Study ot the stress corrosion cracking in the weld seam of low alloyed steels with particular regard to the steel T24

• Applicant: Professor Dr.-Ing. Wolfgang Tillmann
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257480435

Under certain operational conditions (combination of mechanical and corrosive loading at temperatures in the range from 120 to 250°C), an unwanted stress corrosion cracking (SCC) in the region of the weld seams is observed in the steel 7CrMoVTiB10-10 (T24). Within the frame of this project, the mechanisms of this crack initiation and crack propagation process and the possibility to influence using pretreatments [welding, thermal treatment, preoxidation) and the loading conditions (strain rate at monotonic deformation, parameters of superimposed cyclic loading, temperature, O2 content and pH value of the aqueous medium) are studied thoroughly. The aim of the project is the identification of microstructural, environmental and loading factors and criteria that effect the susceptibility to SCC of the material in the region of the weld seam, significantly. After the evaluation of the results, the proposers will determine suitable measures to improve the resistance of the material to SCC. Various commercial measuring as well as analytical procedures will be used for these studies (SEM, SEM-EDX analysis, nanoindentation, optical profile analysis with an infinite focus microscope, residual stress measurements using X-rays and neutrons). Additionally, test methods developed by the proposers will be adapted to the requirements of this project and employd for the studies (slow strain rate tests in high temperature water with controlled water chemistry and a simultaneous analysis of surface strain fields and acoustic signals emitted form the volume). The expected contributions to the existing knowledge and understanding of the SCC phenomena in the weld seam of the steel T24 are also of significance for other ferritic and bainitic, low alloyed and heat-resistant steels.

• DFG Programme: Research Grants
• Participating Person: Dr.-Ing. Reiner Zielke