Authors: Stephanie Sackl Michael Zuber Helmut Clemens Sophie Primig
Publish Date: 2016/05/03
Volume: 47, Issue: 7, Pages: 3694-3702
Abstract
An induction heat treatment is favorable compared to a conventional one mainly due to significant time and cost savings Therefore in this study the microstructure property relationships during induction and conventional heat treatment of a heat treatable steel 42CrMo4 is investigated The yield strength and hardness is slightly higher for the conventionally heattreated steel whereas the induction heattreated condition exhibits a roughly 30 J/cm2 higher impact energy In a previous investigation of the authors it has been proved that the difference in yield strength originates from the smaller block size of the conventionally heattreated steel which was already present after hardening In the present work it can be shown that during tempering the martensitic blocks become equiaxed ferrite grains due to recrystallization as revealed by electron back scatter diffraction Nevertheless a larger grain size usually is less favorable for the impact toughness of steels Therefore another mechanism is responsible for the higher impact energy of the induction hardened and tempered steel With the aid of transmission electron microscopy a finer distribution of cementite was observed in the induction heattreated samples The delay of recovery is the reason for the presence of finer cementite in case of the induction heattreated steel Here the higher heating rates and shorter process times reduce the annihilation of dislocation and as a consequence provide more nucleation sites for precipitation of cementite during tempering From the obtained experimental results it is believed that the finer distribution of carbides causes the observed higher impact toughnessThe financial support by the Austrian Federal Ministry of Economy Family and Youth and the National Foundation for Research Technology and Development is gratefully acknowledged The authors want to thank Tomasz Wojcik for his help regarding the TEM investigations
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