Evaluation of yield strength taking account of particle size-distribution in particle dispersion strengthened ferritic steel

Yield strength of particle dispersion strengthened ferritic steel is discussed in consideration of the size-distribution of particles in some imaginary models with different type of size-distribution and real materials of an Fe-C alloy and Fe-oxide alloys. Estimation of the mean particle spacing (λ) using the models has revealed that λ strongly depends on the type of size-distribution: ideal distribution, nominal distribution and log-nominal distribution, and that the influence of size-distribution on λ becomes more significant with increasing size and volume fraction of particles. This means that the size-distribution has to be considered for the correct estimation of the increment in yield strength (Δσ) depending on particle dispersion strengthening, especially in high strengthened materials. The Δσ measured for the real materials was found to be proportional to λ^-1 regardless of the kind of particles by making an appropriate correction of the size-distribution of particles. Consequently, the increment of yield strength due to particle dispersion strengthening was described as Δσ[MPa]=64/λ [μm] in the iron-base ferritic alloys.