Steel which is to be used for making tools with teeth, such as taps, reamers and milling cutters, should not be annealed too much. When the steel is too soft it is more apt to tear in cutting and makes it more difficult to cut a smooth thread or other surface. Moderate annealing is found best for tools of this kind. TOOL OR CRUCIBLE STEEL Crucible steel can be annealed either in muffled furnace or by being packed. Packing is by far the most satisfactory method as it prevents scaling, local hard spots, uneven annealing, or violent changes in shape. It should be brought up slowly to just above its calescent or hardening temperature. The operator must know before setting his heats the temperature at which the different carbon content steels are hardened. The higher the carbon contents the lower is the hardening heat, but this should in no case be less than 1,450 deg.F. ANNEALING ALLOY STEEL The term alloy steel, from the steel maker's point of view, refers largely to nickel and chromium steel or a combination of both. These steels are manufactured very largely by the open-hearth process, although chromium steels are also a crucible product. It is next to impossible to give proper directions for the proper annealing of alloy steel unless the composition is known to the operator. Nickel steels may be annealed at lower temperatures than carbon steels, depending upon their alloy content. For instance, if a pearlitic carbon steel may be annealed at 1,450 deg.C., the same analysis containing 2-1/2 per cent nickel may be annealed at 1,360 deg.C. and a 5 per cent nickel steel at 1,270 deg.. In order that high chromium steels may be readily machined, they must be heated at or slightly above the critical for a very long time, and cooled through the critical at an extremely slow rate. For a steel containing 0.9 to 1.1 per cent carbon, under 0.50 per cent manganese, and about 1.0 per cent chromium, Bullens recommends the following anneal: 1. Heat to 1,700 or 1,750 deg.F. 2. Air cool to about 800 deg.F. 3. Soak at 1,425 to 1,450 deg.F. 4. Cool slowly in furnace. HIGH-CARBON MACHINERY STEEL The carbon content of this steel is above 30 points and is hardly ever above 60 points or 0.60 per cent. Annealing such steel is generally in quantity production and does not require the care that the other steels need because it is very largely a much cheaper product and a great deal of material is generally removed from the outside surface.