A descriptive presentation on heat treatment analysis of Tempered 2.25Cr-1Mo steel ,commonly known as P22 steel. The presentation includes history of the material, objective and work-plan with procedures adopted to carry out the project.

1. Project Title:- Magnetic NDE characterization of
tempered 2.25Cr-1Mo steel
By
Apoorv Krishna
Department of Metallurgical and
Materials Engineering
2015PGMMMT05
NIT JAMSHEDPUR
“ Under the Guidance of ”
Dr. Rajat Roy
Scientist
NDE & Magnetic Materials Group
AMP Division
CSIR-NML
Mr. Kasimuthumaniyan S
Lecturer
Metallurgical Department
NIT, Jamshedpur

2. Motivation
➢ Recent years, there is an increase in demand to raise
the mechanical strength, and creep resistance of
boiler tubes used in coal fired thermal power plants for
economic and environmental reasons.
Fig: Piping system in a typical coal thermal power plant
 The steel is generally supplied in the normalized and
tempered condition in which initial microstructure of the steel
consists of bainitic phases which is not in stable equilibrium
and it continues to transforms at elevated temperatures.
 The exposure to elevated temperature result in microstructural
evolution in the form of recrystallization, grain coarsening and
nucleation and growth of secondary carbides.
 These microstructural modifications in the steel are likely to
affect its creep properties. Microstructural changes in the steel
during prolonged exposure sometimes lead to deterioration of
ductility and strength.
 Similar investigation indicated that in 2.25Cr-1Mo steel, as
the ageing temperature or time is increased, molybdenum
and chromium carbides get precipitated in the sequence of
M3C, M7C3, M23C6 and M6C at the grain boundaries and within
the grains.
Thermally aged 2.25Cr-1Mo specimens
TEM micrograph showing precipitation of
globular carbides of (a) M23C6 (b) M6C type of
at grain boundary in thermally aged 2.25Cr-
1Mo steel [ Material Science and Engg,Vol-
98(304)]

3. Objective ~
To understand the microstructural behavior of
tempered 2.25Cr-1Mo (grade P22) steel through mechanical
properties and magnetic NDE parameters.
Cr-Mo
Steels
Microstructure
Magnetic
Property
Mechanical
Property

4. WORK PLAN
Literature Survey
Sample Preparation
Heat Treatment of samples
Cr-Mo Steels
Mechanical
Optical
Microscopy
Scanning
Electron
Microscopy
Metallography
Hardness
Testing
Tensile
Testing
Magnetic
Magnetic
Barkhausen
Emission
Magnetic
Hysteresis
Loop
To gain background of study to be done

5. Procedure Adopted
➢As shown above in ‘Work Plan’, initially
the as-received sample water quenched
from solutionizing temperature of 1050°C
with holding time of 30 min.
➢Tempering was performed on the rest of
the samples in the range of 650°C-900
°C.
➢ Mechanical polishing of the samples
were done, and samples for magnetic,
mechanical and microstructural analysis
were separately prepared.
➢Testing of the heat treated specimens
sample for the magnetic, mechanical and
microstructure
Table.1 showing Composition of P22

6. Water-Quenched
750°C 800°C 850°C 900°C
Microstructural Characterization of P22 samples
700°C
650°C

7. Globular
Parallelepiped
Lenticular
750ºC 800ºC 850°C
Element (wt
%)
C Cr Mo Fe
Min 2.68 2.67 1.03 73.37
Max 9.85 12.86 3.97 89.53
Avg 6.26 7.59 2.65 81.25
Std.Dev 2.88 2.87 0.827 4.68
Element (wt
%)
C Cr Mo Fe
Min 5.17 4.73 1.43 81.89
Max 6.46 8.31 3.37 86.08
Avg 5.97 6.66 2.63 84.74
Std.Dev 0.604 1.58 0.92 1.97
Element (wt
%)
C Cr Mo Fe
Min 5.68 4.59 2.6 80.29
Max 9.31 6.23 3.78 84.56
Avg 7.21 5.2 3.02 81.97
Std.Dev 1.88 0.89 0.66 2.27
EDS Analysis of carbide phases at higher tempering temperatures

8.  The Globular shaped carbides as
identified in EDS analysis is reported to be
Cr-rich (M23C6) whereas the needle-like
morphology is known to be Mo-rich (M2C)
 With increasing tempering temperature it is
observed that there is gradual decrease in Cr-
rich carbides in contrast to Mo-rich as shown
in the previous slide.
 Globular carbides show maximum change
while coarsening with mean value varying
from 117 to 316 nm with change in
temperature.
 Meanwhile the equivalent size of rod-like
and globular shaped carbides further reduced
to 74 and 98 nm with increase in
temperature near to 800°C.
A B C
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Meansizeofcarbides(µm)
Tempering Temperature (°C)
Rod-Shape
Globular
700°C
750°C
800°C
Fig: Change in mean carbide size as a
function of tempering temperature.

9. Mechanical Evaluation of 2.25Cr-1Mo steel
 It is observed that the effect of
heat treatment is clearly reflected
in mechanical behavior of the
samples.
 Vickers Hardness was
recorded to fall about 37 %
from water-quenched state to
tempering stage of 650°C, with
corresponding decrease in
strength from 1143 to 720 MPa,
approx. 36%.
 Similar decrease in Vickers
hardness and strength was
observed up to 750 °C

10. Table : 2
Comparison of mechanical hardness and tensile properties of as-quenched and tempered
2.25Cr-1Mo at different temperatures
Sample Condition
Hardness (HV) at
30Kg
Tensile
Strength
(MPa)
Yield Strength
(MPa)
Percentage
Elongation (%)
Water-quenched 380.70 1143 952 8.85
650°C 239.10 720 615 13.81
700°C 203.10 617 557 12.68
750°C 173.40 504 386 20.71
800°C 164.70 548 296 24.37
850°C 166.20 529 302 24.0
900°C 167.80 493 234 24.10
 The decrease in mechanical hardness and strength is attributed to the release of
quenching stresses and annihilation of dislocation density. This phenomenon is
observed up to 750 °C of tempering.
 From 750°C material degradation becomes a function of precipitation of carbides
with change in their morphologies, but this does not affect mechanical properties
significantly.

11.  The adjoining figure shown is the heat treated
sample of P22 which is used under study.
It is known that ferromagnetic materials have sites of
instantaneous magnetism known as domain walls,
which align themselves in an ordered manner on
application of magnetic field.
 Precipitates and secondary phase particles that evolve
during microstructural change are known to act as
pinning sites for these domains.
The hindrance experienced by these magnetic
domains is detected in the form of pulses(voltage)
that is popularly known as Magnetic Barkhausen
emission (MBE)
➢All the magnetic parameters were recorded by an
electromagnetic sensor, named MagStar jointly
developed by CSIR-NML and Techno four.
Fig: Heat treated sample of P22
Magnetic Analysis
Fig: CSIR NML’s developed
Mag-star used for MBE & MHL analysis

12. Magnetic Characterization
• A hysteresis loop shows the relationship between
the induced magnetic flux density (B) and the
magnetizing force (H).
• It is known that macroscopic magnetic
properties such as permeability and remanence
are known to be stress dependent and are
affected by the alteration in stress state of the
material.
Some Important parameters needs to be judged
during magnetic characterization
• Coercivity- The amount of reverse magnetic field
which must be applied to a magnetic material to
make the magnetic flux return to zero. (The value
of H at point c on the hysteresis curve.)
• Permeability- A property of a material that
describes the ease with which a magnetic flux is
established in the component.
Fig: Hysteresis Curve showing
various parameters of
magnetization

13. Effect of tempering on MHL and MBE
650 700 750 800 850 900
40
48
56
64
72
80
Coercivity
Average Permeability
Tempering Temperature (°C)
Coercivity(Oe)
8
9
10
11
12
13
14
15
16
17
AveragePermeability 650 700 750 800 850 900
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
R.M.S
Peak value
Tempering Temperature (°C)
R.M.S(mV)
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Peakvalue(mV)
 Coercivity decreases as a function of tempering temperature whereas Permeability increase in contrast
to Coercivity which may be attributed to the release of quenching stresses with decrease in dislocation
density which supports the formation of magnetic field in the matrix.

14.  Barkhausen noise (MBN) technique is very sensitive to stress within ferromagnetic
materials because of important interactions between domain walls and pinning sites
(dislocations, defects)
 It is known that with the increase in tempering temperature secondary phase
particles (carbides) are introduced. It is clearly shown in plot, that near to 750°C
precipitate effect overcomes effect due to dislocation density.
 R.M.S of the water-quench specimen is recorded as 0.0385 mV. Similarly peak
value for the sample is 0.4785 mV. Such low values is attributed to high dislocation
density post quenching within the material matrix.
 The significant increase in RMS and peak, about 70% and 53% respectively, close to
850°C may be attributed to local change of material chemistry in the matrix and
precipitation stability. This phenomenon of reduced pinning effect at higher temperatures is
reported in many literatures.

15. Table.3 MHL(50mHz 1000Oe) & MBE (40Hz and 500Oe) parameters as
observed after heat treatment of 2.25Cr-1Mo steel
Sample
Condition
Average
permeability
Coercivity
(Oe)
R.M.S Voltage
(mV)
Peak Voltage
(mV)
Water-Quenched 66.75 107.65 0.038 0.48
650°C 152.95 75.23 0.273 2.09
700°C 213.46 125.75 0.245 2.02
750°C 129.48 114.50 0.243 1.90
800°C 94.4 99.19 0.210 1.66
850°C 47.17 97.50 0.128 1.01
900°C 141.36 99.4 0.164 1.22

16. Correlation of microstructure, magnetic and mechanical
properties in response to tempering treatment
 It is seen that there exists an approximate
linear relationship with magnetic property
(Coercivity) and mechanical properties
(Vickers hardness and UTS).
 High Vickers hardness is attributed to
the mechanically harder martensitic
phase that occurs as a result of
quenching, thereby increasing pinning
sites to domain walls movement, results in
magnetically harder nature (Coercivity)
of the specimen.
The lowest coercivity is in the highest
tempered sample in which the material
becomes soft, showing the lowest value of
Vickers hardness and ultimate tensile
strength.

17.  Tempering treatment results in softening of the water-quenched
specimen, reducing dislocation density. Tempering near to 700°C
initiated the formation of carbides. The SEM images show the presence of
needle-shaped carbides with small proportions of globular carbides.
Coarsening of these carbides is examined with increasing tempering
temperature.
Hardness and tensile strength of tempered specimens show a
continuous decrease, relating to stress released through tempering.
Precipitation of the carbides at higher temperatures (700 - 800°C) has
no significant role in the alteration of mechanical properties.
Conclusion drawn ….
Magnetic properties, i.e. coercivity, permeability, r.m.s. voltage etc., are
found to be strongly dependent on the microstructural features of the
specimen.

18.  The coercivity is related to decrease of dislocation density, while
permeability and r.m.s. voltage have a relation with dislocation density
as well as local changes of material chemistry through precipitation.
Future Scope….
 Transmission Electron Microscopy (TEM) analysis of the 2.25Cr-
1Mo water-quenched and tempered samples, so as to clearly indicate
the microscopic variations and change in properties of the specimen
due to evolving carbides of different morphologies.

19. “THANK YOU
FOR YOUR KIND
ATTENTION”
… APOORV KRISHNA