Effects of aging on mechanical properties and microstructures in high-purity Fe50Cr-(0-8)W alloys

The effects of aging on the tensile behavior at 400°C and 600°C and the microstructures of high-purity Fe-50Cr, Fe-50Cr-5W and Fe-50Cr-8W alloys have been examined. The specimens were aged at 400°C and 600°C for 4. 8 × 103 h under vacuum. The yield stress at 400 °C of the Fe-50Cr-(0-8)W alloys aged at 400 °C increased with increasing tungsten content from 530 MPa to 830 MPa. Twining structures were observed in the Fe-50Cr-(0-8)W alloys aged at 400°C. The total elongation of the Fe50Cr and Fe-50Cr-5W alloys was about 16%, but the elongation of the Fe-50Cr-8W alloy was only 3%. In the specimens aged at 600°C, the yield stress also increased with tungsten content from about 300 MPa to 480 MPa. The total elongation in the aged Fe50Cr alloy was about 16% but a few cracks were observed at grain boundaries and in the matrix. The total elongations of the aged Fe-50Cr-5W and Fe-50Cr-8W alloys were more than 20% and grain boundary deformation was observed in the necking region. The change of microstructure of the Fe-50Cr alloy aged at 400 °C was small. In the Fe50Cr-5W and Fe-50Cr-8W alloys aged at 400 °C, tungsten rich Laves precipitates of about 0. 2-2 μm were formed in the matrix. M7C3 carbide with low number density was also formed in the Fe-50Cr-(0-8)W alloys and the size of M7C3 carbide was the largest in the Fe-50Cr-8W alloy. In the Fe-50Cr alloy aged at 600 °C, sigma phase was formed at grain boundaries and M7C3 carbide with low number density was formed in the matrix. In the Fe-50Cr-5W and Fe-50Cr-8W alloys aged at 600 °C, tungsten rich precipitates were formed in the matrix and at grain boundaries