Effect of Nb on Thermal-Shock Resistance of Austenitic Heat Resistant Cast Steel

Abstract

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.

Changes in Carburized Microstructures and Creep Properties of Nb-Added SCH13A Heat-Resistant Cast Steel due to Different Pouring Temperatures

“…．そのような中において，Nb の 添加は耐熱鋼のクリープ特性と熱衝撃特性を向上させるばか りでなく，破断の一因となる浸炭層中のき裂進展を抑制する 効果がある [13][14][15] ．実用面で考えた場合，熱処理治具の実使用 Fig. 12 Comparison of creep rupture time between as-cast samples and 10-cycle vacuum carburized samples.…”