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Hardening and Tempering Steel

The process of heating steel to a red heat and immediately chilling it is the same among all workmen, but the agents employed for chilling are very numerous. The receipts here given are from various sources, and the reader must adopt the one which he finds on trial, is the best adapted to his wants.

In all cases the object should be heated to a red heat before plunging. If an object to be hardened is long and slender, it should invariably be inserted in the hardening compound end-wise, otherwise it will come out warped and distorted. The same rule applies to thin or flat objects. A preparation is used in hardening, consisting of one tea-spoonful of wheat flour, two of salt and four of water. The steel to be hardened, is to be heated sufficiently, dipped into the mixture, to be coated therewith, then raised to a red glow, and dropped into cold soft water. Another method is to raise the object to the required heat and then drop it into a mixture of ten parts of mutton suet, two parts of salammoniac, five parts resin and thirty-five parts olive oil. Oil, tallow, beeswax and resin are also employed for hardening. If an intense brittle hardness is desirable, drop the object into mercury or nitric acid. In heating very small or thin objects, they should be placed between two thin pieces of charcoal and the whole brought to the required heat. In this way you avoid uneven heating and hence it will be uniformly tempered. When it is desirable to harden an article without discoloring its surface, it should be placed in a metal tube or bowl of a clay pipe, and surrounded with charcoal that has been previously heated to expel all moisture, and when raised to the proper heat the whole should be immersed in the hardening liquid. Mat for Steel. The article to be treated must first be ground flat and free from scratches in the usual manner. When this is accomplished take oil stone powder, mix it with oil and then add a little bluestone powder. Grinding is performed best upon a composition or iron plate, or a file of the same material; glass is not as well suited for the purpose. A large quantity of grinding powder and oil should be used. Very hard articles take a good mat grinding with difficulty, and whenever possible it is advisable to anneal them blue.

Do not press too hard in grinding; the small grains of oilstone should assume a rolling motion, whereby they will to a certain extent, wear hollows with their sharp edges in the surface of the steel, all of which together will impart the handsome, mat appearance. If too much pressure is brought to bear, and the grinding material is too dry, it will cake on the steel and produce the disagreeable scratched surface so often seen.

The quantity of bluestone necessary for grinding can be scraped off from a large piece, after which the scrapings must be thoroughly crushed. The oilstone powder must not be too fine and should be of uniform grain. The proportions are 1 part of bluestone to 4 of oilstone powder.