This document discusses time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams. TTT diagrams show the transformation of austenite at constant temperatures over time, indicating what microstructures form during different cooling rates. CCT diagrams track phase changes during continuous cooling at various cooling rates. Both diagrams are important for selecting processing conditions to achieve desired material properties in steels. The document provides detailed explanations of the various microstructures - pearlite, bainite, martensite - that form during austenite decomposition, and how TTT and CCT diagrams can be used to understand their formation.
Iron – Carbon Diagram is also known as Iron – Carbon Phase Diagram or Iron – Carbon Equilibrium diagram or Iron – Iron Carbide diagram or Fe-Fe3C diagram
Iron – Carbon Diagram is also known as Iron – Carbon Phase Diagram or Iron – Carbon Equilibrium diagram or Iron – Iron Carbide diagram or Fe-Fe3C diagram
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
Benefits:-
# Students can catch up on notes they missed because of an absence.
# Underachievers can find peer developed notes that break down lecture and study material in a way that they can understand
# Students can earn better grades, save time and study effectively
Our Vision & Mission – Simplifying Students Life
Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
Like Us - https://www.facebook.com/FellowBuddycom
Presentation on Carburizing (Heat Treatment Process).
Presented To,
Engr. Ubaid-ur-Rehman Ghouri, Department of Industrial & Manufacturing Engineering, UET Lahore (RCET Campus).
Presented By,
Muhammad Zeeshan
Zahid Mehmood
Ali Iqbal
Muhammad Waqas
Recrystallization is the process in which deformed grains of the crystal structure are replaced by a new set of stress-free grains that nucleate and grow until all the original grains have been consumed. The process is accomplished by heating the material to temperatures above that of crystallization.
The process of transformation of a substance from liquid to solid state in which the crystal lattice forms and crystals appear.
•Volume shrinkage or volume contraction
FellowBuddy.com is an innovative platform that brings students together to share notes, exam papers, study guides, project reports and presentation for upcoming exams.
We connect Students who have an understanding of course material with Students who need help.
Benefits:-
# Students can catch up on notes they missed because of an absence.
# Underachievers can find peer developed notes that break down lecture and study material in a way that they can understand
# Students can earn better grades, save time and study effectively
Our Vision & Mission – Simplifying Students Life
Our Belief – “The great breakthrough in your life comes when you realize it, that you can learn anything you need to learn; to accomplish any goal that you have set for yourself. This means there are no limits on what you can be, have or do.”
Like Us - https://www.facebook.com/FellowBuddycom
Presentation on Carburizing (Heat Treatment Process).
Presented To,
Engr. Ubaid-ur-Rehman Ghouri, Department of Industrial & Manufacturing Engineering, UET Lahore (RCET Campus).
Presented By,
Muhammad Zeeshan
Zahid Mehmood
Ali Iqbal
Muhammad Waqas
Recrystallization is the process in which deformed grains of the crystal structure are replaced by a new set of stress-free grains that nucleate and grow until all the original grains have been consumed. The process is accomplished by heating the material to temperatures above that of crystallization.
The process of transformation of a substance from liquid to solid state in which the crystal lattice forms and crystals appear.
•Volume shrinkage or volume contraction
Mumbai University.
Mechanical Engineering
SEM III
Material Technology
MOdule 3
TTT diagram, CCT diagram Hardenability concepts and tests, Graphitization of Iron- Grey iron, white iron, Nodular and malleable irons, their microstructures, properties and applications
Quenching is a vital part of the heat treating process in manufacturing. This presentation by Houghton International will show you how to master the process for the most efficient quenching and heat treating operations.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
State of ICS and IoT Cyber Threat Landscape Report 2024 previewPrayukth K V
The IoT and OT threat landscape report has been prepared by the Threat Research Team at Sectrio using data from Sectrio, cyber threat intelligence farming facilities spread across over 85 cities around the world. In addition, Sectrio also runs AI-based advanced threat and payload engagement facilities that serve as sinks to attract and engage sophisticated threat actors, and newer malware including new variants and latent threats that are at an earlier stage of development.
The latest edition of the OT/ICS and IoT security Threat Landscape Report 2024 also covers:
State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
Expansion of bot farms – how, where, and why
In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
Why are attacks on smart factories rising?
Cyber risk predictions
Axis of attacks – Europe
Systemic attacks in the Middle East
Download the full report from here:
https://sectrio.com/resources/ot-threat-landscape-reports/sectrio-releases-ot-ics-and-iot-security-threat-landscape-report-2024/
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more ‘mechanical’ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
2. Phase Transformations in Steels
• Iron has having different crystal structures at
different temperatures.
• It changes from FCC to BCC at 910o C.
• This transformation results in austenite
transforming to pearlite at eutectoid
temperature.
• This transformation of austenite is time
dependant.
4. Fe-C Equilibrium Diagram
• Though the Fe-C equilibrium diagram is very useful, it does
not provide information about the transformation of
austenite to any structure other than equilibrium
structures, nor does it provide any details about the
influence of cooling rates on the formation of different
structures.
• In other words, Fe-C diagram does not explain the
decomposition of austenite under non-equilibrium
conditions or conditions involving faster rates of cooling
than equilibrium cooling.
• Several structures (e.g. martensite) not appearing on the
equilibrium diagram may be found in the microstructures in
steels.
5. TTT Diagram
• On the other hand, TTT diagram is a more
practical diagram.
• It shows what structures can be expected
after various rates of cooling.
• It graphically describes the cooling rate
required for the transformation of austenite to
pearlite, bainite or martensite.
• TTT diagram also gives the temperature at
which such transformations take place.
6. Phase diagram and TTT diagram
Which information are obtained from phase diagram or
TTT diagram?
• Phase diagram :
– Describes equilibrium
microstructural development
that is obtained at extremely
slow cooling or heating
conditions.
– Provides no information on
time taken to form phase
• TTT diagram
– For a given alloy
composition, the percentage
completion of a given phase
transformation on
temperature-time axes is
described.
7. Transformation Diagrams
• There are two main types of transformation
diagrams that are helpful in selecting the
optimum steel and processing route to
achieve a given set of properties. These are
1. Time-temperature transformation (TTT) diagrams
2. Continuous cooling transformation (CCT) diagrams
8. Transformation Diagrams
• Time-temperature transformation (TTT)
diagrams
1. Indicates the amount of transformation at a
constant temperature.
2. Samples are austenitised and then cooled
rapidly to a lower temperature and held at that
temperature whilst the amount of transformation
is measured, for example by dilatometry.
3. Obviously a large number of experiments are
required to build up a complete TTT diagram.
9. Transformation Diagrams
• Continuous cooling transformation (CCT) diagrams
1. Indicates the extent of transformation as a function
of time for a continuously decreasing temperature.
2. Samples are austenitised and then cooled at a
predetermined rate and the degree of transformation
is measured, for example by dilatometry.
3. In this case also a large number of experiments are
required to build up a complete CCT diagram also
10. Transformation Diagrams
• CCT diagrams are generally more appropriate
for engineering applications as components
are cooled (air cooled, furnace
cooled, quenched etc.) from a processing
temperature as this is more economic than
transferring to a separate furnace for an
isothermal treatment.
13. Fe-C Equilibrium Diagram
• Austenite is stable above A1 temperature
• Below this temperature, austenite is unstable.
Eutectoid
Steel
Spring 2001
Dr. Ken Lewis
ISAT 430
13
14. How Transformation Ocures?
• Transformation of austenite to pearlite ocures
by nucleation and growth mechanism.
• This transformation requires diffusion.
15. Nucleation rate
• As temperature decreases below eutectoid temperature, r* (critical size of
nucleus) decreases increasing the nucleation rate N.
• At very low temperature, nucleation rate decreases due to large decrease
in diffusion rate.
• At intermediate temperature, nucleation rate is maximum
16. Growth of nuclei
– Growth of nuclei is a diffusion controlled process
.
QD
Growth Rate G ce RT
where QD : activation energy for self diffusion
Growth rate decreases with decrease in temperature
17. Transformation Rate
.
.
• Transformation rate of a phase : N G
• Transformation rate first increases, reaches a maximum and then starts
decreasing with decrease in temperature
18. Time for Transformation
•
Time required for transformation as a function of temperature
follows a reverse trend than the rate of transformation.
Time required for transformation fist decreases, reaches a
minimum and then starts increasing with decrease in
temperature.
20. Isothermal transformation of eutectoid steel
Let us take a eutectoid steel and do the following experiment
–
–
–
–
–
Step 1 – Heat the sample above A1 temperature for austenitisation
Step 2 – Transfer the sample to a salt bath kept below A1 Temp.
Step 3 - Keep it at the bath temperature for a specified time
Step 4 - Quench to room temperature
Step 5 – Find out the amount of phases present
21. Isothermal transformation of eutectoid steel
below Eutectoid Temperature
• Determine the amount of pearlite formed after holding at
7050 C for different times
22. Fraction of transformation Vs the logarithm of time at
constant temperature (The S Curve).
Plot the result of the experiment
This is known as S curve
23. Fraction of transformation Vs the logarithm of time at
constant temperature (The S Curve).
The transformation starts but it takes some time before we can see a
precipitate. The time required for transformation required to initiate the
transformation is known as Incubation Period.
The rate of transformation first increases and then starts decreasing
24. Time required for completion of
transformation
• Now repeat the experiment at different temperatures below A1 temp.
• Plot the time for completion of transformation at different temperatures.
30. Let us consider eutectoid reaction as
an example
eutectoid reaction:
γ(0.8 wt% C)
↓
α (0.025 wt% C) + Fe3C
31. Let us consider eutectoid reaction as
an example
The S-shaped curves are
shifted to longer times at
higher T showing that the
transformation is
dominated by nucleation
(nucleation rate increases
with supercooling) and not
by diffusion (which occurs
faster at higher T)
33. TTT Diagrams for Eutectoid Steel
• We can plot the time for start and completion of transformation of
austenite to pearlite at different temperatures or for any other amount of
transformation.
34. Transformations of austenite to Pearlite
pearlite
Transformations of austenite :
→ + Fe3C
1) At slightly lower T below 727 ℃ : T <<
• Coarse pearlite
: nucleation rate is very low.
: diffusion rate is very high.
2) As the T (trans. temp.) decreases to
500 ℃
• Fine pearlite
: nucleation rate increases.
: diffusion rate decreases.
Strength : (MPa) = 139 + 46.4 S-1
S : inter-lamellar spacing
655
℃
600
℃
534
℃
487
℃
35. But at lower temperatures ….
• At lower temperatures, the austenite
transforms to bainite.
• Bainite is also a mixture of ferrite and
cementite but not in the form of alternate
layers.
36. Transformations of austenite to Bainite
3) At further lower temperatures, 250 ℃ < Tt < 500 ℃, below the nose in
TTT diagram.
• Driving force for the transformation ( → + Fe3C) is very high.
• Diffusion rate is very low.
• Nucleation rate is very high.
→ + Fe3C (But not in the form of alternate layers)
: Bainite ; cementite in the form of needle type.
495 ℃
410 ℃
bainite
37. TTT diagram for eutectoid steel
• Plot the time for start and completion of transformation at
different temperatures at still lower temperatures
38. On further decreasing the
transformation temperature
• Below a certain temperature, the austenite
changes or transforms to martensite.
• Martensite is a super saturated solid solution
of carbon in iron.
• It is a diffusionless transformation.
• It is also known as shear transformation as the
interface between austenite and martensite
moves as a shear wave at the speed of sound.
39. Transformations of austenite to Martensite
4. When the austenite is quenched to temp. below Ms
→ ’ (martensite)
: Driving force for trans. of austenite → extremely high.
Diffusion rate is extremely slow.
: Instead of the diffusional migration of carbon atoms to produce
separate and Fe3C phases, the matensite transformation involves
the sudden reorientation of C and Fe atoms from the austenite (FCC)
to a body centered tetragonal (bct) solid solution.
→ ’ (martensite), a super saturated
solid solution of carbon in iron
formed by shear transformation
(diffusionless transformation)
→ very hard and brittle phase
martensite
40. Diffusionless Transformation
1) Diffusionless transformation → no compositional change during
transformation.
2) The temperature at which the transformation of → ’ starts is
known as at Ms temp. and finishes at Mf temp.
3) Degree of super saturation and c/a ratio increases as the carbon
content increases.
42. Time Temperature Transformation
(TTT) Diagram
• Below A1 , austenite is unstable, i.e., it can transform
into pearlite, bainite or martensite.
• The phases finally formed during cooling depend upon
time and temperature.
• TTT diagram shows the time required for
transformation to various phases at constant
temperature, and, therefore, gives a useful initial guide
to likely transformations.
• In addition to the variations in the rate of
transformation with temperature, there are variations
in the structure of the transformation products also.
43. The Time – Temperature –
Transformation Curve (TTT)
•
•
•
Spring 2001
Dr. Ken Lewis
At slow cooling rates the trajectory
can pass through the Pearlite and
Bainite regions
Pearlite is formed by slow cooling
– Trajectory passes through Ps
above the nose of the TTT
curve
Bainite
– Produced by rapid cooling to a
temperature above Ms
– Nose of cooling curve avoided.
ISAT 430
43
44. The Time – Temperature –
Transformation Curve (TTT)
• If cooling is rapid enough
austenite is transformed into
Martensite.
– FCC → BCT
– diffusion separation of carbon
and iron is not possible
• Transformation begins at Ms and
ends at Mf.
– If cooling is stopped at a
temperature between Ms and
Mf , it will transform into
martensite and bainite .
Spring 2001
Dr. Ken Lewis
ISAT 430
44
45. Full TTT Diagram
The complete TTT
diagram for an ironcarbon alloy of eutectoid
composition.
A: austenite
B: bainite
M: martensite
P: pearlite
46. TTT Diagram
• Transformations at temperatures between
approximately 705°C and 550°C result in the
characteristic lamellar microstructure of pearlite.
• At a temperature just below A1 line, nucleation
of cementite from austenite will be very slow, but
diffusion and growth of nuclei will proceed at
maximum speed, so that there will be few large
lamellae and the pearlite will be coarse.
• However, as the transformation temperature is
lowered, i.e., it is just above the nose of the Ccurve, the pearlite becomes fine.
47. Bainite
• At temperatures between 550°C and 240°C (the approximate, Ms
temperature line), transformation becomes more sluggish as the
temperature falls, for, although austenite becomes increasingly
unstable, the slower rate of diffusion of carbon atoms in austenite
at lower temperatures outstrips the increased urge of the austenite
to transform. In this temperature range the transformation product
is bainite.
• Bainite consists (like pearlite) of a ferrite matrix in which particles of
cementite are embedded. The individual particles are much finer
than in pearlite. The appearance of bainite may vary between
– feathery mass of fine cementite and ferrite for bainite formed around
480°C and
– dark acicular (needle shaped) crystals for bainite formed in the region
of around 310°C).
48. Martensite
• At the foot of the TTT
diagram, there are two lines
Ms (240°C ) and Mf (50°C).
• Ms represents the
temperature at which the
formation of martensite will
start and Mf the temperature
at which the formation of
martensite will finish during
cooling of austenite through
this range.
49. Martensite
•
•
•
Martensite is formed by the
diffusionless transformation of
austenite on rapid cooling to a
temperature below 240°C
(approximately) designated as Ms
temperature.
The martensitic transformation differs
from the other transformations in that
it is not time dependent and occurs
almost instantaneously, the
proportion of austenite transformed
to martensite depends only on the
temperature to which it is cooled.
For example the approximate
temperatures at which 50% and 90%
of the total austenite will, on
quenching, transform to martensite
are 166°C and 116°C respectively.
50. Martensite
(i) Martensite is a metastable phase of
steel, formed by transformation of austenite
below Ms temperature.
(ii) Martensite is an interstitial supersaturated
solid solution of carbon in iron having a bodycentered tetragonal lattice.
(iii) Martensite is normally a product of
quenching.
(iv) Martensite is very hard, strong and brittle.
54. The Time – Temperature –
Transformation Curve (TTT)
• Composition Specific
– This curve is for 0.8%
carbon
• At different
compositions, shape is
different
Spring 2001
Dr. Ken Lewis
ISAT 430
54
55. TTT Diagram
• The TTT digrams for hypo-eutectoid steels and
hyper-eutectoid steels will differ from that of
eutectoid steels
• The TTT digrams for hypo-eutectoid steels will
have an additional curve to show the
precipitation of ferrite from martensite before
transformation of remaining austenite to
pearlite
57. TTT Diagram
• The TTT digrams for hyper-eutectoid steels
will differ from that of eutectoid steels
• The TTT diagrams for hyper-eutectoid steels
will have an additional curve to show the
precipitation of cementite from martensite
before transformation of remaining austenite
to pearlite
62. CCT Diagram
• If you don’t hold at one temperature and allow
temperature to change with time, you are “Continuously
Cooling”.
• In continuous cooling, the constant temperature basis of
TTT diagram becomes obviously unrepresentative.
• More relevant information can, thus, be obtained from a
CCT diagram in which phase changes are tracked for a
variety of cooling rates.
• Therefore, a CCT diagram’s transition lines will be different
than a TTT diagram.
• Plotting actual cooling curves on such a diagram will show
the types of transformation product formed and their
proportions.
63. Continuous cooling transformation diagram for eutectoid steels
• Annealing : heat the steel into
region → cool it in furnace
(power off) → coarse pearlite
• Normalizing : heat the steel
into region → cool it in air →
fine pearlite
• Hardening : heat the steel into
region → quench it in water
→ Martensite
65. Effect of Cooling Rate on the Formation of
Different Reaction Products
• Very slow cooling rate (furnace cooling), typical of
conventional annealing, will result in coarse
pearlite with low hardness.
• Air cooling is a faster cooling rate than annealing
and is known as nonmalizing. It produces fine
pearlite.
• In water quenching, entire substance remains
austentic until the Ms line is reached, and
changes to martensite between the Ms and Mf
lines.
66. Effect of Cooling Rate on the Formation of
Different Reaction Products
• It is possible to form 100% pearlite or 100%
martensite by continuous cooling, but it is not
possible to form 100% Bainite.
• To obtain a bainitic structure, cool rapidly
enough to miss the nose of curve and then
holding in the temperature range at which
bainite is formed.
67. Critical Cooling Rate (CCR)
• If the cooling curve is tangent to the nose of
TTT curve, the cooling rate associated with
this cooling curve is Critical Cooling Rate (CCR)
for this steel.
• Any cooling rate equal to or faster than CCR
will form only martensite.
68. Critical Cooling Rate and Hardness of
Different Micro-Structures
Critical
cooling
rate
Hardness
of
different
structures
69. Factors Affecting Critical Cooling Rate
• Any thing which shifts the TTT diagrm towards
right will decrease the critical cooling rate
• The following factor affect the critical coolin rate
– 1. Grain size
– 2. Carbon content
– 3. Alloying elements
Increase in grain size, carbon content or alloying
elements shifts the TTT diagram towards right and
hence reduces the critical cooling rate as shown in
next slide.
70. Effect of Carbon Content and Grain
Size on Critical Cooling Rate
75. Effect of Grain Size
• Fine grain steels tend to promote formation of
ferrite and pearlite from austenite.
• Hence decrease in grain size shifts the TTT
diagram towards left.
• Therefore, critical cooling rate increases with
decrease in grain size.
76. Effect of Carbon Content
• There is a significant influence of composition on
the TTT and CCT diagrams. For the
transformation diagrams we see the effect
through a shift in the transformation curves. For
example:
– An increase in carbon content shifts the CCT and TTT
curves to the right (this corresponds to an increase in
hardenability as it increases the ease of forming
martensite - i.e. the cooling rate required to attain
martensite is less severe).
– An increase in carbon content decreases the Ms
(martensite start) temperature.
77. Effect of Alloying Elements
• Different alloying elements have their
different effects on TTT diagram.
• An increase in alloy content shifts the CCT and
TTT curves to the right and
• Alloying elements also modify the shape of
the TTT diagram and separate the ferrite +
pearlite region from the bainite region making
the attainment of a bainitic structure more
controllable.