Thread: How Hard Are The Vintage Blades

The tang/shank needn't be hardened. With the simple steels that are used, differential heat treating is possible. What's important is the hardness and grain size in the cutting edge.

I was wondering when hardness testing first became commonplace in manufacturing processes, because until that occurred I would expect the hardness to vary over a wide range since evaluation of the hardening/tempering process would be solely based on a craftsman's gut feel.

I spent some google time, but didn't exactly find what I wanted. I did run across a document [here] titled "Introduction to Hardness Testing". In the section "Hardness Testing Theory" I found the following statements:

• Early methods generally consisted of scratching. Scratch hardness testing consists of penetration of the material surface by a testing point and bears a close resemblance to the indentation hardness test. One of the earliest forms of scratch testing goes back to Reaumur in 1722. His scale of testing consisted of a scratching bar, which increased in hardness from one end to the other. The degree of hardness was determined by the position on the bar that the metal being tested would scratch.
• In 1822, the Mohs scale of hardness was introduced for minerals and measures the relative hardness of ten minerals.
• In the late 19th century, more attention was paid to hardness and its measurement. Johann A. Brinell, a Swedish engineer, presented a paper to the Swedish Society of Technologists describing his ball test. This rapidly became known as the Brinell test and became universally used in the metalworking industry.
• Because of the limitations imposed by the Brinell method and increased engineering requirements, several investigators intensified their efforts toward devising other indenters, principally those made from diamond, to accommodate the testing of fully hardened steels. In 1919, the Rockwell test was introduced. It has become, by far, the most popular hardness test in use today, mainly because it overcomes the limitations of the Brinell test. The inventor, Stanley P. Rockwell, a Hartford, Connecticut, heat treater, used the test for process control in heat treating.

So, if I had to guess I'd think that the metallurgy gurus in Solingen most likely wouldn't have gotten the quality control of hardness very accurate until the early 1900's... perhaps as late as 1920. As I understand the process, until hardness testers using diamonds became available accuracy was compromised at the values we expect to see for razor steel.

Could this explain why a small sample of razors (2-5) would yield a wide variety of hardness numbers, particularly if some were forged before and some after hardness testing became commonplace?

Great thread. My guess is probably in the range of 60.

The whole discussion on metal and analysis reminds me of an article I read a long while back in Fine Woodworking where they compared chisels from various manufactures. All were modern and from various manufactures. They did a complete set of functional tests ( hone, cut wood, etc. ) and looked at things like edge wear etc. Also they cut them up and looked at things with an electron microscope to check out grain, etc. Hardness was also in the analysis. I think at the end of the day, the steel quality was the overriding differentiator.

This sound about right when thinking about razors, especially from the older types. Good steel makes for a good razor. What make for good steel? I suppose volumns have been written on the subject.

It's true to an extent. You could give me a blank made of best steel ever but you wouldn't want to shave with it after I put it through the grinder. However a good metalworker will also tend to use good steel so it it's a chicken and the egg sort of a question.

This has me thinking. In times the best steel was identified by where it came from. Was this because the had better raw materials there or better know how or perhaps both. ( Again a chicken edd thing. )

Given our technology today, I wonder how much of the quality is due to raw materials and how much is due to technology. I hear the Paki razors are crap because they have inferior steel. Is this because of inferior technology or raw materials or both?

Originally Posted by azjoe

I was wondering ... (clipped)...Could this explain why a small sample of razors (2-5) would yield a wide variety of hardness numbers, particularly if some were forged before and some after hardness testing became commonplace?

An excellent recitation of the history involved. There could be a lot of variation even in one factory. Example: the quench bath starts out cold in the morning and after a session of multiple razor blades is much warmer by the end of the heat treatment session. There should be measurable differences in hardness between the morning and noon and so on. If the company controls the temperature of the quench bath (marquenching) then the blades should be uniform within a degree of uncertainty. Between different factories using differing processes, all bets are off.

I can block up the flat parts on my Rc machine so as to isolate that from the curvature and get a pretty good reading on the hardest part of the edge. I might be able to set up a curved block and get a range of readings from edge to spine. Then a series from toe to heel and the tang.

Whether the tang is hardened depends on a couple things. The hardenability of the steel, e.g. some steels will not harden all the way through and the section thickness and speed of quench determines the end point. The depth of quenching also, e.g., if the tang is not immersed it may not get to full hardness. And, the tempering cycle can reduce hardness after heat treatment. There are some exotic but not impossible methods to refine grain that can contribute to hardness or weakness depending on what is done. Without knowing the rituals done inside the factory, i can't comment much.

Forging will align some grain, but realistically, there is nothing magical about a forged vs. ground blade. All steels must be forged to some shape at the mill, so a non-forged steel really doesn't exist to compare to. The key is in the steel first, and the heat treatment second, with the HT playing a much larger role. A lesser steel heat treated well can hold it's own against the best steel marginally heat treated.

I think I got all the questions.