Environment-Sensitive Crack Growth

From a practical viewpoint, ATiscc may be defined in terms of the limit of sensitivity of crack growth rate measurements, which typically is of the order of 1 X 10 cm/s, under the best circumstances. However, recognizing that the growth rate at the lower limit is controlled by creep, an argument can be made that the concept of a ATiscc is inappropriate because creep crack growth gradually transitions into environment-assisted crack growth as the environmental conditions become more conducive to the latter. 

R. Raj and V. K. Varadan, The kinetics of hydrogen assisted crack growth. Mechanisms of Environment Sensitive Cracking of Materials, Univ. of Surrey, UK (P. R. Swarm, F. P. Ford, and A. R. C. Westwood, eds ). The Metals Society, April 1977, p. 426. 

Pao, P. S., Wei, W. and Wei, R. P., Effect of frequency on fatigue crack growth response of AISl 4340 steel in water vapour , Proc. of Environment Sensitive Fracture of Engineering Materials, 24-26 Oct. 1977, Chicago, USA, The Metallurgical Society of the AIME, pp. 565-580 (1977)... 

Representative environments for which SCC has been reported in carbon steels are included in Table 7.7. The sensitivity of these steels to changes in composition and environment are illustrated by the effects of potential in Fig. 7.78 to 7.80 and by the slow strain-rate data of Fig. 7.82 and 7.83. These data support the conclusion that environment cracking is related to the susceptibility of the passive films to crack under stress, to the subsequent crack growth due to anodic dissolution and/or hydrogen embrittlement during the period of exposure of the alloy substrate, and to rates of repassivation of the exposed areas. Actual crack-front growth mechanisms are discussed in some detail in a later section. 

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