Co-precipitation mechanism of nanoscale particles and mechanical properties in multicomponent ultra-high strength low carbon steel

Effect of post-heat treatment on microstructure and properties of EH47 steel CGHAZ

“…After the post-heat treatment, the proportion of low-angle grain boundaries (red lines) increases significantly inside the bainite ferrite, and the length percentage increases from 40.6% to 67.3%. Low-angle grain boundaries are randomly distributed at the lath or block boundary of bainite ferrite in the block, and the proportion of the low-angle grain boundaries is proportional to the dislocation density [31,32], which indicates that the increase of dislocation promotes the formation of sub-grain boundaries during the post-heat treatment.

Figure 6 Crystallographic characteristics of the CGHAZ specimens analysed by EBSD.

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“…The EBSD analysis results (Figure 5b) show that the proportion of low-angle grain boundaries inside the blocks of GB and LB increases significantly after post-heat treatment and is distributed near the lath boundaries and M-A constituents. The ratio of the low-angle grain boundaries is proportional to the dislocation density, and the high dislocation density increases the tendency to transform into low-angle grain boundaries by dislocation motion [31,32]. Figures 11(a) and 11(b) are the Kernel Average Misorientation (KAM) maps of CGHAZ, and different colour regions represent the local average misorientation obtained by the EBSD test.…”

“…Considering the microstructure of bainite and grain size of the post-heat CGHAZ are not transformed, it is concluded that the high proportion of low-angle grain boundaries and the iron-carbide particles were responsible for the deterioration the fracture toughness. Li et al pointed out that the high density of high-angle grain boundaries can effectively impede the crack propagation and improve low-temperature toughness, while the high density of low-angle grain boundaries is detrimental to low-temperature toughness [31]. Figure 6(d) shows the high proportion of low-angle grain boundaries for post-heat CGHAZ, which is not conducive to improving low-temperature fracture toughness.…”

“…In the grain boundary maps, the red line represents the lowangle grain boundaries of 2-15°, and the blue line represents the high-angle grain boundaries (θ > 15°). Figures 6(e in the block, and the proportion of the low-angle grain boundaries is proportional to the dislocation density [31,32], which indicates that the increase of dislocation promotes the formation of sub-grain boundaries during the post-heat treatment.…”