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R. Radis, E. Kozeschnik, C. Sommitsch, N. Enzinger, C. Schlacher, P. Mayr:
"Loss of ductility caused by AlN precipitates in Hadfield steel";
Keynote Lecture: THERMEC 2011, International Conference on PROCESSING & MANUFACTURING OF ADVANCED MATERIALS Processing, Fabrication, Properties, Applications, Quebec - Canada; 2011-08-01 - 2011-08-05.

LOSS OF DUCTILITY CAUSED BY ALN PRECIPITATES IN HADFIELD STEEL

R. Radis*, C. Schlacher*, P. Mayr*, N. Enzinger*, E. Kozeschnik**, C. Sommitsch*
*Institute of Materials Science and Welding, Graz University of Technology, Kopernikusgasse 24, A-8010 Graz, Austria
Email: rene.radis@tugraz.at, christian.schlacher@tugraz.at, norbert.enzinger@tugraz.at, ernst.kozeschnik@tugraz.at, christof.sommitsch@tugraz.at

Austenitic manganese steel (AMS), also called `Hadfield steel´, is well known for its unique combination of extraordinary high strain hardening rates together with excellent toughness properties. Two modified X120Mn12 steels, differing in the amount of alloying elements Al and N (alloy 1 (Al=0.0258, N=0.068) / alloy 2 (Al=0.0122, N=0.011)), are analyzed with respect to AlN precipitation and its effects on ductility. Charpy impact tests are performed, demonstrating the loss of ductility in alloy 1 containing a high number density of AlN precipitates.
Characterization of the precipitates is carried out with high resolution scanning electron microscopy (HRSEM). In alloy 1, coarse primary AlN particles as well as finer secondary precipitates are detected on austenite grain boundaries and in the grain interior, whereas only minor amounts of AlN precipitates could be found in alloy 2.
Additionally, thermodynamic equilibrium calculations, Scheil-Gulliver simulations as well as thermo-kinetic simulations of AlN precipitation are carried out, using the software package MatCalc. The evolution of AlN precipitates is evaluated depending on the time-temperature history of the material, taking into account simultaneous precipitation at grain boundaries and on dislocations. Although the coarse primary AlN particles represent the major phase fraction of AlN in alloy 1, the high number density of finer second phase precipitates is made responsible for the poor toughness properties. Thus, Al and N additions must be carefully controlled during the classical production process of Hadfield steel and high contents of both elements together should clearly be avoided.