Grey cast iron is one of the most valued of cast metals. It may be made by melting pig iron and scrap in the cheapest of melting processes, the cupola, and then cast into sand molds. Besides being of low cost, grey cast iron shows properties that make it a valuable metal industrially.
Among its outstanding properties are the following:
1. excellent machinability; 2. excellent wear resistance; 3. tensile strength; 4. grey cast iron has no well-defined elastic limit and may be loaded up to 89 % or more of its maximum strength; 5. it is the only ferrous allow that may be varied in stiffness; 6. included in its properties is its valuable damping capacity for vibrations and its good resistance to corrosion.
The elements in grey cast iron are the same as in steel and the structural constituents formed from these elements are the same in steel as in cast iron (ferrite, pearlite, cementite, and manganese-sulphide). However, due to the greater percentage of carbon and phosphorus, two additional constituents are found in this form of cast iron, namely, graphitic carbon and steatite, a phosphorus eutectic structure. The graphitic carbon found in grey cast iron gives to this form of iron its outstanding properties, and may be considered its most important constituent. It is the amount, size, shape and distribution of the graphitic carbon which determines the physical properties of grey cast iron. Large flakes of graphitic carbon result in a stronger casting. Carbon that does not form graphite is present in the iron as combined carbon (cementite). The amount of cementite present in grey cast iron determines its hardness. Many grey cast irons are now cast with the additions of some alloying elements, such as nickel, copper, molybdenum and chromium. The alloys are used to improve the strength and hardness of castings.
Дополнительные слова:
1) damping, n – глушение, торможение
2) namely, adv – а именно
VIII. Прочтите текст и дайте краткое содержание текста в 4-x предложениях.
IX. Укажите предложения, которые соответствуют содержанию текста.
1. Many gray cast irons are now cast with the additions of some alloying elements.
2. Manganese is often present only as a trace.
3. Many metals which cannot be hot-forged or cold-formed can be easily cast.
4. The open-hearth process is largely used for making steel.
5. The alloys are used to improve the strength and hardness of castings.
6. Iron castings are made by remelting scrap with pig iron in a furnace called a cupola.
X. Определите, о каких из перечисленных ниже фактах можно узнать из текста.
1. Сварочное железо обычно очень легко сломать благодаря вязкости и эластичности.
2. Различные виды серого литейного чугуна сейчас отливают с добавлением некоторых легирующих элементов.
3. Если металл расплавить, то углерод также будет находиться в расплавленном состоянии.
4. Быстрое охлаждение стали известно как закалка.
5. Разница между нормализацией и отжигом состоит в скорости охлаждения.
XI. Сверяясь с текстом найдите правильный перевод следующих словосочетаний:
1) fracture; a) выдающиеся свойства;
2) cast metal; b) основной;
3) outstanding properties; c) различие;
4) percentage of iron; d) процентное содержание железа;
5) valuable metal; e) свойство;
6) principal; f) состав;
7) composition; h) литейный металл;
9) property; i) ценный металл;
10) range; j) каждый;
11) each; k) изменение;
12) variation; l) излом;
13) content; m) состав;
14) casting. n) литье.