Precipitation of M23C6 and its effect on tensile properties of 0.3C–20Cr–11Mn–1Mo–0.35N steel

• Intergranular M23C6 grew along grain boundaries to form film-shaped morphology.
• Cellular precipitation of M23C6 is controlled by the long-range diffusion of C.
• Intragranular M23C6 nucleating on dislocations exhibited stinger morphologies.
• M23C6 improved strength modestly, however, degraded ductility obviously.

The precipitation behavior of M23C6 carbides and its influence on the tensile properties were investigated in a novel 0.3C–20Cr–11Mn–1Mo–0.35N austenitic stainless steel isothermally aged at 900 °C. It was found that typical M23C6 carbides retaining a cube-on-cube crystallographic relation with austenite matrix precipitated on grain boundaries, twin boundaries and dislocations. With increasing aging time, the intergranular M23C6 carbides grew along the grain boundaries and into the adjacent austenite grain to form a film-shaped morphology. The precipitation of cellular M23C6 carbides on grain boundaries was a discontinuous reaction involving both the diffusion of C and Cr. And the formation of lamellar M23C6 carbides on incoherent twin boundaries associated with the gliding of partial dislocations and the formation of stacking faults. Meanwhile, the intragranular M23C6 carbides in rectangular or rhombic shapes initially nucleated on dislocations, and finally arranged in stringers corner-to-corner or face-to-face. The strength of the material was modestly improved by the precipitation of M23C6 carbides, although the strengthening effect was weakened by the dominant precipitation of cellular M23C6 after long-term aging duration. However, the ductility was significantly deteriorated by the intergranular and cellular M23C6.

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