AIŠMAN David UWB in Pilsen

Unconventional Heat and Thermo-Mechanical Treatment of Steel with High Content of Metastable Austenite Gained in Semi-Solid State

Co-authors MAŠEK Bohuslav, JIRKOVÁ Hana

Material processing in the semi-solid state enables very unusual structures to be gained, even using conventional materials. Merely by heating the material to the semi-solid state and subsequent cooling, a significant change of both phase composition and mechanical properties can be achieved. Thanks to the transition through the semi-solid state in minithixoforming, the ledeburitic structure in the tool steel X210Cr12 changes to a structure containing more than 95 % of metastable austenite. The austenite is in the form of polygonal grains with an average size of 19 µm, surrounded by a ledeburitic mesh. This structure can be afterwards modified by another thermo-mechanical treatment. The influence of heat and thermo-mechanical treatment was compared in the experiment. Different grades of austenite decomposition can be gained by changing temperature, e.g. troostite or alternatively a completely changed martensitic or martensitic-austenite-carbidic structure. If deformation is applied after the transition through the semi-solid state there is recrystallization of the austenite grains, which also changes the final microstructure morphology and the size of the grains. Processing by deformation causes the structure to be more evenly dispersed. However, some strategies of thermo-mechanical treatment showed similar mechanical values, no matter if the deformation was used or not.

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