Materials science

a)



b)

6. Figure 2 . a) - the lower left part of the state diagram of alloys of the iron-carbon (cementite) system; b) - cooling curves of iron-cementite alloys

6 .Table 1
Types and properties of structures found in iron-cementite alloys (steels and cast irons).

The name of the structure	The composition of the structure	Carbon content, %	Number of phases	Mechanical properties				Description of the structure
				v , kg/mm ^2	, %	NV
Ferrite	Limited solid solution of carbon in iron	0.006...0.025 (0...727 ^0C)	1	30	40	80...100	Plastic, but low accuracy
Austenite	Limited solid solution of carbon in iron	0.8...2.14 (727...1147 ^0С)	1	60	60	180...200	Very plastic
Cementite	Chemical combination of iron and carbon ( Fe 3 S )	6.67	1	200	0	800	Very hard and brittle
Perlite	A mechanical mixture of ferrite and cementite	0.80	2	60	20	200	Hardness and plasticity are average
Ledeburit	A mechanical mixture of cementite with perlite	4.30	2	100	1...2	7000	Hard and brittle

Table 6.2
Phase changes occurring on the main lines of the ferro-cementite phase diagram

Definition of the line	The changes that occur in the lines of the diagram when the alloys are cooled	Phases name	Number of phases	The number of degrees of freedom of the system ( S )
AS	The beginning of the separation of austenite from the liquid alloy	Austenite+liquid alloy	2	1
AE	Completion of austenite segregation from the liquid alloy	Austenite+liquid alloy	2	1
ES	The end of austenite separation from the liquid alloy, the formation of ledeburite	Austenite+cementite+ +ledeburite	3	0
SD	Primary cementite begins to separate from the liquid alloy	Liquid alloy + cementite	2	1
SF	End of primary cementite separation from liquid alloy, formation of ledeburite	Liquid alloy + cementite + ledeburite	3	0
ESF	Formation of ledeburite from liquid alloy	Liquid alloy+ +austenite +cementite	3	0
GS	Initiation of ferrite segregation from austenite	Austenite + ferrite	2	1
GP	Termination of ferrite segregation from austenite	Austenite + ferrite	2	1
PS	Ferrite separation from austenite ends and pearlite begins to separate	Austenite + ferrite + cementite	3	0
PSK	Formation of pearlite from austenite	Austenite + ferrite + + cementite	3	0
SE	Initiation of secondary cementite segregation	Austenite + cementite	2	1
SK	End of secondary cementite segregation, formation of pearlite from austenite	Austenite + cementite + ferrite	3	0
PQ	Tertiary cementite begins to separate from ferrite	Ferrite + cementite	2	1

6.Table 3
Phase changes occurring at points in the phase diagram of ferro-cementite alloys

Designation of points	Phase changes that occur at points when alloys are heated and cooled	Carbon content, %	Temperature corresponding to the point, ^0C	The name of the phase	Number of phases	Number of degrees of freedom	Reminder
A	Liquid and solidification temperature of pure iron	0	1539	Liquid alloy+ + iron crystals	2	1	Gibbs' rule cannot be applied to one-component systems
B	Fluidization and solidification temperature of cementite	6.6	(1260)	Liquid alloy+ +cementite (primary)	2	1
C	Liquefaction and formation of ledeburite	4.3 4.3	1147	Liquid alloy+ +austenite + cementite	3	0
D	Maximum dissolution of carbon in austenite	2.1 2.1 4	1147	Liquid alloy+ +austenite+cementite	3	0
E	Minimum dissolution of carbon in austenite	0.80 .02	727	Austenite + ferrite + cementite	3	0
F	Conversion of -iron to α -iron or -iron to -iron	0	911	α-iron + - iron	2	1
J	Maximum solubility of carbon in α -iron	0.0 0.0 25	727	Austenite+ferrite+ +cementite	3	0
H	Minimum solubility of carbon in α -iron	0.0 0.06 _	0	Ferrite+ +cementite	2	1
N	There will be no phase changes	6.6	727	Cementite (primary)	1	-
G	There will be no phase changes	6.6	1147	Cementite (primary)	1	-

Work perform for necessary equipment , material and tools : iron - cementite of alloys condition diagram , in the composition each different amount carbon was _ _ of alloys samples , electric oven , microscope , sand paper is small , millimeter paper is small .
Laboratory procedure:

1. 
   Types and properties of structures present in the state diagram of iron-cementite alloys are studied.;
   
2. 
   Changes that occur when heating and cooling iron-carbon alloys are studied using state diagrams;
   
3. 
   The application of Gibbs' phase rule and the rule of cross-sections are studied to analyze the state diagram. Using these rules, the method of determining the composition and quantity of alloys is mastered.
   
4. 
   Using the state diagram, the cooling curves of the alloys are drawn according to the option given by the teacher.
   

Task: Analyze the structural changes that occur in alloys 1 and 2 with a carbon content of x % (the value of x is taken according to the option) when heated to a given temperature. Draw the cooling curve of these alloys starting from their liquidus temperature.
The following shall be included in the laboratory report:

1. 
   Schematic of the ferro-cementite phase diagram, phases, structures and their properties that exist in this system;
   
2. 
   A cooling curve drawn using the state diagram of two alloys of the desired composition; a review of the phase changes that occur when these alloys are heated and cooled (using the Gibbs and cross sections rule);
   
3. 
   According to this option, the amounts of different phases in the alloy with the given composition are determined using the rule of sections;
   
4. 
   General conclusions .
   

Review questions:

1. 
   What does the ferro-cementite state diagram represent?
   
2. 
   What is phase rule or Gibbs law?
   
3. 
   What lines are called liquidus and solidus lines?
   
4. 
   From the ferro-cementite phase diagram, indicate the regions where the alloy is single-phase and two-phase.
   
5. 
   Draw the cooling curves of alloys using phase diagrams.
   

3 - laboratory work
Studying the technology of preparation of macro- and micro- samples


The purpose of the work: to study the technology of preparation of macro- and microslides, to determine the structure of the sample observed under a microscope.


Theoretical information
1) Preparation of macroslide. Examining the external appearance and structure of any materials, i.e. solids, including metals, with the help of an ordinary eye or a lens (loupe) is called determining its macrostructure. Typically, lenses or magnifiers magnify the actual size of objects by up to 30 times. In order to determine the macrostructure of the material, the surface of the samples prepared from it is thoroughly smoothed and cleaned, such a sample is called a macroslide. In the experiment , samples with a thickness of up to 10 are prepared from carbon steels, i.e. rolls, which are not found when determining the macrostructure . 20 mmWhen steels are macro-analyzed, it is often determined that there are liquefaction phenomena in them, the presence of voids: sulfur, phosphorus, manganese and gas bubbles, air voids, cracks or not.
Technology of preparation of macroslide. The macro sample preparation technology is as follows: the tested sample is divided into two using a hacksaw or a lathe. If the macro sample is prepared from the cross-sectional surface of the part, it is called a template . The sample is cleaned on a lathe, using an ego or an abrasive wheel, then it is polished with metallographic grinding papers, gradually moving from large numbers of metallographic grinding papers to small numbers. When moving from one numbered paper to the second numbered paper, the sample is rotated 90 ^{0 .} Grinding is continued until the lines on the surface of the sample disappear. To make the macrostructure appear, it is exposed to various reagents. Under the influence of various reactive solutions, the appearance of the internal structure is formed on the surface of the macrosamples (dendritic crystals and fibrous structures).