| Table C—Percentages of the so-called “Metalloids” by Weight and by Volume | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Silicon | Manganese | Sulphur | Phosphorus | Total Carbon | Iron[[5]] | Total Metalloids | |||||||
| Wt. | Vol. | Wt. | Vol. | Wt. | Vol. | Wt. | Vol. | Wt. | Vol. | Wt. | Wt. | Vol. | |
| Gray Cast Iron | 2.50 | 10.0 | .70 | .7 | .09 | .36 | .75 | 3.2 | 3.45 | 12.1 | 92.5 | 7.5 | 26.4 |
| Semi-Steel | 1.75 | 7.0 | 1.00 | 1.0 | .10 | .40 | .35 | 1.5 | 3.20 | 11.2 | 93.6 | 6.4 | 21.1 |
| Malleable Cast Iron | .70 | 2.8 | .50 | .5 | .15 | .60 | .17 | .7 | 2.75 | 9.6 | 95.7 | 4.3 | 14.3 |
| Cast Steel | .30 | 1.2 | .50 | .5 | .05 | .20 | .04 | .17 | .35 | 1.2 | 98.8 | 1.2 | 3.3 |
| Mild Steel | .05 | .2 | .40 | .4 | .04 | .16 | .03 | .13 | .10 | .35 | 99.4 | .6 | 1.2 |
| Open-hearth Iron | .03 | .1 | .02 | .02 | .01 | .06 | .01 | .06 | .02 | .07 | 99.9 | .1 | .3 |
| Wrought Iron | 1.20 | 5.0 | .08 | .08 | .01 | .04 | .15 | .65 | .05 | .17 | 97.7 | 2.3 | 5.9 |
[5]. These alloys contain small amounts of other elements so these percentages of iron are a little high, though approximately correct. Note the purity (high percentage of iron) of the open-hearth iron.
6. In the cast irons, the carbon occurs not in one only but in two different forms; i.e., as graphitic carbon, commonly called graphite (Gr. C.) and the combined form (C. C.). The sum of these is usually between 3.00 per cent and 3.50 per cent. It is not so much the total amount of the carbon that causes the differences in structure and physical properties which have been noted in 1 and 2 and in 16 and 17 above, as it is the relative proportions in which these two varieties occur.
Exhibition Case Showing Four Well-Known Iron Alloys with Their Metalloids
7. No one knows just when, with increase of carbon, steel ceases to be steel and becomes white cast iron. There is no definite dividing line either in chemical or physical properties. The changes are extremely gradual throughout the scale. Aided by the microscope, modern physical chemistry has disclosed the fact that alloys of iron with carbon “freeze” from molten to solid condition according to two different laws. The change from one to the other occurs somewhere between 1.7 per cent and 2.2 per cent of carbon as is described in Chapter XXII. This is our only basis for calling alloys with less than 2 per cent of carbon, steels, and those with greater amounts, cast irons.
8. For our immediate purposes the other “metalloids” or constituents are of secondary importance and will not be taken up now. From this it must not be understood that they can be slighted by the metallurgist and furnace man in his work. They cannot. Every one of them is of importance and must be accounted for in the final product or trouble results.
Volumetric Analysis of the Iron Alloys
There is a way in which we may visually get a very intimate idea of the relative composition of these alloys.
The cabinet of which a photograph is given is partitioned into four sections. Each one of these contains a bar and six specimen jars. As you may or may not be able to read from the labels, the bars, all of exactly the same size, are soft cast iron, semi-steel (a stronger cast iron), annealed malleable iron and cast steel. The six jars above each bar contain the exact amounts of the various constituents other than iron which are in the bar beneath.