www.sefindia.org

STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

 Forum SubscriptionsSubscriptions DigestDigest Preferences   FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups  RegisterRegister FAQSecurity Tips FAQDonate
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log in to websiteLog in to websiteLog in to websiteLog in to forum 
Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.

Message No 43 on TMT, Thermex and Tempcore bars

 
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies.    www.sefindia.org Forum Index -> E-Conference 20th June 2005
View previous topic :: View next topic  
Author Message
inchak at tatasteel.com
Guest





PostPosted: Sat Jul 09, 2005 10:35 am    Post subject: Message No 43 on TMT, Thermex and Tempcore bars Reply with quote

QUESTION
Dear All:
What is the difference between TMT, Tempcore and Thermex reinforcement
bars?
In India we normally use the word TMT for all quenched and tempered bars
but I believe it has a different connotation than the treatment being used
in India presently.
Could someone pl expand on this.
Thanks,
Alpa

ANSWER
Thanks. This is another FAQ. and very relevant

Actually the base process has a metallurgical terminology of Thermo
Mechanical Treatment (TMT). Thermex and Tempcore are both reputed trade
names registered by the two major providers of this TMT technology. When
PROPERLY OPERATED both Thermex and Tempcore can produce good quality TMT
rebars. However, the technology of imparting online heat treatment to
rapidly moving red-hot bars is quite involved and requires specialised
design of equipment as well as control devices. Computerised process
control is often required to dynamically adjust the many rapidly changing
parameters depending on the chemical composition of the steel, the desired
grade and size of the rebar etc. A makeshift arrangement, irrespective of
the quantity of water used, is highly unlikely to produce the desired
results.

I take this opportunity to provide some insight into the TMT process.
Manufacture of high strength reinforcing steel is usually carried out
through one of three alternative process routes:
1. Hot rolling after micro-alloying
2. Hot rolling followed by cold work and
3. Hot rolling followed by heat treatment (TMT).
The TMT process is actually a heat treatment imparted to steel on-line just
after rolling. . For the larger diameters, a small addition of micro-alloys
may be resorted to.  After leaving the last stand of the rolling mill, the
bars are quenched (rapidly cooled) in water from a final rolling
temperature of about 950 Deg. C.  The quenching is partial - only until a
surface layer has been transformed from austenite (a steel phase stable
only at very high temperatures) to martensite (a steel phase stable at
ambient temperatures). This controlled quenching is achieved in one or more
specially designed on-line water cooling devices through which the steel
passes at a very high speed before reaching the cooling bed.
Because the quenching is only partial, a significant part of the original
heat remains in the core of the bar and, on the cooling bed, this heat
migrates towards the surface. This results in an automatic self-tempering
process where the surface layer of martensite is tempered. This "tempering
temperature" (or equalisation temperature) refers to the maximum
temperature attained by the surface of the bar after quenching. Tempering
enables a partial diffusion of carbon out of the extremely brittle but
strong martensite, thus relieving the inherent stresses locked in during
the sudden quenching of the red-hot steel in cold water. The resulting
tempered-martensite shows improved ductility and toughness compared to the
as-quenched martensite. Due to inherent characteristic of the quenching and
self-tempering (QST) process, the product retains its properties to
temperatures lower than this self-tempering temperature. The core of the
heat-treated rebars consists of ferrite and pearlite - which is not cold
worked and is therefore quite tough. In general, when the TMT process is
carried out properly the resulting product has a much higher level of both
strength and ductility with a much lower carbon equivalent than is normally
attained by the cold working processes like CTD. The fine martensitic
microstructure at the surface also ensures improved resistance to
corrosion, which has been measured to be about 30% higher than the cold
twisted material. While the cold twisted material looses it tensile
strength rapidly on heating about 350deg.C because the annealing action
sets in, the TMT bars are stable up to a temperature of at least 550 Deg.
C, a temperature at which is tempered. This accounts for a much better fire
resistance to the structures made with TMT bars.



********************************DISCLAIMER***********************************
Information contained and transmitted by this e-mail is confidential and
proprietary to Tata Steel Ltd. and is intended for use only by the
addressee. If you are not the intended recipient , you are notified that
any dissemination or copying of this e-mail is strictly prohibited and you
are requested to delete this e-mail immediately and notify the originator.
Tata Steel does not enter into any binding agreement with any party by
e-mail. Any views expressed by an individual do not necessarily reflect the
view of Tata Steel. Tata Steel is not responsible for the consequences of
any actions taken on the basis of information provided. While this e-mail
has been checked for all known viruses the addressee should also scan for
viruses. To know more about Tata Steel please visit www.tatasteel.com
********************************************************************************

Posted via Email
Back to top
Display posts from previous:   
This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies.    www.sefindia.org Forum Index -> E-Conference 20th June 2005 All times are GMT
Page 1 of 1

 

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum


© 2003, 2008 SEFINDIA, Indian Domain Registration
Publishing or acceptance of an advertisement is neither a guarantee nor endorsement of the advertiser's product or service. advertisement policy