PART 2: PRODUCTION OF FERROUS ALLOYS

(cast iron)

A. READING

Ferrous metallurgy is an industry of manufacturing ferrous alloys (cast iron and steel). Ferrous alloys are alloys of iron and carbon, combined with some other elements. Steel is refined from cast iron. So the ferrous metallurgy begins with the production of cast iron in the form of pigs (pig iron).

To produce pig iron iron ore, fuel and flux are needed. An iron ore is a crude containing iron in such amounts as to constitute a promise of its working into marketable product. An iron ore comprises the ore body and the dead rock or gangue. The ore body is the natural chemical compounds of iron, most frequently its oxides, which are found in the ore. The gangue of iron ore may be of various chemical composition. Most frequently it consists of quartzite (SiO₂) or sandstone with an admixture of clayey matter. Iron ores are classified as rich or lean according to the amount of gangue which they contain. After crushing and sizing, rich ores are charged directly into the furnace, where the iron is reduced from its chemical compounds and goes over into the pig iron. Lean ores are subjected to concentration in which the proportion of the ore body (iron oxides) in the ore is increased. This process is called “ore dressing”. The simplest method of ore dressing depends on the fact that in general the metallic compounds have a higher specific gravity than the gangue, and hence settle faster in a stream of water.

For separating iron from impurities the iron ore must be melted at a high temperature produced by burning fuel in a blast furnace. The blast furnace is called so because a blast of hot air is forced into it while producing the pig iron.

Fuel is one of the most important material for producing pig iron. Metallurgical fuel must have high calorific power, high strength, high porosity and contain the least possible amount of sulphur. The chief type of metallurgical fuel is coke. Coke is a solid carbonised residue, formed in the process of heating (dry distillation) of certain grades of coal in retort (coke) ovens. Very high temperatures may be developed in its combustion.

Flux is used for converting gangue, harmful impurities, ash and sulphur of coke into slag. The most commonly used flux is limestone (CaCO₃).

Pig iron making is a complex chemical process. It consists of three stages: a) reducing iron from its oxides; b) converting pure iron into carburized iron; c) slagging, that is converting gangue and some other impurities into slag. This process runs as follow. In the blast furnace the charged materials (iron ore, coke, flux) going from up to down interact with the products of burning, which go from down to up. Burning begins in the bottom of the furnace when the hot air is blasted and the coke burns up. The temperature in the furnace comes to 1800° C. At this temperature, besides iron, manganese, sulpher, phosphorus and silicon are also reduced. In the result of the reduction of all mentioned elements complex alloy of iron and carbon, manganese, silicon, sulpher and phosphorus is produced on the blast furnace. This alloy being melted up is the form of pigs in called pig iron.

EXERCISES:

I. Find in the texts the following topical words and phrases, explain what they mean, and add them to your Active Vocabulary:

blast furnace, an iron ore, coke, rich and lean iron ores, ore body, slagging, charged materials, flux, dead rock, ore dressing.

II. Write out from the texts the sentences or the parts of the sentences which contain the following words and expressions and translate them into Russian:

fuel and flux, lean ores, interact, combustion reaction, crushing and sizing, complex alloy, specific gravity, reduction of all elements.

III. Answer the following questions:

1. What does ferrous metallurgy begin with and why?

2. What is the gangue consist of?

3. What properties must metallurgical fuel have?

4. What stages does pig iron making consist of?

5. What must the iron ore be melted at high temperature for?

6. In what part of the furnace does burning begin?

7. Why is cast iron called pig iron?

8. What are lean ores subjected to concentration for?

B. TRANSLATION

EXERCISES:

I. Before translating the text, find in it the sentences in which you would be able to use the following topical words and expressions:

the earth’s crust, specular and black iron ores and ironstones, a deposit, conversion iron, scrap, cuts and chips, preliminary preparation, sintering, roast blast-furnace gas.

II. Read the text again, find in it the information about the following questions, and answer them using the topical words and phrases:

1. What ores are used for making pig iron?

2. What is sintering (agglomeration)?

3. What is essence of smelting in a blast furnace?

4. What are the products of smelting in a blast furnace?

5. What are lean ores subjected to concentration for?

6. What is roast blast- furnace gas used for?

III. Now translate the text in writing. Use as many topical words and phrases as you can:

Земная кора содержит около 5,1 % железа, в составе различных минералов. Для получения чугуна используют красные, бурые и магнитные железняки (окислы) и железный шпат (карбонат).

Во многих месторождениях железные руды в составе своих минералов кроме железа содержат другие минералы (от долей процента до 1-2%): хром, никель, ванадий, кобальт, титан, медь. Такие руды называют комплексными, а чугуны и стали, выплавляемые из них, - природно-легированными.

Железные руды содержат также марганец (иногда до 10-18 %), однако в большинстве руд содержание марганца ограничивается (до 1-2 %), что является недостаточным для выплавки передельного и даже литейного чугуна, поэтому плавку ведут с добавками марганцевой руды.

В процессе доменной плавки кроме руд используются и различные отходы: чугунный лом, чугунная стружка, загрязненный стальной лом.

Чтобы наиболее экономично и эффективно провести процессы в доменной печи, нужно произвести предварительную подготовку сырых материалов.

Руды подвергают дроблению, обогащению и агломерации.

Кроме того, производится обжиг руд. Обжиг осуществляют для удаления из руды химически связанной воды, углекислоты и для частичного удаления серы.

Агломерацией называется процесс спекания мелких и порошкообразных руд с коксовой мелочью.

Сущность доменной плавки состоит в восстановлении железа из оксидов в руде, науглероживании железа и ошлаковании пустой породы.

Продуктами доменной плавки являются чугун, шлак и доменный газ.

Чугун - основной продукт доменной плавки. Чугун используется для изготовления изделий путем литья либо переплавляется в сталь.

Шлак - побочный продукт, он является очень дешевым и качественным строительным материалом, идет на изготовление цемента, бетона, кирпича, для грунтовки дорог. Количество получаемого при плавке шлака очень велико и составляет примерно 60 % от веса выплавляемого чугуна.

Доменный газ - также важный побочный продукт. Это высококалорийное топливо. Очищенный доменный газ используют для нагрева воздухонагревателей, металлургических печей и для получения некоторых химических продуктов.