A533B Steel Research Articles

Hydrogen embrittlement of a bimaterial

Commonly, within the energy industry, the corrosion resistance of pressure vessel steels is increased by the addition of an overlay coating comprising a nickel-based alloy or a stainless steel. However, the interface between the two alloys is prone to hydrogen-assisted cracking, due to for example carbide precipitation near the interface. In the present study, the sensitivity of the tensile strength of the interface to hydrogen concentration is measured for both notched and un-notched specimens made from the overlay welding of 690 nickel alloy on a low alloy steel A533B. An elastic–plastic finite element analysis is used to determine the stress and strain state near the notch root, and thereby to calculate the local distribution of hydrogen within the lattice and at traps. The observed strength of the notched specimens is best rationalised by assuming that the local cohesive strength of the interface is a function of the lattice hydrogen concentration, with a negligible influence of the trapped hydrogen. The scatter in specimen strength, and the relative strength of the notched and un-notched specimens, are adequately described by Weibull statistics, with a low value of Weibull modulus equal to 3.4.

Applying the Master Curve approach to a JRQ A533B Cl.1 material as part of the surveillance program of two BWR Units

Experimental measurements of the cleavage fracture toughness (KJc) of specimens were used to apply the Master Curve (MC) approach to a reference RPV steel A533B Cl.1 provided by the International Atomic Energy Agency (IAEA) as part of the surveillance programs of two BWR Units. This investigation focused on four practical issues: the effect of specimen geometry, loading rate and irradiation on the MC and the comparison of the MC to the conventional approach using Charpy data. Experiments on pre-cracked Charpy V-notch (PCCv) specimens validated the use of the Weibull model allowing correcting for the loss of constraint effect. These experiments were also used to determine the “bias” value between PCCv and standard compact tension (1T-C(T)) specimens and the effect of the loading rate on the MC. The reference temperatures indexed to T0 (RTTo and ARTTo) were directly measured and compared to the RTNDT and ARTNDT values obtained using the conventional semi-empirical approach of the American Society of Mechanical Engineers (ASME) Code, demonstrating that the latter approach was more conservative.

Application ofT33-Stress to Predict the Lower Bound Fracture Toughness for Increasing the Test Specimen Thickness in the Transition Temperature Region

This work was motivated by the fact that although fracture toughness of a material in the ductile-to-brittle transition temperature regionJcexhibits the test specimen thickness (TST) effect onJc, frequently described asJc∝(TST)-1/2, experiences a contradiction that is deduced from this empirical formulation; that is,Jc= 0 for large TST. On the other hand, our previous works have showed that the TST effect onJccould be explained as a difference in the out-of-plane constraint and correlated with the out-of-planeT33-stress. Thus, in this work, the TST effect onJcfor the decommissioned Shoreham reactor vessel steel A533B was demonstrated from the standpoint of out-of-plane constraint. The results validated thatT33was effective for describing theJcdecreasing tendency. Because the Shoreham data included a lower boundJcfor increasing TST, a new finding was made thatT33successfully predicted the lower bound ofJcwith increasing TST. This lower boundJcprediction withT33conquered the contradiction that the empiricalJc∝(TST)-1/2predictsJc= 0 for large TST.

Concomitant formation of different nature clusters and hardening in reactor pressure vessel steels irradiated by heavy ions

Specimens of A533B steels containing 0.04, 0.09 and 0.21wt%Cu were irradiated at 290°C to 3dpa with 3MeV Fe ions and subjected to atom probe analyses, transmission electron microscopy observations and hardness measurements. The atom probe analysis results showed that two types of solute clusters were formed: Cu-enriched clusters containing Mn, Ni and Si atoms as irradiation-enhanced solute atom clusters and Mn/Ni/Si-enriched clusters as irradiation-induced solute atom clusters. Both cluster types occurred in the highest Cu-content steel and the ratio of Mn/Ni/Si-enriched clusters to Cu-enriched clusters increased with irradiation doses. It was confirmed that the cluster formation was a key factor in the microstructure evolution until the high dose irradiation was reached even in the low Cu content steels though the dislocation loops with much lower density than that of the clusters were observed as matrix damage. The difference in the hardening efficiency due to the difference in the nature of the clusters was small. The irradiation-induced clustering of undersized Si atoms suggested that a clustering driving force other than vacancy-driven diffusion, probably an interstitial mechanism, may become important at higher dose rates.

Effects of dose rate change under irradiation on hardening and microstructural evolution in A533B steel

Iron-ion irradiations were carried out for 0.09wt%Cu A533B steel specimens at 290°C to investigate effects of dose rate change during irradiation; the irradiations consisted of the base irradiation (with an unchanged dose rate) and an additional one with changed dose rates from 1 to 50 times that of the base one. Nano-indentation hardness measurements showed that the increase in hardness was higher for lower dose rate of the base irradiation. A similar trend was identified during the additional irradiation. Transmission electron microscope (TEM) and three-dimensional atom probe (3DAP) analyses were carried out for the quantitative characterization of defect features. Mn/Ni/Si/Cu-enriched clusters and dislocation loops were observed in all specimens. The increase in hardness mainly depended on the formation of the solute atom clusters. The square root of the volume fraction of the solute atom clusters provided a good correlation with the increase in hardness. The effects of dose rate and dose rate change during irradiation were explained by the formation of solute atom clusters.

Effect Analysis of Gurson Model Parameters on Crack Extension of Pipeline

Leakage-before-break technique is widely used in high energy pipeline of nuclear plant, for which crack stability of pipeline under complex loading condition is a key issue, and crack growth resistance curve of pipeline material is the important foundation for crack stability analysis. In this paper, ferritic steel A533B is studied, Gurson damage model is used to simulate crack process of contact tension specimen under unitension, and effect of Gurson model parameter on simulation result is discussed. The following results are found during simulation: initial porosity factor is the main parameter, when it increases gradually, unstable crack extension will be observed; however, only initial J toughness is affected by critical porosity factor; the minor parameter is load step control, when it increases, stable and convergent result is obtained. All results in this paper can be used to determine parameters in Gurson mode, which will be foundation for crack extension analysis of pipeline.

Effect of intergranular failure on the critical fracture stress and the fracture toughness of degraded reactor pressure vessel steel

The fracture mechanisms in the ductile-to-brittle transition (DBT) region of the undegraded and degraded A533B steel have been studied. Two mechanisms were observed in the initial stage of the DBT region: transgranular cleavage fracture and intergranular fracture. Factors affecting the proportion of intergranular fracture on the fracture surface have been investigated by four-point-bending (4PB) mechanical tests, SEM observation and statistical fractographic analysis. The effect of intergranular fracture on the critical fracture stress has been discussed and an empirical equation for the mixed critical cleavage/intergranular fracture stress is proposed. Finally, attention is also drawn to the interesting difference in the intergranular fracture percentages shown on the fracture surfaces of fracture toughness test specimens.

Evaluation of impact properties of weld joint of reactor pressure vessel steels with the use of miniaturized specimens

The effects of specimen size and location of V-notch on the Charpy impact properties were investigated with different sizes of specimens, standard, CVN-1/2, CVN-1/3, and CVN-1.5 mm, for A533B steel, low Mn, high Cu, high phosphorus (P), and high Cu/P steel weld joint. A part of the specimens was irradiated with neutron at 563 K up to 8 × 1019 n/cm2. The heat affected zone (HAZ) specimen is the best in the impact properties among the specimens of base metal, HAZ, and weld metal in the steels with 0.003 wt.% P, while it is the worst in the steels with ∼ 0.3 wt.% P. This indicates that the surveillance test of HAZ specimen can be represented by base metal in the case of A533B steels with lower P content (∼ 0.003 wt.%). The effects of notch location and chemical contents on ductile to brittle transition temperature (DBTT) are almost independent of specimen size within an error of ±5 K, indicating that the miniaturized Charpy specimens are applicable and effective in the surveillance tests of reactor pressure vessel steel of extended operation period. After irradiation, the highest DBTT was observed for the specimen with V-notch in base metal in the case of A533B steel and high Cu steel with 0.003 wt.% P.

Improvement of the extended finite element method for ductile crack growth

The continuum damage mechanics (CDM) model is added to the extended finite element method (XFEM) to provide a model of ductile crack growth. In this model, the criterion for crack growth in the evaluation of ductile materials is the critical damage parameter obtained from continuum damage mechanics. Numerical implementation of the CDM–XFEM model was used to simulate crack growth modeling in comparison with experimental results, and the results are presented in this paper. The CDM–XFEM model was experimentally validated by the ductile damage evolution measured in A533B1 steel through three-point bending and compact tension tests. The identification of damage parameters was performed under various conditions. The critical load at crack growth initiation, the ductile behavior of cracks and the fracture toughness, JIc, were also predicted with the CDM–XFEM model simulations. The results confirm the potential of the CDM–XFEM model for predicting crack growth in ductile materials. Using the proposed model, crack propagation has been simulated within two examples; center inclined crack and single edged notched beam for A533B1 steel.

Effect of carbon on irradiation-induced grain-boundary phosphorus segregation in reactor pressure vessel steels using first-principles-based rate theory model

In this paper, we incorporated the effect of carbon atoms on the irradiation-induced grain-boundary phosphorus segregation into the rate theory model by considering a carbon atom as a trap site of vacancies and self-interstitial atoms, and simulated the grain-boundary phosphorus coverage in the reactor pressure vessel steels, A533B steels which were neutron-irradiated using the Halden reactor. As a result, by selecting the sink strength of vacancies and self-interstitial atoms, the simulation reproduced the experimental grain-boundary phosphorus coverage that was measured using the scanning Auger electron microprobe analysis. It was observed that the grain-boundary phosphorus coverage does not depend on the dose rate regardless of the presence of carbon atoms. Furthermore, it was confirmed that vacancies scarcely transport phosphorus atoms to grain-boundaries as compared to the transport by self-interstitial atoms and it was found that carbon atoms influence the irradiation-induced phosphorus segregation by mainly suppressing the migration of vacancies.

Radiation induced hardening of ion irradiated RPV steels

It is well known that radiation hardening and embrittlement of A533B steels is very sensitive to minor solute content. To investigate the effect on microstructural evolution of these materials, A533B steels with different Cu levels were irradiated by 2.4MeV Fe ions. The ion irradiation was performed at 290°C and also at room temperature up to a dose of 2dpa. After the irradiation, the microstructure of the specimens was observed by transmission electron microcopy. Small dislocation loops formed in the matrix and also in the vicinity of dislocation were identified as interstitial dislocation loops, using additional electron irradiation at room temperature in the HVEM.

Effects of stress on radiation hardening and microstructural evolution in A533B steel

Bent specimens of A533B steel (0.16 wt% Cu) were irradiated at 290 °C to 1 dpa with 6.4 MeV Fe 3+ ions. Calculated tensile stresses at the irradiated surface were set to 0, 250, 500 and 750 MPa. The specimens were subjected to hardness measurements, transmission electron microscopy (TEM) observations and three-dimensional atom probe (3DAP) analysis. The radiation-induced hardening decreased with increasing stress to 500 MPa which was near the yield strength. TEM and 3DAP results showed that well-defined dislocation loops and solute clusters were formed. The diameter of dislocation loops increased and the number density decreased when the stress was applied, whereas the diameter and number density of solute clusters decreased. The hardening was mainly attributed to solute cluster formation. Application of tensile stress would control hardening by suppressing the solute cluster nucleation and growth.

Effects of Chemical Composition on the Impact Properties of A533B Steels

In order to estimate the long life integrity of vessel steels with considering various material compositions and irradiation conditions, it is necessary to understand physical mechanisms of the degradation of mechanical properties. In this research, chemical composition effects were investigated for Reactor Pressure Vessel Steels (RPVS) to apply small specimen test technique to surveillance test method. All specimens used in this study were machined from the A533B plate material, which are standard, low Mn, high Cu, high P, and high Cu and high P steels. Tensile strength is increased by phosphorous and copper additions. Charpy tests were carried out at temperature from 73 K to 473 K. The ductile to brittle transition temperature (DBTT) is shifted to higher temperatures with phosphorus additions accompanied by the reduction of the upper shelf energy (USE). The fracture mode of P-added A533B steels at temperatures in the lower shelf energy (LSE) region is intergranular cracking. Test results were discussed in view of the differences on elements of Cu, Mn and P.

Effects of chemical composition and dose on microstructure evolution and hardening of neutron-irradiated reactor pressure vessel steels

The correlation of microstructure evolution and hardening was studied in two kinds of A533B-1 steel with high and low levels of Cu irradiated in a range of dose from 0.32 to 9.9 × 10 19 n cm −2 ( E > 1 MeV) under a high flux of about 1.7 × 10 13 n cm −2 s −1 using three-dimensional local electrode atom probe (3DAP), positron annihilation (PA) techniques, and Vickers microhardness. The early rapid hardening was found to be caused by mainly matrix defects such as mono- or di-vacancies ( V 1 − V 2) and/or dislocations indicated by the PA analysis. The 3DAP analysis showed that dense dispersion of dilute Cu rich clusters and lean distribution of Mn–Ni–Si rich clusters, which were identified to possess the same dislocation-pinning effect by applying a Russell and Brown model, were responsible for large and small hardening in high- and low-Cu steels irradiated above 0.59 × 10 19 n cm 2, respectively.

Hardening and microstructural evolution in A533B steels under neutron irradiation and a direct comparison with electron irradiation

A533B steels irradiated at 290 °C up to 10 mdpa in the Kyoto University Reactor were examined by hardness, positron annihilation and atom probe measurements. Dose dependent irradiation hardening and formation of Cu-rich clusters were confirmed in medium Cu (0.12% and 0.16%Cu) steels whereas neither hardening nor cluster formation was detected in low Cu (0.03%Cu) steel. No microvoids were formed in any of the steels. Post-irradiation annealing in medium Cu steels revealed that the hardening recovery at temperatures above 350–400 °C could be attributed to compositional changes and dissociation of the Cu-rich clusters. Compared to electron irradiation at almost the same dose and dose rate, KUR irradiation caused almost the same hardening and produced Cu-rich clusters, more solute-enriched with larger size and lower density. Considering lower production of freely-migrating vacancies in neutron irradiation, the results suggested that cascades enhance the formation of Cu-rich clusters.

One-dimensional motion of self-interstitial atom clusters in A533B steel observed using a high-voltage electron microscope

One-dimensional motion of self-interstitial atom clusters in A533B steel was observed using high-voltage electron microscopy. The frequency and distance of one-dimensional motion under electron irradiation were measured. One-dimensional motion occurred frequently at room temperature, but it occurred only slightly at 563 K. The frequency of one-dimensional motion was decreased by annealing at 473 K and higher temperatures. The decreased motion frequency gradually increased under prolonged irradiation. Although annealing reduced the motion frequency of clusters that had been formed before annealing, reduction of the motion frequency was not detected for clusters that formed after annealing.

Experiments and predictions of the effects of load history on cleavage fracture in steel

A series of experiments conducted on two steels, A533B and A508, are summarised. Tests were conducted to explore the influence of different room temperature pre-loading cycles on subsequent low temperature (−150 °C and −170 °C) cleavage fracture. In all cases the low temperature fracture toughness was modified, with tensile pre-loading increasing the toughness and precompression reducing the toughness. Results from finite element simulation of the pre-loading cycles are illustrated. Tensile pre-loading created compressive residual stresses and precompression generated tensile residual stresses. The residual stresses were adopted in a stress based local approach to fracture model using Weibull statistics and applied to the experimental results. The parameters in the Weibull model were calibrated for the virgin steels prior to its application to prior loading cases. The model is found to be successful in predicting the change in toughness relative to the virgin material for pre-loading in tension of A533B steel. The model underestimated the change in toughness for tensile pre-loading of A508 steel and overestimated the toughness change for precompression of both steels.

Simulated heat affected zone in ASTM A533-B steel plates under low heat inputs

To investigate the weldability of A533-B steel plates, simulations of the coarse grained region of heat affected zone (with heat inputs of 10, 20 and 30 kJ cm −1) followed by inter-pass heating at 300 °C and post-weld heat treatments at 590 °C were carried out. The microstructural evolution, the hardness and the toughness of the simulated heat-affected zone were studied. With heat inputs of 10 and 20 kJ cm −1, both of the simulated microstructures contain mixtures of lower bainite and auto-tempered martensite. With heat input of 30 kJ cm −1, the simulated microstructure is composed mainly of lower bainite. The Charpy impact toughness has also been measured for the simulated heat input specimens, which were treated by inter-pass heating at 300 °C and post-weld treatment at 590 °C.

Irradiation-Induced Grain-Boundary Solute Segregation and Its Effect on Ductile-to-Brittle Transition Temperature in Reactor Pressure Vessel Steels

Abstract A study on grain-boundary segregation and embrittlement in terms of the Charpy ductile-to-brittle transition temperature (DBTT) has been performed for the neutron-irradiated A533B steels with typical contents of impurities of Japanese reactor pressure vessel ones. The neutron irradiation was conducted at 563 K to a fluence of 1.3× 1024n/m2 (E>1 MeV) using material testing reactors. The neutron irradiation induced the P and Ni segregation and the reduction in C in some cases at grain-boundaries. The increase in the P segregation at high fluence (>5×10 23n/m2, E>1 MeV) was less than 0.1 in monolayer coverage for the steels with the bulk content of P not exceeding 0.02 wt%. The hardening more strongly affected the DBTT shift than the P segregation for those steels. The reduction in segregated C that enhances the grain-boundary cohesion by neutron fluence is not large enough to cause the DBTT shift.

A Revised Procedure for the Construction of a 3-Parameter JR Resistance Curve and the Determination of Initiation Toughness J0.2

Abstract Fracture toughness testing procedures often advocate the use of a 3-parameter offset power law fit to define a resistance curve, and subsequently an estimate of initiation toughness (e.g., J0.2). JR=A+α(Δa)β. Experience has indicated that the fit coefficients A, α, and β are highly variable. What is required is a consistent method of estimating A and thus α and β to reflect physical sense. In this paper it is proposed that the offset A is defined using a J-elastic term Je given by A=Je=W/2(σy2∕E′)f(ao∕W). Experimental data are provided in support of the use of Je for a well characterized A533B-1 steel. Tests were made at ambient temperature using geometrically scaled plain-sided and side-grooved compact C(T) specimens of sizes 20<W<200mm. The fixing of A through the use of Je provides less variable α and β parameters. The exponent β is found to be independent of W, noting that βSG<βplain, as is the α coefficient for side-grooved specimens (αSG). The α coefficient for plain-sided specimens (αplain) may be related to specimen width and thus thickness (B) for geometrically-scaled specimens, noting that α∞ approximates to αSG. αplain=α∞(1+1∕B). The results indicate that the JR curves and thus J0.2 vary with specimen width W. For conventional laboratory-sized C(T) specimens (i.e., 25<W<100mm) the variation in J0.2 with a size over this range is of the same order as the general level of scatter observed in the J0.2 measurement. However, for specimen sizes outside of this range size effects may be predicted.