INTRODUCTION OF CARBON
The matter to which these notes are primarily directed is the introduction of carbon into the case of the article to be hardened. In the first place the chances of success are increased by selecting as few brands of steel as practicable to cover the requirements of each component of the mechanism. The hardener is then able to become accustomed to the characteristics of that particular material, and after determining the most suitable treatment for it no further experimenting beyond the usual check-test pieces is necessary.
Although a certain make of material may vary in composition from time to time the products of a manufacturer of good steel can be generally relied upon, and it is better to deal directly with him than with others.
In most cases the case-hardening steels can be chosen from the following: (1) Case-hardening mild steel of 0.20 per cent carbon; (2) case-hardening 3½ per cent nickel steel; (3) case-hardening nickel-chromium steel; (4) case-hardening chromium vanadium. After having chosen a suitable steel it is best to have the sample analyzed by reliable chemists and also to have test pieces machined and pulled.
To prepare samples for analysis place a sheet of paper on the table of a drilling machine, and with a 3/8-in. diameter drill, machine a few holes about 3/8 in. deep in various parts of the sample bar, collecting about 3 oz. of fine drillings free from dust. This can be placed in a bottle and dispatched to the laboratory with instructions to search for carbon, silicon, manganese, sulphur, phosphorus and alloys. The results of the different tests should be carefully tabulated, and as there would most probably be some variation an average should be made as a fair basis of each element present, and the following tables may be used with confidence when deciding if the material is reliable enough to be used.
| Carbon | 0.15 to 0.25 per cent |
| Silicon | Not over 0.20 per cent |
| Manganese | 0.30 to 0.60 per cent |
| Sulphur | Not over 0.04 per cent |
| Phosphorus | Not over 0.04 per cent |
A tension test should register at least 60,000 lb. per square inch.
| Carbon | 0.12 to 0.20 per cent |
| Manganese | 0.65 per cent |
| Sulphur | Not over 0.045 per cent |
| Phosphorus | Not over 0.04 per cent |
| Nickel | 3.25 to 3.75 per cent |
| Carbon | 0.15 to 0.25 per cent |
| Manganese | 0.50 to 0.80 per cent |
| Sulphur | Not over 0.045 per cent |
| Phosphorus | Not over 0.04 per cent |
| Nickel | 1 to 1.5 per cent |
| Chromium | 0.45 to 0.75 per cent |
| Carbon | Not over 0.25 per cent |
| Manganese | 0.50 to 0.85 per cent |
| Sulphur | Not over 0.04 per cent |
| Phosphorus | Not over 0.04 per cent |
| Chromium | 0.80 to 1.10 per cent |
| Vanadium | Not less than 0.15 per cent |
Having determined what is required we now proceed to inquire into the question of carburizing, which is of vital importance.