低応力拡大係数領域における種々の高張力鋼の疲れ破面の解析

概要

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The fatigue tests were performed to obtain thresholds of stress intensity factor range, ⊿K_<th>, by the incremental step method in air at R=0.1 using HY140, HY240, HP9-4-20, 18Ni (200) maraging, 18Ni (250) maraging, MAS-MA-164, and PH13-7 steels. The informations obtained from fracture surfaces were analyzed in the low stress intensity factor range. The results are as follows ; 1) The fracture surface consists of unit region, which is a bundle of lath-like-pattern, and flat area just like a grain boundary. 2) The size of the fracture unit increases with ⊿K. 3) The size of units is about one half of the pre-austenitic grain size at the threshold region. 4) The width of lath-like-patterns is 0.2 to 1.0 μm at the theshold region. This width is almost same as the lath width. This width increases with ⊿K. 5) The direction of the bundle of the lath-like-pattern is quite randum to the direction of the macroscopic growth. With ⊿K increasing, however, the direction of the bundle approachs to the macroscopic direction of crack growth. 6) The maximum intergranular fracture rate generally arises at about 30kg/mm^<3/2> of ⊿K. The maximum values of steels containing no carbon is two or three times as large as thoes of steels containing carbon. 7) The ⊿K_<th> of steels containing carbon is generally lower than that of steels containing no carbon.
1979-05-01