Christian Doppler Laboratory for Diffusion and Segregation during Production of High Strength Steel Sheet
Head: Dr. Michael Rohwerder
The main focus of the Christian Doppler Laboratory for Diffusion and Segregation during Production of HIgh-Strength Steel Sheet is on fundamental diffusion and segregation problems encountered during the different production steps of high strength steel sheet.
The technical motivation behind this is that the development of high strength steels with their characteristic alloying element composition leads to new challenges for the production and processing of steel sheets in order to meet the product requirements. The focus here is on selective grain boundary oxidation during hot rolling and its consequences for pickling, and on hydrogen detection and its uptake kinetics in different process steps. The related questions are of significant scientific interest and the related research of considerable experimental challenge.
Cooperation partners are voestalpine and the Faculty of Technical Chemistry TU Wien.
The Objectives are adressed withing the lab in three modules:
Selective Enrichment (SE) Module
- Layered structure of a grain boundary oxide: EDX elemental maps of a FIB-prepared cross-sectional TEM lamella of ternary Fe−3Al−0.8Cr model alloy annealed at 700 °C, in 2/2.5%H2/9000ppmH2O, for 2 hours (green Cr, purple Al).
Within this module the activities focused mainly on two approaches: fundamental investigation of grain boundary oxidation based on dedicated model alloys (Fig) and developing a new simulation tool for describing grain-boundary oxidation on a theoretical level [1-3]. One important result found within the reporting period was that it is mainly the interaction between some of the key alloying elements in high strength steels that is responsible for significantly enhanced internal oxidation. This is at the focus of current research and will be investigated experimentally and theoretically.
Pickling (P) Module
This module deals with pickling after hot rolling and is carried out mainly by Prof. DI Dr. Herbert Danninger at the Faculty of Thechnical Chemistry, TU Wien.
Hydrogen (H) Module
- Detecting hydrogen on a 50×50 µm² surface area of a H charged austenitic steel after evaporation of a 100 nm Pd film. Potential map of this area obtained after 28 h in the Kelvin probe mode. The dark spots indicate sites with especially high hydrogen concentrations (traps).
The hydrogen uptake of the material is a significant problem especially for high strength steels, as small amounts of hydrogen in the range of ppm can cause retarded brittle fracture. Uptake during several wet processing steps as well as corrosion and recrystallization annealing is investigated. For the latter an important question is information about the distribution of oxides at the different stages of the annealing [4], which is now also investigated by ambient ESCA. Here a main focus in the reporting period was the successful development of a novel method for spatially resolved highly sensitive hydrogen detection [5,6].
[1] Auinger, M.; Naraparaju, R.; Christ, H.-J.; Rohwerder, M., Modelling High Temperature Oxidation in Iron-Chromium Systems: Combined Kinetic and Thermodynamic Calculation of the Long Term Behaviour and Experimental Verification, Oxid. Met. 76 (2011), no. 3-4, 247-258, DOI: 10.1007/s11085-011-9252-8
http://edoc.mpg.de/572372
[2] Auinger, M.; Borodin, S.; Swaminathan, S.; Rohwerder, M., Thermodynamic Stability and Reaction Sequence for High Temperature Oxidation Processes in Steels, Mater. Sci. Forum. 696 (2011), 76-81,
http://edoc.mpg.de/572374
[3] Auinger, M.; Rohwerder, M., Coupling Diffusion and Thermodynamics - exemplified for the gas nitriding of ironchromium alloys, HTM J. Heat Treatm. Mat. 66 (2011), 100-102,
http://edoc.mpg.de/572373
[4] Swaminathan, S.; Rohwerder, M., Segregation and Selective Surface Oxidation at the Intermediate Steps of Recrystallization Annealing, Defect and Diffusion Forum Series 309-310 (2011), 203-208 , DOI:10.4028/www.scientific.net/DDF.309-310.203
http://edoc.mpg.de/579673
[5] Evers, S.; Rohwerder, M., The hydrogen electrode in the “dry”: A Kelvin probe approach to measuring hydrogen in metals, Electrochemistry Communications 24 (2012), 85-88, DOI:10.1016/j.elecom.2012.08.019
http://edoc.mpg.de/624681
[6] Senöz, C.; Evers, S.; Stratmann, M.; Rohwerder, M., Scanning Kelvin Probe as a Highly Sensitive Tool for Detecting Hydrogen Permeation with high local Resolution, Electrochemistry Communications 13 (2011), 1542-1545,
http://edoc.mpg.de/577499
