鐵-9wt.%鋁-30wt.%錳-1.3wt.%碳合金於熱軋延狀態 之高溫下機械性質與其顯微結構之研究

Abstract

The mechanical properties and microstructures of the as-hot-rolled Fe-9wt. %Al-30wt. %Mn-1.3wt. %C alloy after being tensile tested at 573K, 773K and 973K were investigated by using optical microscopy, scanning electron microscopy, X-Ray diffraction and transmission electron microscopy, respectively. The mechanical properties and fracture modes were also investigated. The microstructure of the alloy in the as-hot-rolled condition was full austenite phase containing a high density of Ƙ'-carbides with L'12 structure (ordered face-centered cubic). The volume fraction of the Ƙ'-carbides was about 32% and the average particle size is about 26nm. The Ƙ'-carbides were formed by spinodal decomposition during quenching in the matrix, and with no precipitates were found on the grain boundaries. At 573K, the ultimate tensile strength (UTS), yield strength (YS) and elongation(El) is 679MPa, 462MPa and 62.5%, respectively 604MPa, 374MPa and 43% at 773K, 312MPa, 296MPa and 46% at 973K, respectively. The heterogeneous Ƙ-carbides were not only grown up on the grain boundaries but also consumed the carbon atoms besides at 573K. Additionally, the heterogeneous Ƙ-carbides can help the grain boundaries to resist the high-temperature fracture. Therefore, The mechanical properties will not decrease at high-temperature significantly. The heterogeneous Ƙ-carbides’ size was bigger at 773K than that at 973K, but it can no resistance high-temperature fracture. The dimple fractures were found on the fracture surfaces at each experimental temperature. It is the characteristic of ductile fracture mode of the as-hot-rolled alloy tested at high-temperature.