite grain size ~= 1500+2/sqrt(6^-8) = 1500+2*4082 = 9665 MPa <= stronger than Carbon Fiber!

 

[shqxk]

I wonder how you rate your special heat treated 52100 against CPM-3V which has been rapid quench with cryo as part of the quench and 3 times 400F tempering?

Will this nano grain size 52100 suffer less damage cutting through hard material?

 

[BluntCut MetalWorks]

Assuming 3V ht (better than you described, i.e. no wonky M23C6 cooling form/precip and wacky phrase/diffusion) to 6-7um grain dia and aggressively guess its tensile strength(TS) to be 4GPa. When 52100 with grain size of 300nm, TS ~= 5.1GPa, then yeah 52100 is stronger. Since I can't resolve my 52100 grain size with SEM & BSED imaging (up to 100K magnification), after many days, 60nm is my best guess. At 60nm grain, TS ~= 9.7GPa. At nanograin, plastic component of ductility has a narrow range. Note - grain size is proportional to ductility. So large grain is more ductile.

3V has very low carbide volume in spite of its high alloying elements. Those elements (extra V, W, Mo, Cr, Si) help reduce (by pinning) grain size and prevent cooling precipitation. RA+those elements, especially along grain boundary, allow it to absorb impact energy, thus it renown for high impact toughness. Its 5% MC (mostly in VC form ~1-3um in size) provides good wear resistant; however at cost of fracture toughness.

Under SEM & BSED my 52100 carbides are smaller than 200nm. Each carbide under external pressure (e.g. push cut against metal), stress concentrating along carbide boundary (interface) with matrix. My 52100 distributed such pressure over many order # of tiny carbide, as long as stress than boundary yield strength, no carbide tear or crack initiation. While 3V has 1-3um VC, stress energy at interface will be square or cubic compare to 200nm carbide, therefore once exceed ys, carbide tear + matrix deformation (depends on ht microstructure). Long windedly, Yes, nano grain & carbide steel will sustain less damage when cutting through hard material. Wear resistant is another wordy subject - save for later

Here is a practical way to look at TS. e.g. A cantilever with max load of 10Kg using 2mm thick steel TS at 2GPa. In order to use same arm dimension except only 1mm thick, the steel TS need to be 8GPa. Basically, it's a volume calculation, hence cubic (W x H x L).

OTOH caution - I am not a metallurgist :very_drunk:

I wonder how you rate your special heat treated 52100 against CPM-3V which has been rapid quench with cryo as part of the quench and 3 times 400F tempering?

Will this nano grain size 52100 suffer less damage cutting through hard material?

 

[HeavyHanded]

Long windedly, Yes, nano grain & carbide steel will sustain less damage when cutting through hard material. Wear resistant is another wordy subject - save for later

Two words and exclamation point come to mind...

Bolo Machete!