1977 年 26 巻 280 号 p. 44-49
The effects of temper embrittlement on the crack initiation properties of 3.5 Ni-Cr-Mo-V steel for large rotor forgings have been studied by using the burst tests with application of internal pressure on thin tubular specimens. The results obtained are as follows.
(1) Temper embrittled steels with severe segregation show premature fracture before the point of plastic instability, and the fracture appearance has a very brittled grain boundary fracture mode.
(2) The strength against crack initiation, which can be measured by the critical circumferential strain at bursting, decreases remarkably in the materials with fracture appearance transition temperature, FATT, above 100°C.
(3) Temper embrittled steels with light segregation, however, fracture at the point of plastic instability and show a more ductile shear fracture mode.
(4) The materials having higher yield strength show a noticeable decrease in crack initiation strength.
(5) The metal resistance against crack initiation depends upon the nature of defects and properties of surrounding matrix. Temper embrittlement enhances the notch-sensitivity of the matrix.