Measurements of Secondary Phases Content in a 22Cr 5Ni Duplex Stainless Steel

摘要

A duplex stainless steel (DSS) containing nominally 22Cr, 5Ni, 3.2Mo and 1.5Mn has been investigated for secondary phases precipitation, after ageing at 780, 850 and 900 deg C. Selective etching with different reagents, OM and SEM-BSE have been used to quantify ferrite, austenite and secondary phases. A critical discussion of different metallographic techniques (use of OM and/or SEM-BSE) applied to measure inter-metallic content is presented, including an attempt to distinguish chi and sigma. The chemical composition of the phases has been determined by means of EDS, the effects on mechanical properties have been studied with a hardness test. The hardness increases with holding time for all temperatures. The rate of secondary phases increases with the holding time. The 850 deg C treatment is the most effective for increasing hardness and secondary phase precipitation.