It has been seen that their micrographs quite definitely differentiate them and probably no one will have difficulty in recognizing and naming such specimens. As testing this it may be interesting to note photomicrograph No. 8. Two different iron alloys made up the material from which this photomicrograph was taken. Apparently the bar was one made by heating and rolling together scrap metals. Such material is on the market. The photomicrograph shows that some of the scrap used was wrought iron and some of it mild steel of about .08% carbon.
Classification by Chemical Analysis and by Physical Tests
So far not much has been said about composition except that upon it to a great extent depends the structure and physical properties of the alloy. Composition and physical characteristics as well as structures are necessary to a fair
| Table B—Chemical Composition and Physical Properties | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Per Cent Silicon | Per Cent Graphitic Carbon | Per Cent | Per Cent Total Carbon | Beginning of Freezing[[2]] | Tensile Strength[[3]] | Elongation[[4]] | Welding Properties | Principal Uses | ||
| 1. | Sand Cast Pig Iron | 2.50 | 3.75 | .25 | 4.00 | 2100 | Further Refining. | |||
| 2. | Machine Cast Pig Iron | 2.50 | 3.00 | 1.00 | 4.00 | 2100 | Further Refining. | |||
| 3. | Open-Hearth Iron | .03 | .00 | .02 | .02 | 2740 | 50,000 | 2½″ | Good | Bars, pipe, sheet. |
| 4. | Wrought Iron | Slag | .00 | .05 | .05 | 2740 | 52,000 | 2¼″ | Fine | Bars, pipe, boiler tubes, stay bolts. |
| 5. | Mild Steel | .05 | .00 | .10 | .10 | 2740 | 55,000 | 2½″ | Good | Bars, pipe, wire, sheet, shafting, tubes. |
| 6. | Medium Steel | .05 | .00 | .25 | .25 | 2720 | 65,000 | 2¼″ | Good | Bars, plate, structural. |
| 7. | Rail Steel | .05 | .00 | .60 | .60 | 2680 | 90,000 | 1¾″ | Fair | Rails, gears. |
| 8. | Low Carbon Tool Steel | .15 | .00 | .75 | .75 | 2660 | 100,000 | 1¼″ | Fair | Hammers, cold chisels, saws, springs. |
| 9. | Medium Carbon Tool Steel | .15 | .00 | 1.00 | 1.00 | 2630 | 120,000 | 1″ | Poor | Lathe tools, chisels, drills, dies, springs. |
| 10. | High Carbon Tool Steel | .15 | .00 | 1.25 | 1.25 | 2600 | 135,000 | 1⅛″ | Slight | Lathe tools, chisels, files, saws. |
| 11. | Very High Carbon Tool Steel | .15 | .00 | 1.50 | 1.50 | 2560 | 124,000 | ¼″ | Slight | Razors, lancets, graving tools, saws for steel. |
| 12. | High Steel | .00 | 1.75 | 1.75 | 2530 | 0 | None | Dies for wire drawing. | ||
| 13. | White Iron | .00 | 2.50 | 2.50 | 2460 | 0 | None | Dies for wire drawing. | ||
| 14. | White Cast Iron | .70 | .10 | 2.65 | 2.75 | 2400 | 41,000 | 0 | None | For malleableizing, carwheels. |
| 15. | Annealed Malleable Cast Iron | .70 | 2.70 | .05 | 2.75 | 40,000 | ½″ | None | Railway and agricultural castings, fittings. | |
| 16. | Cast Iron for Chilled Castings | 1.00 | 1.00 | 2.00 | 3.00 | 2330 | 35,000 | 0 | None | Rolls, gears, brakeshoes. |
| 17. | Semi-Steel | 1.75 | 2.80 | .40 | 3.20 | 2300 | 35,000 | 0 | None | Gears, steam cylinders, valves. |
| 18. | Gray Cast Iron | 2.00 | 3.10 | .30 | 3.40 | 2200 | 25,000 | 0 | None | Machine parts, grates, radiators, valves, soil pipe. |
| 19. | Soft Gray Cast Iron | 2.50 | 3.30 | .15 | 3.45 | 2200 | 23,000 | 0 | None | Stoves, hollowware, pipe fittings, misc. |
[2]. In degrees Fahrenheit. For our purposes, the same as the melting points of the alloys.
[3]. Pounds required to pull apart lengthwise a bar one inch square.
[4]. Number of inches that a bar eight inches long will stretch before it breaks.
Iron and Steel Test Pieces and Instruments Used in Measuring Their Size, Elastic Limit and Elongation
understanding of the subject. There is given therefore, a table showing approximate comparative values of chemical compositions and physical properties of the alloys under discussion.