Effects of Cold Work, Heat Treatment and Volume Fraction of Ferrite on Stress Corrosion Cracking Behavior of (α-γ) Duplex Stainless Steel

Abstract

The effects of cold rolling, heat treatment and volume fraction of ferrite on stress corrosion cracking (SCC) behavior of duplex stainless steel have been studied with means of U-bend method in boiling 42% MgCl₂ solution. The main results obtained are as follows:
(1) SCC susceptibitity of the solution treated material is small at about 50% α, but it has a tendency to be increased with either way of increase or decrease of α content from about 50% α. Solution treatment temperature resulting in abrupt increase of SCC susceptibility shifts to higher temperature with the decrease of α content.
(2) SCC susceptibility is increased by grain growth of α and γ that occurred with extension of holding time at solution temperature, and otherwise, by cold work in the case of the materials having much volume fraction of α.
(3) On aging at 475°C, the hardness is increased by spinodal decomposition of α. The crack resistance increases remarkably with the progress of aging in the case of materials having much α, and corresponds to age hardening behavior.
(4) In the case of heating at 700°C, the SCC behavior of aged materials has not been made clear by U-bend method because of σ embrittlement.