Examination of hydrogen interaction in carbon steel by means of quantitative microstructural and fracture descriptions Maria Sozan ´ska a, *, Jaroslav Sojka b , Petra Bet ˘ a ´kova ´ b , Catherine Dagbert c , Ludmila Hyspecka ´ b , Jacques Galland c , Miroslav Tvrdy ´ d a Department of Materials Science, Silesian University of Technology, ul. Krasin ´skiego 8, PL-40 019 Katowice, Poland b Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava, Czech Republic c Ecole Centrale Paris, CFH, Grande Voie des Vignes, 92 295, Cha ˆtenay-Malabry, France d Research and Development, Vı ´tkovice a. s., Phranic ˘nı ´ 31, 706 02 Ostrava, Czech Republic Received 21 December 2000; received in revised form 5 February 2001; accepted 8 February 2001 Abstract The relations between the quantitative microstructural characteristics and the resistance of carbon steels to hydrogen-induced cracking (HIC) were studied for plates used in the oil and refinery industry. The width of the pearlitic bands and the degree of banding were considered if the testing of the resistance to HIC was performed in accordance with the NACE TM 0284 standard. The role of the degree of banding was important while that of the width of pearlitic bands was negligible. Additional hydrogen embrittlement testing of tensile specimens oriented in longitudinal and through-thickness directions revealed that hydrogen strongly increased the anisotropy of mechanical properties. These changes could be correlated with the geometric characteristics of nonmetallic inclusions (MnS) and the pearlitic bands in different metallographic sections. A quantitative description of fracture surfaces has been made by means of a profilometric method. D 2001 Elsevier Science Inc. All rights reserved. Keywords: Hydrogen-induced cracking; Hydrogen embrittlement; Quantitative metallography; Quantitative fractography 1. Introduction Hydrogen-induced cracking (HIC) or stepwise cracking is a problem encountered in carbon and low alloy steels operating in hydrogen sulphide- containing environments, especially in steels used for pipelines and pressure vessels in the oil and refinery industry. The mitigation of this damage may be achieved by understanding and controlling the factors which contribute to the observed effects. It is generally recognised that the resistance of steels to HIC can be correlated with some microstructural features [1,2]. For those steels the microstructure consists predom- inantly of ferrite and pearlite, there are two favourable sites for HIC – nonmetallic inclusions (especially MnS) and the segregation bands containing pearlite or even bainite. This explains that the most important micro- structural parameters that have to be taken into account are the nature and geometric characteristics of the nonmetallic inclusions, the local chemical composition and the width of the segregation bands and also the 1044-5803/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved. PII:S1044-5803(01)00130-9 * Corresponding author. Tel.: +48-32-256-31-97; fax: +48-32-256-31-97. E-mail address: mariasoz@polsl.katowice.pl (M. So- zan ´ska). Materials Characterization 46 (2001) 239 – 243