Effects of internal hydrogen on fatigue strength of type 316 stainless steel.

摘要

To promote the use of hydrogen gas in fuel cells and other devices as an alternative energy source to fossil fuels a better understanding of effects of hydrogen gas on the material properties of structural steels is needed. It is well known that hydrogen gas that has diffused into a structural metal can cause deleterious effects to a wide variety of material properties by means of hydrogen embrittlement. Little research has been conducted concerning the effects of diffused hydrogen on the fatigue strength of structural metals. This thesis will aim to examine hydrogen-assisted fracture due to internal hydrogen charging using type 316 stainless steel as a model system and to assess the use of the R.R. Moore rotating bending fatigue machine as a high throughput method for material evaluation.;The tensile properties and high cycle fatigue life of two type-316 stainless steel alloys were studied---one of nominal nickel, high carbon content, and the other of low nickel, low carbon content. Following internal charging with hydrogen at 573K in 138 MPa hydrogen gas for a period of 10 days, tensile test results of each alloy showed an increase of 10--15% in ultimate tensile strength and a decrease in ductility of 19--23%. Greater nickel content was shown to have a beneficial effect to resisting hydrogen-assisted fracture in tensile tests. Internal hydrogen charging resulted in an increase of number of cycles to failure by 5 to 6 times that of uncharged specimens. No significant increase was seen in the endurance limit when compared to the S-N curve of non-charged alloys. Hydrogen charging was shown to provide a resistance to crack nucleation in fatigue tests for both alloys tested.