Hydrogen Effects on Austenitic Stainless Steels and High-Strength Carbon Steels

Olga Todoshchenko

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    The resistance to hydrogen embrittlement is an important factor in the development of new steel grades for a variety of applications. The thesis describes investigations on hydrogen effects on two classes of steels - austenitic stainless steels and advanced high-strength carbon steels. Hydrogen solubility and diffusion in metastable austenitic stainless steels are studied with thermal desorption spectroscopy (TDS). This method, together with the mathematical modeling of the processes of hydrogen uptake and desorption, allows to analyse hydrogen diffusion and trapping in a metal. Temperature dependencies of hydrogen desorption for the studied steels manifest a complex peak. Specific features of hydrogen uptake and desorption for a multi-component alloy in comparison with that for pure metals are analysed by the proposed model. It was found that plastic strain affects the shape of the TDS peak for all the studied materials. In metastable austenitic stainless steels the parameters of hydrogen diffusion and trapping in martensite phase, which is forming under pre-straining, were estimated by the proposed model. High-strength carbon steels of the strength level from 1000 to 1400 MPa with different contents of Ti were studied. It was found that there is an optimal content and size distribution of Ti-based non-metallic inclusions (NMI) when the steel is most resistant to hydrogen embrittlement. Fractography of the studied steels shows that the fracture mechanism depends on the chemical composition of the studied steels and hydrogen-induced cracking exhibits intergranular or transgranular character occurring often in the form of hydrogen flakes. It was found that hydrogen-induced cracks of the hydrogen flakes initiate at Ti-based NMIs. TDS analysis evidences that the main trapping sites for hydrogen in the high-strength carbon steels are NMI interfaces. The mechanisms of hydrogen interaction with NMIs are discussed. All the studied high-strength carbon steels are sensitive to hydrogen under slow strain rate tensile tests. Constant load tests show that different processes influence on hydrogen-induced fracture at low and high applied stresses for the high-strength carbon steels with high Ti-alloying. Tempered high-strength carbon steels are less sensitive to hydrogen embrittlement than their non-tempered counterparts.
    Translated title of the contributionVedyn vaikutus austeniittisiin ruostumattomiin teräksiin ja ultra-lujiin hiiliteräksiin
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Hänninen, Hannu, Supervising Professor
    • Yagodzinskyy, Yuriy, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-6205-1
    Electronic ISBNs978-952-60-6204-4
    Publication statusPublished - 2015
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • hydrogen embrittlement
    • austenitic stainless steels
    • high-strength carbon steels
    • thermal desorption spectroscopy
    • fracture
    • non-metallic inclusions

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