Neutronographic Residual Stress Analysis for Materials With Depth Gradients of the Strain Free Lattice Parameter d0{{{d}}}_{0} for the Example of a Case-Hardened Steel 20MnCr5

In the present work, ring-shaped samples made from steel 20MnCr5 were low-pressure carburized (LPC) and subsequently hardened by gas quenching (case-hardened). This results in a near-surface gradient in chemical composition, microstructure- and hardness distribution, as well as a three-dimensional residual stress (RS) distribution, which was investigated by neutron diffraction. Near-surface RSs in the ferrite-/martensite- and austenite phase are additionally determined by X-ray diffraction. It is shown that the chemical gradient has an influence on the chosen ${{{d}}}_{0}$ strategy and how such a reference sample should be extracted. If near-surface RS values are to be determined by neutron diffraction, the pseudo-strain effect must be taken into account. For this purpose, a suitable approach using the ‘‘open source’’ software SIMRES and STRESSFIT is also presented. By combining neutron and X-ray diffraction data, a complete RS distribution over the whole sample can be obtained

Effects of finish turning on an austenitic weld investigated using diffraction methods

Arc welding generally introduces undesired local residual stress states on engineering components hindering high-quality performance in service. Common procedures to reduce the tensile residual stresses are post-heat treatments or mechanical surface treatments like hammering or shot-peening. Assessments of residual stress profiles of post-weld treatments underneath the weld surface are essential, especially in high safety exigency systems like pressure vessels or piping at power plants. In this study, neutron diffraction is used to determine the stress profile after finish milling of an austenitic steel weld in order to verify a chained finite element simulation predicting the final residual stress fields including milling and welding contributions. Non-destructive measurements with spatial resolutions of less than 0.2 mm within the first 1 mm from the surface were mandatory to confirm the finite element simulations of the coarse-grained austenitic material. In the data analysis procedure, the obtained near-surface data have been corrected for spurious strain effects whenever the gauge volume was partially immersed in the sample. Moreover, constraining the surface data to values obtained by x-ray diffraction and data deconvolution within the gauge volume enabled access of the steep residual stress profile within the first 1 mm

Instrumented clamping device and numerical simulations to study machining distortion

Machining part distortion is due to residual stresses induced by previous manufacturing processes. This study aims to evaluate the influence of machining conditions on AISI 316L plate distortion. Therefore, a special experimental device with force sensors integrated in the clamping system and numerical model of distortion were developed. Residual stresses due to previous machining processes were measured using a layer removal method and neutron diffraction technique. Then, distributions of these residual stresses were integrated in a developed model of machining distortion, which considers the clamping and machining sequence effects after each stage of the toolpath. A comparison of the experimental and numerical results revealed that the finite element method can adequately predict machining distortion. The results also suggest that clamping and machining sequence can affect part distortion

A complete reassessment of standard residual stress uncertainty analyses using neutron diffraction emphasizing the influence of grain size

The determination of residual stress in engineering materials with large grains is a challenge when it comes to using diffraction techniques. Not only are the accuracies of the residual stresses themselves important but also the accurate evaluation of their uncertainties. An austenitic steel three-pass slot weld (NeT- TG4) with varying grain size high-lights the potential problems with the data evaluation when grain size is not taken into account whilst measuring strain. Neutron diffraction results are compared with each other (with combinations of slit and radial oscillating collimator beam defining optics) and with high energy synchrotron radiation results with a spiral slit gauge volume defining system. The impact of the grain size on the determination of residual stresses and their associated uncertainties when using diffraction techniques in engineering components is emphasized and discussed. A simple model to estimate the extra random uncertainty contribution due to the so-called grain size statistics is applied and verified. The benefit of continuous or stepwise oscillation to increase the number of detected grains on the detector is discussed together with how to optimize the time of a measurement. From the data obtained, best practice guidelines will be suggested on dealing with large grains when determining strain and stress with neutron diffraction

Quantification of Residual Stress Relief by Heat Treatments in Austenitic Cladded Layers

The effect of the heat treatment on the residual stresses of welded cladded steel samples is analyzed in this study. The residual stresses across the plate’s square sections were determined using complementary methods; applying diffraction with neutron radiation and mechanically using the contour method. The analysis of the large coarse grain austenitic cladded layers, at the feasibility limits of diffraction methods, was only made possible by applying both methods. The samples are composed of steel plates, coated on one of the faces with stainless steel filler metals, this coating process, usually known as cladding, was carried out by submerged arc welding. After cladding, the samples were submitted to two different heat treatments with dissimilar parameters: one at a temperature of 620 °C maintained for 1 h and, the second at 540 °C, for ten hours. There was some difference in residual stresses measured by the two techniques along the surface of the coating in the as-welded state, although they are similar at the welding interface and in the heat-affected zone. The results also show that there is a residual stress relaxation for both heat-treated samples. The heat treatment carried out at a higher temperature showed sometimes more than 50% reduction in the initial residual stress values and has the advantage of being less time consuming, giving it an industrial advantage and making it more viable economically

Anisotropic elastic constants calculation of stainless steel cladded layers of pressure vessel steel plate

Cladding stainless steel layer on the inner surface of ferrite pressure vessel is a common method to improve the corrosion resistance and save the economic cost. However, the movement of heat source and temperature gradient in the process of cladded welding will lead to the anisotropy of cladded layer material. When measuring the residual stress of pressure vessel steel plate with stainless steel cladded layers (SSCL) by contour method, it is necessary to know the elastic mechanical properties of stainless steel cladded layers accurately. The assumption of transversely isotropy (TI) was employed, and the relationship between the material compliance matrix and the elastic modulus of transversely isotropic material was utilized. Based on the elastic modulus of each cladded layer and the whole steel plate from the longitudinal direction (0°) until the transverse direction (90°) measured by the experiment, the independent constants S11, S13, S33 and S44 in the compliance matrix of each cladded layer and the whole steel plate were obtained by regression analysis method. Furthermore, by using the relationship between the independent constants of the stiffness matrix of the transversely isotropic material and the single crystal material, the independent constant S12 in the compliance matrix of each stainless steel cladded layer and the whole steel plate were obtained. And then the independent constants of the stiffness matrix of each cladded layer and the whole steel plate were acquired. Hence, a method for calculating the anisotropic elastic constants of the stainless steel cladded layer and the whole steel plate was proposed. The results will provide material data support for measuring residual stress of pressure vessel steel plate with stainless steel cladded layers by contour method