Precipitation of M_(23)C_6 and its effect on tensile properties of 0.3C-20Cr-11Mn-1Mo-0.35N steel

摘要

The precipitation behavior of M_(23)C_6 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 ℃. It was found that typical M_(23)C_6 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 M_(23)C_6 carbides grew along the grain boundaries and into the adjacent austenite grain to form a film-shaped morphology. The precipitation of cellular M_(23)C_6 carbides on grain boundaries was a discontinuous reaction involving both the diffusion of C and Cr. And the formation of lamellar M_(23)C_6 carbides on incoherent twin boundaries associated with the gliding of partial dislocations and the formation of stacking faults. Meanwhile, the intragranular M_(23)C_6 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 M_(23)C_6 carbides, although the strengthening effect was weakened by the dominant precipitation of cellular M_(23)C_6 after long-term aging duration. However, the ductility was significantly deteriorated by the intergranular and cellular M_(23)C_6.