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Austenitic stainless steel E309L is frequently used for welded repairs on 13%Cr-4%Ni martensitic stainless steel blade runners. However, very high tensile residual stresses are found in the upper layers of these repairs, thus reducing the fatigue resistance of the repaired area in comparison with the free of residual stress base material. The use of hammer peening to increase the fatigue life of E309L welded on UNS-S41500 base metal plates has been investigated using welded samples replicating in situ blade runner repairs. Residual stress measurements using the contour method on these samples have confirmed the high stresses caused by flux cored arc welding (FCAW) of E309L, leaving stress magnitudes close to the ultimate tensile strength of the base material. Hammer peening of the surface beads effectively creates high compressive stresses at the weld’s surface up to 3 mm depth. Alternating bending fatigue tests conducted on hammer peened samples have shown an average life increase of 5.8 times at S a = 330 MPa over unpeened samples. Fatigue tests have however shown diminishing returns when overpeening the samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] Induction heating is used to introduce residual stresses (RS) in hollow fatigue specimens. [•] The effect of RS on fatigue life of AISI 304L stainless steel is investigated. [•] A statistical method is used to assess the validity of the experimental results. [•] RS evolution during the tests is shown to affect significantly the fatigue life. [•] Life prediction based on stabilized RS correlates well with nonzero mean stress fatigue tests. [Copyright &y& Elsevier]

A new experimental method for the incorporation of residual stresses (RS) in standard fa-tigue steels specimens was developed. RS were introduced by means of high frequency (360 kHz) induction heating. Suiface tensile RS resulted from cooling down the specimen subjected to a high thermal gradient. To preserve the mechanical properties of the steel, it was necessary to circulate a coolant at the center of the specimen. The 304L austenitic stainless steel does not undergo phase transformation nor micro structural changes in the solid state and was thus selected for this purpose. Multiphysics finite element (FE) analysis was used to calculate the distributed RS in the fatigue samples. These calcula-tions were compared to XRD measurements and a veiy good agreement was obtained. It was therefore demonstrated that RS induced with induction heating could be numerically assessed. This conditioning method was then proved efficient to study the only influence of a predetermined amount of RS on the fatigue properties of austenitic 304L steel with-out undergoing influences of other parameters such as microstructure, surface finish and geometry. [ABSTRACT FROM AUTHOR]

This paper presents an analysis method based on explicit dynamic analysis, enabling detailed and representative investigations of the mechanical effects of low-impedance faults in power equipment. To illustrate the effectiveness of the proposed method, a given transformer design having caused the projection of a heavy chimney/bushing assembly over a significant distance is used as a case study. A comparison about the observed projection distance of this assembly shows that the method provides representative results, thus offering the significant advantage of replacing costly and unpractical tests. The method is then used to study the retrofit measure proposed in this case to retain the chimney, further exemplifying its power to effectively study different design and retrofitting options. [ABSTRACT FROM AUTHOR]

Dilatometric experiments were conducted with the main purpose of measuring the transformation-induced coefficients of 13% chromium and 4% nickel, which are martensitic stainless steel base and filler materials used for hydraulic turbine manufacturing. To this end, a set of experiments was conducted in a quenching dilatometer equipped with loading capabilities. The measurement system was further improved by means of modified pushrods to allow for the use of specimens with geometries that are compliant with tensile test standards. This improvement allowed for the measurement of the materials' phases and respective yield strengths. The dataset was further used to determine the relationship between the applied external stress and the martensitic start temperature ( M s ) upon cooling. The TRIP coefficient's K values for both the S41500 steel and E410NiMo filler material were measured at 8.12 × 10 − 5 and 7.11 × 10 − 5 , respectively. Additionally, the solid phase transformation model parameters for both the austenitic and martensitic transformation of the filler material were measured. These parameters were then used to model austenitic-phase-transformation kinetics and martensite transformation, including transformation-induced plasticity effects. Good agreement was achieved between the calculation and the experiments. [ABSTRACT FROM AUTHOR]

The austenitic stainless steel E309L filler is a commonly used material for in-situ crack repairs of hydro-turbines due to its high weldability, mechanical and chemical compatibility with the turbine's base material. However, experimental data for the as-welded E309L filler is scarce. In this paper, the mechanical properties of as-deposited 75% Ar/25% CO 2 flux-cored arc welding E309L austenitic stainless steel are investigated. The material is shown to be rate- and temperature-sensitive. Furthermore, although the directional nature of the welding/repair process might suggests otherwise, the response is found to be isotropic. Finally, a classic three-dimension Johnson-Cook plasticity theory is implemented and reproduces the experimental results with good accuracy. [ABSTRACT FROM AUTHOR]

In this paper, the industrial hammer peening process is optimized using multi-objective, sequential approximate optimization, which is a mathematics- plus finite element- based algorithm. Since the number of design and objective variables is significant, the global optimization problem is split into two, more manageable multi-objective subproblems. The use of surrogate modelling together with an intensification and diversification strategy for solving the optimization subproblems allows for significant computational cost savings without loss of accuracy. Additionally, we propose a Bayesian inference criterion-based sensitivity approach for 'filtering-out' design variables which do not significantly affect objectives variables. Finally, guidelines for selecting appropriate Pareto optima are given using $N-1$ Pareto diagrams, where N is the number of objective variables. [ABSTRACT FROM AUTHOR]

Abstract: In the as-quenched state, 13%Cr–4%Ni martensitic stainless steels are essentially 100% martensitic. However, a certain amount of austenite is formed during the tempering of this alloy. This reformed austenite is thermally stable at room temperature but can transform to martensite under stress. This transformation is known to happen during impact testing but it has never been established if it occurs during fatigue crack propagation. This study presents the results of X-ray diffraction measurements of reformed austenite before and after crack growth testing. It has been found that reformed austenite does transform to martensite at the crack tip and that this transformation occurs even at a low stress intensity factor. Low-cycle fatigue tests were conducted to verify austenite transformation under cyclic straining. It was found that reformed austenite transforms only partially during the first strain reversal but that essentially all austenite has disappeared after 100 cycles. The relation between austenite transformation under low-cycle fatigue and its transformation during crack growth is also discussed. [Copyright &y& Elsevier]