Effect of Composition and Structural Conditions on Mechanical Properties of Cr-Ni Stainless Steel

Effeet of Ni and Mo

Abstract

This report concerned effects of Ni and Mo content on structure of Cr-Ni stainless steels, especially on the amount of δ ferrite and effects of composition and structural conditions on aging hardness, tensile strength and creep-rupture strength.
Specimens used in the experiment were 18Cr-12Ni austenitic stainless steels containing 4%, 6% and 8% Mo (M series) and 18Cr-4Ni, 18Cr-5Ni and 18Cr-6Ni martensitic stainless steels (S series).
With specimens of S series, γ phase precipitated from surrounding portion of δ ferrite and secondnry ferrite precipitated in matrix during aging at 750°C. phase was formed from ferrite after a long-time aging. Specimens were hardened by 5 precipitation of a secondary ferrite and formation of a phase from ferrite.
With specimens of M series, 5 phase was formed quite rapidly from δ ferrite during aging at 750°C.
Tensile strength of specimens of S series depended not on Ni content but on structures.
Tensile strength was increased with raising the amount of δ ferrite and martensite at a test temperature below 500°C.
But strength of δ ferrite was lower than that of austenite above 600°C. Tensile strength of specimens of M series was increased with Mo content.
Creep rupture strength at 650°C was increased with Ni and Mo content but decreased with enhancing the solution-treatment temperature because the amount of δ ferrite was increased with raising the solution-treatment temperature.