If open-hearth steel of high carbon is not uniform, it is clearly because the maker would not take a little trouble to have it so.

Assuming that for convenience cast steel is graded for carbon content by even tens, and that the different tempers are separated half-way between the tens, we have:

Carbon.
.10 including from .05 to .15
.20““.16“.25
.30““.26“.35
.40““.36“.45
.50““.46“.55
.60““.56“.65
.70““.66“.75
.80““.76“.85
.90““.86“.95
1.00““.96“1.05
1.10““1.06“1.15
1.20““1.16“1.25
1.30““1.26“1.35
1.40““1.36“1.45
1.50““1.46“1.55

This covers the usual commercial range from what is known as dead-soft steel up to a high, lathe-temper steel.

Higher steels are used sometimes, even up to 225 carbon, but they are so exceptional that it is not worth while to continue the list above 150.

This list allows a variation of .05 carbon above and below the datum of each temper; some margin must be had of course, and this is sufficient in the hands of a careful steel-maker; it is found in practice to be satisfactory to the user. Even in the highest lathe-steel where the strains from hardening are the greatest, because the change in volume due to a degree of temperature is the greatest, a variation of three or four points above and below the mean does not make enough difference in the results to throw a skilful temperer off from his desired conditions.

On the other hand, a difference of a full temper will throw the most skilful worker off from the track, and so that much variation is not allowable. For instance, if a man be working 130 carbon, and he should receive a lot of steel of 120 carbon, he would get his work too soft in following his regular methods; then if he doubted himself, as he would be apt to do, and raised his heat to correct his supposed aberration, he would get his work too hard, coarse-grained, and brittle; if he tried to correct this by drawing to a lower temper color, his tools would be too soft. Again, if he received a lot of steel of 140 carbon and proceeded in his regular way, he would get a lot of cracked tools. So that in either case the result would be confusion. It is probable that in almost any case either 120 or 140 carbon would make a thoroughly good tool if the temperer knew what he was working with and adapted his heats to the carbon. But he does not know of the variation, and even if he did he would say, very rightly, that he did not propose to make daily changes in his methods to suit the convenience or the carelessness of the steel-maker.

It must not be understood, however, that this narrow range for each temper limits the capacity of the steel; it merely gives the limit for regular easy working.

To illustrate: A good lathe-tool may be made of 100-carbon steel, and of 150 carbon; but no worker could use these tempers indiscriminately, nor even alternately, although he knew which was which, because he could not change all of his heats say every five minutes and turn out satisfactory work. A spring of given size, and to carry a given load, may be made equally good of 60-carbon steel or of 140 carbon, and such work is done frequently in shops that are attached to steel-works; but the spring-maker must be told beforehand what he is to work with, and he must be given enough of one kind of steel to make say a day’s work, so that he can go along regularly. The springs will be good, but the one containing 140 carbon will have the highest elasticity and the most life, although both will have the same modulus of elasticity. The spring-maker who buys his steel will not submit to any such variations, and he ought not to be asked to do it, because one temper of steel costs no more than another, and the selecting out and separating the tempers is only a matter of a little care.

Is it practicable to keep steel uniform in carbon within such narrow limits?