High strength quenched and tempered steel has been produced in Australia by Bisalloy Steels since 1979.
Quenched and tempered steels are established in the Australian steel plate market, accounting for approximately 5 per cent of the total structural plate market consumption. Their local availability from an Australian manufacturing source since 1979 has encouraged designers, fabricators and end-users to utilise these steels in a range of applications, recognising potential advantages arising from lighter structures, greater load carrying capacities and improved service life, especially in abrasive environments.
The increased strength of BISALLOY® Structural steel grades allows engineers and architects to design and write specifications for structures that only a few years ago would have been impossible to build.
While there has been significant use of high strength steels for structural applications in a number of international markets, it is fair to say that in the last 20-30 years the predominant use of high strength steel plate in Australia has been in the mining and resources sector for equipment such as dump truck bodies, storage bins, hoppers and chutes where lighter weight, wear resistance and impact resistance, combined with straightforward fabrication, has facilitated ready adoption.
The recent resources boom has been instrumental in developing local capacity and capability to manufacture quality high strength plate.
Contemporary high strength quenched and tempered steels are all generally considered low to medium alloy content steels, exhibiting high strength and hardness coupled with good formability and weldability. They also maintain exceptionally low temperature notch toughness and crack propagation resistance despite the high strength levels involved. This unique combination of properties is the result of careful selection of both chemical composition and heat treatment.
Principal alloying elements in modern quenched and tempered steels like the BISALLOY® Structural steel range are nickel, manganese, chromium, copper and molybdenum, with additional hardening often being provided by smaller but more precisely controlled additions of boron (typically 0.002% B). These elements are often used in combination, such that quenched and tempered steels can be classified as multiple low to medium alloy heat treated steels.
Most quenched and tempered steels also incorporate one or more micro-alloying elements such as aluminium, niobium, titanium, vanadium, or zirconium.
At Bisalloy Steels, specific composition ranges for each element are adjusted, insofar as steel specifications might allow, by the steel manufacturer according to strength and other property requirements, and to provide the necessary hardenability. Comparatively higher alloy contents are required in thicker plates to offset the retardation in cooling rate which inevitably accompanies quenching of the heavier plate sections.