The effect of Nb on microstructure and thermal-shock resistance was investigated for as cast and annealed JIS SCH21 steels. Primary NbC carbide were crystallized together with M 23 C 6 at grain boundary in as cast steel. Decomposition of primary M 23 C 6 was detected, while NbC was also hardly decomposed when annealed at elevated temperature. It was found that chromium carbides had low thermal stability but primary NbC carbides played a role in preventing propagation of micro-cracks and restraining shape deformation under condition both heating and quenching. As a result, thermal-shock resistance was improved in the Nb-added steel.
The effect of Nb on microstructure and thermal shock resistance was investigated for as cast and annealed JIS SCH21 steels. Primary NbC carbide were crystallized together with M 23 C 6 at grain boundary in as cast steel. Decomposition of primary M 23 C 6 was detected, while NbC was also hardly decomposed when annealed at elevated temperature. It was found that chromium carbides had low thermal stability but primary NbC carbides played a role in preventing propagation of micro cracks and restraining shape deformation under condition both heating and quenching. As a result, thermal shock resistance was improved in the Nb added steel.
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