等温変態線図を基にした焼入性の予測

抄録

A quantitative prediction of hardenability of eutectoid steels from the corresponding isothermal tranformation diagram is considered. A general equation expressing the transformation kinetic during continuous cooling of eutectoid steel is derived by combining the isothermal transformation kinetics with the cooling curves under the assumption that the transformation is additive over the whole transformation temperature range. Based on this equation, the simple equations expressing the values of critical cooling rate α_u and α₁, Jominy distance J₀ and ideal critical diameter D_I using the values obtained from the isothermal transformation diagram are developed. The relationships between D_I and J₀ and D_I, H and D₀ which had been derived by Grossmann et al. based on the half temperature time are reconsidered from the continuous cooling transformation point of view. The main results obtained are as follows :
(1) The transformed fraction X of pearlite during continuous cooling can be expressed as,
X=1-exp[-{∫^T=T _T=Te e-a/n(T-b)²/dT/dt dT}ⁿ 1n2/tⁿ₀]
(2) Upper and lower critical cooling rate α_u and α₁, Jominy distance J₀ and ideal critical diameter D_I can be expressed as,
α_u = 1/Ζ (69)^1/n, α₁ = 1/Ζ(0.15)^1/n
J^1.4₀=3.12×10^-5 (T₁-T₂) (b-T₂)Ζ
D²_I=2.56 × 10^-2 f²(T₁-T₂) (b-T₂)Ζ where Ζ=t₀√a/nπ
(3) The values of D_I derived from J₀ and D₀ derived from D_I and H using Grossmann's method may be smaller and larger respectively than the actual ones.