Ni-Cr鋼の高温焼戻し脆性におよぼす不純物元素の影響

抄録

Temper embrittlement of the nickel-chromium steels containing P, As, Sb, Sn, or Mo has been investigated. The impact properties of the non-embrittled steels quenched after tempering and of the embrittled steels step-cooled following tempering were studied by the instrumented Charpy test.
Susceptibility to temper embrittlement was measured by comparing the transition temperature and the effective surface energy of nonembrittled steels and the step-cooled steels. The embrittling treatment applied to steels with Sb, P or Sn caused very much increase in transition temperature, but the same treatment applied to the steels with As or Mo caused less increase in transition temperature. The mechanical properties of the steels embrittled by step cooling were characterized by the low fracture load, low effective surface energy and the small deflection of the specimen to fracture.
The fracture mode of the step-cooled or the non-embrittled steels tested at low temperatures was of intergranule along the prior austenite grain boundary or of quasi-cleavagerespectively.
The technique of Ion Micro spectroscopy and the Auger electron spectroscopy used to study the segregation of impurity elements to prior austenite grain boundaries, and it was found that Sb, P and Sn segregated at grain boundaries during tempering of the steels containing Sb, P or Sn.