I.
GENERAL DESCRIPTION OF STEEL AND
OF MODES OF ITS MANUFACTURE.
Steel may be grouped under four general heads, each receiving its name from the mode of its manufacture; the general properties of the different kinds are the same, modified to some extent by the differences in the operations of making them; these differences are so slight, however, that after having mentioned them the discussion of various qualities and properties in the following pages will be general, and the facts given will apply to all kinds of steel, exceptions being pointed out when they occur.
The first general division of steel is cemented or converted steel, known to the trade as blister-steel, German, shear, and double-shear steel.
This is probably the oldest of all known kinds of steel, as there is no record of the beginning of its manufacture. This steel is based upon the fact that when iron not saturated with carbon is packed in carbon, with all air excluded, and subjected to a high temperature,—any temperature above a low red heat,—carbon will be absorbed by the iron converting it into steel, the steel being harder or milder, containing more or less carbon, determined by the temperature and the time of contact.
Experience and careful experiment have shown that at a bright orange heat carbon will penetrate iron at the rate of about one eighth of an inch in twenty-four hours. This applies to complete saturation, above 100 carbon; liquid steel will absorb carbon with great rapidity, becoming saturated in a few minutes, if enough carbon be added to cause saturation.
MANUFACTURE OF BLISTER-STEEL.
Bars of wrought iron are packed in layers, each bar surrounded by charcoal, and the whole hermetically sealed in a fire-brick vessel luted on top with clay; heat is then applied until the whole is brought up to a bright orange color, and this heat is maintained as evenly as possible until the whole mass of iron is penetrated by carbon; usually bars about three quarters of an inch thick are used, and the heat is required to be maintained for three days, the carbon, entering from both sides, requiring three days to travel three eighths of an inch to the centre of the bar. If the furnace be running hot, the conversion may be complete in two days, or less. The furnace is then cooled and the bars are removed; they are found to be covered with numerous blisters, giving the steel its name.
The bars of tough wrought iron are found to be converted into highly crystalline, brittle steel. When blister-steel is heated and rolled directly into finished bars, it is known commercially as german steel.
When blister-steel is heated to a high heat, welded under a hammer, and then finished under a hammer either at the same heat or after a slight re-heating, it is known as shear-steel, or single-shear.
When single-shear steel is broken into shorter lengths, piled, heated to a welding-heat and hammered, and then hammered to a finish either at that heat or after a slight re-heating, it is known as double-shear steel.