Austenitic Steel Components Research Articles

Prediction of inter-granular crack initiation susceptibility in post irradiated grade 300 steels

Grade 300 austenitic steel components are subjected to irradiation-assisted stress corrosion cracking hazard, in the context of nuclear pressurized water reactor operation. In this paper, it is assumed that inter-granular cracking susceptibility primarily depends on sub grain plasticity mechanisms, controlling the slip band thickness and spacing achieved for a plastic strain level imposed. A computational model evaluating the related grain-boundary stress evolutions is developed and evaluated, using actual post-irradiation observations. In practice, we calculate a quantitative damage susceptibility factor R depending on the characteristic local slip band arrangements and the grain to grain misorientation. The statistical R evolutions obtained are consistent with the strain localization and related intergranular crack susceptibility trends, under corresponding irradiation and deformation conditions.

Clean-integrity processing and characterization of nuclear-grade austenitic steel components

ABSTRACT Clean-integrity processing of nuclear-grade AISI 316L austenitic stainless steel components finished by the wire brush and sequent flap discs is performed for high-performance manufacturing of the nuclear power plant equipment. Two steel wire brushes of AISI 304 austenitic stainless steel and 65Mn carbon spring steel are used for the grinding under a spindle speed of 550–2000 rpm. Sequent polishing is carried out by the flap discs using silicon carbide cloth under 2000 rpm. An equivalent pitting corrosion resistance to that of the original stainless steel in 3.5% NaCl solution is obtained for finished samples by the combined processes. The contaminants composition of ground stainless steel samples is determined by the redness degree of chromaticity inspection. The contaminants microstructure and finishing-induced microstructure are dependent on the impedance phase angle change in eddy current impedance diagrams. The surface clean-integrity of nuclear-grade stainless steel is characterized by the series of nondestructive evaluation methods.

Microstructure and Corrosion Properties of Wire Arc Additively Manufactured Multi-Trace and Multilayer Stainless Steel 321

Because low thermal conductivity and high viscosity are common characteristics of austenitic steel, it is easy to cause a large amount of heat accumulation in the chip area, resulting in tool edge collapse or wear, and the traditional preparation method is unsuitable for preparing large and complex austenitic steel components. Wire + arc additive manufacturing (WAAM) provides a great application value for austenitic stainless steel because it can solve this problem. The cold metal transfer (CMT)-WAAM system with good control of heat input was used to fabricate the multi-trace and multilayer stainless steel 321 (SS 321) workpiece in this study. The microstructure and corrosion properties of the SS 321 workpiece were observed and compared with those of an SS 321 sheet. The results showed that the microstructure of the SS 321 workpiece from top to bottom was regularly and periodically repeated from the overlapping remelting zone, inter-layer remelting zone, and primary melting zone. There was white austenite matrix and black ferrite, and a small amount of skeleton and worm ferrite was distributed on the white austenite matrix. The average hardness value from the top to the bottom region was approximately uniform, indicating that the workpiece had good consistency. The corrosion properties in 0.5 mol/L H2SO4 solutions were compared between the SS 321 workpiece and the SS 321 sheet. The results showed that the corrosion properties of the top region of the workpiece were better than that of the middle and bottom part, and the corrosion properties of the SS 321 workpiece were better than that of the SS 321 sheet.

On the Laplace-Young equation applied to spherical fluid inclusions in solid matrices

A continuum theory of surfaces is successfully applied to analyse a set of molecular dynamics results obtained on systems consisting of nanosize fluid bubbles trapped in a solid matrix. The equations of this theory supplied with molecular dynamics data allowed calculating the Γ factor from the Laplace-Young equation as applied to systems of industrial interest, such as the helium bubbles that form along the ageing of some austenitic steel components of the nuclear reactors. The Γ factor was found to have a non-linear dependency on the helium/steel interface strain. These findings are in contradiction with the implicit assumption made in some published literature considering Γ as a constant.

Effect of A-TIG welding on deformation of austenitic steel components

Effect of A-TIG welding on deformation of austenitic steel components

Simulation of the surface crack detection using inductive heated thermography

During thermo-inductive inspection, an eddy current of high intensity is induced into the inspected material and the thermal response is detected using an infrared camera. Anomalies in the surface temperature during and after inductive heating correspond to inhomogeneities in the material. A finite element simulation of the surface crack detection process using active thermography with inductive heating has been developed. The simulation tool was tested and used for investigations on austenitic steel components with different longitudinal orientated cracks. The shape of the crack varies in the crack opening and the depth. The simulation model was based on the finite element programming software ANSYS. The suitability of the developed simulation of the inductive excited thermography for crack detection will be demonstrated by calculations and experiments. This paper focuses on longitudinal orientated cracks in austenitic steel, which are opened to the surface. The results show that depending on the shape of the crack the temperature distribution of the material under test made of austenitic steel is different. It will be shown how the crack size affects the temperature difference between the crack and the surrounding surface.

Investigation of phase composition of high temperature chromium steels and chromonitriding process in austenitic alloys

The creep resistance of 9% chromium high temperature steels is determined by the alloy content and structure resulting from heat treatment. This paper describes the analysis of the phase composition using CALPHAD numerical modelling methods, of known modifications of 9% high temperature chromium steel: 9Cr–0·1C, 0·9Mo, 0·21V, 0·1Nb, 0·04N (P91) and 9Cr–0·1C, 2W, 0·5Mo, 0·21V, 005Nb, 0·05N, 0·005B (P92). The effect of alloying elements on the phase composition of the steel and the mutual effect of the composition on the nature and quantity of the phases Me23C6 and Me(CN) in the temperature range 570–620°C is described. On the basis of calculated data and experimental results, a composition for new high temperature steels with additional Co alloying (up to 3%) and varying carbon contents in the range 0·02–0·10% is proposed. Results are shown for investigations on high temperature chromium steels containing cobalt, including: effect of complex alloying with tungsten, molybdenum, and cobalt on the service properties and structural composition of steels; heat treatment processes for alloy variants and kinetics of structural change during creep and prolonged thermal aging. Data have been obtained comparing calculated and experimental data for the phase composition in chromium steel, also the effect of the phase composition on creep characteristics. On the basis of a complex laboratory investigation and industrial pilot heats, optimal composition variants for the alloy content of high temperature Cr–Mo–V–Co steels have been determined for practical applications. CNIITMASH has developed a chromonitriding technology for improving the corrosion, wear and scratch behaviour, as well as for protection against self-welding and other service characteristics of austenitic steel components and nickel alloys. Chromonitriding technology includes saturation of the component surface with chromium and nitrogen. The technology is intended for strengthening valves and bushings, water pump components, and components operating in liquid metal, burnt fuel residue, and other aggressive environments. The conditions governing the formation of the strengthening layers, consisting of an austenitic matrix (γ solid solution) and containing Cr2N with a depth of up to 250 μm and a hardness of 750–950 HV have been determined. Thermodynamic analysis of phase formation conditions during the chromising and subsequent nitriding process over a wide range of temperatures and saturating media has been carried out. The technology has been optimised for process and media composition leading to a structure with maximum surface properties.

Modeling of transducer fields in inhomogeneous anisotropic materials using Gaussian beam superposition

This article describes a three-dimensional Gaussian beam model for calculating transducer-generated ultrasonic wave fields in inhomogeneous anisotropic media. The model is based on a formulation presented recently for homogeneous anisotropic materials. The inhomogeneity is modeled by dividing the material into several homogeneous layers, the approach accounting for the propagation through the various layers and the reflection/refraction processes at the interfaces. It thus calculates ultrasonic field patterns, including proper amplitude information and allows a quick evaluation of the sound fields. Application of the model in view of ultrasonic nondestructive testing of layered composite material and of austenitic steel components is addressed. In the latter case, examples are given for various weldment structures, wherein ultrasonic inspection using commercial angle beam transducers is of interest.

Neutron strain scanning of a small welded austenitic stainless steel plate

Neutron strain scanning has been used to determine the residual stress distribution over the area of the mid-thickness plane of a small austenitic steel piate across which a weld had been laid. The longitudinal and transverse stresses in the centre of the plate and weld are strongly tensile. Stresses normal to the plane of the plate are low everywhere except near the ends of the weld where tensile ‘hot-spots’ are observed. Near the edges of the plate the effects of boundary and balancing conditions are evident. Longitudinal and transverse stresses tend to zero along the edges of the plate to which they are perpendicular but become strongly compressive near the middle regions of the edges to which they are parallel. The results are compared with published data from other welds that were made and constrained differently. The accuracy of the technique is discussed and the results obtained by measuring with different reflections are compared. It is shown that neutron strain scanning is an acceptable, and unique, method for determining non-destructively the residual stress distribution throughout small austenitic steel components with sufficient accuracy to provide data for design purposes and to validate model calculations.

Ultrasonic beam profiles and beam propagation in an austenitic weld using a theoretical ray tracing model

A model for ultrasonic wave propagation in anisotropic and inhomogeneous materials is applied to the case of ultrasonic inspection of an austenitic V-butt weld manufactured by the downhand Manual Metal Arc technique. We examine the propagation behaviour of waves within the weld region and, in addition, model beam divergence behaviour. From this work we predict directions of low inspection sensitivity and also identify regions of material to which no ultrasound penetrates. The relative merits of the three different wave modes are examined, showing clearly the advantages of horizontally polarized shear waves for austenitic steel inspection. Vertically polarized shear waves are shown to be the least effective for such inspections. We discuss the relevance of this work to the ultrasonic non-destructive testing of austenitic steel components, concluding that care is needed over the choice of wave modes and angles, to ensure sensitive inspection of the whole weld material.

Effect of rolling at sub-zero temperatures on mechanical properties of austenitic steels

1. Cold rolling of austenitic steels to increase their tensile characteristics is most effective at sub-zero temperatures. Tensile and yield strengths are increased by up to 20–30% over those after rolling at ordinary temperature, without impairing the ductility. 2. At low temperatures, austenitic steels have high reduction of area and elongation, irrespective of the previous strain hardening at ordinary temperatures. 3. Austenitic steel components for service at sub-zero temperatures should be preferably strain-hardened at ordinary or slightly elevated temperatures. In this way, they retain good low temperature ductility. 4. Sub-zero working of austenitic steels is equally effective on soft and on strain-hardened metal. 5. Plastic working at low temperatures causes martensite to form on three octahedral planes. At room temperature, however, it forms only on one crystallographic plane.