书城教材教辅科学读本(英文原版)(套装1-6册)
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第148章 第二册(65)

"Some of it is afterwards cut up into small pieces, and melted in strong wrought-iron crucibles, or pots, in a very hot furnace. The melted metal is poured out of the crucible into molds, and left to cool. It makes a special kind of steel fit for special purposes. It is known as cast steel.

"Some of the steel is not melted in crucibles, butsimply heated, and hammered, and welded, again and again, just as the wrought iron is served in the puddling furnace. Steel treated in this way makes quite another kind of metal. It is known as shear steel.

"Cast steel is as fusible as cast-iron, but it is as malleable as wrought iron.""That must make it doubly useful." said Willie. "Yes," said Fred, "it does. Don"t you remember teachersaid that the cast steel can be used for moulding or casting, or it can be heated in the forge, and then worked up, beaten, welded, rolled, or cut, just as they treat wrought iron?""Our great guns are made of this cast steel," said Willie, "and so are most of the steel parts of engines and other machines. Shear steel is used for making knives and all cutting tools, as well as springs for watches, locks, doors, and carriages. It is very elastic."SUMMARY