Grain Boundary Segregation Behavior and Thermodynamic Analysis Based on CALPHAD Method for B Added High Carbon Steel

抄録

Segregation behaviors on the prior austenite grain boundaries for the B-doped high C case hardening steel (Fe-0.82C-0.22Si-0.86Mn-0.02P-1.1Cr-0.21Mo-0.005B (mass%)) were evaluated using a three-dimensional atom probe (3DAP). Results revealed the intense segregation of C, Mo, Cr, and B on the grain boundaries. Findings also confirmed suppression of the segregation of P, known as a strong segregation element for steel. Thermodynamic analysis based on the parallel tangent law by McLean–Hillert was conducted to validate the segregation of each element. To evaluate the chemical potentials while taking interaction with multiple elements into account, the Calculation of Phase Diagram (CALPHAD) method was used, where liquid phase was adopted to estimate the Gibbs free energy of grain boundaries. The calculation results represent the segregation tendencies obtained from 3DAP. Detailed investigations of the interaction effects of C, B, and Mo on the other elements were also conducted. Results showed the suppression of P segregation by increasing the B content, therefore demonstrating the efficiency of the segregation prediction method which implemented CALPHAD for the B-added high C steels.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 193–199. Figure 6 was slightly modified.