Self-hardened steel may be annealed so that it can be machined, but it is by no means as soft and ductile as well-annealed carbon steel. Manganese steel has not been annealed at all; it cannot be annealed by any of the well-known annealing processes; some new way of doing it must be discovered. Therefore it is proper to say that the peculiar hardening properties of these two steels are due to manganese.
NICKEL STEEL.
The addition of a few per cent of nickel to mild steel adds greatly to its strength—so much so that nickel steel is now world-renowned as used in armor-plate for navy vessels, and for great guns. Recent reports from the ordnance bureaus indicate that it will also be of great use in the barrels of small arms, by means of which they may be made lighter, and still of sufficient strength. Nickel is so expensive and it adds so much to the cost of steel that its use for ordinary structural purposes, bridges, etc., has not been found to be economical.
Some years ago careful experiments were made with nickel alloy in a fine grade of high-carbon tool-steel to find out whether such steel would be improved as much as are the mild steels.
In such case the expense would not count, for if the best steel can be made better there are many users who would gladly pay a higher price for a better service.
The results were not encouraging. The high-carbon nickel steel was not as strong as the same quality of steel without nickel; the mixture seemed to be imperfect, containing little dark specks, supposed to be carbon thrown into the graphitic state. The steel did not refine as well and was not as strong as the carbon steel.
All of this applies to high-carbon tool-steel, hardened and tempered; no tests were made of the steel unhardened, for they would have been of no practical use.
ALUMINUM STEEL.
When a heat of steel is boiling violently, is wild, and unfit to be poured, the addition of a minute quantity of aluminum will have the effect of quieting it quickly. Half an ounce to an ounce of aluminum to a ton of steel will be enough usually, and for this purpose aluminum has become useful to steel-makers. If a little too much aluminum be added, the ingots will pipe from end to end; therefore the use of aluminum is restricted to small quantities. Experiments have shown that a considerable percentage of aluminum adds no good properties to steel; therefore aluminum steel so called may be treated later under a different heading.