Effect of Input Structure of Blank on Development of Final Structure when Processing at Temperatures between Solidus and Liquidus

The article describes the effect of input material structure on the structure development during the subsequent processing by mini-thixoforming technology. Two different initial states were prepared from X210Cr12 tool steel for the experiment. The first semi-product was used in the soft-annealed state with ferritic-carbidic microstructure and coarse primary chromium carbides. Ferritic grain size 13,7 μm and the hardness was 210 HV30. The second state was prepared by high temperature annealing at 1200 °C for 1 hour. The microstructure then consisted of austenite and carbides. The grain size was in the range of cca 37 to 50 μm, hardness was 300 HV30. Treatment consisted of heating to a semi-solid state at the temperature 1265 °C in 9 s. That was followed by direct cooling to room temperature in 2 s. The grain size and distribution of eutectic in the volume of the processed material were selected as the attributes for microstructure evaluation after mini-thixoforming. The structure after processing in a semi-solid state consists of polyhedral austenite with a grain size of 43-59 μm, compared to the initial range 37-50 μm. This compares to the soft annealed state when, after semi-solid processing, the grain size was only 10 to 13 microns.