Fatigue crack growth rates in air in the threshold region have been measured in an Fe-Ti-C steel heat treated to produce a range of ferrite grain sizes and yield strengths. At a constant ferrite grain size, the threshold value at R = 0 (∆K0) was decreased by increasing the yield strength by precipitation hardening. Reducing the ferrite grain size decreased ∆K0. In each microstructure the threshold value was reduced by increasing the load ratio, the load ratio sensitivity being greatest for low yield strengths. The results are consistent with a model, proposed by Ritchie, based on environmental interactions at the crack tip. The grain size effect on the threshold cannot be fully explained.
Get full access to this article
View all access options for this article.
References
1.
RITCHIER. O. and KNOTTJ. F.: Proc. Conf. Mechanics and Mechanisms of Crack Growth, 1973, paper12.
2.
WEISSV. and LALD. N.: Metall. Trans., 1974, 5, 1946.
3.
RITCHIER. O.: Met. Sci., 1977, 11, 368.
4.
MASOUNAVEJ. and BAILONJ.-P.: Scr. Metall., 1976, 10, 165.
5.
COOKER. J. and BEEVERSC. J.: Mater. Sci. Eng., 1974, 13, 201.
6.
COOKER. J., IRVINGP. E., BOOTHG. S., and BEEVERSC. J.: Eng. Fracture Mech., 1975, 7, 69.
7.
KLESNILM. and LUKASP.: Mater. Sci. Eng., 1972, 9, 231.
8.
IRVINGP. E. and BEEVERSC. J.: ibid., 1974, 14, 229.
9.
FEENEYJ. A., McMILLANT. C., and WEIR. P.: Metall. Trans., 1970, 1, 1741.
10.
CARLSONM. F. and RITCHIER. O.: Scr. Metall., 1977, 11, 1113.
11.
PRIDDLEE. K.: ibid., 1978, 12, 49.
12.
BEEVERSC. J.: Met. Sci., 1977, 11, 362.
13.
COOKER. J. and BEEVERSC. J.: Eng. Fracture Mech., 1973, 5, 1061.
14.
DAVENPORTA. T. and HONEYCOMBER. W. K.: Proc. R. Soc., 1971, A322, 191.
15.
FREEMANS. and HONEYCOMBER. W. K.: Met. Sci., 1977, 11, 59.
16.
BATTEA. D. and HONEYCOMBER. W. K.: Met. Sci. J., 1973, 7, 160.
17.
WALKERE. F. and MAYM. J.: BISRA Report MG/E/307/67.
18.
KITAGAWAH., YUNKIR., and OHIRAT.: Eng. Fracture Mech., 1975, 7, 515.
