Mechanism for hydrogen-induced brittle fracture of austenitic stainless steels

Internal hydrogen embrittlement of several austenitic stainless steels is known to be accompanied by a change in fracture mode. Type 304L stainless steel is representative of these alloys. In other austenitic stainless steels, Type 310 for example, no change in fracture mode has been reported and gas phase charging of the alloy causes little change in strength or ductility. Cathodic charging, however, introduces extremely large amounts of hydrogen and ductility losses are observed. The embrittlement mechanism proposed in this paper for Type 304L stainless steel and similar alloys is based on results of a continuing program to investigate hydrogen embrittlement of austenitic stainless steels. The proposed mechanism, therefore, is tentative insofar as future results may contradict current beliefs or permit a more definitive mechanism to be developed. One central notion of this proposal is that of microcrack formation. The present fracture model envisions the nucleation step as taking place via a Zener--Stroh--Petch mechanism rather han a Cottrell coalescence model as proposed by Blanchard and Troiano

Microstructural Changes Accompanying Annealing of Cold-Worked Uranium

Recovery of the capacity for plastic deformation by annealing previously cold-worked uranium plays a key role in the mechanism proposed for the cavitational swelling observed in irradiated uranium. Consequently, an investigation of recovery of yield strength was undertaken for unalloyed uranium and several selected alloys. During the course of this study, variations in the volume fraction of twins in the various specimens of unalloyed uranium suggested that twinning might be a mechanism of the recovery process. Results of four experiments in this study are described in this report

Hydrogen Solubility in Austenitic Stainless Steels

Hydrogen solubility was directly measured in specimens of Types 304L, 21-6-9, and modified A-286 austenitic stainless steels saturated with hydrogen at 69 MPa pressure at 470 K. Nitrogen in Type 21-6-9 stainless steel and precipitate morphology in the modified Type A-286 stainless steel altered the hydrogen solubility. Cold work and surface treatment had only minor effects on hydrogen solubility in the three stainless steels. This reports discusses this study

A Technique for the Rapid Measurement of Thermoelectric Power

A new technique is described for rapid measurement of the thermoelectric power of rod-shaped specimens over a wide temperature range. The apparatus utilizes sensitive commercial dc amplifier for the sample and temperature gradient voltages and a multiple-point recorder for sampling these voltages as well as the sample temperature signal. The technique eliminates spurious thermal emf\u27s in the leads and is based upon on-the-run recording of the sample and temperature gradient voltages as the temperature gradient slowly increases. As a test of this technique, the thermopower of pure nickel was measured between 4.2 and 300 K and the results are compared with other measurements using conventional techniques. ©1969 The American Institute of Physic

Mechanical Properties of Uranium Alloys

Cavitational swelling in uranium-base fuel has been attributed to boundary sliding arising from internal stresses due to anisotrophic growth. This document presents the results of room-temperature tensile tests made on a series of alloys to explore the possibility of such a relation and isolate the specific properties of major importance

Hydrogen assisted fracture of sensitized Type 304L austenitic stainless steel

Sensitized specimens of Type 304L stainless steel were tensile tested in atmospheres of hydrogen and helium at high pressure, and in air at ambient pressure. Comparison tensile tests were made with solution-annealed specimens of Type 304L stainless steel in the same atmosphere. When both specimens were tested in high-pressure hydrogen, the sensitized specimens had greater loss in ductility and increased tendency to intergranular fracture. For the sensitized specimens, plastic strain to failure (epsilon/sub p/ = 1n A/sub 0//A/sub f/) in hydrogen at 69 MPa was reduced by 60 to 70% in comparison to similar tests in helium. In addition, a notch with a stress concentration factor of about 3 reduced plastic strain an additional 50 to 60%. In all cases, the nominal tensile strength of Type 304L stainless steel was increased by the notch. There was no evidence of intergranular failure in notched specimens of solution-annealed Type 304L stainless steel tested in high-pressure hydrogen environments

Surface effects on tritium diffusion in materials in a radiation environment

Tritium transport and distribution in a material are controlled by chemical potential and thermal gradients and cross-coupling to impurities and defects. Surfaces influence tritium diffusion by acting as sources and sinks for defects and impurities, and surface films restricting tritium transfer between the solid and surrounding fluids. Radiation directly affects boundary processes such as dissociation or adsorption, may erode a surface film or the surface itself, and introduces defects and impurities into the solid by radiation damage, transmutation, or ion implantation, thereby modifying tritium transport within the solid and its transfer across external interfaces. There have been no definitive investigations of these effects, but their practical significance has been demonstrated in tritium release or absorption studies with stainless steel, Zircaloy, niobium, and other materials. (auth

Effects of tritium on material properties

The effecs of tritium on deformation and fracture of metals are reviewed with emphasis on similarities and differences between tritium and the other hydrogen isotopes. Helium generated by radioactive decay of tritium introduces time dependent property changes not observed with protium or deuterium. On-going studies and topics for further investigations are identified. 17 refs., 6 figs., 9 tabs