New Zealand Steel: Glenbrook Steel Site

Glenbrook Steel Site

Situated at Glenbrook, south of Auckland, New Zealand Steel's fully integrated steel mill produces a range of flat steel products for both domestic and export markets.

Slabs are rolled into hot and cold rolled products, which are then on-sold or further processed into products like hollow sections, galvanised steel, ZINCALUME® steel and COLORSTEEL® steel.

New Zealand Steel uses locally sourced ironsand and coal to produce about 650,000 tonnes of steel a year.

From Sand to Steel

New Zealand Steel is unique among world steelmakers in its use of ironsand to make iron and steel.

The ironsand comes from the Waikato North Head mine site and concentration plant, situated 18 kilometres south of New Zealand Steel’s Glenbrook mill.

The ironsand is initially concentrated using double drum magnetic separators, further cleaned before stockpiling. The ironsand is transported as a slurry through an underground pipeline to the mill.

Ironmaking - Iron Oxide Becomes Molten Iron

Along with coal and limestone, the primary concentrate (ironsand) is heated and dried in one of four multi-hearth furnaces. It is then fed into the four reduction kilns, where it is converted to 80% metallic iron. Two melters then convert this into molten iron.

The iron, at around 1480°C, is transferred to the Vanadium Recovery Unit (VRU), where vanadium-rich slag is recovered for export and further processing into a steel strengthening additive.

The Ironmaking Plant at Glenbrook has the capacity to produce 650,000 tonnes of molten iron.

Steelmaking - Iron Becomes Steel

The molten iron is a key ingredient in the steelmaking process that takes place in the Slabmaking Plant.

This Plant consists of an oxygen steelmaking furnace (KOBM) and a continuous slab casting machine.

To produce steel, the KOBM uses a mixture of scrap steel and the molten iron from the melters.

Further refining occurs at the Ladle Treatment Station (LTS), where ferro-alloys are added to bring the steel composition up to its required specification.

The molten steel from the LTS is then transferred to the continuous caster, where it is cast into slabs.

Hot Rolling

The slabs cool outside before being reheated in the reheat furnace.

The slab (210 mm thick and weighing over 10 tonnes) is then transferred into the reversing rougher mill. The steel is reduced in thickness with each pass.

The steel is rolled down to about 25 mm when it is coiled in the coil box (to retain heat). It then passes through the finishing mills to achieve its final thickness.

The steel is water cooled and coiled ready for further processing.

Cold Rolling

The pickled and oiled coil is now moved to the cold rolling mill. Some of the steel is rolled on the six high reversing stand to its final thickness ready for the metal coating line.

Other steel is annealed and rolled to achieve the required mechanical properties.

Metal Coating

New Zealand Steel's metal coating line produces both ZINCALUME® coated and galvanised steel.

Cold rolled strip is delivered from the cold rolling mills to the metal coating line. The strip is cleaned to remove grease, oil and iron oxide before travelling through the annealing furnace (with a hydrogen and nitrogen atmosphere) to anneal or stress relieve to the specified strength.

The strip travels into the molten metal through the "snout", where it emerges below the surface of the metal. The strip travels vertically from the pot, passing through air knives which control the coating thickness.

The coating is cooled and moved through the skin pass to flatten the metallic coating on the strip.

To protect the surface from oxidation, a passivation solution is applied to the strip. The strip is branded and wound, ready for packing.