英文科學(xué)讀本 第二冊(cè)·Lesson 29 Steel

Lesson 29 Steel

Fred, said Willie, "I have been thinking about our lesson ever since we left school. Steel must be a very wonderful metal. Why, we might almost say it is two metals all in one."

Well, replied Fred, "there are two kinds of steel, and each of them is very unlike the other in many ways."

How very strange, Fred, said Norah, "and yet I think you told me that all steel is simply iron in another form."

I can't tell you exactly how the steel is made, said Fred. "It is kept for weeks in a furnace at one fixed heat, and then left to cool.

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, but simply 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 teacher said 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

Cast-steel is easily fusible, like cast-iron, but it is malleable, and can be worked up at the forge like wrought iron. Cast-steel is used for making machinery and great guns.

Shear-steel is used for making cutting tools and springs. It is very elastic.