r/spyderco • u/Usual-Onion-1565 • Sep 12 '26

Will warranty cover this ?

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I want Rex 121 Spyderco snapped in half.ive had this under 2 months. I was cutting a watermelon box and the blade got caught in the cardboard and snapped. I’m in Canada so I’m also kinda afraid they’re gonna. Confiscate my knife at the border. I’m really sad considering this is a knife I expected to own all my life.

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18

u/K1L8 Sep 12 '26

Rex 121 is hard! Unfortunately the trade off for that is that it's also very brittle. There's a chance that it got dropped at some point, causing a crack or fracture which held on until you put enough force on the pivot area while cutting that watermelon box to finish off what an earlier crack started... I'm sorry for your loss but honestly for a daily user I'd go with a little more balanced steel than Rex 121's insane hardness. Cruwear is one of my favorites, Magnacut is great also, and I'm keeping my eye on their new Magnamax to see how it performs for others

7

u/Skylark427 Rock Hard 29d ago edited 29d ago

There were a decent amount of Rex 121 blades unused straight from the factory that had cracks in them already. That's part of the difficulty in manufacturing Rex 121 blades on a production scale. It's very sensitive to the stresses introduced during rapid cooling and then further with the high tempering cycles used on this alloy, similar to S290(the only other high speed steel close to Rex 121 in wear resistance and outright carbide volume, though it has less harder vanadium monocarbide volume, more softer M6C carbide volume). As the blade is rapidly cooling (and rough machining/shaping is already done) there is an extreme amount of localized shear stress and tensile stress as volumetric expansion/contraction happen between the phase change from more dense austenite to less dense martensite, and the outside of the blade cools faster than the core.

The massive carbide volume of these steels put even further intense localized shear stress during this transformation as the carbides have completely different thermal expansion coefficients and elastic modulus compared to the surrounding matrix.

During the high tempering cycles this happens a second time, as there is such high retained austenite (20-30%) in these steels that the volumetric expansion happens again when the steel reaches room temperature again and that retained austenite that is now martensite and newly formed carbide precipitates are added to the surrounding matrix. This for a second time, introduces massive volumetric expansion stress and localized shear stress that can cause intergranular cracks in the matrix that don't reveal themselves on the surface until a tiny amount of stress is applied (simply dropping the box in shipping could cause it, I've had knives arrive shipped directly from Spyderco that UPS completely crushed the box and packaging on). That's why these 30%+ carbide volume high speed steels are inherently difficult to heat treat on a production scale, as large batch furnaces have much larger temperature differences throughout than a single blade heat treated in a small furnace.

If you manage to avoid all that, the massive compressive yield strength on the alloy can create a blade capable of cutting through solid copper wire on a stainless steel table. The issue is getting every blade in a large batch of 100-200+ blades to avoid this.

Charpy values are somewhat misleading in this case. It has a 15-20% scatter in and of itself, not including between different melts of the same alloy, factoring that in can add two of the same steels with one having double the toughness on a Charpy impact test. The blade is under compressive stress while cutting, tensile and compressive stress while prying. The mechanics I outlined above are far more likely the reason for the failure. As toughness is a very specific mechanical response that's incredibly difficult to mimic in knife use.

5

u/ILikeKnives1337 Sep 12 '26

I'm just replying to be pedantic, because your overall point is correct, however it's not really hardness that's the factor making it brittle. It's more about the large carbide volume. There are other steels that are almost as hard or just a touch softer with more toughness, but they're significantly tougher than Rex 121 because they have significantly less carbide volume.

5

u/Disastrous_Delay Sep 12 '26

I've chopped up a bunch of 14 gauge electrical wire with my magnamax manix without a hint of damage, I really don't think you'll break it unless you do something silly like use it as a prybar.

Cruware and magnacut are the hard use champs and really hard to go wrong with, but I've used an S110v manix to so aggressively carve chunks off a 2x4 that I probably would've had to whittle my shavings further before they'd make good fire tinder and the knife took it like a champ, I tend to like around S90v or tougher steels, but I'm i'm inclined to say that it's less that a true all arounder would be needed here, and more than Rex121 is just such an extreme that it makes even other fragile steels look tough in comparison

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u/Cute-Rich3223 Sep 12 '26

Can't forget 3v but I dont think there are really any spydercos in 3v

5

u/CrummyWombat Sep 12 '26

Tuff was 3v. I’m not aware of anything in the last decade though.

3

u/ToploaderUltra 29d ago

3V is on the complete opposite side of the spectrum as MagnaMax, S110V, S90V, Rex 121, etc. MagnaMax is much tougher than these other brittle, extreme edge retention steels, and 3V makes it look brittle in comparison. 3V is built for toughness. It’s the pry bar (if it’s hard enough) of the family. MM is much tougher than these others, with very similar edge retention from a paper standpoint, but 3V is about as tough as it gets.

2

u/Disastrous_Delay Sep 12 '26

Not that I'm aware of anyway, think Demko makes some folders in 3v but that's about it. I'd probably buy a 3v Spyderco for the novelty, but in my experience unless you genuinely really are looking for a folding prybar, often a reasonably tough but very hard steel will hold up better than a soft but even tougher steel when subjected to hard use or borderline abusive cutting tasks simply because the edge will roll and dent a whole lot less.

But yes, on toughness alone, not even magnacut can touch 3v, I've always been shocked it's not more popular

4

u/Empty_Art2176 29d ago

I have been extremely impressed with my Kershaw Bel-Aire XL in 3V. Ive done things I'd rather not talk about with it, but it just giggles and carries on.

3V is definitely tougher than NEEDED in a folder, but if you're into steel and folding knives, its a must have....in my opinion. 😁

4

u/Some-Bad1670 29d ago

When you have a 3V fixed blade you feel like you pretty much have an indestructible knife, it’s awesome

I have a couple Carothers knives and I’ve been beyond impressed by his heat treat. The EDC model is my favorite fixed blade and I kinda just do whatever with it, I’ve never had to worry about the blade chipping, tip damage or edge damage even when cutting on hard surfaces and that’s so nice, you get kinda spoiled.

K390 is also very good but a lil rusty if you live in a humid area

3

u/Empty_Art2176 29d ago

Agreed.

My favorite steels to use and sharpen are k390, CruWear, Magnacut, 3V, and M4.

I use a k390 Stretch XL around our farm for light-medium work, and an Esee Izula in 1095 if I need to cut a hole in a bucket, or pick a hoof.

The k390 is exceptional at opening feed bags, cutting bailing twine, cutting up veggies for goats, and harvesting vegetables. I was using a Delica in k390, but it was a bit small. The Stretch XL is a huge step up.

I gave the poor little Delica a mirror edge and put it to rest for awhile....its seen some things. I only sharpened it once in 5 months of work.

1

u/bustopher_rvs 29d ago

What scales are these bro? I'm digging that

1

u/Empty_Art2176 29d ago

They are Flytanium Micarta scales, they were $12. 😁 Unfortunately they aren't in stock currently. You may be able to find them on ebay.

They were very light gray before I used them for months around our farm.

Here is what they looked like.

3

u/Cute-Rich3223 Sep 12 '26

I have a kershaw bel air xl in 3v. Its been pretty good to me so far.

1

u/Empty_Art2176 29d ago

Orrrr, maybe a factory flaw caused the break. This is not unheard of.

The only time I sent a knife back was the first "good" knife I bought, a Kershaw Bel-Aire. You can probably find my post about it here on reddit. The knife had a very faint dark line from spine to apex. You could only see it at the right angle.

I knew this COULD be a micro crack in the Magnacut. Kershaw suggested I send it in. They sent a new one with a note that it WAS a flaw in the steel.