Abstract
The creep rupture properties of AISI 347 stainless steel,and the structural changes during creep rupture testing at 650°C have been investigated with forged material. The following are the conclusions were as follows: (1) The fine granular NbC precipitates at an early stage, and the thread-like NbC precipitates in the matrix after longer hours. (2) The grain size has only a slight bearing upon the creep rupture strength. (3) With low-temperature solution treatment, the creep rupture strength decreases and the rupture elongation increases; and with high-temperature solution treatment, the creep rupture strength increases and the rupture elongation decreases. However, the increase of creep rupture strength with the rise of heat-treating temperature is rather slight in the range higher than 1100°C than in the lower range. (4) As the precipitation hardening due to NbC is greater and continues longer than that due to TiC, the creep rupture strength of AISI 347 is larger than that of AISI 321 and the rupture elongation is smaller. (5) The long-time creep rupture strength of the cold-worked specimens decreases due to recrystallization during creep rupture testing. In the case of AISI 347 stainless steel, however, since the precipitation of the fine granular NbC remains in the original crystals for a long time, the growth of the recrystallized grain is slow, and the decrease in the long time rupture strength is smaller than in AISI 321 stainless steel.
