MS44-P09 Impact of Tempering Temperature on the Properties of Steel: An In-situ X-ray Diffraction Study Andreas Pein (Anton-Paar GmbH, Graz, Austria) Manfrad Wiessner (Anton Paar GmbH, Graz, Austria)email: andreas.pein@anton-paar.comMaterial properties are strongly dependent on the structure and arrangement of the 
atoms / molecules of which the material is comprised. For steel, different properties are required for the wide range of possible applications. Heat treatment (tempering) can be used to alter the microstructure and phases present within the steel and, therefore, change the material properties. In-situ X-ray diffraction measurements can be used to study these changes.
The mechanical properties of soft martensitic steels, which find use in a wide variety of applications, are strongly dependent on the microstructure which develops during heat treatment. After treatment, the steel consists of different phases; typically a combination of martensite, reverted or retained austenite, and carbide precipitates. Reverted austenite is the austenite which forms at sufficiently high temperatures during the tempering process.
Some superior properties found in these steels are high values in both fracture toughness and impact strength. These are caused by the microstructural arrangement of reverted austenite and martensite. It is therefore clear that the mechanical properties of the steel are dependent on the heat treatment as this influences the development of different phases and the microstructure within the steel.
In order to identify the effect of tempering temperature on the mechanical properties, in-situ high temperature X-ray diffraction is employed to study the microstructural changes occurring during tempering (1). This includes following the formation of different phases, as well as monitoring the dislocation densities; these can then be related to mechanical properties such as the impact strength and tensile strength. In this way, an improved understanding can be developed to optimize the tempering process in order to obtain steels with the desired properties.

[1] Wiessner, M. et al. (2017) Materials Science & Engineering, A682, 117-125
Keywords: in-situ X-ray diffraction, steel, copper tempering