オーステナイト・ステンレス鋳鋼の極低温における組織安定性と機械的性質に及ぼす合金元素の影響

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A study was made of the effects of alloying elements on the δ-ferrite formation, athermal and deformation-induced martensitic transformation and mechanical properties of SCS13 & SCS14 austenitic stainless steels at cryogenic temperature.The results obtained are as follows:1) Emperical equation for δ-ferrite formation can be expressed as a function of Ni equivalent (Δ) as: δ(%)=-2.17×(Δ)+4.242) Athermal martensite of Fe-18Cr-Ni alloys formed at -196°C shows a good agreement with that of calculated values according to the equation proposed by Magee. Martensite content of cast alloys is greater than that of wrought alloys for the same Ni content, because of larger grain size of cast alloys.3) With increasing Ni, Mn and N content of metastable austenite, the tensile strength lowers due to stabilization of austenite.0.2% proof stress at 20°C does not change by Mn addition, however increases by N addition.Elongation increases with increasing Ni and N content, and shows the maximum by Mn addition at about 6% Mn.4) Impact value at -196°C lowers by Mn and N addition, but does not change by Ni addition.5) Relationship between δ-ferrite and impact value at -196°C can be expressed as: vE=-1.25×(δ%)+2.286) Nv values of δ-ferrite are from 3.31 to 3.70 and that of bulk is 2.85. Judging from the obtained TTT curve for δ to σ transformation, δ-ferrite easily transforms to σ phase during water-quenching from 1100°C.7) The formation of σ phase more than 1% extremely deteriorates the impact values.

オーステナイト・ステンレス鋳鋼の極低温における組織安定性と機械的性質に及ぼす合金元素の影響

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