52100, how do I reach max hardness without chipping?

DeadboxHero

DeadboxHero

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Getting deeper into 52100,

Two hunting blades of 52100 with different heat treatment protocols but with the same hrc of 65.

One of them is tougher, why?

How does a knife stay tougher then another at the same hrc?

Is it normalizing the steel before austenizing?
Soak time?

What are the variables?
 
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Edge geometry could play a significant role.
 
Grain size can play a pretty decent role in how tough a steel is. Smaller the grain, the better. You mentioned two different heat treat protocols. OK, let's take a blade in 52100 that has been normalized, but not thermal cycled, and goes to hardening and comes out at 67HRC. Take another blade, 52100, normalize AND thermal cycle, harden and quench, and it also shows 67HRC. But the thermal cycled blade, due to it's smaller grain size because of the cycling it underwent, will be a bit tougher.

Another possible situation you may run into (guys check me on this...I believe this is correct but would like some verification or correction if needed) to get a tougher blade but identical RC values for both. Take two 52100 blades that have been normalized and cycled or whatever, they have received the same treatment thus far. But one is hardened at 1575°F, the other hardened at 1475°F. The 1475 blade comes out 67HRC, the 1575 blade comes out 65HRC....but ALSO saw a sub zero treatment, which brings it back up to 67 after the ice bath. Both blades are now 67, identical, but the one hardened at 1475 will be tougher, more towards lathe martensite than plate. The 1575/sub zero blade will have "too" much carbon in solution, and it's plate martensite matrix will be more brittle.

But your question posed in your subject line, "How do I reach max hardness without chipping?", is kinda difficult to answer. For me anyway! Let's see, max hardness out of quench with 52100 is going to be 67HRC or thereabouts. Can you use that as quenched hardness without chipping? Well, maybe a dedicated protein slicer in the kitchen....maybe. Max WORKABLE hardness without chipping is still pretty difficult to nail down, because of the variables in what is being cut, cutting technique, probably more variables that I can't recall immediately. I would say max working hardness with 52100, general use not babying the blade, maybe 62 or 63HRC. That is just an opinion from the peanut gallery here, and the max working hardness for 52100, may vary a bit.
 
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samuraistuart said:
Grain size can play a pretty decent role in how tough a steel is. Smaller the grain, the better. You mentioned two different heat treat protocols. OK, let's take a blade in 52100 that has been normalized, but not thermal cycled, and goes to hardening and comes out at 67HRC. Take another blade, 52100, normalize AND thermal cycle, harden and quench, and it also shows 67HRC. But the thermal cycled blade, due to it's smaller grain size because of the cycling it underwent, will be a bit tougher.

Another possible situation you may run into (guys check me on this...I believe this is correct but would like some verification or correction if needed) to get a tougher blade but identical RC values for both. Take two 52100 blades that have been normalized and cycled or whatever, they have received the same treatment thus far. But one is hardened at 1575°F, the other hardened at 1475°F. The 1475 blade comes out 67HRC, the 1575 blade comes out 65HRC....but ALSO saw a sub zero treatment, which brings it back up to 67 after the ice bath. Both blades are now 67, identical, but the one hardened at 1475 will be tougher, more towards lathe martensite than plate. The 1575/sub zero blade will have "too" much carbon in solution, and it's plate martensite matrix will be more brittle.

But your question posed in your subject line, "How do I reach max hardness without chipping?", is kinda difficult to answer. For me anyway! Let's see, max hardness out of quench with 52100 is going to be 67HRC or thereabouts. Can you use that as quenched hardness without chipping? Well, maybe a dedicated protein slicer in the kitchen....maybe. Max WORKABLE hardness without chipping is still pretty difficult to nail down, because of the variables in what is being cut, cutting technique, probably more variables that I can't recall immediately. I would say max working hardness with 52100, general use not babying the blade, maybe 62 or 63HRC. That is just an opinion from the peanut gallery here, and the max working hardness for 52100, may vary a bit.
Click to expand...

Whoa, thanks bro.

May I ask more about,
Thermal cycling?

Plate and lathe martensite?

Also, I wasn't aware of the cryo increasing the hardness, I thought it just removed the Retained Austenite.


Thanks Samurai
 
Disclaimer....NOT a metallurgist here! VERY EXTREMELY limited knowledge. I'm just trying to get this kick started for ya!

Thermal cycling. Performed after a normalizing heat, mainly to reduce grain size. Example:
Normalize: 1650 then air cool
Thermal cycle: 1550 air cool or quench
Thermal cycle: 1450 air cool or quench
Thermal cycle: 1350 air cool or quench
Austenitize: 1475 for 10 minutes, quench

Some smiths may not do the reducing heats each cycle, like follows:
Normalize: 1650
Thermal cycle: 1475
Thermal cycle: 1475
Thermal cycle: 1475
Austenitize: 1475 for 10 minutes then quench

Plate martensite is different from Lathe martensite. I forget the cutoff point, I think it's around .7% carbon in solution. The martensite formed with carbon in solution < or = .7% is lathe martensite. The martensite formed with carbon in solution > .7% is called plate martensite, and is a more brittle form than lathe.

Cryo is liquid nitrogen temperatures, like -300°F or whatever it is. Dry ice/alcohol slurry is probably better termed "sub zero".....just for our sake talking here. I think Jay Fisher will use the term "shallow cryo" for a dry ice/alcohol mix (-100°F). Just so there is a distinction, because the two are different. I'll be discussing sub zero dry ice/alcohol here, not LN. If you quench 52100 and you reach max hardness out of the quench, then the sub zero treatment will not add RC points. If your blade reads 67 or so out of quench, then a sub zero treatment is not going to make it 69. What it does is help convert most of the retained austenite over to untempered martensite. This is desirable when making knives and you're wanting as much martensite as possible. I go with that theory myself. Some guys, who make larger choppers, may actually DESIRE some level of retained austenite, because it does add some bit of toughness to the blade. Not the edge apex, however, but the blade. Retained austenite is not good for high apex stability. But when a smith quenches, let's use 52100, using lower aus temps and soak times, retained austenite is going to be pretty low, so low that sub zero isn't going to do much. However, if the goal is MORE carbon in solution, you use the higher temperatures. So when you quench 52100 at 1575, you will not reach max hardness, at least to my understanding. Going that high will actually drop you a point or two. So then a sub zero would be a good idea, to help bump up the hardness from 65 to 67, mas o menos.
 
Stuart, I have heard that for stock removal, you probably need to include a 1750 initial cycle to break up the spheroidal carbide thingies.
samuraistuart said:
Disclaimer....NOT a metallurgist here! VERY EXTREMELY limited knowledge. I'm just trying to get this kick started for ya!

Thermal cycling. Performed after a normalizing heat, mainly to reduce grain size. Example:
Normalize: 1650 then air cool
Thermal cycle: 1550 air cool or quench
Thermal cycle: 1450 air cool or quench
Thermal cycle: 1350 air cool or quench
Austenitize: 1475 for 10 minutes, quench

Some smiths may not do the reducing heats each cycle, like follows:
Normalize: 1650
Thermal cycle: 1475
Thermal cycle: 1475
Thermal cycle: 1475
Austenitize: 1475 for 10 minutes then quench

Plate martensite is different from Lathe martensite. I forget the cutoff point, I think it's around .7% carbon in solution. The martensite formed with carbon in solution < or = .7% is lathe martensite. The martensite formed with carbon in solution > .7% is called plate martensite, and is a more brittle form than lathe.

Cryo is liquid nitrogen temperatures, like -300°F or whatever it is. Dry ice/alcohol slurry is probably better termed "sub zero".....just for our sake talking here. I think Jay Fisher will use the term "shallow cryo" for a dry ice/alcohol mix (-100°F). Just so there is a distinction, because the two are different. I'll be discussing sub zero dry ice/alcohol here, not LN. If you quench 52100 and you reach max hardness out of the quench, then the sub zero treatment will not add RC points. If your blade reads 67 or so out of quench, then a sub zero treatment is not going to make it 69. What it does is help convert most of the retained austenite over to untempered martensite. This is desirable when making knives and you're wanting as much martensite as possible. I go with that theory myself. Some guys, who make larger choppers, may actually DESIRE some level of retained austenite, because it does add some bit of toughness to the blade. Not the edge apex, however, but the blade. Retained austenite is not good for high apex stability. But when a smith quenches, let's use 52100, using lower aus temps and soak times, retained austenite is going to be pretty low, so low that sub zero isn't going to do much. However, if the goal is MORE carbon in solution, you use the higher temperatures. So when you quench 52100 at 1575, you will not reach max hardness, at least to my understanding. Going that high will actually drop you a point or two. So then a sub zero would be a good idea, to help bump up the hardness from 65 to 67, mas o menos.
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Stuart explained it well in technical terms.

To put it into plain terms - Two blades done by different HT regimes but being the same hardness can be as dissimilar as two women both weighing 120 pounds can be.
 
Kevin cashen worked the spheroid carbide problem when it first reared its head with Aldo's 52100. His recommended normalizing heat was 1650f. I'll go to 1750f normalizing CFV. Not that it needs it for stock removal really I just do it. I've used 1650 since his recommendation on 52100 and get excellent results. He also said it was 1750 area heat when grain growth starts to be of concern with 52100.
 
DeadboxHero said:
Getting deeper into 52100,

Two hunting blades of 52100 with different heat treatment protocols but with the same hrc of 65.

One of them is tougher, why?

How does a knife stay tougher then another at the same hrc?

Is it normalizing the steel before austenizing?
Soak time?

What are the variables?
Click to expand...

To answer this we'll need more info. What heat treating procedure did you follow? What did you do to determine one chipped and one didn't? How sure are you that both were tested the same? How close are the edge geometries to each other?
 
I may have got the numbers mixed up from those two. Did the 1750F number for the CFV come from Adam?
samuraistuart said:
Kevin cashen worked the spheroid carbide problem when it first reared its head with Aldo's 52100. His recommended normalizing heat was 1650f. I'll go to 1750f normalizing CFV. Not that it needs it for stock removal really I just do it. I've used 1650 since his recommendation on 52100 and get excellent results. He also said it was 1750 area heat when grain growth starts to be of concern with 52100.
Click to expand...
 
me2 said:
To answer this we'll need more info. What heat treating procedure did you follow? What did you do to determine one chipped and one didn't? How sure are you that both were tested the same? How close are the edge geometries to each other?
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There are no knives. I just wanted to understand the metallurgy.
I'm working on a heat treat oven now.

Soon.

Thanks for all the info guys
 
Adam Desrosiers use O1, CruForgeV, 52100 at 62HRC+ on his chopper many times.

I ask him about the process, he replied that after normalizing and rough grind, you need to do the pre-quench and double 1250F stress relive then heat in molten salt at 1475F, air cool. Heat to 1475F in salt and quench in oil then temper in low temp salt again. Temper in low temp salt at 350F for 2 hours, water quench and 325F for another 2 hours.

He suggest that he can't achieved the result without high-temp and low-temp salt equipment. I guess the super precise control and quick equalizing temp are the key.
 
Stuart gave very sound and detailed explanations, i couldn't add anything.
As John pointed out, to compare different treatments we need 2 thin and sharp blades, with the same geometry, as 2 axes may not readily show subtle differences in their heat treatment.
 
DeadboxHero said:
There are no knives. I just wanted to understand the metallurgy.
I'm working on a heat treat oven now.

Soon.

Thanks for all the info guys
Click to expand...

Not trying to be hard on you, but you are just wasting people's time when you post a thread asking specific metallurgical info on a comparison of two knives that do not actually exist. Make-believe isn't what we do here.


The info you got will help with HT, but not with building a HT oven. What helps with HT is repeating the process many times and keeping good records.
 
JDM....yes, sir. Adam suggested 1750°F with CFV. I was using 1650°F, ala 52100, he suggested higher for the CFV. He also mentioned that CFV doesn't like to be below 60-61. 1510°F was his aust temp, IIRC. I use 1490°F.

"He suggest that he can't achieved the result without high-temp and low-temp salt equipment". Not sure what is meant by that.
 
Stacy E. Apelt - Bladesmith said:
Not trying to be hard on you, but you are just wasting people's time when you post a thread asking specific metallurgical info on a comparison of two knives that do not actually exist. Make-believe isn't what we do here.


The info you got will help with HT, but not with building a HT oven. What helps with HT is repeating the process many times and keeping good records.
Click to expand...

Understood.
 
I have never used CFV for stock removal so it always gets that hot anyway. :D Likewise, I have used the old 1500F/400F recipe and that gives about 61Rc. I typically don't leave anything below 60 Rc anyway. That is a fairly good for everything except hand sanding, right? :eek:
samuraistuart said:
JDM....yes, sir. Adam suggested 1750°F with CFV. I was using 1650°F, ala 52100, he suggested higher for the CFV. He also mentioned that CFV doesn't like to be below 60-61. 1510°F was his aust temp, IIRC. I use 1490°F.

"He suggest that he can't achieved the result without high-temp and low-temp salt equipment". Not sure what is meant by that.
Click to expand...
 
Let's rephrase - For a hunting knife in 52100 steel with hardness at 65rc. What is a practical/achievable highest N unit Izod impact?

Note:

1. Seek maximum N IzI unit at 65rc. Where N in either J/m[SUP]2[/SUP] or ft-lb/in[SUP]2[/SUP]. Sub question - will this N satisfy intended/hunting uses?

2. HRC (Rockwell Hardness C-Scale) is a composite/crude scale value(inverse penetration probe depth) to quantify compressive strength. Crude because it's worthless to test a material with porifera structure super hard wall membrance and soft cell. Well, hardened steel has grain; grain boundaries; crystal phases and habit+slip planes.

3. Although edge geometry is super important in practice however we can factoring/leaving it out by standardize/normalize geometry, thereby kept a lot of variables out of the equation.


Optimizing 52100 for N probably involve these key variables:
aust grain; martensite; particle(carbide+); RA; bainite and pearlite.

Practically, 65rc requirement eliminated pearlite variable. RA & bainite must be small volume fraction, otherwise porifera problem with hrc #.

Another big challenge - in order to have a reading of 65rc, strain/disallocation need to be very high, so volume fraction of plate martensite probably will be high, thereby substantially lowering N. Hence minimize % of plate martensite (relative/combine with other variables) can be effective.

With decend ht, we can further simplify by remove particles/carbides from equation, regardless of particle type & size because ~3% aren't signifficant in overall toughness. Specifically, when these particles aren't conglomeated at grain boundaries.

Optimization
*Fine aust grain - it can minimize the damage when the impact force is greater than N. i.e. a small chip instead of a huge half circle chip. Grain size would be proportional to chip size (note: microchip is mostly a cluster of grains). Grain boundaries play important sub-role too.

Reduce plate martensite % in conjunction with RA & bainite %. But there aren't much margin/room to play with

Perhaps, better ask - for hunting (common uses) IzI unit, optimize for max HRC.

:p Feasible 52100 hunting knive: 63-65rc, edge 0.3mm(0.012") thick, 15dps and no chopping
 
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