Rate, excel, replace, exist, retard, abrasion, power, prolong

1. Many properties of alloy steels do not … in carbon steels.

2. Vanadium makes steel more resistant to ….

3. Manganese can … wear life of steel.

4. The tools made of alloy steels considerably … in quality the tools of carbon steels.

5. Zirconium added to steel can … grain growth.

6. Cutting tools made of alloy steels work at high cutting ….

7. Special alloy steels are widely used in … engineering.

8. Nonmagnetic steels often … expensive nonferrous metals in precision instruments.

1. Agree or disagree with the following statements. Prove your reason. Use the expressions: I’m absolutely sure that …, No doubt that ….

1. It is possible to add only one alloying element to steel.

2. Silicon can never be used as an alloying element of steel.

3. Alloy steels do not have the shortcomings of carbon steels.

4. Nothing can change the permeability of steel.

5. Three categories of alloy steels are known according to the purpose they serve.

6. The amount of alloying elements added to alloy steels is always the same.

7. Alloy steels with specific chemical properties find wide application in industry.

8. An alloying element added to steel can enhance only one of its properties.

8. Translate the text in writing. Use a dictionary. Find answers to the questions:

1. What is the main difference between carbon steel and stainless steel?

2. What is passivation?

3. Why does chromium remain lustrous when it is exposed to oxygen?

4. How did the corrosion-resistance of iron-chromium alloys become known to people?

Stainless steel

Stainless steel differs from carbon steel by the amount of chromium present. It is a steel alloy with a minimum of 10.5 % chromium content by mass. Carbon steel rusts when exposed to air and moisture. The iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steel does not stain, corrode or rust as easily as ordinary carbon steel. Stainless steel contains sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the internal structure of metal. This phenomenon is called passivation and is seen in other metals such as aluminum and titanium. High oxidation-resistance in air at ambient temperature is normally achieved by addition of a minimum of 13% (by mass) chromium, and up to 26% is used for harsh environments. Chromium forms a passivation layer of chromium oxide (Cr₂O₃) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous. The layer is impervious to water and air, thus protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched.

The corrosion-resistance of iron-chromium alloys was first recognized in 1821 by the French metallurgist Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery. However, metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be practical.

In the late 1890s Hans Goldschmidt of Germany developed an aluminothermic process for producing carbon-free chromium. Between 1904 and 1911 several researchers, particularly Leon Guillet of France, prepared alloys that would today be considered stainless steel.

Unit 13

1. Memorize the following words:

prevent acquire burn support line reflect plate chlorine flame poisonous hydrogen rubber layer core abundant foil insulation bend protective paint

предотвратить приобретать гореть поддерживать облицовывать отражать наносить покрытие хлор пламя ядовитый водород резина слой стержень распространенный фольга изоляция гнуть защитный краска

запобігти набувати горіти підтримувати облицьовувати відбивати, відображати наносити покриття хлор полум’я отруйний водень гума шар стрижень поширений фольга ізоляція гнути захисний фарба

1. Pracrise the reading of the following words:

Hydrogen, burn, chlorine, acquire, core, support, prevent, poisonous, desirable, characteristic, quality, frequently, lead, zinc, aluminum, occur, sulfide, per cent, tough, oxide, discoloured, soothing, malleable, aqueduct, ductile.