Let the following squares represent the apparent sizes of the grains:
| 1. | The natural bar, untreated. | |||
| 2. | Grain | due | to | dark orange or orange red. |
| 3. | “ | “ | “ | medium orange. |
| 4. | “ | “ | “ | bright orange. |
| 5. | “ | “ | “ | dark lemon. |
| 6. | “ | “ | “ | medium lemon. |
| 7. | “ | “ | “ | bright lemon. |
| 8. | “ | “ | “ | very bright lemon, or creamy. |
These designations are used because steel in cooling down, or in heating up, runs through a series of yellow tints, not reds. It is common to see the expression “glowing white” applied to steel that is not even melted, when as a matter of fact melted wrought iron is not quite white. An occasional heat of steel may be seen that could fairly be called white, and then the melter knows that it is altogether too hot, and that he must cool the steel or make bad ingots. “Glowing white,” like “cherry red,” will do for ordinary talk, but not for accurate description, although “cherry red” comes nearer to describing the dying color than “glowing white” comes to describing the highest heat.
An arc light may be “glowing white,” and sunlight is “glowing white,” and when either light falls upon melted steel it shows how far the steel is from being “glowing white.”
Referring to the squares: If a bar that has been heated to No. 8 be re-heated to No. 2 and be kept at that color a few minutes to allow the steel to arrange itself, in other words, to provide for lag, and then be cooled, it will be found to have grain No. 2. Sometimes in performing this experiment the fracture will be interspersed with brilliant spots as if it were set with gems; this shows that not quite enough time was allowed for lag. Another trial with a little more time will bring it to a complete No. 2 fracture. If now it be heated to No. 4, or 5, or 6 in the same way, it will be found to have when cold the grain due to No. 4, or 5, or 6 temperature.
This may be repeated any number of times, and the changes may be rung on all of the numbers, until the disintegrating effect of numerous heatings begins to destroy the steel. This property of registering temperature, this steel thermometer, is of great value, and it will be referred to frequently.
EFFECTS OF MECHANICAL WORK.
When an ingot is heated and then hammered, rolled, or pressed hot, its density will be increased, as well as its strength when cold under all strains.
If it be hammered carefully, with heavy blows at first, and with lighter and quicker blows at the last, the grain will become very close and fine; it is called “hammer-refined.”