A lot of confusing and not quite accurate stuff in this thread. The straight facts:
London Spring Steel was not marketing hype. It was, in fact, steel that was made in England, mostly Sheffield. Before Henry Disston figured out a way to make cast steel in volume in 1855, all steel that could be used for cutting, saws included, was made in England. That is not to say that there wasn't some backwoods tool maker that took a piece of wrought iron, sealed it in an iron box with some toe nail clippings and saw dust and burned it in the fire for days to get the carbon in the box to migrate into the steel. That did happen, but the result was highly variable. The folks in Sheffield had it down pat, and so all the steel in those early days was made in England.
So it went until Disston figured out how to make crucible steel in volume in 1855. He patented it, produced it, and even successfully lobbied Congress to impose a tariff on tool steel coming into the country (what's old is new again) to allow domestic production to flourish. It did. At that point, Disston continued using the name "London Spring Steel" as that was what the discerning customer was used to at the time. Just as McDonalds today would not change the name of their Big Mac sandwich to Jimmy's Funk Burger if the company sold, so too did Disston realize the importance to keep the name of London Spring Steel associated with the Highest Quality Saws he made. The other saws like the #7 and other did not sport this name, and were also the stuff he made, just without the distinction.
Spring Steel today still means something, it is not marketing hype. Spring Steel is steel which is hardened, and nominally used to make, among other things, springs. It is typically regular carbon steel with between .75 and 1% carbon added, and then tempered. Can you anneal spring steel and reharden it? No, not really. The steel is so thin that the act of heating it up in atmosphere and then quenching and drawing it would burn most all the carbon out of it which is what makes it useful for holding and edge in the first place. Spring steel is not expensive or hard to find. I have 100s of pounds of it in my basement. I would never consider reworking a blade that is kinked, I would just drive the old blade off the back, cut a new one and reassemble.
Finally, there are many different kinds of scales involved in steel hardness testing. The two major ones are the Superficial and the Normal Scale. The most common type of tester was made by Wilson. They made stand alone units that just measured on the normal scales (includes A, B and C which is the one most people recognize). They also made a unit that just tested the superficial scales among which are the 15N, 30N and 45N scales. They also made a unit called a Twin Tester which allowed testing of both scales in one machine. That is the unit I have. The deal is that with thin pieces of steel, the diamond indenter can actually poke through the sample which distorts the reading. That is why those scales use a reduced weight to drive the indenter only "superficially" into the sample, hence the name. The 15N, 30N and 45N represents the kilograms of force needed for the test. The Rockwell C test uses a full 150 kilograms of force. There are conversions to translate superficial readings into normal readings if needed.
Hope this helps. I've attached a picture testing the hardness of a pure lead ingot. In this case, I used a 10mm steel ball and didn't use the scale at all as the hardness is calculated from the diameter of the resulting depression and the force applied. It is a very handy tool for many uses.
Attachment 380564
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Originally Posted by Pete Taran
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