Effect of Grain Boundary Segregation of Interstitial Elements on Hall–Petch Coefficient in Steels

Abstract

The yielding behavior of interstitial-free steels and low-carbon steels with varying amounts of C and N were investigated in connection with the HallPetch relation. The HallPetch coefficient is as small as 150 MPa·µm 1/2 in interstitial-free steels but it increases to 600 MPa·µm 1/2 by adding solute carbon up to 60 ppm. Nitrogen does not have a significant effect on the HallPetch coefficient. The results of three-dimensional (3D) atom probe analysis indicated that carbon has 34 times greater segregation potential in comparison with nitrogen. The small effect of nitrogen on the HallPetch coefficient in steel is probably due to the small segregation potential of nitrogen. It was also confirmed that discontinuous yielding occurs when the difference between the yield stress and friction stress is increased by grain-refinement strengthening and that yielding occurs by dislocation emission from grain boundaries where primary dislocations have piled up. Carbon atoms segregated at grain boundaries seem to play a role in stabilizing dislocation emission sites at the grain boundaries, which enhances the HallPetch coefficient of iron. These results support the dislocation pile-up model of explaining yielding in polycrystalline metals.

Mechanical Characterization of a Nano-ODS Steel Prepared by Low-Energy Mechanical Alloying

“…where σ 0 is the friction stress, i.e., the matrix yield stress for a grain of theoretically infinite size, which was evaluated to be~13 MPa [35], K = 0.18 MPa m 1/2 and the average grain size D = 400 nm. In fact, as discussed by Schneibel et al [36], such mechanism losses his efficiency as the effect of Coble creep becomes predominant (Hall-Petch breakdown), namely when σ CC < σ HP .…”

Mechanisms of Dynamic Recrystallization in Aluminum Alloys

“…In the last case, deformation banding plays an important role in introducing initial moderate-to-high misorientation that highly facilitates the formation of 3D arrays of LABs. The pinning efficiency of incoherent or semicoherent Al 3 Zr dispersoids is sufficient to stabilize 3D arrays of deformation-induced LABs within zones of severe plastic deformation providing their gradual transformation to HABs [9]. However, no formation of recrystallized structure takes place outside of areas of severe localization of the plastic flow due to the fact that a material with UFG structure becomes superplastic.…”

“…Hall-Petch strengthening in aluminum alloys is not so efficient as in steels [3] due to a low value of k y ranging from 0.06 to 0.26 MPa×√m [4,5]. Therefore, extensive grain refinement up to sub-micrometer level is required to attain significant grain size strengthening.…”

Effect of the Surface Layer Strained by Mechanical Grinding on X-ray Diffraction Analysis

“…7) In order to eliminate the dislocations and small crystalline size introduced by cold rolling, the samples (size: 15 l × 15 w × 1 t mm) were fully recrystallized at 750°C (Argon atmosphere), and then slowly cooled (~1.5°C/min) to room temperature. The yield stress (σ y ) was about 73 MPa with average grain size of 39 μm.…”