Steel or Stupid.....pick one.

L

Lavan

Joined
Nov 8, 2000
Messages
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Okay, I got a new knife coming. It's touted as bein 58-60 hardness. So... is that likely to be closer to 58 or 60? Or ....59?
Is the reason for "ranges" that it is hard to be exact or does the blade test differently in different areas?
Or is it just "playing it safe" with ambiguity?

Now.... for the STUPID.

Why, other than hype, did I order the knife in 154CM at 58-60 rather than 440C at the same 58-60? That seems nuts but feels right.

Am I lost?

:)
 
The answers are:

Unknown.

yes, yes

Why, other than hype, did I order the knife in 154CM
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There's nothing wrong with 154Cm as far as I know. Othwerwise your motives are unknown to probably everyone,including God.

Am I lost?
Click to expand...

yes.
 
The defination for a range means that you expect a high probability to be in the middle and an equal chance to be drift towards either end. In reality, for heat treatment of knives the hardness will drift toward the low end and below becuase heat treating doesn't act like a normal distribution. Pretty much everything you do less than optimal tends to soften the knife and some effects such as austenization stabilization can be really significant. This is why for example if you see a knife cited at 58/60 HRC and ask around for makers who have done hardness testing then the values go as low as 55 HRC but rarely approach 60 HRC.

In regards to precision, the actual ability of a Rockwell testor isn't in the decimal points. You are looking at tolerance of less than one HRC point only with a very well maintained machine and calibrated against high standard reference blocks. Even then you are looking at a significant fraction of a HRC point as the tolerance. The main reason there is a range is because the knives are not individually tested and due to variances in the production heat treating and steel composition.

Note for example that when you look up the composition of a steel there are ranges like 0.65-0.75% carbon and 16-18% chromium. Well if you do the same heat treatment on 0.65/18 you get a fairly significantly difference responce than 0.75/16. The standard hardness quoted in reference books assume an average composition so on an actual sample of steel, even if you did the heat treatment exact right you would expect the variance in the steel composition to effect the results easily that much.

This is why makers like Wilson will HRC test blades during the heat treatment and adjust accordingly, and not assume all the steel is identical, they will also confirm their HRC testors are getting the same results as other calibrated machines, etc.

-Cliff
 
and the answers are
playing it safe
154cm just sounds cooler
hey don't worry it's a cool knife in a good steel, what could go wrong?
later,ahgar
 
This is like worrying if you Chocolate Chip Cookies were made with butter or crisco or butter and crisco.
Taste the cookie and see if it is good.

When you get the knife, cut stuff and see if it is good or not.
 
I always figured that the testers were generally only accurate to +/- 1 point, so that was the best the manufacturers could advertise at without leaving themselves open. Cold Steel likes to use a definite HT value, which I think could bite them in the ass, if anyone cared to pursue litigation over something like that. Of course, Lynn's probably pretty safe from such a scenario.

154CM and 440C will perform differently, even at the same hardness. The difference shouldn't be astounding, but hey, you can use it to justify the purchase :)
 
154CM and 440C will perform differently, even at the same hardness.
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I'll be danged. I was WONDERING why BM would change from 440C to 154CM.

I guessed it was for the hype.

Now....HOW...would they cut differently?

The only reason I selected the 154CM was because I have a 910 in that steel and it takes a bodacious edge. I can get nearly the same edge on Buck's 420HC but it takes much longer and resists it.

For me anyway.
 
Companies don't test the hardness of every knife. So they offer a "range" which you can expect the knife to fall into. Heat treat and steel varies.

Hardness is not the only measure of a blade. 440C at 58 HRC and 154CM at 58 HRC will not perform the same. Even though they are the same hardness, they will wear differently, have different levels of corrsion resistance, different levels of toughness etc... and as Cliff will explain, they have different carbide structures, so they will cut differently.

I believe that (both steels at the same hardness), 154CM will hold an edge longer (it is more resistant to abrasion), but that 440C is less brittle (it is tougher). 440C is more stain resistant, but 154CM has a carbide structure that is superior for push cutting.

Cliff will go into more detail.
 
hardheart said:
Cold Steel likes to use a definite HT value, which I think could bite them in the ass, if anyone cared to pursue litigation over something like that.
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Generally when you cite specificiations they are assumed to be mean values, it is rare for these variations in general to be cited publically aside from research issues. In is also assumed when errors are not given they are implied to be in the last digit. Thus saying 59 HRC states you would never expect to see knives of 49 or 69 HRC but deviations in the 9 are possible and to be expected. If you wanted to say the nine was absolute as well then you would say 59.0 which implies that at most you would see deviations in the decimal place.

Lavan said:
I'll be danged. I was WONDERING why BM would change from 440C to 154CM.
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I would assume because they can sell more 154CM blades.

These two steels are in the same class, high carbon, high wear, stainless steels. 154CM has better heat resistance, higher max hardness, higher wear resistance and a finer carbide structure, though is still really coarse. 440C actually retains as-cast primary carbides and Buck's CATRA data showed it to be outperformed significantly by 420HC. Even though the 440C had better edge retention, meaning the degredation of cutting ability was lower, the initial cutting ability was so poor it was outperformed by the 420HC blade. Many people have critized Buck for "degrading" the product by switching from 440C however they actually do research on steels/geometries and have data which show it was to enhance performance. This is the same type of data which many makers/manufacturers use to argue for the superiority of S30V and you can't of course accept one and rebuke the other.

-Cliff
 
Ya mean my sharpening and Buck's CATRA came to the same conclusion vis-a-vis 420HC vs 440C.

I am so puffed up now I can't stand myself.

:D

imagesdu9.jpg
 
Cliff Stamp said:
Generally when you cite specificiations they are assumed to be mean values, it is rare for these variations in general to be cited publically aside from research issues. In is also assumed when errors are not given they are implied to be in the last digit. Thus saying 59 HRC states you would never expect to see knives of 49 or 69 HRC but deviations in the 9 are possible and to be expected. If you wanted to say the nine was absolute as well then you would say 59.0 which implies that at most you would see deviations in the decimal place.
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Yeah, but if IIRC, Lynn (or whoever writes for him in the catalogs) said he thought the margin of error was just sloppy HT, and CS doesn't do sloppy work, so they can give you the exact measurement that is the same for every knife. This was a while back, haven't looked at a spec plus catalog in a few years.
 
Yes, that is typical sales pitch. Generally you should be fairly skeptical of any information given to you by someone selling you a product unless it has been independently confirmed.

-Cliff
 
What is the percentage difference in hardness between say HRc 58 and HRc 60? Is HRc 58 (58/60) 96.66666666666667 percent of the hardness of an Hrc60 steel or is it a logarithmic calculation of some sort?

And what's the significance, if any, in these deviations?

I didn't realize 440-C was a courser grain than 154CM. I always thought of them as close 1st cousins.
 
Levan -

Good question.

What is the percentage difference in hardness between say HRc 58 and HRc 60? Is HRc 58 (58/60) 96.66666666666667 percent of the hardness of an Hrc60 steel or is it a logarithmic calculation of some sort?

And what's the significance, if any, in these deviations?
 
DGG said:
What is the percentage difference in hardness between say HRc 58 and HRc 60? Is HRc 58 (58/60) 96.66666666666667 percent of the hardness of an Hrc60 steel or is it a logarithmic calculation of some sort?
Click to expand...

http://www.bladeforums.com/forums/showpost.php?p=3950272&postcount=68

And what's the significance, if any, in these deviations?
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As noted in the above post, it is more to do with the other properties that result from the heat treatment which produce that hardness than the hardness itself.

I didn't realize 440-C was a courser grain than 154CM. I always thought of them as close 1st cousins.
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They are, they are both very coarse carbide steels, 440C (45 microns) and 154CM (25 microns). In comparison for example, the low alloy tool steels are sub-micron in carbide size. For knives you also need to consider not just the size of the carbides but the volume and segregation. Some of the P/M's like S60V have an small average carbide size, but there is so much carbide and it is significantly segregated so that P/M S60V has a lower edge stability than ingot 154CM. Both are of course very low, but S60V is lower.

-Cliff
 
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