Incorporation of Y2O3 Particles into 410L Stainless Steel by a Powder Metallurgy Route

Addition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria. © The Author(s) 201

Investigation of shot-peened austenitic stainless steel 304L by means of magnetic Barkhausen noise

Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite α′ at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes

Magnetic measurements for evaluation of radiation damage on nuclear reactor materials

It is important for the plant lifetime management to estimate the loss of toughness and other effects, e.g. increase of yield strength and hardness, caused by irradiation. This paper deals with the use of magnetic measurements to determine the irradiation effects on nuclear reactor structural materials. Three types of nuclear reactor materials were studied. Samples of the materials were irradiated with different neutron fluences. The Magnetic Barkhausen Emission was measured using stabilised flux mode, i.e., control of the magnetic flux within the sample to compensate for leakage and variations on the flux. The samples were carefully identified according to position and the cutting direction within the steel forging block. Anisotropy effect due to sample cutting direction was observed and it masks the magnetic signal results induced by the irradiation effects. The results on the specimens cut in the same direction shows correlation with irradiation induced material hardening and its dependence on fluence. Different materials show different hardening levels. Barkhausen emission results were correlated to neutron fluence taking into account the cutting direction

Comparison of four NDT methods for indication of reactor steel degradation by high fluences of neutron irradiation

Results of three magnetic nondestructive methods, Magnetic Barkhausen Emission (MBE), magnetic minor loops Power Scaling Laws (PSL) and Magnetic Adaptive Testing (MAT), and of one reference mechanical measurement, Vickers Hardness (HV), applied on the same series of neutron heavily irradiated nuclear reactor pressure vessel steel materials, were normalized and presented here for the purpose of their straightforward quantitative mutual comparison. It is uncommon to carry out different round-robin testing on irradiated materials, and if not answering all open questions, the comparison alone justifies this paper. The assessment methods were all based on ferromagnetism, although each of them used a different aspect of it. The presented comparison yielded a justified recommendation of the most reliable nondestructive method for indication of the reactor steel irradiation hardening and embrittlement effects. The A533 type B Class 1 steel (JRQ), and the base (15Kh2MFA) and welding (10KhMFT) steels for the WWER 440-type Russian reactors were used for the investigations. The samples were irradiated by high-energy neutrons (>1 MeV) with up to 11.9 × 1019 n/cm2 fluences. From all the applied measurements, the results of MAT produced the most satisfactory correlation with independently measured ductile-brittle-transition temperature (DBTT) values of the steel. The other two magnetic methods showed a weaker correlation with DBTT, but some other aspects and information could be assessed by them. As MAT and MBE were sensitive to uncontrolled fluctuation of surface quality of the steel, contact-less ways of testing and more conveniently shaped irradiated nuclear pressure vessel steel samples were suggested for future measurements. © © 2013 Elsevier B.V. All rights reserved

Microstructure, tensile and creep properties of an austenitic ODS 316L steel

ODS 316L, an austenitic grade of oxide-dispersion-strengthened (ODS) steel, was fabricated by mechanical alloying, hot isostatic pressing and forging. A broad characterisation study was conducted, including High-Resolution Transmission Electron Microscopy (HRTEM) to investigate the microstructure and the interface between oxide particles and the 316L matrix. Mechanical properties at room and elevated temperature were determined by means of tensile and creep tests. Data from the room temperature and high temperature tensile tests were compared with those from conventional 316L. Creep data were used to assess the performance of the ODS 316L against standard assessment codes and in comparison with conventional 316L. Higher mechanical strength was found for the ODS 316L, in comparison to conventional 316L, at room temperature. UTS at high temperature was lower for the ODS 316L, but its yield strength was twice that of 316L. It was found that, although compliant with the Design and Construction Rules for mechanical components of nuclear installations (RCC MR) [1] code for the creep test conditions imposed, the ODS 316L studied is lower strength and has shorter rupture-life than its conventional counterpart. The HRTEM investigations indicated that small oxide particles, <15 nm in size, were coherent or semi-coherent with the steel matrix, whilst larger particles were incoheren