Focused Ion Beam-Induced Displacive Phase Transformation From Austenite to Martensite during Fabrication of Quenched and Partitioned Steel Micro-Pillar.

We report evidence of a displacive phase transformation from retained austenite to martensite during preparation of quenched and partitioned steel micro-pillars by using a focused ion beam (FIB) technique. The BCC phase produced by the FIB damage was identified as martensite. The invariant-plane strain surface relief associated with the martensitic transformation was observed in the retained austenite phase immediately after a FIB scan of the surface with the Ga+ ion beam. Use of a low acceleration voltage appears to lower the probability of the phase transformation, while a decrease of the acceleration voltage will result in an increase of the total milling time required to prepare a micro-pillar. This report addresses challenges related to the preparation of austenite micro-pillars by a conventional FIB technique.

Effects of Al-Si Coating and Zn Coating on the Hydrogen Uptake and Embrittlement of Ultra-High Strength Press-Hardened Steel.

Press-hardened steel (PHS), used for automotive safety-related structure parts, is sensitive to hydrogen embrittlement due to its martensitic microstructure. Hydrogen is introduced in PHS during the hot press forming (HPF) process, by an atmospheric corrosion process. In this study, the hydrogen embrittlement behavior of uncoated, aluminized, and galvanized PHSs was investigated. The Al-10%Si coating promoted the absorption of diffusible hydrogen at elevated temperature during the HPF while the reacted coating layer prevented the absorbed hydrogen from out-diffusing through the reacted coating surface layer at room temperature. Therefore, the aluminized PHS showed a greater sensitivity to both the hydrogen uptake and the resultant embrittlement, as compared to the uncoated and galvanized PHSs. Use of galvanized PHS for HPF application reduces the risk of hydrogen embrittlement, since the Zn coating effectively prevents the hydrogen uptake. The greater embrittlement resistance of the galvanized PHS is possibly due to the inhibition of the hydrogen generation reaction by the surface ZnO oxide layer and the low rate of hydrogen transport through the liquid Zn phase.

Data related to dislocation density-based constitutive modeling of the tensile behavior of lath martensitic press hardening steel.

The data presented in this article are related to the research article entitled "On the plasticity mechanisms of lath martensitic steel" (Jo et al., 2017) [1]. The strain hardening behavior during tensile deformation of a lath martensitic press hardening steel was described using a dislocation density-based constitutive model. The Kubin-Estrin model was used to describe strain hardening of the material from the evolution of coupled dislocation densities of mobile and immobile forest dislocation. The data presented provide insight into the complex deformation behavior of lath martensitic steel.