Testing the hardness of vintage steel

Ernie1980

Ernie1980

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I collect and use vintage knives, and have often wondered about the hardness of the blades. There is a huge range in hardness that I have observed by sharpening, but I was wondering about a more narrowed-down number. I came across a file set where you test the files on the metal and get an approximate value of its hardness. Has anyone used anything like this? If so, how well does it work?
 
Earnie, I'm not familiar with the files but I can give some historical background. The Rockwell scale and testing equipment wasn't invented to the 1910s and it was used in knife manufacturing much later. So there are no Rockwell numbers used in early manufacturing.

This 1907 description of hardening and tempering talks about the color of the heat:

"Hardening is effected by bringing it to a red heat and dipping it in water up to the choil. The tang is left soft, so it may be readily filed, drilled, stamped with the maker's name , and fitted in the handle. Tempering is often accomplished by bringing the blades to a purple heat on a thin copper plate..."

Here's an excerpt from a hundred year old article on Remington:

"After the blades are pierced, making ready for the rivet, they are forwarded to the Heat Treatment Department where they are hardened and tempered... Men who are able to perform this work day in and day out, producing a high uniform standard, are rare birds. The long experience of the Company in hardening and tempering gun parts, bayonets and other like products has been utilized to the utmost in this process. This room is screened so the light is very evenly diffused daylight in order that the operators may easily judge the color of the metal. After the blades are hardened and tempered they are tested and straightened. In order to test the blades for flaws, each one is thrown against a block of steel. Blades which do not ring true are rejected."

This very basic article from the "Associated Cutlery Industries of America" in 1950 still describes the color of the heat but also gives a temperature range....

"Whereas originally temperature of heat was determined by the color perception of the workman, and his judgment alone determined the temperature of the quench, these are now determined without the hazard of human judgment by precision instruments known as pyrometers, with resulting uniformity in hardness obtained...."
 
IIRC there was a topic about this several years ago here in Trads.

In the former days they used to check out the hardness by a file and a wire. The wire was of not known hardness - while the file was known of its hardness.

... Now my memories are fading away. I can´t remember the procedure how the hardness was checked or even listed. But that was out of the HR-C register.

Well - maybe some of the more wise memebers here lnow about the procedere.

There was a series of knives made by Queen, at the S&M brand there was a "File and Wire Tested" series of knives being made.

As I stated before... all memories from a long time ago.
 
Humppa has it correct except the wire used was of a known hardness so the blade could be tested by cutting thru the wire without leaving a "dent" in the edge. I am assuming that the files of that time were all pretty close as to there hardness but anyway they should be harder than the blade and should mark it. To assure the blade wasn't to soft or to brittle.

Dave
 
Thanks for the background information!
The file set I was talking about sounds similar to the method you mention Dave- files of known and various hardness are tested on the unknown piece of metal to see which will leave a mark. That is great background information about the file and wire series name:)
 
I have used the file hardness testing set working as a machinust. It works alright for an estimation. However, I doubt it will get you to where you want to go. If I remember correctly, they are spaced in increments of 5. 40-45, 45-50, 50-55, 55-60, 60-65 RC. The problem is that most of these knives seem to range from 54 rc to 58 rc. A typical high quality mill file is about 55 rc. So I just use the file. Then you can guesstimate the hardness relative to the file about as accurately as the special set. And most people already have a file on hand.
 
One thing to keep in mind is that the tang may not be a good place to test if it is left soft or annealed. I also wonder if old knives that have been resurfaced have been ruined. The old catalogs made a point of not "burning" the blades during grinding. And some of the knives on Ebay have been resurfaced considerably.

1907 Schatt & Morgan catalog
Grinding Department: Here is where all blades in our knives are ground. We say without hesitation this is the finest grinding room in America. Perfect light, perfect ventilation, grinding troughs of our own design and make, insuring absolute safety for our workmen. Surrounded by the most perfect arrangements we are enabled to secure the most skilled workmen in the trade, consequently, our blades are always properly ground, and never burned in this operation. Another reason why we can GUARANTEE UNCONDITIONALLY - we know they are right.

Tempering Department: The original method of tempering was on a copper plate. Then the operator's eye was the whole thing. If his eyesight was poor one day, that was the day we had poor blades. With our modern gas tempering furnace, that is all changed. The blades are submerged into hot oil, the furnace sealed, and heated to a certain degree of temperature, and the work is done, every blade is of the same degree of hardness, the same today, tomorrow, or at any time. One reason we can GUARANTEE UNCONDITIONALLY - because we know they are right.
 
any of these methods would mark the blade, as that is how they work, right? I suppose if the knife is already a scarred veteran it might not be an issue, but i would be careful before i decided to do this to a pretty knife.
 
I was thinking about how you would want to avoid the tang based on your above article! And yes, lots of knives on the bay have been cleaned (some to the point of ruin) by someone. I wish that sellers would just let them go as found and let the final owners decide how to clean them.
 
knowtracks said:
Humppa has it correct except the wire used was of a known hardness so the blade could be tested by cutting thru the wire without leaving a "dent" in the edge. I am assuming that the files of that time were all pretty close as to there hardness but anyway they should be harder than the blade and should mark it. To assure the blade wasn't to soft or to brittle.

Dave
Click to expand...

wonder if thats true, or if it still applies :eek:
 
It was not a correction Humppa just a clarification! :D
Great Info supratentorial!! :cool:
We must be thinking of a different Rockwell grade of testing jmarston....I believe most carbon steel knives are about 59 to 61 on a Rockwell C grade and a file is much harder than that. o_O BUT I have been wrong before....I think...:(;)
No Way Jack!! Not with all the tech we have today. ;) Just the selling hype they use. :eek::D



Dave
 
knowtracks said:
It was not a correction Humppa just a clarification! :D
Great Info supratentorial!! :cool:
We must be thinking of a different Rockwell grade of testing jmarston....I believe most carbon steel knives are about 59 to 61 on a Rockwell C grade and a file is much harder than that. o_O BUT I have been wrong before....I think...:(;)
No Way Jack!! Not with all the tech we have today. ;) Just the selling hype they use. :eek::D



Dave
Click to expand...
I believe a lot of the carbon steel blades are closer to 54-58, just from memory, knarfeng knarfeng would be way more versed on these things.
 
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I have heard that most makers shot for around 55 or maybe a bit higher, but would love to hear from someone who has tested any!
 
I think anything much above 58 would be brittle and prone to chipping, with carbon steel.
 
knowtracks said:
Yes! knarfeng would know!! :thumbsup: But a file still has to be WAY harder than 55rc ;)

Dave
Click to expand...
From what I remember reading, the HRC tests require a perpendicular surface for testing, so ground blades with their inherent angle eliminate an accurate reading, because the equipment could not deal with these angles. Annealed tangs also impede accurate testing. 54-56 RC was a good range to shoot for, and the cutler that could get consistent results near 58 had to be really on their game, or the blades would be too hard and chip or tips would snap off easily. Schrade had some of the best and most consistent carbon steel blades back in the day, and I think they were more towards the 58 end of the scale...all of this is from old memory, and to be taken with a grain of salt, and a shot of tequila ;) it's pretty hard or impossible for an average guy to test accurately for blade steel hardness. There are too many obstacles in the way...
 
Ernie1980 said:
I collect and use vintage knives, and have often wondered about the hardness of the blades. There is a huge range in hardness that I have observed by sharpening, but I was wondering about a more narrowed-down number. I came across a file set where you test the files on the metal and get an approximate value of its hardness. Has anyone used anything like this? If so, how well does it work?
Click to expand...

It's a pretty approximate method. The files in most file sets are 5 points apart. So, the result you will get from them is on the order of "harder than 55 but less than 60." ±5 points is a pretty wide gap for cutlery. A couple of points can make a noticeable difference in cutting performance. The file test method is technique sensitive, too. Results are dependent to a certain extent on how much pressure you use.

knowtracks said:
It was not a correction Humppa just a clarification! :D
Great Info supratentorial!! :cool:
We must be thinking of a different Rockwell grade of testing jmarston....I believe most carbon steel knives are about 59 to 61 on a Rockwell C grade and a file is much harder than that. o_O BUT I have been wrong before....I think...:(;)
No Way Jack!! Not with all the tech we have today. ;) Just the selling hype they use. :eek::D

Dave
Click to expand...

Your numbers are too high. Most "carbon steel" runs from the middle to high 50's, depending on the manufacturer. It's true that carbon steel can be hardened to a max of something like 64, but to my knowledge only a few custom makers run it at 60 or above.

I've heard reports that Case CV, which is kissing cousin to a true carbon steel, is run at 58, but I can't confirm it.
Camillus used to run their 0170-6c, another kissing cousin, at a nominal 58.
Ka-Bar runs their 1095 Cro Van at a nominal 57.

One of the our makers, whose name escapes me at the moment, performed Rockwell testing on some pocket knives made in the 1940's. He reported surprisingly low hardness numbers. If memory serves he said they were in the mid-40's.
 
Standard Rockwell testers require the sample to have a parallel top and bottom.
I've been told, that there are micro hardness testers that can bypass that requirement. Don't know. Never actually seen such a machine.
 
I can tell you most older knives (I'm talking roughly 50's or older) that I've tinkered with are easier to file a sharpening choil and remove metal in general. The difference is sometimes huge, actually. You can remove good sized chips in seconds flat with a coarse silicon carbide stone on a lot of the old knives. It's really nice, and SO quick and easy to get them to a very high level of sharpness. Also it's nice as they are easier on files, and you can no longer buy newly USA made files, so they need to last.

Not specific or scientific of course but I find it interesting.
 
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