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The properties of alloy steels depend on what phases the alloying elements form
with iron and carbon. Most of the alloying elements form solid solutions and carbides.
Classification and centering of steels. Steels are
classified according to a
number of parameters . For example : according to the composition, according to the
amount of carbon, according to the quality, according to the
application , etc.
are divided into low carbon (S
0.25% ), medium carbon (0.25
S
0.6) and
high carbon (S 0.6%) steels.
Depending on the type of alloying substances, steels are divided into chrome,
chrome-nickel, manganese and other steels.
By quality, steels
are divided into quality (SR 0.025%) steels.
All alloy steels are quality and high quality steels. According to the total amount
of alloying substances, steels are low-alloyed (
5%). It is medium alloyed (5-10%)
and highly alloyed (
10%).
Marking of steels. Standard quality steels are marked with the letters S t and 6
from O is determined by numbers up to For example, StO, St2, St5.
Quality carbon steels are marked with two numbers. Example , steel 10: steel
65. Numbers, steel10: steel 30, steel65 . The numbers indicate the percentage of carbon
in the steel.
High carbon tool steels are called U7, U8, U 10 A. The numbers on these steel
grades indicate the carbon content of the steel in tenths of a percent.
shows the amount of carbon, alloying substances and their percentage .
Alloying substances are indicated by letters in the steel brand: Ni-H, Gr-X, Mn-
G, M
0
-M, Ti-T, VF, Si-C, Al - Yu, Su-D, etc.
For example: steel 25XNZA. It is chrome-nickel steel , carbon content is 0.25%,
chromium content is 1 % , nickel content is 3%, "A" at the end of the brand indicates
that the steel is of high quality.
Additional information related to the classification of steels is given in the
relevant parts of materials science.
Gray, high strength and malleable cast iron.
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Depending on the form of carbon contained in cast iron, cast iron is divided into
white, gray, high strength and malleable cast iron. According to the structure of the
metal base, cast irons are divided into ferritic, pearlite and ferrite-pearlite cast irons.
Carbon in white cast iron is in the form of cementite, i.e. chemically bonded with
iron, so white cast iron is very hard and brittle. Car details are not made from it.
Gray, malleable and high-strength cast iron with high strength and technological
properties are used for machine details. In these cast irons, all or a certain part of the
carbon is in the pure form of graphite: in gray cast irons it is plate-shaped, in malleable
cast irons it is cucumber-shaped (papapaga) and in high-strength
cast irons it is
spherical. will be in the form
The strength of graphite is very small, so it would not be wrong to say that the
places with graphite are gaps and cracks. Especially plate-shaped graphite
in gray cast
iron sharply reduces the strength of cast iron, the spherical form of graphite is the most
optimal in terms of strength. For example, the relative elongation of plate graphite cast
iron is 0.2-0.5%, and the relative elongation of spheroidal graphite cast iron is 10-15%.
Graphite, on the one hand, reduces the strength of cast iron, and on the other
hand, increases the workability of cast iron.
Cast irons are not sensitive
to stress concentrations, corrosion resistant, and
cheaper than steel.
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