The HIC resistant steel is a continuously cast steel with an ultra-low sulphur content, less than 0.001 per cent S, and with substantially reduced centre-line segregation so that there are fewer sites for hydrogen accumulation. It has also been found that the presence of small amounts of copper in the steel composition reduces the rate of hydrogen absorption. The ability to produce such very low sulphur steels is a direct consequence of the introduction of extensive desulphurizing equipment, a new technology introduced at Port Kembla works in 1984.

A second new steel developed by BHP Slab and Plate Division was a special plate for use in the fabrication of North West Shelf LNG storage facilities. This steel had to meet very stringent property requirements, including toughness at -50°C. The final steel was a controlled rolled low carbon, manganese steel to which a small amount of titanium had been added. The new steel comfortably met the minimum specified toughness levels even in the weld effected zones.

Controlled rolling is a new technique developed on the Port Kembla Plate Mill and involves tight control over the temperature schedules during the rolling of steel plate.

Steels for the automotive industry

The Australian Automative Industry consists of five manufacturers producing some 13 different model lines for a total population of some 15.5 million people. On average about 450,000 new passenger vehicle registrations are made each year. These features, together with relatively arduous driving conditions and long distance travel, have necessitated a joint steel grade development program involving automotive companies, steel makers and sheet producers. Due to the small size of the industry, there was a need, firstly, to minimise the number of grades of steel to reduce manufacturing and stock holding costs, and secondly, to retain tooling in production up to ten years, which reduced the opportunity to make special tooling to suit only the new steel grades.

A new series of steels was produced, including high strength, low alloy type (HSLA), recovery heat treated steels, rephosphorized, cold rolled and coated steel grades. Two hot rolled high strength, low alloy Xtraform grades were developed with yield strengths 380 and 480 MPa respectively. Production of these steels relied on the modernized facilities involving new techniques at BHP Slab and Plate Division including the slab caster, the 275 tonne vacuum degasser as well as hot metal and ladle desulphurizing.

An extra-deep drawing cold rolled steel was developed in conjunction with Coated Products Division for production of complex shaped parts such as floor and oil pans. This was a low carbon, aluminium-killed steel which achieved the low carbon content by hot metal vacuum decarburizing during steel making. A further superior grade containing lower carbon content and small additions of titanium was produced for the few most severe drawing applications. After a thorough review of trends in high strength steel for skin and inner panels of automobiles, Coated Products Division in conjunction with the industry decided to confine development to a single rephosphorized steel grade which has been used extensively with considerable success.

Australian Academy of Technological Sciences and Engineering