Further observations on the fracture of a quenched and tempered steel in hydrogen
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b/a 1.2 1.5 2.0 2.5 3.0 3.5 4.0
Error Introduced by Use of Planar Expressions
EPSTI Pct 0.0227 0.112 0.326 0.567 0.809 1.05 1.27
EPSTB Pct - 1.14 -1.07 -0.902 -0.716 -0.529 -0.347 -0.173
order one pct for the range of b / a of practical interest. With respect to the breakthrough time, the negative error means that the experimenter would find a smaller diffusivity by using the planar expression rather than the cylindrical expression [Eq. 6]. In conclusion, Eqs. 4 and 6 represent generalized expressions for the inflection and breakthrough times for the given boundary conditions in flux measurements. For planar and spherical geometries, it is shown that the expressions reduce to simpler forms, Eqs. 7a and 7b, in agreement with those given in Reference 3. In cylindrical geometry, the expressions require the solution of the Bessel function eigenvalue problem, evaluation of T~ and/'2, and are available only in numerical form. We have shown that the errors resulting from the use of the planar or spherical expressions for ti or tb, rather than the exact expression for the cylindrical geometry, are of the order of one pct. Therefore, only a small error would be introduced into the measured diffusivities for samples of cylindrical geometry by using planar expressions for the inflection or breakthrough time.
cracking ( P R H I C ) to stress-controlled, intergranular, hydrogen-induced cracking in HY 130-type steel. The transition occurs as the intergranular concentration of embrittling elements (P, Sn, Si, and so forth) is increased, and it is accompanied by a large reduction in the effective threshold stress intensity KVH for hydrogen-induced crack growth. In the present communication we wish to report on the effect of H2 on the other two fracture modes observed in these steels: rupture and cleavage. The compositions and other data for the heats to be discussed are given in Table 1. The experimental procedures were as reported earlier. ~ Heat A, which contained low Mn and Si, but high A1, was a clean, tough steel highly resistant to both temper-embrittlement and hydrogen-induced cracking. Heat J, which contained low Si and A1, but high Mn, was prone to rupture (when not temper embrittled) because of the nature of its inclusion content. Heat G, which contained low Mn, but high Si and AI, was prone to cleavage, even at room temperature. The heats were tested in the form of bolt-loaded modified W O L precracked specimens 2 and four-point notched bend specimens, 3 as before. ~ Only the precracked specimens will be discussed here, but the notched specimens gave generally similar results.
ACKNOWLEDGMENTS
The work was supported by the Department of Energy under contract DE-AC02-76ER01198.
REFERENCES 1. R. M. Barter: Diffusion In and Through Solids, Cambridge Press, 1941.
2. W.M. Robertson: Zeit. Metallk., 1973, vol. 64, p. 436. 3. N. Boes and H. Zuchner: J. Less-Com. Metals, 1976, vol. 49, p. 223. 4. J. Crank: The Mathematics of Diffusion, Oxford, 1975, pp. 50, 84, 99.
Further Observations on the Fracture of a Quenched and
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