High Damping Capacity Of Fe-Cr-Mo Alloys At High Temperature

Considering the applications, this paper explores the damping capacity of Fe-Cr-Mo alloys at room temperature and at high temperature. It analyses the effects of the heat treatment, microstructures and ferromagnetics on the damping capacity. And through the tests on the mechanical properties of Fe-Cr-Mo alloy, the possibility is analyzed that Fe-Cr-Mo high damping alloys substitute of OCrl8Ni9Ti stainless steel in the circuit of nuclear pile.The inverted torsion pendulum technique (JN-1 vacuum internal friction technique) was used to test the damping capacities of Fe-Cr-Mo and Fe-Cr-Al-Si alloys. The results indicate that heat-treating temperature affects obviously the damping capacity of these alloys. As the heat-treating temperature rises, the damping capacity of Fe-Cr-Mo reaches two peaks respectively at 900℃ ( δ =0.161 )for two hours followed by water cooling and 1100℃ ( δ=0.151) for two hours followed by furnace cooling. And the damping capacity of Fe-Cr-Al-Si reaches two peaks at 800℃ ( δ=0.134) for two hours followed by water cooling and 950# (δ =0.097) for two hours followed by furnace cooling. And these values (damping capacity) are ten times higher than OCrl8Ni9Ti stainless steel.The cooling rate during heat treatment can affect obviously thedamping capacity of Fe-Cr-Mo alloy. There exists a critical temperature at 1000℃. Below it, the damping capacity of Fe-Cr-Mo by water cooling is higher than that by furnace cooling.Heat-treating time can affect obviously the damping capacity of Fe-Cr-Mo alloy. When heated at 1100℃ by water cooling from half hour to eight hours , the damping capacity of Fe-Cr-Mo alloy decrease gradually. After two hours, the damping capacity of Fe-Cr-Mo drops sharply.By studying the damping capacity of the Fe-Cr-Mo and Fe-Cr-Al-Si alloys at high temperature, the damping character and variation are made clear. As the testing temperature increase, the damping capacity 8m or strain amplitude y c of Fe-Cr-Mo and Fe-Cr-Al-Si alloys decrease gradually, but at 300℃ (even other higher.temperatures ), the damping characters of these alloys are still higher ( δ=0.084) . These results have not been reported for these years.Alternating magnetic filed can affect obviously the damping capacity of alloys. As the magnetic filed strengthens, the damping capacity of Fe-Cr-Mo alloys fall down gradually. When the alloys are magnetic saturation, the damping capacity reaches at the minimum.The microstructure of Fe-Cr-Mo is examined under optical microscope and electron microscope (SEM) and XRD. The influencing factors of the damping capacity are analyzed.The tensile properties are investigated. The results indicate Fe-Cr-Mo alloy possess the best mechanical property at 900℃ for two hours followed by water cooling. Its tensile strength(σb) is 467Mpa, yield strength(σs) is 278Mpa, and longation percentage is 23%. After all , with suitable heat treatment, Fe-Cr-Mo alloy possesses the highest damping capacity and good mechanical property.