The Role of Dynamic Strain‐ageing in the Environment Assisted Cracking Observed in Pressure Vessel Steels

Abstract

The dynamic strain ageing (DSA) behaviour of A533B Class 1 reactor pressure vessel (RPV) steel, containing 5ppm of free nitrogen, has been investigated over a wide range of strain rates from 3 x lo-' to 3-10-3 s-l and temperatures from 20 to 350°C. The DSA was observed within certain temperature ranges at all strain rates tested and its hardening effect in terms of the maximum strengthening stress (up) decreased linearly with the increase of log strain rate. The temperature to stimulate DSA was observed to increase with increasing strain rate. The apparent activation energies of the characteristic strain rates for the onset, and peak of DSA have been determined, and their implications have been discussed. Compared with the available data, a positive effect of free nitrogen content on up has been evaluated. It has been found that the occurrence of susceptible environment assisted cracking (EAC) of A533B steel in high temperature water is co-related to the DSA behaviour. The results suggest that DSA reduces the ductility of RPV steel and its role in enhancing the EAC of RPV steels should not be neglected, in view of the coincidence with susceptibility zones for DSA and EAC in terms of strain rate and temperature.Keywords-Dynamic strain-ageing; Environment-assisted cracking A533B Class 1 steel; Strain rate and temperature effects. NOMENCLATURE Do = diffusion coefficient Q = apparent activation energy Q , , , = apparent activation energy of strain rate for the onset of DSA Qp = apparent activation energy of strain rate for the peak of DSA Qd = apparent activation energy of strain rate for the disappearance of DSA R = load ratio R =gas constant T = temperature up = peak strengthening stress uuTs = ultimate tensile stress (tensile strength) uo.2 = 0.2% proof (yield) strength 5, =crack tip strain rate to,, = strain rate for the onset of DSA tp =strain rate for the peak of DSA da/dN =crack growth rate RA = reduction in area t = time t = strain rate

The Effect of Microstructure on Stress-Strain Behaviour and Susceptibility to Cracking of Pipeline Steels

“…The serrations are affected by strain rate (Figure 3) and the size of the maximum load drop due to serrations decreases as the strain rate increases over the range tested. A test at a strain rate of 2.3 × 10 −5 s −1 and a temperature of 75 • C produced no serrations which agrees with previous work [16][17][18] and indicates that serrations occur at a matching combination of strain rate and temperature for a low carbon steel. The strain rate for the onset of serrations at 75 • C is approximately 1 × 10 −5 s −1 .…”

Effects of temperature and pressure on stress corrosion cracking behavior of 310S stainless steel in chloride solution

“…2, all the tensile curves show the trend of dynamic strain aging(DSG) and get more notable with temperature up. Theories of KATAD [20] and ASKINSON [21] , et al, suggested that DSG will promote environmentally assisted cracking(EAC), which causes the markedly reduced of metal material. The tensile strength of samples decrease with the increase of temperature and decrease more at 10 MPa than that at 16 MPa.…”

Fatigue as a process of cyclic brittle microfracture

“…Time‐dependent effects of environment include the phenomenon of dynamic strain ageing, 5 dynamic embrittlement, 6 hydrogen embrittlement 7 and nitrogen embrittlement 8 . According to diffusion theory, the mere presence of a gaseous environment around a solid promotes diffusion of the former into the latter.…”

“…Intergranular diffusivity is much greater than transgranular diffusivity and is in fact referred to as ‘short‐circuit’ diffusion 9 . Most work on the subject considers the diffusion process to be time‐dependent, intergranular and as encompassing material depth of the order of at least a few grains 5–8 . Transgranular diffusion has also been studied, but under conditions that differ considerably from those associated with fatigue 10,11 .…”

“…9 Most work on the subject considers the diffusion process to be timedependent, intergranular and as encompassing material depth of the order of at least a few grains. [5][6][7][8] Transgranular diffusion has also been studied, but under conditions that differ considerably from those associated with fatigue. 10,11 A central feature of all these studies is the recognition that gas-metal diffusion kinetics is driven by both gas pressure as well as near-surface hydrostatic stress on the side of the metal.…”