Production Terms

Production Terms

Hot Rolled Steel | Micro-Alloyed Deformed Bars and Coil | Contistretch Coil | Quench and Self Tempered Deformed Bar | Hard Drawn and Cold Rolled Bar | Indented Wire | Cold Worked Bars (1957-1983) 

Hot Rolled Steel 

A product rolled to final shape and tolerances at a temperature of about 1150ºC. The strength properties at room temperatures are obtained by chemistry or by rolling techniques. The finished surface may be plain or deformed.

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Micro-Alloyed Deformed Bar and Coil

This is a low carbon, micro–alloyed high strength hot rolled reinforcing bar. Its strength comes from a small controlled addition of Vanadium, or similar alloying element, to the steel composition during smelting. ARC processes N12 and N16 coils and N40 and D450N50 mill bars as micro-alloyed bars. Micro-alloyed bars have constant metallurgical properties across their section which gives superior welding characteristics to quench and self tempered bars.

The N12 and N16 coils are a continuous length of finished low carbon steel, coiled hot as the final part of the rolling process from a billet. The current maximum size of deformed bar available in Australia in coil form is 16 mm, although 20 mm is available overseas. Coiled bar may be straightened and then cut to length, or straightened and bent to shape in one operation. 

The surface finish and physical properties allow it to be used in its ‘as rolled’ condition. The coil mass is typically two tonnes. Coils of up to five tonnes are produced.

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Contistretch Coil

Contistretch is a low carbon steel produced from 400 MPa feed. Final yield strength of 500 MPa is achieved by cold working (stretching). Contistretch is available in N12 and N16 coils and is processed in ARC production facilities to customer requirements. Typical coil weight is three tonnes.

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Quench and Self Tempered Deformed Bar (QST)

This is a low carbon, hot rolled steel which obtains its high strength from a mill heat treatment and tempering process. After the bar is rolled to size and shape, it passes through a water cooling line where the surface layers are quenched to form martensite while the core remains austenitic. The bar leaves the cooling line with a temperature gradient through its cross-section. The natural heat within the core flows from the centre to the surface resulting in self tempering of the martensite. The core is still austenitic. Finally, the austenitic core transforms to ferrite and pearlite during the slow cooling of the bar on the cooling bed. The product therefore exhibits a variation in mircostructure in its cross-section with a tough tempered martensite as the surface layer, and a ductile ferrite-pearlite core.

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Hard Drawn and Cold Rolled Bar

A continuous length of finished material produced from coiled rod having a very low carbon content and a yield stress of approximately 300MPa.

The hot rolled rod is subjected to two or more cold rolling operations which produces a circular or triangular cross-section. An additional pass through a set of deforming rollers produces the required surface pattern.

Bar, whether hard drawn or cold rolled, is covered by AS/NZS 4671. Previous codes referred to hard drawn and cold rolled products as wire.

Production can be by rolling under intense pressure, or by drawing the rod through a ‘die’ having a diameter smaller than the rod, or both. Rolling followed by drawing provides a smooth surface.

During rolling or drawing, the diameter of the rod is reduced to approximately 88% of its original value. This gives a reduction in area of approximately 20-25% with a consequent increase in length. The mass of the original rod and the final wire coil is not changed. The cold work process raises the yield stress of the finished bar to above 500MPa. 

As a generalisation, cold working rod by drawing or rolling has the following effects on steel:

• The yield stress is increased: eg, from 300 MPa to 500 MPa.
• The tensile strength is increased above the original hot rolled value: eg, from 500 MPa to 600 MPa.
• The Agt is reduced: eg, from 20% to 1.5%.
• The strain ageing properties become worse.
• The effect of rebending may be severe.
• Galvanising bent material can increase brittleness.

Bar produced by cold rolling has the following characteristics:

• Close control of quality since the operation is largely automatic.
• Deformations can be added during the rolling process.
• The cross-section is almost circular allowing good control and thus improved bending accuracy.
• The surface appearance is rougher than hard drawn material, but this is of little consequence for reinforcement after it is encased in concrete. Surface roughness improves anchorage in the concrete.
• Alternately rolling followed by drawing can provide a smooth surface finish.
• Cold rolled wire does not require a lubricant during manufacture, as does drawn wire. Although this lubricant may postpone for a few days the advent of rusting, the fine film of rust which appears on rolled wire soon after exposure to weather is more likely to improve the bond than to reduce it.

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Indented Wire

Here the outer shape is formed firstly by drawing hot rolled rod through a die of circular cross-section, and then a pattern is indented into the surface. This product is common in Europe, but not in Australia or USA.

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Cold Worked Bars (1957-1983)

Cold working is a process by which the final properties of a steel are provided by rolling, twisting, drawing or tensioning a hot rolled steel, or by a combination of two or more of these processes. Between 1957 and 1983, the only high strength steels in common use were cold worked.

Before twisting, the Grade 230 bars were either of square section (1957 to 1963) or deformed (1963 to 1983). After twisting, the yield stress (at 0.2% proof stress) was 410MPa for design calculations and they were designated as Grade 410C bars.

Cold worked bars are no longer produced by ARC and are not included in AS/NZS 4671.

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