Mechanical properties of low-alloy-steels with bainitic microstructures and varying carbon content

International Conference on Materials, Processing and Product Engineering 2015

Weber, A.^1,4 ; Klarner, J.^2 ; Vogl, T.^2 ; Schöngrundner, R.^2 ; Sam, G.^3 ; Buchmayr, B.^4

Materials Center Leoben Forschungs GmbH, Roseggerstraße 12, Leoben

A-8700, Austria^1

Voestalpine Tubulars GmbH AndCo KG, Kindberg, Austria^2

RAG Rohöl-Aufsuchungs Aktiengesellschaft, Wien, Austria^3

Department of Metal Forming, Department of Product Engineering, Montanuniversitaet Leoben, Austria^4

关键词: Bainitic microstructures;    Carbide-free bainites;    Environmental conditions;    High-tensile strength;    Quasi-static tensile test;    Seamless steel tube;    Tempered martensite;    Time temperature transformation;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/119/1/012005/pdf
DOI  :  10.1088/1757-899X/119/1/012005

来源: IOP

【 摘 要 】

Materials used in the oilfield industry are subjected to special conditions. These requirements for seamless steel tubes are between the priorities of strength, toughness and sour gas resistance. Steels with bainitic microstructure provide a great opportunity for those harsh environmental conditions. With different morphologies of bainite, like carbide free, upper or lower bainite, the interaction of high tensile strength and elongation is assumed to be better than with tempered martensite. To form carbide free bainite two ways of processing are proposed, isothermal holding with accurate time control or controlled continuous cooling. Both require knowledge of time-temperature transformation behaviour, which can be reached through a detailed alloying concept, focused on the influence of silicon to supress the carbide nucleation and chromium to stabilize the austenite fraction. The present work is based on three alloys with varying silicon and chromium contents. The carbide free microstructure is obtained by a continuous cooling path. Additionally different heat treatments were done to compare the inherent performance of the bainitic morphologies. The bainitic structures were characterized metallographically for their microstructure and the primary phase by means of transmission electron microscopy. The mechanical properties of carbide-free structures were analysed with quasi-static tensile tests and Charpy impact tests. Moreover, investigations about hydrogen embrittlement were done with focus on the effect of retained austenite. The results were ranked and compared qualitatively.