Good steel may be described as having a bluish-gray color, uniform grain as seen by the naked eye, and little lustre. But it should have some lustre and a silky appearance. When it is right, a steel-worker will say it is “sappy,” and that name, absurd as it may sound when applied to a metal, really expresses an appearance, and implies an excellence that it would be hard to find a better word for. If the structure be dull and sandy-looking, the steel-worker will say it is “dry,” and that term is as suggestive and appropriate as the word “sappy.”
If the fracture be granular with bright, flashing lustre, the steel-worker will say it is “fiery,” and again his term is expressive and proper.
It is perfectly safe to say that steel of a “sappy” appearance is good steel; but in order to know what it is it must be learned by observation, it cannot be described in exact terms.
It is equally certain that a “dry” fracture indicates a mean steel, a steel inherently mean,—too much phosphorus, or silicon, or oxides, or all combined,—and such a steel is incurable.
A “fiery” fracture indicates too much heat. It may be found in the best steel and in the poorest; it may be corrected by simply heating to a proper temperature. It shows that some one needs to be reprimanded for careless work.
If now an inquirer will take a piece of good steel of “sappy” fracture, and of “dry” steel of dull, sandy fracture of the same carbon, and will heat them say first to dark orange, then to bright orange, dark lemon, and so on, and examine the fractures after each heating, he will find a “fiery” fracture in the “dry” steel at a heat much below that which is necessary to make the “sappy” steel “fiery.” This is one proof that good steel will endure more punishment than poor steel.
Cold steel is not plastic in the common acceptance of the word; strictly speaking it has some plasticity, as shown in the extension noted in pulling it; this is its measure of ductility.
Also it may be drawn cold to fine wire of only a few thousandths of an inch in diameter, and it has been rolled cold to one five thousandth of an inch thick. But this work must be done with great care; the steel soon becomes brittle, and a little overdrawing or overrolling will crush the grain and ruin the steel; therefore the work must be done a little at a time, and be followed by a careful annealing.
To reduce a No. 5 wire rod to .005 inch diameter will require with high steel suitable for hair-springs about fourteen annealings.
A skilful hammerman will take a piece of mild cold steel, and by means of light, rapid blows he will heat it up to a bright lemon heat without fracturing it; then he will have it thoroughly plastic and malleable.