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Chemical Quality of TMT bars
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bijoyav
SEFI Member
Joined: 13 Dec 2008
Posts: 11 / Posted: Mon Nov 15, 2010 12:38 pmPost subject: Chemical Quality of TMT bars /
Now the steel market is flooded with TMT bars made from scrap. Often, they possess better "workability" for the workers. Even though, their mechanical properties conform to IS specifications, I doubt, contents in the steel (metallurgy) are not good from the durability point of view, after seeing the fast rate of corrosion.
Is my doubt has any relevance? How can I ascertain good chemical quality of a steel bar?
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manojkamra
SEFI Member
Joined: 20 Oct 2010
Posts: 10
Location: Rajasthan / Posted: Mon Nov 15, 2010 8:25 pmPost subject: chemical quality of TMT bars /
Dear Sh.Bijoyav,
Thanks for raising very important but most neglected issue of structural engineering. IS-1786 covers most of the desireable aspects of structural steel.Entire structural engineering is meaningless WITHOUT KNOWING QUALITY OF STEEL. Our education system does not motivate to know the actual quality of steel by knowing its production process---whether billets manufactured from iron ore from mines OR from scrape. Faculty remains busy in gathering consultancy works from the deptts for minting money.
So 90% stuructural engineers in our country have no concern with production process of steel.They have their scope limited to design software and timely submission to clients.Ethically speaking, what is the use of STAAD pro and other softwares ,if scrape steel is to be used for major structures.
As per steel ministery norms, steel producers are of three categories depending upon the production capacity,furnace etc.
(1) Main producers---Only three are main producers---TATA,SAIL,RINL
(2) Major producers--Only four are major producers--JSW,JSPL,ESSAR,ISPAT
(3) other producers--There are more than 3000 other producers in our country.
So it is clear that for major structures , only steel from main and major producers should be used. For it, BIS have submitted one draft for gazette notification in 2007 which has been kept in abeyance by ministry of consumer affairs till date (permitting entire scrape in the prices of TATA , SAIL etc.)under pressure from the lobby of secondary steel producers.
On contacting consumer affairs ministry about current status ofgazette notification of 2007 for banning sale of 17-items ofsteel in our country without BIS certificates. We get the reply that matter is pending for consideration at steel ministry. Steel ministry says quality control is the job of consumer affairs ministry.
So , until that gazette notification comes into force, our major structures will continue to be poisoned by scrape steel and lead to premature deaths.
ManojK.Kamra
Location: new delhi / Posted: Mon Nov 15, 2010 11:19 pmPost subject: Chemical Quality of TMT bars
dear sir,
get it tested as per the IS:1786 for the chemical constituents
cheers
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Quote:
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olavocarvalho
SEFI Regulars
Joined: 08 Sep 2008
Posts: 26 / Posted: Tue Nov 16, 2010 7:42 amPost subject: Chemical Quality of TMT bars /
------Forwarded message ------
From: OlavoCarvalho < ()>
Date: Mon, Nov 15, 2010 at 11:34 PM
Subject: Re: [SEFI] Chemical Quality of TMT bars
To:
Hi MrBijoyav, IS 1785:2008 is quite vocal about these aspects.
I quote below two paras from the above code:
``1.6. Deformed bars produced by re=rolling finished products such as plates and rails (virgin or used or scrap), or by rolling material for which the metallurgical history is not fully documented or not known, are not acceptable as per this Indian Standard.
Annex A: ....Sometimes it becomes necessary to determine if a particular reinforcing bar/wire, or lot, has undergone proper heat treatment or is only a mild steel deformed bar.
Because the two cannot be distinguished visually, the following field test may be used for purposes of identification.
A small piece (about 12 mm long) can be cut and the transverse face lightly ground flat on progressively finer emery paper upto `0` size. The sample can be macroetched with nital (5 percent nitric acid in alcohol) at ambient temperature for a few seconds which will reveal a darker annular region corresponding to martensite/bainitemocrostructure and a lighter core.
However this test is not to be regarded as a criterion for rejection......
I think this will parlly answer your query
OlavoCarvalho
Goa
tmtctdmicroalloying
Difference between tmtbar,ctd and micro alloying
Steel is produced from iron,carbon and alloys.Demand in thisworld is of high quality steel at low price.In cold twisted deformed bars(CTD),Strength was increased from 250 N/mm2 to 420N/mm2 by twisting.But increase in strength comes at the cost of ductility.Elongation value dropped less than 12%.It causes
stress on surface.It also increases the labourcost.Another proposed method is micro alloying.Here metals like Nickel,chromium,nibolium,etc are added to attain desired properties.But it increases the cost of steel signifacantly.So the demand of high strength steel with good elongity and ductility at low price remain unfulfilled.The best way to achieve it was to change the process of steel manufacturing.
In 1980's two methods "Quenching and tempering" were developed.These processes (heat and deformation) change the shape and refine the microstructure.
Deformation brings about repeated re- crystallization as a result of decomposition of original grains and formation of new fine grains. In this process,the temperature must be kept low enough to control grain growth.Quenching is controlled by diameter of TMT Bar,volume of water and temprature to increase strength from 250N/mm2 to 500N/mm2.The result of this thermo mechanical treatment is TMT bars.
TMT bar is thermo mechanically treated steel.TMT steel is prepared by thermo mechanical treatment.Its a process to increase strength without sacrifice of ductility, toughness and corrosion resistance.
---======…
Properties of tmt bars
Tmtbars : 9 properties
- 1--Resists fire: Survives high temperatures.
2---Resists corrosion: The TMT process gives the bar anti-corrosive properties.Twisting operation is not involved in the production of the TMT steel bar.Hence no residual stress resulting in high corrosion resistance to chloride .Resists fire: Survives high temperatures.
3---Earthquake resistance: The soft pearlite core enables the TMT bar to have high strength ,highductility.It can easily survive seismic zone of 5.
4---Enables welding: Tmt steel has just .2 percent of carbon.It gives high weldaility without compromising on strength.
5---Safety : because of higher Strength combined with higher Ductility.
6---Formability: Due to very high elongation values and consistent properties through out the length of bar, TMT rebars have excellent workability and
bendability
7---Malleability: TMT bars are most preferred because of their flexible nature
8---Bonding strength: External ribs running across the entire length of the TMT bar give superior bonding strength between the bar and the concrete.
9---Cost-effective: A high tensile strength and better elongation value gives you great savings.It is easier to create at working sites so Reduces Transportation Costs.
Fraud tmt bar
Fraud Tmt steel bars
Any rolling mill creates products that require quenching and tempering.So a bar produced in normal furnace may be labelled as TMT Bar.But TMT steel means steel produced by quenching and tempering process at right tempratures
Quenching by spraying of cold water with correct tempraturedrop.So while buying TMT Bars you must check it for its strength,ductility and elongation values.It must have a minimum strength of 415N/mm2.Instead of TMT Bars as used in india,proper terms like "Quenching and tempering" must be used as in west.
……………………….
Billet and TMT Bar
Billet is the raw material required to create TMT Bars
Steel billets :undergoes a melting process in a furnace for refinement to make high-quality steel billets.
Reinforcing bars: The billets with chemical composition are further heated in a controlled furnace and rolled through series to reduce billets to final size and shape of reinforced bars.The bars that come out of mill stand with 1250 degrees temperature.
TMT Bars :When the bar is quenched and tempered to produce the final prod