1985 年 3 巻 3 号 p. 505-511
Comparison between Implant test, RRC and side-slotted JIS-y (Tekken) tests has been performed using the authors' new cracking parameter PHA which was introduced previously based on JIS-y test data.
New formulae for predicting critical rupture stresses in 8-7 mm D Implant test have been developed by multiple regression analysis of 102 test data on HT50 to HT80 low-alloy high strength steels of low carbon contents of 0.04 to 0.18%. The formulae proved to be more accurate than conventional formulae thus far proposed.
The 8-7 Implant critical rupture stresses of the tested HT50 to HT80 steels were compared with the critical crack initiation stresses in RRC and JIS-y tests predicted by PHA analysis. Equivalence of critical stress values between 8-7 Implant and RRC or side-slotted, JIS-y tests has been found to exist only in a limited stress range of 340 to 540 N/mm2, provided the test steel, electrode hydrogen content, and the cooling time are kept the same, respectively, in both the tests. In the higher stress range exceeding 540 N/mm2 in HT50 steels, the 8-7, Implant critical stress condition which leads to microvoid coalescence type fracture, does never seem to be realized in RRC and JIS-y tests.
The estimated relationship between critical preheating temperature and Pcm obtained via Implant test seems to be practically identical to that via RRC or side-slotted JIS-y test, only in the case of critical stress level of approximately 451 N/mm2. Taking the critical stress to be equivalent to the yield stress of base metal seems to be reasonable only in the case of the said stress level and practical welded joint of mild restraint.