Effect of Ti and Si on Precipitation Hardening of Martensitic Stainless Steel

Abstract

The effects of Ti and Si on the age-hardening response and ductility after aging were studied for low C, N-14Cr-7Ni martensitic stainless steel, and the main results obtained are as follows:
(1) The age-hardening response of steels containing Ti singly is dependent on the logarithm of effective Ti contents ([Ti]) and the effect of [Ti] is almost the same as that in Fe-18Ni alloy.
(2) While the age-hardening response of steels containing Si alone is small, that of steels containing Ti in the presence of more than 2 at% Si is very large. In this case, the effects of [Ti] and Si on the equal age-hardening response are dependent on the value of ln[Ti]⁶Si⁷. This can be explained by the solubility of G phase (Ni₁₆Ti₆Si₇) in matrix.
(3) In the steels containing both Ti and Si, the age-hardening rate is controlled by the super saturation of G phase.
(4) A higher ductility of steels can be attained at higher strength level by combined additions of Ti and Si than by single addition of Ti. This is explained by the fact that in the latter steels δ phases (Ni₃Ti) precipitate easily along grain boundaries and intergranular fractures occur at lower stress level.