A Model to Account for the Effects of Load Ratio and Hydrogen Pressure on the Fatigue Crack Growth Behavior of Pressure Vessel Steels.

A phenomenological model for estimating the effects of load ratio and hydrogen pressure PH2 on the hydrogen-assisted fatigue crack growth rate (HA-FCGR) behavior in the transient and steady-state regimes of pressure vessel steels is described. The "transient regime" is identified with crack growth within a severely embrittled zone of intense plasticity at the crack tip. The "steady-state" behavior is associated with the crack growing into a region of comparatively lower hydrogen concentration located further away from the crack tip.

Double twist torsion testing to determine the non recrystallization temperature.

A double-twist torsion testing technique has been developed using a 316 stainless steel as an exemplar material to experimentally assess recrystallization behavior and determine the non-recrystallization temperature (T). This new method was compared to the traditional methods of double-hit compression and multi-step hot torsion testing. The double-twist torsion test allows T to be related to the extent of austenite recrystallization through measurements of fractional softening while accommodating multiple deformation and recrystallization steps with a single specimen.

Transgranular Cracking in a Liquid Zn Embrittled High Strength Steel.

Intergranular Zn-assisted liquid metal embrittlement (LME) cracks have been frequently reported in steels, involving austenite grain boundary penetration of liquid Zn at high temperature. In the present study, a Zn-coated high strength steel was deformed at an intercritical temperature, and the characteristics of LME cracking were studied in a mixed microstructure composed of ferrite and austenite. Crack propagation was intergranular in austenite; in contrast, the ferrite exhibited both intergranular LME and LME.