Sulphur segregation and high-temperature brittle intergranular fracture in alloy steels |
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| Affiliation: | 1. College of Chemistry and Materials Science, Ludong University, Yantai 264025, China;2. School of Chemistry and Material Engineering, Changzhou Vocational Institute of Engineering, Changzhou 213164, China;3. Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou 213164, China;1. Department of Chemical Engineering, Virginia Tech, Blacksburg, VA 24061, USA;2. Macromolecules and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA;3. Department of Mathematics, Virginia Tech, Blacksburg, VA 24061, USA;1. German Aerospace Center (DLR), Institute of Solar Research, Paseo de Almería 73, 04001 Almería, Spain;2. Departamento de Ingeniería Eléctrica y Térmica, Universidad de Huelva, Campus de La Rábida, Carretera de Palos de la Frontera S/N 21071 La Rábida, Palos de la Frontera (Huelva), Spain;3. Dept of Mechanical and Aerospace Engineering, UCSD Center for Energy Research, University of California, 92093-0411 La Jolla, USA;4. CIEMAT, Energy Department – Renewable Energy Division, Av. Complutense, 40, 28040 Madrid, Spain;5. Energy Meteorology Unit, Energy and Semiconductor Research Laboratory, Institute of Physics – Oldenburg University, 26111 Oldenburg, Germany;6. German Aerospace Center (DLR), Institute of Solar Research, Linder Höhe, 51147 Cologne, Germany;1. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China;2. School of Advanced Engineering, University of Science and Technology Beijing, Beijing 100083, China;3. Henan Key Laboratory for High-temperature Structural and Functional Materials, Henan University of Science and Technology, Luoyang, Henan 471003, China |
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| Abstract: | High temperature brittle intergranular fracture has recently been identified as a mode of failure in alloy steels. It is associated with the dynamic segregation of sulphur to cracks in hard microstructures stressed at elevated temperatures in a manner analogous to hydrogen embrittlement at ambient temperature. Several models have been proposed to describe the action of sulphur, but insufficient experimental data have been available for their evaluation. The present study characterises sulphur enrichment at cracks and on free surfaces at high temperature in detail using scanning Auger spectroscopy. Both intergranular and transgranular surfaces were studied at pressures of air from 10−9 to 10−3 torr. Two types of sulphur enrichment at cracks were identified; general segregation to crack faces and local enrichment close to crack tips. The source of sulphur was largely that dissolved in the ferrite matrix. Large sulphides, intersecting grain boundaries, made a minor contribution, while small “overheated” intergranular sulphides were inoperative as sulphur sources. The role of stress in encouraging sulphur segregation was confirmed. In addition, an intermediate pressure of air was found to enhance sulphur enrichment, but only at surface oxygen coverages of 15–25 at.%. These observations were generally consistent with the influence of the crack tip stress field on migration of the sulphur solute, described by the “pure drift” model of high temperature brittle intergranular fracture. Refinement of the model, using finite element stress analysis, is included. |
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