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The kinds of steel used where elasticity is desired are known as spring steel, blister steel, and shear or double-shear steel, although, for small springs, steel of the tool-steel class is often employed.

To form cast steel the bars of blister steel are broken into pieces and melted into crucibles.

The iron combines with a portion of the carbon to form blister steel, so named because of the blisters which are found on the surface of the bars when they are removed from the furnace.

The bars of blister steel are broken into pieces about 18 inches long, and tied together in bundles by strong steel wire.

Open hearth steel, crucible steel and blister steel, prior to this, had been the principal products, but were manufactured by processes too slow and too expensive to take the place of iron.