Internal hydrogen-induced subcritical crack growth in austenitic stainless steels
- PDF / 4,499,259 Bytes
- 14 Pages / 612 x 792 pts (letter) Page_size
- 93 Downloads / 265 Views
INTRODUCTION
A U S T E N I T I C stainless steels are generally considered to have good resistance to hydrogen embrittlement; however, service failures attributable to hydrogen suggest a need for more detailed understanding of the compatibility of austenitic stainless steels with hydrogen. The most damaging aspect of the effects of hydrogen in structural materials is delayed failure, in which a specimen, smooth or notched, fails suddenly after a period of time of exposure under load. If the environment is a gaseous hydrogenic species, this is called gaseous hydrogen embrittlement. Hydrogen entry from an acid solution may also be responsible for some failures classified as stress corrosion cracking or sulfide stress cracking. A number of theories have been proposed to explain hydrogeninduced subcritical crack growth (SCG) in steel and other structural materials. The hypothesis that the rate of crack propagation is controlled by the rate of supply and accumulation of hydrogen in an embrittled region at the crack tip has been shown to be qualitatively correct in high-strength steels, rl-91 Hydrogen-induced SCG has also been observed in stainless steels. [~~ After measuring the hydrogen permeability and diffusivity in stainless steels, Perng and Altstetter carried out constant load tests
J.-H. HUANG, formerly Research Assistant, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, is Associate Professor, Department of Nuclear Engineering, National Tsing-Hua University, Hsinchu, Taiwan, People's Republic of China. C.J. ALTSTETTER, Professor of Physical Metallurgy, is with the Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Manuscript submitted December 18, 1989. METALLURGICAL TRANSACTIONS A
in austenitic stainless steels types 301 and 310 in hydrogen gas environments, t11-151 No SCG was observed for AISI 310, while in AISI 301, cracks propagated above a threshold stress intensity, Kth, and a typical three-stage log d a / d t vs K curve was observed. Hydrogen-induced SCG was favored by the presence of a ' phase (bcc), which was rationalized in terms of the difference in hydrogen permeation in the bcc and fcc phases. The relatively high cracking velocity of AISI 301 in hydrogen gas was attributed to the fast transport of hydrogen through the stress-induced a ' martensite at the crack tip. This, coupled with a low escape rate of hydrogen through y phase in the surrounding region, leads to a faster accumulation rate of hydrogen in the embrittlement region and higher cracking velocities. It is reasonable that the failure criterion and diffusive transport hypothesis are applicable to both external and internal hydrogen; however, there are important differences in the two cases. For the internal hydrogen case, when hydrogen is already uniformly distributed on a macroscopic scale, surface reactions are eliminated as rate-controlling steps in the supply of hydrogen. They still might play a role in the loss of hydrogen from t
Data Loading...
