TY - THES

T1 - Austenite Grain Growth in a Microalloyed X80 Line Pipe Steel

AU - Tichauer, Walter

N1 - no embargo

PY - 2017

Y1 - 2017

N2 - Pipelines are used to transport, among others, oil and gas over long distances. The use of an optimized material for the production of pipelines results in reduced costs. Smaller wall thicknesses and higher operating pressures become feasible. Widely used base materials for these pipelines are thermomechanically treated microalloyed steels, e.g. an X-80 steel grade. It offers a combination of required mechanical properties such as high strength, ductility and excellent weldability. These properties are determined by the microstructure of the steels, which evolves during thermomechanical processing and also during welding. A key parameter to describe the microstructure and to obtain the above mentioned properties is the grain size [1], [2]. It is thus of both scientific and industrial importance to observe the evolution of the grain size and grain size distribution in time during heat treatment. Classical metallographical methods allow to measure grain sizes only after quenching the samples to room temperature. However, the in-situ evolution of the grain sizes can be monitored by novel experimental techniques such as high temperature laser scanning confocal microscopy (HT-LSCM) and laser ultrasonics technique (LUT). Both techniques HT-LSCM and LUT have advantages and drawbacks when investigating grain growth and coarsening. HT-LSCM is a surface technique, i.e. it is only applicable to microstructures where the microstructural parameters do not alter significantly from surface near regions to the bulk material. The HT-LSCM is a powerful technique since the microstructural changes at the surface can be observed directly. LUT provides the average grain sizes in the bulk material during heat treatment; however, information about the grain size distribution is not available [3]. It is the goal of this master thesis to compare the experimental results of both techniques (i.e. HT-LSCM and LUT). It is expected that the experimental findings become more meaningful than using only one of the techniques as HT-LSCM and LUT complement each other. In particular multimodal grain size distributions can be identified by an appropriate evaluation of the HT-LSCM. In order to have a better understanding of the grain-size distribution evolution, the kinetics of grain growth will be analyzed. References [1] K. Banerjee, M. Militzer, M. Perez and X. Wang, “Nonisothermal Austenite Grain Growth Kinetics in a Microalloyed X80 Linepipe Steel,” Metallurgical and Materials Transactions A, no. 41A, pp. 3161-3172, 2010. [2] P. Schaffnit, C. Stallybrass, J. Konrad, A. Kulgemeyer and H. Meuser, “Dual-scale phase field simulation of grain growth upon reheating of a microalloyed line pipe steel,” International Journal of Materials Research, no. 101, pp. 549-554, 2010. [3] M. Maalekian, R. Radis, M. Militzer, A. Moreau and W. J. Poole, “In situ measurement and modeling of austenite grain growth in a Ti/Nb microalloyed steel,” Acta Materialia, no. 60, pp. 1015-1026, 2012.

AB - Pipelines are used to transport, among others, oil and gas over long distances. The use of an optimized material for the production of pipelines results in reduced costs. Smaller wall thicknesses and higher operating pressures become feasible. Widely used base materials for these pipelines are thermomechanically treated microalloyed steels, e.g. an X-80 steel grade. It offers a combination of required mechanical properties such as high strength, ductility and excellent weldability. These properties are determined by the microstructure of the steels, which evolves during thermomechanical processing and also during welding. A key parameter to describe the microstructure and to obtain the above mentioned properties is the grain size [1], [2]. It is thus of both scientific and industrial importance to observe the evolution of the grain size and grain size distribution in time during heat treatment. Classical metallographical methods allow to measure grain sizes only after quenching the samples to room temperature. However, the in-situ evolution of the grain sizes can be monitored by novel experimental techniques such as high temperature laser scanning confocal microscopy (HT-LSCM) and laser ultrasonics technique (LUT). Both techniques HT-LSCM and LUT have advantages and drawbacks when investigating grain growth and coarsening. HT-LSCM is a surface technique, i.e. it is only applicable to microstructures where the microstructural parameters do not alter significantly from surface near regions to the bulk material. The HT-LSCM is a powerful technique since the microstructural changes at the surface can be observed directly. LUT provides the average grain sizes in the bulk material during heat treatment; however, information about the grain size distribution is not available [3]. It is the goal of this master thesis to compare the experimental results of both techniques (i.e. HT-LSCM and LUT). It is expected that the experimental findings become more meaningful than using only one of the techniques as HT-LSCM and LUT complement each other. In particular multimodal grain size distributions can be identified by an appropriate evaluation of the HT-LSCM. In order to have a better understanding of the grain-size distribution evolution, the kinetics of grain growth will be analyzed. References [1] K. Banerjee, M. Militzer, M. Perez and X. Wang, “Nonisothermal Austenite Grain Growth Kinetics in a Microalloyed X80 Linepipe Steel,” Metallurgical and Materials Transactions A, no. 41A, pp. 3161-3172, 2010. [2] P. Schaffnit, C. Stallybrass, J. Konrad, A. Kulgemeyer and H. Meuser, “Dual-scale phase field simulation of grain growth upon reheating of a microalloyed line pipe steel,” International Journal of Materials Research, no. 101, pp. 549-554, 2010. [3] M. Maalekian, R. Radis, M. Militzer, A. Moreau and W. J. Poole, “In situ measurement and modeling of austenite grain growth in a Ti/Nb microalloyed steel,” Acta Materialia, no. 60, pp. 1015-1026, 2012.

KW - Kornwachstum

KW - Korngröße

KW - Korgrößenverteilung

KW - mikrolegierter Stahl

KW - Kinetik

KW - Röhrenstahl

KW - Hochtemperatur-Laserscanning-Konfokalmikroskop

KW - Laserultraschalltechnik

KW - Pipeline

KW - grain growth

KW - grain size

KW - grain size distribution

KW - microalloyed steels

KW - kinetics

KW - line pipe steel

KW - high temperature laser scanning confocal microscopy

KW - laser ultrasonics technique

KW - pipeline

M3 - Master's Thesis

ER -