[en] Within the CASTOC-project (5^th EU FW programme), the environmentally-assisted crack (EAC) growth behaviour of low-alloy reactor pressure vessel (RPV) steels is experimentally investigated under simulated transient and steady-state boiling water reactor (BWR) power operation conditions by six European laboratories. The present report is a summary of the third and fourth test of working package (WP) 3 with loading transients, performed at Paul Scherrer Institut (PSI). Two different low-alloy steels (20 MnMoNi 5 5, 0.015 wt.% S and 22 NiMoCr 3 7, 0.007 wt. %S) were investigated in oxygenated high-temperature, high-purity water (T = 240 ^oC, DO = 400 ppb) in a daisy chain at two different load ratios (R = 0.8 and 0.2). In the first part of the experiments, asymmetrical saw tooth loading with different rise times Δt_R of the load and different loading frequencies were applied. Then the loading conditions were changed to an asymmetrical trapezoid waveform loading (periodical partial unloading, PPU) and the hold time Δt_H at maximum load was varied. In the final phase of WP 3 PSI tests 3 and 4 the SCC behaviour was investigated under constant load. With decreasing loading frequency the corrosion fatigue (CF) crack advance per cycle Δa/ΔN_EAC of material A increased. Sustained EAC crack growth could be maintained down to low frequencies of 10^-5 Hz. The time-based crack growth rate (CGR) da/dt_EAC decreased with decreasing frequency. In material B no effect of the loading frequency could be resolved. Up to a hold time of 1 h at maximum constant load the CGR da/dt_EAC seemed to be independent of the hold time. Above hold times of 1 h the CGR decreased and dropped down to CGR values in the range or below the BWR VIP 60 SCC disposition lines. This behaviour was observed in both investigated materials. The cycle-based CGR Δa/ΔN_EAC remained approximately constant with increasing hold time. The low-frequency corrosion fatigue (LFCF) CGR Δa/ΔN_EAC of material A and B significantly exceeded the 'Wet' reference fatigue CGR of the current ASME BPV Code, Appendix A, Section XI in high-temperature water of 240 ^oC under oxidising and low-flow conditions. The LFCF CGR of both materials were conservatively covered by the 'high-sulphur line' of the GE-model for all loading frequencies. The transition curves between the 'low-' and 'high-sulphur line' seemed to be non-conservative under the investigated oxidising conditions. A simple 'Superposition'-model and 'Time-Domain' evaluation, which include frequency and ECP effects, were briefly presented. They could be used to develop more realistic reference fatigue crack growth curves for a new BWR/NWC code case. No SCC under constant load could be detected in material B by DCPD-method or by fractography with SEM. In material A sustained, stationary SCC under oxidising and low-flow conditions at relatively high stress intensity factors K_I = 70 MPa.m^l/2 could be observed for up to 95 h after switching from cyclic to constant load. Thereafter cessation of the crack growth occurred and CGR well below the BWR VIP 60 SCC disposition lines were observed. (author)