On the Characteristics of Strength at High Temperature of Iron-Base Heat-Resisting Alloys of Precipitation Type. (Study on the Heat-Resisting Alloy (4))

Abstract

In a previous report, the author introduced that the modified iron-base heat-resisting alloys of precipitation type were comparable to Nimonic 80A in creep-rupture properties. In this investigation, the author studied the high temperature properties of modified alloys containing a small amount of Mo,W,V,Nb,Ti,Al and B in iron-base Cr 16%, Ni20% and Co 20% alloys. 16 mmφ forged bars were used for solution annealing, age hardening, short-time tensile tests, high temperature creep-rupture tests, electron-microscopic and X-ray diffraction tests. Specimens containing Ti+Al have remarkable age-hardenable characteristics and short-time high-temperature tensile strength. The creep-rupture properties of alloys having the highest strength in these modified alloys, investigated up to 732°C, were better than those of commercial alloys such as Nimonic 90, Inconel X or Nimonic 95 and were comparable to those of Nimonic 100 or M-252. By the X-ray diffraction data on the electrolytic extracts from these specimens after creep-rupture tests, MC, M₂₃C₆, σ phase, Laves phase, γ′ phase, β phase and boride have been identified. There control alloys precipitated Laves phase by adding Nb and β phase by increasing Al content in Ti+Al. The author found that the deterioration of high temperature characteristics of these control alloys have relation to precipitations of massive β and L phase. It might be suggested that the remarkable age-hardening and the high rupture strength properties of these alloys are principally caused by precipitation of aluminum-poor γ′ type Ni₃(AlTi).