Конструкциялық материалдар және термоөңдеу Конструкционные материалы и термообработка Constructional materials and heat treatment Учебное пособие для специальности: 5В071200– «Машиностроение»

179 
In the range of temperatures 1392-1539C, α-iron exists which designate also 
δ-iron. 
Carbon and its properties. 
Carbon is a nonmetallic element. Temperature of melting of carbon is 3500?С. 
Carbon in the nature can exist in two polymorphic updating: diamond and 
graphite. The diamond form in alloys doesn't meet. 
Carbon is in a graphite form in iron carbon alloys at the free form. Crystal 
structure of graphite is the layered. Durability and its plasticity is the very low. 
Carbon is dissolved in iron in liquid and firm conditions, can form chemical 
connection – cement carbide, can be in a free look in the form of graphite. 
Structural components of iron carbon alloys. 
Iron carbon alloys can have the following structural components. 
Ferrite (Ф) - firm solution of introduction of carbon and other elements in α-
iron. It has the volume aligned cubic lattice. Solubility of carbon in ferrite is 
very small: at room temperature to 0,005 %. Ferrite is high plasticity and soft, is 
well processed by pressure in a cold condition. 
Austenite (And) - firm solution of carbon and other elements in γ-iron. It 
exists only at high temperatures. Austenite is high plasticity, but firmer, than 
ferrite. 
Cement carbide (C) - a chemical compound of iron with carbon. Cement 
carbide contains 6,67 % of carbon. Melting temperature of cement carbide is
near 1600?С. It has a difficult crystal lattice. It is the firmest and fragile 
component of iron carbon alloys. The more cement carbide is in an iron carbon 
alloy, the more is its hardness. 
Graphite – allotropic modification of carbon. Graphite is soft, its durability is 
very low. It contains in a type of inclusions of various forms in cast iron and 
graphitic steel. The form of graphite inclusions influences mechanical and 
technological properties of an alloy. 
Pearlite (П) - a mechanical mix of ferrite and cement carbide, containing 0,8 
% of carbon. It is formed at recrystallization (disintegration) of austenite at 
temperature 727?С. This decomposition is called as eutectoid, and a pearlite - 
eutectoid. The pearlite possesses high durability, hardness and increases 
mechanical properties of an alloy. 
Ledeburite is a mechanical mix of austenite and cement carbide, containing 
4,3 % of carbon. It is formed as a result of eutectic transformation at 
temperature 1147?С. At temperature of 727?С austenite turns into a pearlite, and 
after cooling ledeburite represents a pearlite mix with the cement carbide. 
Ledeburite has high hardness and big fragility. It contains in all white cast iron. 

180 
Dependence of properties of iron carbon alloy from the content of carbon and
constant impurity. 
Industrial steel and cast iron- is multicomponent alloys which structure besides 
iron and carbon includes so-called constant impurity. Constant impurity are 
manganese, the silicon which existence is caused by technological features of 
production, phosphorus and sulfur, and also gases - oxygen, nitrogen, hydrogen 
which is impossible to remove from metal completely. The content of carbon 
and impurity influences properties of iron carbon alloys. 
Carbon makes a great impact on mechanical properties of the steel. The steel 
of carbon in steel is higher, the more in its structure contains cement carbide. As 
cement carbide possesses high hardness and fragility, the increase in its quantity 
leads to increase of durability and hardness steel, to reduction of its plasticity 
and viscosity. With increase in the content of carbon in steel the density, elektro 
conductivity, heat conductivity, magnetic permeability decrease, electro 
resistance grows. 
Silicon and manganese consider as useful impurity. When smelting steel it add 
for deoxidation. Incorporating to oxygen ferrous oxide, they in the form of 
oxides pass to slag. As a result of a deoxidation the property of steel 
improves. 
The silicon which has remained in steel after the deoxidation, raises a fluidity 
limit that reduces its ability to cold processing by pressure. Therefore in the steel 
for punching the content of silicon should be lowered. 
Manganese considerably increases durability of steel, without reducing its 
plasticity, sharply reduces fragility at high temperatures, deleting sulfur from 
liquid melt. 
Phosphorus and sulfur are harmful impurity. Phosphorus reduces plasticity and 
viscosity became, increases her tendency to formation of cracks at low 
temperatures. Sulfur reduces impact strength, plasticity, an endurance limit, a 
fusibility and corrosion firmness of the steel. Sulfur causes a steel embrittlement 
at high temperatures. The content of sulfur and phosphorus in steel is strictly 
limited .Oxygen, nitrogen, hydrogen negatively influence properties of the steel. 
In machine-building cast iron carbon is present at a type of graphite. Graphite 
possesses very low mechanical properties. Therefore than more graphite is 
present at structure of cast iron and the its inclusions are more rough, the 
properties of cast iron are worse. But it promotes workability increase cast iron 
cutting, gives them antifrictional properties at a friction and extinguishes 
influence of vibrations and blows. 
Silicon essentially influences cast iron structure, strengthening its 
graphitization. Manganese increases mechanical properties of cast iron and 
interferes with their graphitization. Phosphorus increases wear resistance, but 
emrittle of cast iron. Sulfur of property of cast iron worsens. 

181 
Production of steel in oxygen converters. 
Still two processes of melting of steel in converters were quite recently 
applied: bessemerovskiya and tomasovskiya. Despite some distinctions in 
designs of converters and processes, the essence of these ways of receiving steel 
was the same and was that through liquid cast iron air there was an oxidation of 
impurity was blown. Now these two ways (bessemerovskiya and tomasovskiya) 
aren't applied, as are replaced in more progressive way - melting became in 
oxygen converters. 
Oxygen steel-making process consists in a purge of liquid cast iron in the 
converter with the main line up by oxygen from above through water cooled 
lance, lowered through a mouth. Now in oxygen converters make about 30 % of 
all melted steel. 
Application for blasting of pure oxygen allows to receive in oxygen converters 
steel with the content of nitrogen no more, than in martin steel, and 
approximately the same quality. 
Oxygen steel-making process allows to apply high-capacity converters. Now 
converters in capacity 300 t. already work. 
When melting steel in the oxygen converter apply liquid cast iron, scrap 
material, iron ore, a lime, fluorspar, rolling scale as initial materials. 
Production of steel in martin furnaces. 
Heat transfer to metal in these furnaces occurs generally emission (about 90 % 
from all transferred heat) and only 5-10 % convection. The majority of high-
capacity furnaces now heat natural gas with a fuel oil additive. 
These furnaces have regenerators which serve for heating of air and gas that 
allows to increase torch temperature to 1800?С. 
The capacity of martin furnaces reaches 900т. About 60 % of all steel are 
melted in martin furnaces. 
The working melting space of the furnace from above is limited to the arch, 
from below - bottom, from the lateral parties - a lobby and back walls and from 
end faces - "heads". Bottom has a form of an oblong bowl (bath) extending up. 
Burden materials load on bottom through charging windows in a forward wall of 
the furnace. In the lower part of a back wall there are openings for production of 
slag and the ready steel, closed up by a fire-resistant stopper which at release 
punch. In the heads symmetrical from both parties of the furnace, there are 
channels through which gas and air arrive and burning products are removed. In 
the lower part of a head incorporate to the regenerators intended for heating of 
gas and air. During the moment when in the left head there is a fuel mixing to air 
and receipt of products of burning in melting space, through the right head and 
channels adjoining it from the furnace the products of the burning which have 
been heated up to 1500-1600zs are removed. Flue gases after cleaning of firm 

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