The presentation is part of the national level technical symposium held in 2013 at Jawaharlal Nehru Technological University. This paper explains the characteristics of Thermo Mechanically Treated Steels, the manufacturing processes, microstructures and advantages against the Cold Twisted and Deformed steels. The paper was authored by Mr. Praveen Kumar Jaisawal and Mr. Himalaya Bir Shrestha, both Mechanical Engineering students, which won them the first prize at the event.

1. Presenting ppt on:
Thermo Mechanical Treatment(TMT) Steels
BY
PRAVIN KUMAR JAISAWAL
III MECH.
udayapur.pravin@gmail.com
HIMALAYA BIR SHRESTHA
III MECH.
himal_shrestha2000@yahoo.com
SRI VENKATESWARA COLLEGE
OF ENGINEERING &
TECHNOLOGY,(autonomous)
R.V.S.Nagar,Chittoor.

2. TMT Steels

3. Thermo Mechanical Treatment
 Thermo-Mechanical Treatment (TMT) is also known
as Thermomechanical processing.
 It is a metallurgical process that integrates work hardening and heat-
treatment into a single process to alter the shape and structure.
 The structural changes caused by TMT depend
on the nature and density of the imperfections.
Heat + deformation = fine grain structure

4. HISTORY
 The combination of plastic deformation with phase
transformations was introduced in the early 20th
century.
 Low temperature TMT
process was first tested in
1954 in the USA.
 USSR introduced high
temperature TMT for
mass-scale production.

5. CTD bars
 Cold Twisted and Deformed (CTD)
steels, are also called as torsteel.
 Stages in CTD bars production:-
i. steel bars rolled in the mills at
high speed.
ii. tempered in open air for at least
24-36 hours depending on the
diameter.
iii. manually lifted from the
dumping yard to twisting
machines.
iv. Cold twisted after elongation to
impart greater tensile strength.

6. Cons of CTD bars
Low strength Intensive labour-oriented
Time Consuming Cost Ineffective Doesn’t conform
to standards

7. Manufacturing of TMT bars
 The chief raw material is
inexpensive low carbon steel.
 Heated to approximate 1100°C.
 Progressively hot rolled.
 Water quenched.
 Subsequently tempered in
cooling bed.

8. TMT processes
1.Thermax Process
2.Tempcore Process
3.Turboquench Process

9. Thermax Process
 The word ‘Thermax’ is derived
from ‘thermal exchange’.
 High pressure water is used for
quenching hot rolled bars.
 Peripheral structure transforms
into martensite while the core
into ferrite pearlite.

10. Tempcore Process
This process involves three
stages of treatment:-
i. Quenching
ii. Self-tempering
iii. Atmospheric Cooling
It doesn’t require costly
alloying elements(V, Nb).

11. Turboquench Process
Three types of
transformations are involved
here:
i. Tempered martensite in
periphery.
ii. Intermediate ring of
martensite and bainite.
iii. Ferrite pearlite core.

12. Continuous Cooling Transformation
Diagram
 The cooling rate I is very
fast(350oC/s) and forms
martensite.
 The critical cooling rate
II(140°C/s) just suppress
pearlite & bainite
formation.
 The cooling rate IV(35°C/s)
gives fine pearlite and V
gives coarse pearlite.

13. Transformations occuring in TMT bars

14. Microstructures inside TMT bars

15. Why Tempered Martensite?
Fig: Effect of tempering Fig: Variation of energy absorbed
with temperatures for 3 structures

16. Microhardness of TMT bars
The above figure indicates the micro
hardness of a thermo processed bar from
the surface to the core.
Microstructure of TMT bars
surface coreHARDNESS

17. Attributes of TMT bars

18. CTD bars VS TMT bars
Properties CTD bars TMT bars
Strength Avg(normally upto Fe415
grade)
High(Grade Fe500 is easily
available)
Elongation Approx 14.5% High
Weldability Weak Better and more strength
Formability Average Excellent due to uniform
elongation
Ductility &Fatigue Strength Average High
Corrosion Resistance Low High
Ribs Manual & Non uniform Computerised and uniform
Grains Coarse Fine/ultra fine
Safety Low Better
Cold forming Poor Good

19. Applications of TMT bars
Houses and Apartments Bridges
Flyovers Highrise Buildings

20. Applications of TMT bars
Dams Industrial Structures
Railway and Metro Platforms Thermal and Hydel Power Plants

21. CONCLUSION
Thermo mechanically
treated (TMT) steels:-
• are the new-generation-
high-strength steel.
• meet the highest
international quality
standards.
• mostly used as
reinforcing bars with
concrete.

23. Backup Slides

24. Hardness Explained

25. Designation of Steels
As per AISI and SAE standards:
First Number Type of steels
1 Carbon Steels
2 Nickel Steels
3 Ni-Cr Steels
4 Mo Steels
5 Cr Steels
6 Cr-V Steels
7 Tungsten Steels
8 Ni-Cr-Mo Steels
9 Si-Mn Steels

26. Crystal Structures

27. Iron-Iron Carbide Diagram

28. Transformation diagram of TMT