Beneficial Effects Induced by Cycling at high temperature in an aged Duplex Stainless Steel

ARMAS, A. F.; SUZANNE DEGALLAIX,; GÉRARD DEGALLAIX,; SILVINA HEREÑÚ,; CECILIA MARINELLI,; ALVAREZ ARMAS, IRIS

Busan, Korea

Conferencia; 10th INT CONF ON THE MECHANICAL BEHAVIOR OF MATERIALS, 2007; 2007

Korean Insitute of Metals

Due to their excellent performance under severe mechanical and environmental conditions Duplex Stainless Steels (DSSs) have become the main competitor of the standard austenitic stainless steel grades. However, a major drawback of DSS is the susceptibility of the ferritic phase to undergo spinodal decomposition into chromium-rich and iron-rich regions at intermediate temperatures, what induces embrittlement. The few available reports about the aging effects on the fatigue properties of DSS were concentrated on tests performed at room temperature. To our knowledge no work exists in the literature about the cyclic behavior of thermal aged DSS at high temperature. Preliminary tests performed in our laboratory on both as-received and aged DSS show that the synergetic effect between temperature and mechanical cycling could produce beneficial effects on the fatigue life of embrittled samples. During cycling, spite the high initial stress level in aged steel, after a similar cyclic hardening period for both materials, the aged steel shows a pronounced and very short softening stage that continues up to reach a cyclic stress level similar to that presented by the as-received material. The most surprising and interesting fact is that embrittled DSS shows a lifetime comparable to that of the as-received steel. It is proposed that at high temperature the to and fro movement of dislocations can dilute, at least partially, the chemical composition fluctuations promoting an erasure of the spinodal decomposition formed in aged steels. The wavy slip character of the deformation in a bcc crystal assists in diluting the segregated regions.