Fast nanoindentation technology is a new method used to generate performance maps showing the hardness and elastic modulus distribution of each position, and it has become a research focus. In this paper, nanoindentation combined with scanning electron backscatter diffraction (EBSD) is used to analyze the micro-regional properties of single-phase interstitial-free (IF) steel. Hardness, elastic modulus and the orientation of a 200 μm × 200 μm area were characterized in situ. The relationships between hardness, elastic modulus and orientation were analyzed. The experimental results showed that the hardness varied from 1.25 GPa to 2.57 GPa, while the modulus varied from 122 GPa to 227 GPa with different crystallographic orientations. The hardness value of the (111) crystal plane was particularly high, with an average hardness of about 1.84 GPa, which is due to its higher work hardening rate. This result is consistent with the EBSD kernel average misorientation (KAM) micrograph. The harder locations with greater misorientation are more difficult to deform compared to locations with small hardness regions, for example, the (001) crystal plane. However, there seems to be no obvious strong relationship between modulus and orientation. The modulus of the regions with lower hardness seems to be smaller. The results of the KAM diagram are consistent with those of hardness mapping.

This paper employs in situ Electron Backscatter Diffraction (EBSD) tensile technology to thoroughly consider the evolution of microstructure, grain size, grain boundary characteristics, orientation differences, and dislocation density of H13 steel during the elastic and plastic stages of room temperature tensile testing. The study unveils the deformation mechanisms of inclusions, carbides, and the matrix in H13 steel during the various stages, providing a comprehensive explanation for the slightly superior tensile properties of H13 steel when refined by Vacuum Induction Melting combined with Vacuum Arc Remelting (VIM + VAR) over those when refined by Electroslag Remelting (ESR). This discrepancy is primarily attributed to the differences in inclusions and carbides present in the two refining processes. The quantity and size of inclusions and carbides are closely related to material fracture. Large-sized carbides and inclusions were shown to be more likely to cause dislocation pile-ups and stress concentration. This, in turn, leads to faster crack initiation and propagation during plastic deformation. Conversely, the formation of micro-pores within these fine inclusions and the matrix is contingent on greater plastic deformation, resulting in a gradual and incremental linkage of these micro-pores to form dimples beneath the influence of slip.

A series of high-cycle rotating-bending fatigue tests was conducted on H13 steel produced by electroslag remelting (ESR) and by vacuum induction melting followed by vacuum arc remelting (VIM+VAR). At 10⁷ cycles, the fatigue strength of VIM+VAR steel was 1040 MPa, which is greater than the 967 MPa of ESR steel. A metallographic analysis was conducted to compare the structure and grain size of the two steels. The results indicated that while the two steels were similar, ESR steel contained a greater number of larger inclusions and carbides. The mean inclusion size in VIM+VAR steel was approximately 55% of that in ESR steel, and the maximum inclusion size was around 44%. Notwithstanding this finding, the fatigue strength of VIM+VAR steel was found to be approximately 7.5% higher. Scanning electron microscopy of fracture surfaces revealed that the primary cause of crack initiation was predominantly oxides or oxide-sulfide composites. The measurements obtained for inclusion size, fisheye diameter, and crack propagation length indicated that the fatigue life of the material is governed primarily by the applied stress and the size of the inclusion. The presence of larger inclusions has been demonstrated to reduce the crack-propagation stage and decrease the steel’s tolerance to defects, thereby reducing fatigue life and endurance limit. The researchers derived formulae relating inclusion size to stress intensity factor and fatigue life by utilizing the Paris law. These equations ·the fatigue-fracture mechanism and provided a basis for predicting the rotating-bending fatigue life of H13 steel.