• Гідрологія і Гідрометрія
• Господарське право
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• Економіка природокористування
• Економічна теорія
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• Міжнародний маркетинг
• Основи екології
• Предмет Політологія
• Соціальне страхування
• Технічні засоби організації дорожнього руху
• Товарознавство продовольчих товарів

Text A. Steel

The most important metal in industry is iron and its alloy steel. Steel is an alloy of iron and carbon. It is strong but corrodes easily through rusting, although stainless and other special steels resist corrosion. The amount of carbon in steel influences its properties considerably. Steels of low carbon content (mild steels) are quite ductile and are used in the manufacture of sheet iron, wire and pipes. Medium-carbon steels containing from 0.2 to 0.4 per cent carbon are tougher and stronger are used as structural steels. Both mild and medium-carbon steels are suitable for forging and welding. High-carbon steels contain from 0.4 to 1.5 per cent carbon, are hard and brittle and are used in cutting tools, surgical instruments, razor blades and springs. Tool steel, also called silver steel, contains about 1 per cent carbon and is strengthened and toughened by quenching and tempering.

The inclusion of other elements affects the properties of the steel. Manganese gives extra strength and toughness. Steel containing 4 per cent silicon is used for transformer cores or electromagnets because it has large grains acting like small magnets. The addition of chromium gives extra strength and corrosion resistance, so we can get rust-proof steels. Heating in the presence of carbon or nitrogen-rich materials is used to form a hard surface on steel (case-hardening). High-speed steels, which are ex­tremely important in machine-tools, contain chromium and tungsten plus smaller amounts of vanadium, molyb­denum and other metals.

Questions:

What kinds of steel do you know? Where are they used?

Text B. Arabic Numerals

The Arabic system of numerical notation is used in most parts of the world today. This system was firstdeveloped in India in the 3rd century ВС. At that time the numerals 1, 4, and 6 were written in the same form as today.

The important innovation in the Arabic system was the use of positional notation, in which individual number symbols assume different values according to their position in the written numeral. Positional notation is made possible by the use of a symbol for zero. The symbol 0 makes it possible to differentiate between 11, 101, and 1,001 without the use of additional symbols, and all numbers can be expressed in terns of ten symbols, thenumerals from 1 to 9 plus 0. Positional notation also greatly simplifies all forms of written numerical calculation.

Читайте також:

1. Ancient Steel-Making Secret
2. I. Text A: «Metals», Text B: «Steel», Text C: «Methods of steel heat treatment»

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