A comparative study was performed on the microstructures and the mechanical properties of STD11 and 8Cr steel. The specimens were quenched from 1030 o C and tempered at 240 o C and 520 o C. Vickers hardness, impact toughness and tensile tests were conducted at various tempering temperatures. Microstructural characterization to measure grain size, volume fraction of retained austenite and distribution of carbides was carried out by using SEM, EBSD, TEM and X-ray diffraction techniques. Due to

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... er M 7 C 3 carbides dispersed, 8Cr steel showed larger impact toughness and plasticity than STD11 irrespective of the tempering temperature. While 8Cr steel had lower hardness in as-quenched state and after tempering at 240 o C owing to smaller carbide content and more retained austenite, it was harder after tempering at 520 o C due to larger precipitation hardening from finer M 23 C 6 .