Analysis of this bar is given in [Table II] in the last column.
A test of ½-inch wire to show effect of cold-drawing, tempering, annealing, and hardening and tempering. Four pieces were cut from the same bar. It is probable that the first piece would have given a little higher tensile if it had not broken in the grip; it was clamped too tight. The second piece was heated until it passed through all of the temper colors and turned black, technically called “drawing black,” or drawing out all of the temper. It is not quite annealing; the idea was to find the effect of temper-drawing upon a cold-hardened drawn wire.
The effect of this operation was to lower the ultimate and raise the elastic strength, increasing also the ductility.
The third piece was heated carefully to the recalescence-point, and cooled slowly, thus annealing it completely, and giving the normal strength of a bar of this composition.
The fourth piece was heated to recalescence and quenched, hardening and refining it thoroughly; it was then tempered through all of the colors until it turned black; the result shows the enormous potencies there are in the hardening and tempering operations.
The cases given in [Table II] were selected indiscriminately, so as to show better the effect of carbon, as we here have tests of ordinary test-bars, boiler-sheet, small eye-bars, and drawn wire.
The 96-carbon eye-bar and the 115-carbon ½-inch wire are the nearest to the 100-carbon saturation limit mentioned before, and they show the highest strength. The 96-carbon eye-bar had a slight flaw in the fracture, which doubtless caused it to break below its real strength.
The 135-carbon eye-bar broke in the head in a way to indicate that there was some local strain there, due to forging.
These examples are not given as establishing any general law; they are illustrations of what all experience shows to be the fact, that the strength of steel is affected profoundly by the quantity of carbon present, and also by heat and by mechanical work. From 46,800 lbs. to 248,700 lbs. tensile strength per square inch is an enormous range, and these figures probably represent pretty closely the ultimate limits at present attainable.
An inspection of the analyses makes it clear that the other elements present in addition to carbon were not there in sufficient quantity or variety to have had much effect upon the results.