Refined Cast Steel
London Spring Steel
Refined London Spring Steel
Extra Refined London Spring Steel
The Real Deal on Steel
Before the 20th century, the secrets of steel making were closely guarded by the few who had learned it over years of apprenticeship. The chemistry of metalurgy was not understood or taught in schools of engineering. Instead it was a form of alchemy and the whole process was give a mystical aura that served to protect jobs and keep prices high.
Andrew Carnegie's corporation, United States Steel, led the way to automation of the steel industry, shifting control of steel manufacturing away from the worker and over to the company. The science of metalurgy was developed, and processes became predictable and repeatable.
Henry Disston approached steel making in much the same way, first making saws from steel he had made himself. There was no significant amount of steel being produced in the United States prior to the 1850's, and no saws were being manufactured with steel that did not come from Great Britain. The opinion at that time was there was no good steel produced in the U.S., so even if an American tried to produce steel, it would be hard to sell. Disston began rolling steel in 1855, but didn't advertise it until after the Civil War broke out in 1861. High tarrifs on foreign steel made domestic production a necessity. Because Disston was already in the business, he was poised to sell goods and war materiel made from his own steel.
I had five Disston saws analyzed to find the elements contained in the steel and had the hardness tested. I had expected to finally see what the difference was between the No. 7's Cast Steel, the D-8's Refined Cast Steel, and the No. 12's London Spring Steel. A "one-son" No. 4, 10-inch backsaw from the period 1865-71 was tested to learn about the early Disston saws, and a D-23 from the early 1950's was checked to see what the last "real" Disston saws were like. The No. 7 and D-8 saws were manufactured between 1917 and 1928. The No. 12, 22-inch panel saw was made between 1893 and 1917. All dates are based on the saws' medallions. The results are shown below:
|backsaw||1.343 %||0.1862 %||0.3877 %||0.1656 %||0.0436 %|
So what is the difference between the steel in a No. 7, a D-8, a No. 12, and a D-23? In a word, nothing. In general, the saws were made from medium-carbon steel with little, if any, alloy. The result of using such a simple steel is low production cost and a saw plate with small carbides that are less likely to create a brittle saw.
The chemical elements found in significant amounts in the saws are as follows: carbon; silicon, which is the result of a step in the steel-making process; manganese, also part of the processing; chromium, found only in the 1950's D-23 saw; and nickel, also found in the D-23 saw. Other elements found in insignificant, residual levels in the saws were: phosphorus, sulfur, selenium, alumuminum, copper, cobalt, titanium, vanadium, molybdenum, tungsten, tin, arsenic, niobium, lead, selenium, tantalum, and boron.
The level of chromium found in the post-WWII model D-23 is not sufficient to suggest it was added to the steel for any purpose. This is even more the case for the other saws with even lower levels of chromium. It was probably a residual element from the scrap that was used by Disston to produce the steel. The nickel level in that same saw is possibly an intended alloy that would give a higher level of wear resistance. Another possibility to consider is that it may be, like the chromium in this saw, a residual element that came in the scrap. Chromium and nickel are alloys which can be added to steel at much higher levels, a composition of several percent each, to produce stainless steel, which these saws obviously are not.
The old backsaw (1865-71) has a high level of carbon, probably too high. It is worth noting that this saw was brittle and the teeth broke easily when I tried to sharpen and set teeth on it. The saw now resides on display and is not in use. It also proved to be the softest of the five saws, despite the brittleness, as shown below:
|model||backsaw||No. 7||D-8||No. 12||D-23|
The saws with multiple values for hardness were hardest in the area under the handle, and softest in the area close to the teeth. As can be seen, the No. 12 saw with London Spring Steel is no harder than the other handsaws. In fact there is no pattern or significant difference in hardness between the saws, with the exception of the old backsaw. If the backsaw had been made as hard as the other saws, it likely would have broken in use, since, as noted before, the teeth were too brittle to set as it is.
My conclusion, based on this limited but reasonable sampling of Disston saws, is there was no significant difference between the models with regard to steel, and that the naming of four or five different grades of steel was strictly a marketing ploy. Chemically they are all the same: medium carbon steel with little, if any, intentional alloy. The only exception is the early backsaw. Because of limited scientific method used in steel production in the 1860's, it's reasonable to expect to find inconsistancy and inferior quality, as decribed earlier. Perhaps the only other test that could be done would be microscopic analysis of molecular structure to see if there were any differences in the processing of the steel used in the various models. I doubt that was the case, since greater improvements in steel at lower cost would have been realized with the introduction of alloys than by constantly varying the process for each batch of steel.
-- Thanks to the chemistry lab at Crucible Specialty Metals, Inc. in Syracuse, New York and Mike von Sneidern for assistance in obtaining the data for this article.