The boundary lines of the crystals or grains may be plainly seen. Each grain should show practically white. The dark parallel lines, the dots, and the grayish portions result from inequalities in the polishing and etching.
No. 1d. Section of Wrought Iron Cut Lengthwise of the Bar. Black Patches and Filaments Are “Slag” or “Cinder”
After noting the appearance of photomicrograph No. 99b, which is of a nearly pure iron, one need have no difficulty in realizing that pig iron and the steels are alloys and not simple metals. The truth is that of all alloys some of the well-known iron products which we are studying are by far the most complicated, much more so than are the nonferrous alloys, which include the brasses, bronzes, babbitts, German silver, etc.
Physical Test Room Where 15,000 Specimens Are Tested Each Year
This should not worry us, however, for we shall not attempt to follow them into their complications.
No. 3b. Steel Containing .10 Per Cent of Carbon. The Carbon is in the Black Patches
The important point just now is to observe the crooked black flakes of crystalline graphite in this photomicrograph No. 198. It is largely because of these flakes of brittle, soft graphite that pig iron and the cast irons are so fragile. One has no difficulty in realizing that these flakes, which cut in every direction through the metal, make it structurally weak, especially toward a sudden blow.