A
PROFILE
OF STRENGTH
 

Is a Greenfield Steel rolling bar mill at Bhaipheru 40 km away from Lahore being implemented by Siemens Vai Metal Technologies and ASI Ansaldo Sistemi Industrial spa. The mill is the state of the art new automatic plant with initial capacity of 350,000 tons per annum which will produce hot rolled high tensile, deformed steel bars of sizes ranging from 8mm to 50mm in length 12 meters in bundles of approx. 2000 kgs using THERMEX Bar Quenching process in conformity to international standard like BS 4449-2005, ASTM 706A, ASTM A615 and PS1612–2007.

The fully automatic new plant of Dost Steels assures the customers that they are buying the finest steel bars available in the country made only from Prime Billets fulfilling all the technical specifications of reinforcement bars (rebars). The customers are assured that the quality will always be consistent, in uniform length, ends will be clean cut – all the time – every time.


 
 
Around 1970, cold twisted deformed (CTD) was developed in Europe and sold under the brand name Torsteel. Many mills in Europe adopted this process with some automation of twisting and bundling facilities. However, this had a short life in Europe where it was developed. In this process, the yield strength is raised to desired levels by cold working or cold twisting but at the cost of ductility. The resultant total elongation values were poor a maximum of only 14% was specified for yield strength of 415 N/ mm2 and still lower for the desired level of 500 N/ mm2. Thus Europe was forced to abandon use of CTD bars within a few years of its development by about 1974 after which quenching technology was developed and subsequently hot rolled bars have been in use all over the world since the last 25 years.
 
 
Steel billets are heated in a reheating furnace and rolled through a sequence of rolling stands which progressively reduce the billet to the final size and shape of the reinforcing bar. The THERMEX Process takes over and the bar is subjected to heat treatment in three successive stages. The first stage of ‘QUENCHING’ begins when the hot rolled bar leaves the final mill stand and is rapidly quenched by a special water spray system. This converts the surface layer of the bar to a hardened structure called ‘Martensite’ while the core remains austenitic. The second stage of ‘Self tempering’ begins when the bar leaves the quenching box with a temperature gradient through its cross section, the temperature of the core being higher than that of the surface.

This allows heat to flow from the core to the surface, resulting in tempering of the surface, giving a structure called ‘Tempered Martensite’ which is strong and tough. The core is still austenitic at this stage. The third stage of ‘Atmospheric Cooling’ takes place on the cooling bed, where the austenitic core is transformed to a ductile ferrite-pearlite core.
 
 
 
 
 
In Bar quenching process, the rebar properties are attained by regulating the microstructure of a strong tempered martensite ring with a ductile core which enables the use of lower carbon and manganese contents. Combination of this microstructure and lower alloy content gives better rebar ductility, more strength and good weld ability. Then rapid Air-cooling on the automatic cooling bed at lower temperatures results in a thin and compact mill scale on the rebar surface.

In the conventional Hot Rolling Process, the properties are achieved by regulating the chemical composition. Use of higher carbon and manganese content though increase the strength but may impair rebar ductility and / or weld ability. The slow air-cooling results in a thick but flak mill scale layer on the rebar surface. The microstructure of the rebar is ferrite – paralytic, typical of any medium carbon steel.
 
 
Though Dost Steels hot rolled deformed bars have identical strength levels as a conventional cold twisted bar, it has following important advantages over a conventional cold twisted bar.
 
This combination results in added safety of the structure compared to very low safety in cold twisted steel bars due to low ductility.
 
The superior bend ability of the Dost Steels bar compared to a conventional cold twisted bar makes the bar easy to fabricate with.
 
The precise control of the thermo mechanical treatment process, results in a uniform and thick tempered martensite rim, completely free from internal stresses. This martensite rim improves the corrosion resistance of Dost Steels bar as well as the fatigue strength, when compared to traditional cold twisted bars.
 
Dost Steels bar is supplied with mass/metre on the negative side of the specified tolerance on a weighted average basis. This further reduces consumption because of extra length per unit mass.
 
Dost Steels bar have better resistance to high temperatures in case of fire.
 
Due to its unique combination of strength and high ductility, Dost Steels bars carry higher fatigue resistance and can adequately support a seismic design. When evaluated for resistance to seismic loads on column joints in a RCC structure, the energy dissipation has been found to be almost same for each cycle indicating very high and uniform ductility maintained under such loads. Dost Steels bars meet the technical specification of new version of BS 4449-2005 (effective from January 2006) and ASTM 615A, ASTM 706A that cover the seismic zones requirements. This caters to the increasing demand of high ductility requirements in re-bars for Pakistan because nearly 75% of the country falls in the high seismic hazard category.
 
Dost Steels bars are higher strength rebars with elongation implying that you can economize on steel consumptions by about 15% without sacrificing safety. Secondly due to ease of working time is also saved at construction time
 
 
Typical DOST 75 rebar properties are:
Yield Strength 500N/sqmm;
Stress Ratio (UTS: YS) 1.20;
Uniform Elongation 7.5-9% (Total elongation 16-20%)

Typical DOST 60 rebar properties are:
Yield Strength of 420N/sqmm;
Stress Ratio (UTS: YS) 1.25;
Uniform Elongation 8-10% (Total elongation 16-22%)

It is the change in color of thin surface oxide layer due to atmospheric exposure without any negative affects on the material properties. Discoloration effects a thin surface layer only without penetration into the material and does not affect the main characteristic of the bar.
 
It is the result of severe reaction between material and the atmosphere leading to degradation of material properties. It results from the interaction of the rebar material with the corrosive environment and its effect penetrates into the material and thus degrades its properties.
   
 
 
Dost Steels will fulfill the country’s steel demand and will make import substitution for deformed steel bars in the country.
Dost Steels will replace the cold rolled / twisted TOR steel in the country by offering a world standard hot rolled deformed steel.
Dost Steels is introducing a world class product on a large scale through out the country.
Dost Steels is the only first mill in Pakistan to make 100% of its production in hot rolled deformed steel bars.
Dost Steels will be using only prime billets for the production of steel bars. No scrap/ship plates, inferior quality raw material will be used.
Dost Steels is introducing in Pakistan THERMEX quenched steel bars.
Dost Steels will introduce in Pakistan issue of test reports to customers for each bulk dispatch.

 
www.doststeels.com
Sales & Marketing

2A/ 27-28, FCC, Syed Maratib Ali
Road, Gulburg IV, Lahore
UAN : 111-STEELS (783357)
FAX : (92-42) 577-7856
Registered Office

Plot No. 222, Sector 39, Korangi Creek Industrial Area,
Karachi - 74900
TEL : (92-21) 5110421-22
FAX : (92-21) 511-0423