Practical forging and art smithing

by Thomas F. Googerty

Welding Steel.

All small pieces of tool and spring steel should be welded with separate heats. A little practice and a clean fire, with some good welding compound, are necessary. In separate heat welding of flat steel, the flat sides of the scarfs are put together instead of the beveled ones. The scarfs are shown in Figure No. 115. The method of riveting and splitting small pieces of flat steel to hold them together while taking the heat is not to be recommended because after they are put together in this manner the lap is double thick, and in raising the heat there is always danger of over-heating each side of the lap. Separate heats and a clean fire is the best method to use to make a good weld, unless the steel is heavy. In this case, it is split and forked as previously explained.

Fig. 115. Welding Thin Steel.

Case Hardening.

The difference between wrought iron and tool steel lies in the absence of carbon in the iron. Tool steel can be hardened because it contains carbon, and when heated and suddenly cooled becomes hard thruout. The surface of wrought iron or mild steel can be carbonized and then made very hard. This is called case hardening because about ¹⁄₁₆ inch or less of the outside of the bar is made hard while the center is soft. There are several methods. One is to place the articles in a tight cast iron box and surrounded with ground bone before placing in a furnace. The box is then brought to a high heat of about 1700 degrees Fahrenheit. It is held at this heat for several hours and then let cool. When cool, the pieces are reheated and dipped in salt water to harden them or they may be cooled with the first heating. By another method the pieces are placed in an iron ladle with cyanide of potassium and heated. Iron may be heated red and rolled in the cyanide, then reheated and plunged into water. Care must be taken in handling cyanide as even the fumes are poisonous.

Coloring Steel.

Very bright pieces of soft steel can be case hardened and colored at the same time. In doing this, cyanide is heated in an iron box, and the steel articles are put into it. When heated they are removed and dipped into a solution of water and salt peter to cool and harden them. This gives them a mottled effect with many colors. A pint of salt peter to about four gallons of water makes a solution strong enough. This bath becomes poisoned from the cyanide. It should be kept clean and labeled “Poison.”

Annealing.

A piece of metal of any kind is said to be “annealed” when made very soft. Steel should be annealed before it is filed, drilled, or machined, as it is a very hard metal to work when cold. The method of annealing is first to heat the piece to a red heat. It is then covered with warm, slacked lime so that the air will not come in contact with it until cool. A simple way to anneal, when in a hurry, is to heat the steel red, setting it in a dry place on the forge until black. It is then plunged into water quickly and brought out. This operation is repeated until the piece is cool. Steel is also annealed by heating the piece red and setting it on the forge until cool. The slower steel is cooled, the softer it becomes. Wrought iron and mild steel forgings should always be annealed when used in work where there is danger of breaking them.