Cryo for steel is useless??

[Thomas Linton]

A stainless Mora (I'm not sure if you are familiar with those) is usually about 10-12% RA and they are really tough blades. But they are used almost as pry-bars as cutting tools.

I have never seen any MORA that I thought of as a pry-bar, but all the broken blades on folding knives testify to such use - regardless of suitability.

 

[Razorsharp244]

I have never seen any MORA that I thought of as a pry-bar, but all the broken blades on folding knives testify to such use - regardless of suitability.

I have never considered using Moras as prybars either.

But here in Sweden Moras are used as disposable knives by carpenters, construction workers, electricians and so forth. These people abuse these knives alot. Opening paint buckets, scraping of paint, cutting copper wire and other kind of knife-unfriendly things.

My point in the previous post is that maybe a general recommendation of 10-15% RA is a bit high. Since the stainless moras with maximum 12% has really high toughness, proven by all this abuse. So maybe going for lower RA, like Larrin does, will increase the edge performance without making the blade brittle. Although decreasing RA will always decrease the toughness tosome extent.

 

[mitchshrader]

and therein lies the question.. microcrystalline precipitated carbides in lattices, mmm. that's not 'less RA' .. that's 'a new thing'.. (at least, a thing with differing properties than simple martinsite)..

what is being claimed almost resembles the claims made for dendritic casting or bulat wootz.. a lattice matrix with tiny carbides held in crystals of greater strength (toughness and wear resistance both) than the UN-crystallized (un-latticed) but chemically identical alloy.

whether the esoteric claim is true, and to what degree it is true, explains some of the properties claimed for all of the above.

this is fairly obviously QUITE DIFFICULT TO QUANTIFY and would vary per each individual knife and according to the quality and the design and the application intended.

so if cryo moves things towards a crystal lattice (even micro crystals).. with tiny precipitated carbides.. then it DOES.. or, if it don't, a microscope will prove it.. (all proper procedures being followed in the analysis) ..

claims that a PARTICULAR cryo treatment adds any relevant strengths are much less defineable than whether ANY cryo treatment works. that it MAY work, I submit, has been proven.. in particular applications with particular desired results and particular methods.. ie, SOMETIMES it works.

that the CLAIM is valid, in any particular case, is another story entirely. i can claim my cryo-treated knife is ninja certified and cuts through armor like butter but that doesn't make it true..

at the metal end, it works sometimes. at the hype end, it works sometimes.

hey, it only took 3 pages to get to 'Maybe'..

 

[Razorsharp244]

and therein lies the question.. microcrystalline precipitated carbides in lattices, mmm. that's not 'less RA' .. that's 'a new thing'.. (at least, a thing with differing properties than simple martinsite)..

what is being claimed almost resembles the claims made for dendritic casting or bulat wootz.. a lattice matrix with tiny carbides held in crystals of greater strength (toughness and wear resistance both) than the UN-crystallized (un-latticed) but chemically identical alloy.

whether the esoteric claim is true, and to what degree it is true, explains some of the properties claimed for all of the above.

this is fairly obviously QUITE DIFFICULT TO QUANTIFY and would vary per each individual knife and according to the quality and the design and the application intended.

so if cryo moves things towards a crystal lattice (even micro crystals).. with tiny precipitated carbides.. then it DOES.. or, if it don't, a microscope will prove it.. (all proper procedures being followed in the analysis) ..

claims that a PARTICULAR cryo treatment adds any relevant strengths are much less defineable than whether ANY cryo treatment works. that it MAY work, I submit, has been proven.. in particular applications with particular desired results and particular methods.. ie, SOMETIMES it works.

that the CLAIM is valid, in any particular case, is another story entirely. i can claim my cryo-treated knife is ninja certified and cuts through armor like butter but that doesn't make it true..

at the metal end, it works sometimes. at the hype end, it works sometimes.

hey, it only took 3 pages to get to 'Maybe'..

Many big words in this post, too many for a simple guy -like me. However since I do occasionally give H/T-advice (Hardening/Tempering) I feel I must make some comments to this.

Precipitated carbides is not the issue here, they do not change with cryo, they are primarly a function of quench speed. Slow quench forms precipitated carbides. Cryo will not affect this.

Actually carbides or carbide structure is not in any way affected by cryo. Only the steel mass (matrix) itself.

Cryo can increase mechanical properties. But it requires more changes to the H/T process than simply adding cryo. So I agree with you saying that it "occationally" works, but "occationally" does in no way mean "random". Cryo works, but only if done right.

The REASON for cryo is however to reduces retained austenite by making it into martensite. Depending on the H/T programme that will be beneficial in some ways and negative in others.

Good for: mechanical properties like hardness.
Bad for: toughness.

Simple yes/no answers are hard to find when it comes to heat treating metals. But "hey, it only took 3 pages to get to 'Maybe'.. [/" is a bit to simplified for my taste.

 

[mete]

You have it mixed up ! Quenching does not produce precipitated carbides !! Quenching produces martensite. When tempering carbides are precipitated. Yes the HT always is a balance between properties .In this discussion martensite with a desired amount of RA for some added toughness.

 

[Razorsharp244]

You have it mixed up ! Quenching does not produce precipitated carbides !! Quenching produces martensite. When tempering carbides are precipitated. Yes the HT always is a balance between properties .In this discussion martensite with a desired amount of RA for some added toughness.

Yes, quenching transforms austenite to martensite (exactly the same way cryo does), but if done too slow it also produces precipitated carbides. And as long as the temp is above 600 deg C it produces precipitated carbides in a hurry.

Tempering also produces precipitated carbides, but since tempering temperature is low (usually less thean 350 deg C) the transition is controlled. I do not have it mixed up.

Since tempering is done after cryo I did not discuss that in this tread.

The more alloys in a steel, the more difficult is the transition from austenite to martensite. This means that cryo has most impact on highly alloyed steels with lots of Cr, Mo, V and such.