=85. Selecting and Working Steel.=—In making a tool, the differences in quality of steel should be considered, because steel suitable for a razor would not do for a cold chisel or any battering tool. (See sec. 181.)
If the steel at hand is not exactly suitable, but the selection must be made from it, then that should be chosen which will most nearly meet the requirements, and tempering must be relied upon to make up the deficiency. In most large factories all grades of steel are kept on hand and are assorted in the stock room so that there need be no difficulty in making the proper selection.
The percentage of carbon in steel represents the amount of carbon it contains. A steel that is called a 75-point carbon steel is one that contains (.75) seventy-five one hundredths of one per cent, each point representing (.01) one one hundredth of one per cent.
Some steel makers use the word “temper” to indicate the amount of carbon, expecting the user of the steel to be familiar with the amounts of carbon each different temper represents. For instance, a razor-temper steel represents one that contains 1.50 per cent carbon and a tool-temper steel represents one containing about 1.25 per cent. The word “temper” as used in this connection should not be confused with the word as it is used in the art of tempering, where it indicates the operation of reducing the hardness of the metal in order to make it less brittle and more suitable for some particular use.
=86. Uses of Different Grades of Steel.=—As the percentage of carbon, and consequently the quality of steel, will vary somewhat with different makes, it is rather difficult to give a rule that will apply generally, but the following list of different grades of carbon will give a general idea of how steel should be selected, forged, and hardened.
Steel of 0.7 to 0.8 per cent carbon should be used for snaps, rivet sets, cupping tools, etc. This grade of steel should be forged at a light red heat. It can be welded easily and will harden at a light red heat.
Steel from 0.8 to 0.9 per cent carbon should be used for drop-forging dies, hammers, cold sets, track chisels, blacksmith’s tools, well drills, etc. It should be forged at a light red heat; it welds easily and hardens at a light red heat.