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Micro-tensile tests based on small-scale specimens were carried out to investigate the microstructure dependence of strain hardening behavior along a Ni–Cr–Mo–V steel welded joint. Results indicated the weld metal (WM) had higher tensile strength but lower strain hardening exponent than base metal (BM), whereas a gradient distribution of strain hardening exponents was observed within the heat-affected zone (HAZ). Bainitic microstructures showed weaker strain hardening capacity than lathy martensites. A Kocks–Mecking type plot of strain hardening rate versus true stress presented at least two hardening stages (stages III and IV) with varied duration along the whole welds. Larger grain size and more lathy martensites were beneficial to prolong the hardening period. A new strength prediction model was developed by considering the size effect on tensile strength. The predicted strength distributions along the welds were in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Tensile and impact behavior of dissimilar weld joints of newly developed rotor steels 23CrMoNiWV88 and 26NiCrMoV145 were conducted at various temperatures below 350°C. Inhomogeneous microstructures and asymmetrical micro-hardness along the dissimilar welding joint were observed. With the increase of temperature, strength decreased which was associated with the increased plasticity, and fracture location changed from weld metal (WM) to intermediate pressure (IP) base metal (BM) at around 300°C. Compared to the homogeneous impact specimen with two fracture zones at fracture surface, a combined quasi-cleavage and ductile fracture mode with three zones is observed at the fracture surface of the dissimilar weld joint when the testing temperature is in the range of 0–40°C. The occurrence of separated zones are mainly ascribed to the multi-layer welding process and thus improved the impact toughness of the welding joint. [Copyright &y& Elsevier]

Abstract: In terms of the representative unit cell (RUC) with tri-layers, the time-dependent fracture performance of interfacial crack in multilayered structures was studied by using the finite element method (FEM). The feasibility of integral-type crack driving force parameter C ∗ for interpretation of interfacial creep crack growth (CCG) of multilayered systems were reexamined. Results indicate that the magnitude of the interfacial creep crack growth driving force was related to the mismatch factor of multi-layers and was significantly affected by the thickness of interlayer. [Copyright &y& Elsevier]

Abstract: Three different treatments, including the heat treatment, deep cryogenic treatment and laser surface melting, were carried out on the 30Cr2Ni4MoV rotor steel. Electrochemical polarization curve and stress corrosion test at the high temperature autoclave were employed to evaluate the corrosion resistance of treated specimens in high temperature water. Results indicate that the conventional heat treatment will increase the value of K IH for specimens with the lower yield strength, and hence reduce the susceptivity of stress corrosion cracking. However, for the deep cryogenic treated specimen, no apparent improvement was observed on the hardness and corrosion resistance due to the limited carbon precipitate and austenite transformation. In comparison, the best corrosion resistance of laser treated specimens was gained among the three-method-treated specimens according to results of the electrochemical polarization tests at temperature of 90°C. Nevertheless, some micro-cracks produced on the tensioned surface during the fabrication of self-loaded U-bend specimen due to the large deformation, and thus lead to a decreased stress corrosion cracking resistance in the environment of high temperature water. [Copyright &y& Elsevier]

Pit initiation and growth in a 25Cr2Ni2MoV welded joint in the simulated environment of a low pressure nuclear steam turbine was addressed by using U-bend samples. Different pit densities in various zones of the welded joint were observed with the order: weld near heat affected zone > base metal near heat affected zone > heat affected zone. This was partly ascribed to the galvanic effect and material difference. Pits in the base metal emanated from local deep grooves of surface machining, while they nucleated from surface inclusions in weld metal. A model for pit distribution of the welded joint was developed and verified accordingly. [ABSTRACT FROM AUTHOR]

In the present paper, a modified fatigue life model is proposed based on stress field intensity (SFI) approach, where the average weight function is introduced as the denominator of the traditional model and a modified definition of the fatigue zone is given using the concept of characteristic stress. Combined with finite element analysis, the fatigue life predictions of a central hole specimen from the literature and the notched plate specimens/a simulated engineering component conducted by the authors are carried out by the new model. Results indicate that the predicted lives are in good agreement with the experimental results and the modified stress field intensity approach is convenient for practical use. Unlabelled Image • Fatigue tests of notched plate specimens and a simulated engineering component are conducted. • A modified stress field intensity approach is proposed for fatigue life prediction of the component. • The proposed model could provide an adequate prediction solution and reduce computation efforts. [ABSTRACT FROM AUTHOR]