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Ex. 22 Agree or disagree with the following statements:

1. 
   Hot –worked products have better ductility and toughness than the unworked casting.
   
2. 
   During the forging and welding of a bar, the grains of the metal become greatly elongated in the direction of flow.
   
3. 
   The ability of a metal to resist thinning and fracture during hot – working operations plays an important role in alloy selection.
   
4. 
   The best alloys are those which don’t grow stronger with strain.
   
5. 
   Fracture of the workpiece during forming can result from inner flaws in the metal.
   
6. 
   The ability of the metals from one group to undergo strain varies.
   

Ex.23. Answer the questions:

1. 
   What process improves the mechanical properties of metals?
   
2. 
   What new properties have hot – worked products?
   
3. 
   How does the forging of a bar affect the grains of the metal? What is the result of this?
   

1. 
   4. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?
   

4. 
   What are the best strain – hardening alloys? Where can we use them?
   
5. 
   What are the inner flaws in the metal?
   

IX. Oral practice


Ex. 24. Give information about hot working of steel using questions of the ex. 23 as a plan.
Supplementary reading
Texts for written translation.
Read the texts and translate them in writing. Use a dictionary.


Iron
Iron is an element that has a chemical symbol Fe and is the father of the ferrous family. It is obtained by filling a blast furnance with iron oxides or carbonates and cone, setting light to the mass and blowing air through it. The carbon in the coke and the oxygen in the iron oxide combine to produce carbon monoxide that burns and takes more oxygen from the iron part of the furnance charge to give carbon dioxide. As the temperature increases the iron melts and, from time to time, is allowed to flow out of the bottom of the furnance into special troughs cut into the sand floor of the iron works.
Iron is a lustrous, silvery soft metal. It is one of the few ferromagnetic elements.
Iron and nickel are notable for being the final elements produced by stellar, and thus are the heaviest elements which do not require a red giant or supernova for formation. Iron and nickel are therefore the most abundant metals in metallic meteorites and in the dense-metal cores of planets such as Earth. Iron and iron alloys are also the most common source ferromagnetic materials in everyday use.
Iron is believed to be the sixth most abundant element in the universe, formed as the final act of nucleosynthesis by carbon burning in massive stars. Iron is the most abundant element on Earth. While it makes up only about 5% of the Earth’s crust, the earth’s core is believed to consist largely of a metallic iron-nickel alloy comprising 35% of the mass of the Earth as a whole. Iron is the fourth most abundant element in the Earth's crust and the second most abundant metal (after aluminium). Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite, magnetite. About 5% of the meteorites similarly consist of iron-nickel alloy. Although rare, these are the major form of natural metallic iron on the earth's surface.
Cast iron. Ordinary cast iron is produced by melting pig iron and pouring it into moulds, made of sand, to get it into complex shapes. It is a cheap material that is soft, fairly brittle and unsuitable for anything that takes a tension or bending load. In comprehension there is virtually no plastic deformation or elasticity; it just suddenly fractures across a plane at about 55 ^0. So cast iron is used for casting such as crank – cases, gearboxes and rear axles.
Because cast iron is comparatively brittle, it is not suitable for purposes where a sharp edge or flexibility is required. It is strong under compression, but not under tension. Cast Iron was first invented in China, and poured into molds to make weapons and figurines. Historically, its earliest uses included cannon and shot. In England, the ironmasters of the Weald continued producing these until the 1760, and this was the main function of the iron industry there after the Restoration, though probably only a minor part of the industry there earlier.
The development of the steam engine by Thomas Newcomen provided a further market for cast iron, since this was considerably cheaper than the brass of which the engine cylinders were originally made. A great exponent of cast iron was John Wilkinson, who amongst other things cast the cylinders for many of James Watt’s's improved steam engines until the establishment of the Soho Foundry in1795.
If the pig iron used for casting is specially selected to have smaller amounts of carbon and a low sulphur and phosphorous content and the rate of cooling the casting is controlled to a slow rate, then the structure of the iron is improved. The graphite can be made to form into balls or modules, which are stronger than the usual plates or starfish shapes and the iron part tends to form as pearlite. These cast irons are two or three times as strong in tension as ordinary grey cast iron and have a certain amount of elasticity and less brittleness. They are used for crankshafts as it is much easier to cast a crankshaft shape than to forge it.


Blast furnance – домена піч
To set light – заплювати
To blow air – продувати повітря
Charge – шихта
To melt –плавити
To flow out – витікати
Trough - желоб
Impurities -включення
Pig iron – чушковий чугун
To forge – кувати
To roast – вижигати
Casting – відливка