Two heats of low activation martensitic (LAM) steels with Ti and Ta (denominated as 9Cr-Ti and 9Cr-Ta),respectively,developed as candidate structure materials for nuclear reactor were characterized.This paper was focused on the effect of titanium on the microstructures and mechanical properties of 9Cr LAM steel in as-received condition (normalized at 950 ℃ for 30 min with water quenching plus tempered at 780 ℃ for 90 min with air cooling).Chemical analysis and microstructure observation were conducted on 9Cr-Ti and 9Cr-Ta with optical microscopy,X-ray diffraction analysis,scanning electron microscopy and transmission electron microscopy.Impact properties and tensile strengths were measured with Charpy impact experiments and tensile tests.The results indicated that 9Cr-Ti and 9Cr-Ta were fully martensitic steels in as-received condition.MX type and M23C6 type precipitates were observed distributing along boundaries of prior austenite grains and martensite laths in 9Cr-Ti.The addition of titanium accelerated the precipitation of TiC and TiN,and produced much finer grains in 9Cr-Ti than 9Cr-Ta at the same normalization temperature.Mechanical properties tests showed the ductile brittle transition temperatures of 9CrTi and 9Cr-Ta were about-90 ℃ and-85 ℃,respectively.The ultimate tensile strengths at room temperature and 600 ℃ were 680 MPa and 365 MPa for 9Cr-Ti,and 660 MPa and 335 MPa for 9Cr-Ta,respectively.The favorite impact toughness and tensile properties of 9Cr-Ti could be attributed to the fine grains in as-received condition.
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