Effect of ageing time on microstructure and mechanical properties of SAF 2205 duplex stainless steel

Abstract

Purpose: SAF 2205 duplex stainless steels (DSSs) are materials characterized by a favourable combination of the properties of ferritic and austenitic stainless steels. This type of stainless steel presents good weldability, corrosion resistance especially for stress corrosion cracking (SCC). However, this steel presents an unavoidable disadvantage that is its potential microstructural instability. Although duplex stainless steels design idea is to present two main types of microstructure, other phases and carbides or nitrides can precipitate. In the case of DSS SAF 2205, in addition to austenitic and ferritic microstructure, during heat treatment processing, welding or use may occur precipitation of undesirable intermetallic phases such as chi, Widmanstätten austenite, sigma besides carbides and nitrides. The precipitation of s-phase is associated with effects that cause both reduction of toughness and decreases the corrosion resistance on austenitic, ferritic and duplex stainless steels. Design/methodology/approach: This study evaluated the aging treatment effect on hardness, impact toughness and ferrite content of a SAF 2205 duplex stainless steel. Samples were solubilized at 1150°C, quenched in water and aged at 850°C during 1, 5, 10, 30, 60 or 180 minutes. After aging, cooling was to room temperature in air. Findings: Aging time promoted s-phase precipitation and hardness increase. Hardness and ferrite volume measurements, microscopy and the prediction of sigma phase bases the discussion. Impact toughness decreased with time aging and intermetallic phase precipitation. Research limitations/implications: As future work could be performed some corrosion test, vary the cooling rate after aging, and using other techniques to identify phases. Focus the research at lower aging times to try the describe Cr partitioning process to form sigma phase. Practical implications: High aging time should be avoided for SAF 2205 DSS. Originality/value: Usually sigma-phase precipitation on DDS is correlated to welding process. This paper correlates it to aging heat treatment.