Prominent role of reversed austenite on corrosion property of super 13Cr martensitic stainless steel

Abstract

The microstructure and corrosion property of super 13Cr martensitic stainless steel (S13CrMSS) processed by quenching, one-step tempering and two-step tempering were investigated by XRD, SEM, EBSD and TEM-EDS analysis. It has been found that volume fraction of the reversed austenite in the sample treated by two-step tempering treatment was 13.5 vol. % up to the maximum. The reversed austenite almost always nucleated and distributed in martensite laths boundary during tempering and the diffusion of Ni, Mn and C promoted its growth. Enrichment of such elements as Ni, Mn, C and the ultrafine size of the reversed austenite were considered to be the main factor that accounted for the stability of the reversed austenite. At the same time, martensite and reversed austenite satisfy the (1 1¯ 1)γ // (011)α' and [011]γ // [1¯1¯ 1]α' Kurdjumov-Sachs (K–S) orientation relationship. Potentiodynamic polarization curves and electrochemical impedance spectroscopy indicated that two-step tempered specimen exhibited a higher pitting potential, lower corrosion current density, thicker passivation film and superior pitting resistance than the quenching specimen (without reversed austenite) as well as one-step tempering specimen (3.6 vol.%). It has been confirmed that the reversed austenite has a beneficial effect on the corrosion property of S13CrMSS.

Keywords

• Super 13Cr martensitic stainless steel
• Two-step tempering
• Reversed austenite
• Potentiodynamic polarization
• Electrochemical impedance spectroscopy