凝固割れ感受性を考慮した鋼材ダンパー用耐疲労合金の開発

抄録

A new weldable ferrous-based Fe-Mn-Si (FMS) seismic damping alloy with excellent fatigue durability was developed by optimizing the phase transformation behaviors in both fatigue deformation and solidification. Fatigue and welding tests were performed on prototype alloys with nominal compositions of Fe-15Mn-(10+2X)Cr-(8-X)Ni-4Si, (X=0, 0.5, 1, 2). The fatigue lives of these alloys were superior to those of general steels, and the fatigue lives of the alloys with X=0.5 were comparable to those of the previously developed FMS alloy, X=0. However, the fatigue lives decreased with increasing X (increase in Cr and decrease in Ni). The analysis on the microstructure after fatigue fracture suggests that the decrease in fatigue life was due to the deformation-induced formation of α’-martensite that might have inhibited the fatigue damage mitigation mechanism through the bidirectional transformation between γ-austenite and ε-martensite (BTRIP). On the other hand, increasing X resulted in a change in solidification mode and improved solidification cracking susceptibility: significant segregation and solidification cracking were observed for X=0, while segregation was eliminated and no cracking occurred in X=0.5. These results indicate the Fe-15Mn-11Cr-7.5Ni-4Si corresponding to X=0.5 has excellent properties as a second-generation FMS alloy that can realize a welded assembly damper with excellent fatigue durability.