Why are some steel construction products preferentially produced by different production routes?

Why are some steel construction products preferentially produced by different production routes?

All steel construction products can be produced using either of the two principle steelmaking routes, i.e. primary Blast Furnace-Basic Oxygen Furnace (BF-BOF) or the secondary, Electric Arc Furnace (EAF) route. However, for various technical and economic reasons, some products are preferentially produced by one or other of these routes.

The central issue relates to the quality control of the raw materials input to the steelmaking process and the required quality of the finished product. In BF-BOF steelmaking, the primary raw material input is iron ore and controlling the quality of the iron ore is relatively easy and therefore high and consistent quality steel can be made cost effectively via this route. The quality is particularly important for producing flat, relatively thin products like plate.

In EAF steelmaking, the primary input is scrap steel and the quality of the steels produced are dictated by the quality and blend of the scrap. Scrap steel is usually contaminated with tramp elements and some of these elements remain in the finished products which can affect its quality. Therefore, if high quality control, i.e. sorting and blending of scrap is done, steels of high quality, such as stainless or engineering steel, can be produced. On the other hand, if the quality control is low then relatively low quality steels can be cost produced via EAF cost effectively.

For the above reasons, structural steel plate used in the UK is produced via the BF-BOF. Hot-rolled sections are produced, equally efficiently, via either production route.

Steel is used in numerous construction products, however the main generic groups are:

  • Rolled sections used as structural members and for piling,
  • Rebar and mesh used for reinforcing concrete,
  • Steel plate used to fabricate larger structural elements,
  • Hollow or closed sections used as structural members,
  • Light gauge flat steel generally galvanized, used in many construction applications including floor decking, cladding and studs for light steel framing.

All of these products can be produced via either of the two principle steelmaking routes, i.e. the primary Blast Furnace-Basic Oxygen Furnace route (BF-BOF) or the secondary, Electric Arc Furnace (EAF) route. However, for various technical and economic reasons, some products are preferentially produced by one or other of these routes. In some countries, geographical and historical factors also influence the preferred steelmaking route for some products. The availability and cost of scrap is also a factor.

The central issue relates to the quality control of the raw materials input to the steelmaking process and the required quality of the finished product. In BF-BOF steelmaking, the primary raw material input is iron ore and controlling the quality of the iron ore is relatively easy and therefore high and consistent quality steel can be made cost effectively, via this route.

In EAF steelmaking, the primary input is scrap steel and the quality of the steels produced are dictated by the quality and blend of the scrap. Scrap steel is usually contaminated with tramp elements such as copper, nickel, chromium, molybdenum, cobalt, antimony, arsenic, tungsten, tin, and zinc and some of these tramp elements remain in the finished products which can affect its quality. In addition, the nitrogen content of EAF steel is higher than BF-BOF steel. Therefore, in EAF production, if high quality control, i.e. sorting and blending of scrap is done, steels of high quality, such as stainless or engineering steel, can be produced. On the other hand, if the quality control is low then relatively low quality steels can be cost effectively produced via EAF.

Of the above product groups, rolled sections and rebar are classified as long products in which some tramp elements and a relatively high nitrogen content in steel are allowed. For flat products, groups 3, 4 and 5 above, the presence of tramp elements and gases has to be controlled, since they cause deterioration in surface quality and the mechanical properties of steel and therefore BF-BOF production is generally the preferred production route for these products.

EAF technology is however improving and, in certain countries, notably the USA which has a reliable supply of scrap, EAF technology is now being used to produce some flat products including steel plate. Part of the reason for this is the introduction of a proportion of pure iron (Direct Reduced Iron, DRI) or high quality clean scrap to the EAF to ensure that the quality of the steel is kept sufficiently high to roll flat products of the required quality.