Brittle blade after tempering

[Jonny C]

Hello! I’m having problems with some 1084 that was given to me, the steel is flat stock and was previously tempered to soft spring, i annealed the steel prior to working with it, once shaped I quenched in warm canola oil and it skated a file, I tempered in my home oven at 425 degrees for two one hour cycles, the blade broke in two when I stress tested it, this is my first broken blade and my first “known” steel blade, very disappointed, any advice would be appreciated, thanks.

[Vern Wimmer]

I would ask about your annealing process. There have been quite a few supposed annealing processes suggested over the years that really weren't. 

My next question would be about what temperature you quenched at and what was your criterion or yardstick for determining when it was proper quenching temp. Did you do any thermal cycles?

You didn't mention if you had made the blade by strictly stock removal or forging. If you did any forging at the wrong temperature it could have caused cracks that led to the failure. It is also possible that whatever use 1084 was tempered to a spring temper, if it was used, might have fractured it.

[MacKINNON]

218 C is a hell of a hard temper on Carbon steels. OK, on differentially hardened blades but I wouldn't want to be bending a 1084 blade that hard.

 

 

Edited January 17, 2019 by MacKINNON

[Alan Longmire]

More importantly, got a picture of the grain at the break?  That will tell you a lot.

[Jonny C]

I’ll try to add some pictures, after questioning my temprature and looking at a tempering chart I used a torch to temper the remaining steel, I got a fairly consistent shade of blue thru the steel but after testing it broke again, and this was just a stock removal and the steel didn’t have any signs of use or wear and tear, i did 3 normalization cycles prior to quench and steel was above none magnetic 

[Jonny C]

Also I annealed the steel by getting it above none magnetic, kept it at that temperature for about 20 minutes then buried it in sand overnight 

[Joël Mercier]

It's not that hard. If you take 80CrV2 as an example, it should not be tempered above 200°c because beyond that is the brittle range. 

I have bent my 1095 and 80CrV2 kitchen blades a lot and no break so far and that's with 375° and 350° respectively. 

From Johnny's annealing technique and the absence of normalization , I suspect massive grain size. 

[Alan Longmire]

That "anneal" is the problem.  What you did was basically cause massive grain growth followed by a lamellar carbide structure.  The large grain combined with segregated carbides made for a blade that would be brittle no matter what.  

Large grain is more hardenable, but it is a weak structure.  The lamellar carbides (which aren't that bad in 1084 since it doesn't have a lot of excess carbon or carbide-forming elements) will make drilling holes difficult. 

If you have any more of that steel left, you can fix it by doing three or four normalizing cycles to reduce the grain size and redistribute the carbides.  This is just taking it to critical (a little above nonmagnetic for 1084) and letting it air cool to black.  Do that three or four times, then do your shaping.  At no point should you let it soak at heat, not even (especially not even) the final quench.  

[Jonny C]

1 minute ago, Alan Longmire said:

That "anneal" is the problem.  What you did was basically cause massive grain growth followed by a lamellar carbide structure.  The large grain combined with segregated carbides made for a blade that would be brittle no matter what.  

Large grain is more hardenable, but it is a weak structure.  The lamellar carbides (which aren't that bad in 1084 since it doesn't have a lot of excess carbon or carbide-forming elements) will make drilling holes difficult. 

If you have any more of that steel left, you can fix it by doing three or four normalizing cycles to reduce the grain size and redistribute the carbides.  This is just taking it to critical (a little above nonmagnetic for 1084) and letting it air cool to black.  Do that three or four times, then do your shaping.  At no point should you let it soak at heat, not even (especially not even) the final quench.  

So I should just do the normalization cycles rather then “annealing”? There’s a lot of information online and YouTube (which has been my source for information) where people are burying steel in sand or cat litter to anneal, this isn’t accurate?

[Cody Killgore]

You can anneal like that; but, like alan mentioned, you can end up creating some carbide sheets and such in your steel that can give you an issue drilling holes. Personally, I would just normalize a few times.

Your big issue was not the fact that you annealed, but that you held the steel above critical temperature for an extended period of time. This causes massive grain growth. If you were going to anneal that way, get it above critical and then immediately stick it in your sand.

[Jonny C]

I’ve made a couple knives in the last month from semi truck leaf springs, which required many hours of forging, and I’m happy to say I ended up with very durable blades, and I simply forged the spring after normalization, guess I should have just stuck with my routine, my first basic stock removal with a known steel and it’s a disaster! Go figure lol

[Alan Longmire]

59 minutes ago, Jonny C said:

So I should just do the normalization cycles rather then “annealing”? There’s a lot of information online and YouTube (which has been my source for information) where people are burying steel in sand or cat litter to anneal, this isn’t accurate?

Yes, just do the normalizing.  The "bury it in sand, ashes, lime, vermiculite, etc." is an old myth that won't go away.  

[Joël Mercier]

26 minutes ago, Jonny C said:

and I simply forged the spring after normalization,

You may want to reverse this process. Forge, normalise, quench. 

[Jonny C]

I normalize before forging and before quench, is that ok to do?

[Joël Mercier]

Don't bother doing it before forging, it's useless.

To be more precise, forge, normalise, grind, quench, temper, final grind.

[Jonny C]

But if I’m working with tempered steel I should normalize it prior to forging, right?

[Alan Longmire]

No need.  Getting it to forging heat erases all prior heat treatment.

[Jerrod Miller]

Also, if you do heavy grinding, an extra normalize after grinding may be beneficial.  I don't think I would go as far as to say "necessary" though.  

[Jonny C]

Oh ok, thanks for the help everyone, it’s hard to weed thru all the info out there, my usual routine is normalize, forge, grind, normalize, quench, temper, finish grind.             Here’s a picture of my leaf spring camp knife, I’ve heard leaf springs aren’t the best for knives but it sure takes a beating and I hacked thru a copper pipe without chipping so I guess it worked alright, I’ll post some pictures of the grain in my broken blade so you can verify the fault