Obiettivo
Hydrogen induced cracking (HIC) is a microstructural defect related phenomenon attributable principally to non-metallic inclusions which act as sites for crack nucleation due to the build-up of hydrogen pressure. Once nucleated, crack growth is progressive but the rate of growth and crack morphology is greatly dependent on the microstructure and the presence of hard carbide containing phases such as martensite, bainite and pearlite have been shown to exert a powerful detrimental influence on HIC. Although the HIC resistance of pipeline steels has been vastly improved by attention to steel cleanness, the situation has been exacerbated by continuous casting, which inevitably results in centreline segregation leading to the presence of a discontinuous band of martensite/bainite. Attention is now being focused on low carbon steel compositions which do not give high segregation zone hardnesses and which are claimed to give good HIC resistance. These materials, based on acicular ferrite microstructures, offer the prospect of satisfying future demand for higher strength HIC resistant steels and also for meeting increasingly stringent sour environment test conditions. It is necessary to confirm these claims and to determine the broad compositional limits necessary to achieve the combination of microstructure, mechanical properties and HIC resistance.
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S60 3AR ROTHERHAM
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