Time-temperature-precipitation characteristics of high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N steel |
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Authors: | Tae-Ho Lee Sung-Joon Kim Setsuo Takaki |
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Affiliation: | (1) ECO-Materials Research Center, Korea Institute of Machinery and Materials, 641-010 Changwon, Korea;(2) Department of Materials Science and Engineering, Kyushu University, 819-0395 Fukuoka, Japan |
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Abstract: | The time-temperature-precipitation (TTP) and corresponding mechanical properties in high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N
steel (all in weight percent) were investigated using electron microscopy and ambient tensile testing. The precipitation reactions
can be categorized into three stages: (1) high-temperature region (above 950°C)—mainly coarse grain-boundary (intergranular)
Cr2N; (2) nose-temperature region—integranular Cr2N→cellular Cr2N→intragranular Cr2N+ sigma (σ); and (3) low-temperature region (below 750°C)—intergranular Cr2N→cellular Cr2N→ intragranular Cr2N+σ+chi(χ)+M7C3 carbide. After cellular Cr2N precipitation became dominant above 800°C, yield and tensile strength gradually decreased, whereas elongation abruptly deteriorated
with aging time. On the contrary, prolonged aging in the low-temperature regime increased tensile strength, caused by the
precipitation of fine χ and M7C3 within grains. Based on the analyses of selected area diffraction (SAD) patterns, the crystallographic features of the second
phases were analyzed. |
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