Temperature Embrittlement Research Articles

Effect of Texture on Secondary Work Embrittlement of IF Steels

The relationship between texture and secondary work embrittlement of interstitial-free steels was studied by X-ray analysis technique and scanning electron microscopy analysis technique. The results indicated that the stronger the γ fiber texture was, the higher the plastic strain ratio (r-value) was, and Secondary work embrittlement temperature rose as r-value increased or γ fiber texture intensified. The mode of secondary work embrittlement fracture was a blend of cleavage fracture and intergranular fracture, and the fraction of cleavage fractures decreased gradually as secondary work embrittlement temperature rose.

Effects of Si on the stability of retained austenite and temper embrittlement of ultrahigh strength steels

Effects of silicon (Si) content on the stability of retained austenite and temper embrittlement of ultrahigh strength steels were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and other experimental methods. The results show that Si can suppress temper embrittlement, improve temper resistance, and hinder the decomposition of retained austenite. Reversed austenite appears gradually with the increase of Si content during tempering. Si has a significant effect on enhancing carbon (C) partitioning and improving the stability of retained austenite. Si and C atoms are mutually exclusive in lath bainite, while they attract each other in austenite. ɛ-carbides are found in 1.8wt% Si steel tempered at 250°C, and they get coarsened obviously when tempered at 400°C, leading to temper embrittlement. Not ɛ-carbides but acicular or lath carbides lead to temper embrittlement in 0.4wt% Si steel, which can be inferred as cementites and composite compounds. Temper embrittlement is closely related to the decomposition of retained austenite and the formation of reversed austenite.

Mechanism of Embrittlement and De-Embrittlement for 2. 25Cr-1Mo Steel

Abstract The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 2. 25Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation. The mechanism of step-cooling test and mechanism of de-embrittlement for 2.25Cr-1Mo steel were explained. The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature. There is one critical temperature of embrittlement corresponding to each embrittlement degree. When the further heat treating temperature is higher than critical temperature, the heat treating will become a de-embrittlement process; otherwise, it will be an embrittlement process. The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement. As a result, some stages of step-cooling test would change into a de-embrittlement process. The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion, and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve.

Critical Embrittlement Temperature for Tube Steels Used at Atomic Power Stations

During the exploitation of the atomic power stations the tubing metal is exposed to the influence of temperatures in the range of 290-320С. It can lead to thermal ageing and to the decrease of the embrittlement resistance. The critical embrittlement temperature is the main value which is needed to calculate the embrittlement resistance of materials. The metal properties degradation is taking into account by introduction of the shift of critical embrittlement temperature. The presented data ensure the prognosis of tube steels properties and shift of the critical embrittlement temperature for 60 years resource.

Study on the mechanism of de-embrittlement based on the theory of grain boundary segregation for 2.25Cr–1Mo steel

The mechanism of embrittlement and de-embrittlement for 2.25Cr–1Mo steel was studied based on the theory of grain boundary segregation, and the idea of critical temperature of embrittlement for embrittled material was proposed according to the iso-segregation curve in this paper. There is one critical embrittlement temperature corresponding to each degree of embrittlement. When further heat treating temperature is higher than critical temperature, it is a de-embrittlement process. Otherwise, it is an embrittlement process. The model of segregation that element P segregates to intragranular from grain boundary in the de-embrittlement process was deduced based on the theory of atom diffusion. The de-embrittled test and Auger electron spectroscopy analysis were conducted for the matrix of hydrogenation reactor served for 12 years, and the theoretical calculation is consistent with the experimental results, which indicates that the further embrittlement or de-embrittlement mechanism can be explained both qualitatively and quantitatively with combination of the theory of iso-segregation curve and the de-embrittled model derived.

Relationship Between Grain Boundary Segregation of Antimony and Temper Embrittlement in Titanium-Doped Nickel-Chromium Steel

The antimony segregation at grain boundary was observed and the temper embrittlement in titanium-doped nickel-chromium steel was analyzed. It is concluded that the antimony segregation at grain boundary is nonequilibium and the kinetics of temper embrittlement agrees well with those of nonequilibrium antimony segregation at grain boundary. Besides, the mechanism of nonequilibrium antimony segregation at grain boundary proved to be the most satisfactory one among the existing mechanisms to interpret the antimony-induced embrittlement kinetics in the nickel-chromium steel. Based on these, the activation energy and frequency factor of diffusion of antimony-vacancy complexes were obtained according to the concept of critical time in nonequilibrium grain boundary segregation theory.

Effects of Recycled Asphalt Pavement Amounts on Low-Temperature Cracking Performance of Asphalt Mixtures Using Acoustic Emissions

Significant increases in the cost of asphalt paving and increased awareness of the need for sustainable infrastructure in recent years have in turn increased the use of recycled asphalt pavement (RAP) in the manufacture of hot-mix asphalt (HMA). The use of RAP reduces the overall cost of HMA and provides significant environmental benefits. Experience has shown, however, that the addition of RAP to HMA can have a negative effect on the low-temperature fracture characteristics of the pavement. The purpose of this study was to determine the effects of RAP amounts on the low-temperature cracking performance of asphalt mixtures. Different percentages of RAP material, ranging from 0% to 50%, were studied. The embrittlement temperature of mixtures was determined with the use of an acoustic emissions technique. The disk-shaped compact tension [DC(T)] test was used to determine the fracture energy of asphalt mixtures. DC(T) fracture tests were conducted on two control mixtures with no RAP and mixtures that contained 10%, 20%, 30%, 40%, and 50% RAP. Both control and RAP mixtures were manufactured with PG 64-22 and PG 58-28 as the virgin binders, which brought the total number of mixtures tested to 12. In addition to DC(T) fracture testing, indirect tensile testing was conducted on HMA specimens that contained 20% and 40% RAP. Test results clearly indicated the effects of the presence of RAP materials on the low-temperature performance of mixtures. This study demonstrates the benefit of performing fracture tests before RAP is added to the asphalt mixture, and it demonstrates the use of an acoustic emissions-based testing procedure to screen mixtures susceptible to cracking at low temperatures.

Baysesian Neural Network Approach to Detecting Temper Embrittlement of 30Cr2MoV Rotor Steels

Baysesian Neural Network approach for predicting the temper embrittlement of steam turbine rotor in service was proposed. The FATT50 (the fracture appearance transition temperature) of the rotors was predicted as a function of ratio of the two peak current densities (Ipr / Ip ) tested by electrochemical potentiodynamic reaction method, temperature of electrolyte, J-factor and grain size ( N ). A database was obtained from the test of electrochemical potentiodynamic reaction and Charpy impact. The Bayesian neural network technique was used for modeling of temper embrittlement. The neural network shows a more precise prediction of temper embrittlement of rotor steels than the prediction using multiple linear regression. The training error and verifying error is with the scatter of ±20°C. The results show that, for the temper embrittlement of rotor steels prediction, the prediction model based on Bayesian neural network is feasible and effective.

Evaluation of Temper Embrittlement Effect and Segregation Behaviors on Ni-Mo-Cr High Strength Low Alloy RPV Steels with Changing P and Mn Contents

Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than 300°C and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment (450°C, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of M3P phosphide or the coarsening of Cr carbides. (Received October 7, 2009)

Effect of Tempering on Mechanical Properties of V-added AISI 4335 Steel

The structure–property relations of V-added AISI 4335 steel forgings tempered at different temperatures have been examined to delineate the effect of tempering on their ductility and toughness characteristics. The experimental work involved characterization of the microstructures and determination of hardness, tensile properties, impact toughness and plane strain fracture toughness of a series of hardened and tempered samples. The tempering treatments were carried out at eight different temperatures in the range of 633–833 K. The obtained results have shown that hardness and strength decrease in a monotonic fashion with tempering temperature while impact toughness and ductility increase with increasing tempering temperature with an inflection around 753 K. Analyses of the results highlight that the variations of impact toughness and ductility with tempering temperature possess the potential to directly reveal the embrittlement temperature range. It has been also found here that the embrittlement temperature range can be delineated from the variation in the rate of change of fracture toughness with tempering temperature. These observations have been discussed considering the energy absorbed by the initiation and growth of cracks during fracture of a specimen by tensile, impact and fracture toughness tests.

Innovative materials for energy technology

Abstract High performance materials are indispensable for economical and environmentally acceptable operation of fusion power and innovative fission reactor systems. In order to provide materials design data for short term needs of the ITER Test Blanket Modules and for a Fusion Demonstration Reactor, the international fusion materials community is concentrating their R&D work mainly on the four reduced-activation structural materials 8 – 9 CrWTa ferritic/martensitic steels, V – Ti – Cr alloys, W alloys and SiCf/SiC composites as well as on functional materials such as CVD diamond windows. Besides the development of the European reduced activation reference steel EUROFER, emphasis will be placed on synergies between fusion and fission materials R&D, namely the development of ductile oxide dispersion strengthened ferritic/martensitic steels with nano-scaled Y2O3 or Y2Ti2O7 particles that increase not only high temperature strength but also substantially the microstructural stability against irradiation embrittlement and high temperature ageing. Finally, the corrosion behaviour of zirconium-1.5 wt.% tin alloy, a well established cladding material for nuclear fuel rods, will be shown in different environments.

Predicting Temper Embrittlement of 30Cr2MoV Rotor Steel with Genetic Programming

Predicting Temper Embrittlement of 30Cr2MoV Rotor Steel with Genetic Programming

Advances in nano thermal analysis of coatings

This article discusses AFM-based localized thermal analysis of crosslinked polymer coatings based on a recent breakthrough in nanoscale thermal probe technology. The addition of a thermal tip to a conventional AFM adds a new and valuable capability of spatially resolved thermal analysis to the AFM. It is particularly useful for thin films since it enables the measurement of transition temperatures (melting (Tm) or glass (Tg)) on selected regions of the sample aiding in the identification and characterization of phases on the length scales approaching macromolecular dimensions. Examples include the monitoring of the softening point of automotive clearcoat systems, as a function of cure time and cure temperature and characterization of degradation and embrittlement of weathered acrylic-polyurethane coatings. Comparison of nano thermal analysis with bulk DSC and MDSC is made and its inherent advantages over DSC in analyzing surfaces, is demonstrated.

Nanoscale Thermal Property Characterization of Automotive Polymer Coatings

Abstract This article discusses AFM-based localized thermal analysis of crosslinked polymer coatings based on a recent breakthrough in nanoscale thermal probe technology. Examples include the monitoring of the softening point of automotive clearcoat systems, as a function of cure time and cure temperature and characterization of degradation and embrittlement of weathered acrylic-polyurethane coatings. Comparison of nano thermal analysis with bulk DSC and MDSC is made and its inherent advantages over DSC in analyzing surfaces is demonstrated.

Temper Embrittlement and Fracture Control Method Based on NGS Theory and Grain Refinement Technique

Temper embrittlement and fracture control method based on both non-equilibrium grain-boundary segregation (NGS) theory and grain refinement technique are studied in this paper. Grain refinement technique by deformation induced phase transformation in low-alloy steels, 12Gr1MoV and 2.25Gr1MoNb, is investigated. A single-pass hot rolling process by using a Gleeble-1500 system is performed. Experimental results show that steel strength and toughness may be controlled and improved by grain refinement, and that the grain sizes were affected by the deforming temperature, strain reduction, and strain rate. According to the NGS theory, a control method of brittle fracture along grain-boundary is proposed so that some catastrophically brittle fracture failure may be averted. Grain refinement may decrease both the concentration of phosphorus at grain boundaries and the critical time. With the grain refinement technique, the temper embrittlement of steel may be improved, and the critical time may be shortened. The cost of heat treatment for fracture control will therefore be reduced.

Effect of Isothermal Holding Temperature on NGS Kinetics of Phosphorus and Temper Embrittlement

When failure occurs in material, it is often occurs by fracture along some grain boundaries and often by the micro-segregation of embrittling impurity to the grain boundaries. In the present work, the non-equilibrium grain-boundary segregation (NGS) kinetics of phosphorus and the temper embrittlement at the same solution treatment and different isothermal holding temperature in steel 2.25Cr1Mo are studied. The NGS kinetics curves of phosphorus at the same solution temperature （1050 oC ）and different isothermal holding temperature (540 oC and 600 oC) are given. Experimental results provide a direct evidence of NGS kinetic model and show that the grain boundary segregation concentrations of phosphorus for specimen isothermal holding at 540 oC are higher than those at 600 oC. The peak values of AES patterns of solute atoms for specimen isothermal holding at 540 oC are also higher than those at 600 oC. It is therefore concluded that the lower the isothermal holding temperature, the higher the segregation concentration of phosphorus at the grain-boundaries, and also the higher the degree of embrittlement.

Reactor pressure vessel embrittlement of NPP borssele: Design lifetime and lifetime extension

Embrittlement of the reactor pressure vessel of the Borssele nuclear power plant has been investigated taking account of the design lifetime of 40 years and considering 20 years subsequent lifetime extension. The paper presents the current licensing status based on considerations of material test data and of US nuclear regulatory standards. Embrittlement status is also evaluated against German and French nuclear safety standards. Results from previous fracture toughness and Charpy tests are investigated by means of the Master curve toughness transition approach. Finally, state of the art insights are investigated by means of literature research. Regarding the embrittlement status of the reactor pressure vessel of Borssele nuclear power plant it is concluded that there is a profound basis for the current license up to the original end of the design life in 2013. The embrittlement temperature changes only slightly with respect to the acceptance criterion adopted postulating further operation up to 2033. Continued safe operation and further lifetime extension are therefore not restricted by reactor pressure vessel embrittlement.

Grain Boundary Segregation Behavior in 2.25Cr-1Mo Steel During Reversible Temper Embrittlement

Low alloy steels serving for a long time at high temperature, e.g., around 500 °C, are very sensitive to temper embrittlement due to segregation of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type of segregation in combination with various environmental effects can adversely affect the fracture resistance and fatigue crack propagation rate with subsequent change in fracture morphology of low alloy steels. This article describes the segregation behavior of various elements in 2.25Cr-1Mo pressure vessel steel investigated by AES, FEG-STEM, SEM, and EDS analyses. As confirmed by AES and FEG-STEM, phosphorus is found to be the main embrittling element for isothermal embrittlement. Sulfur and Mo segregation is only evident after longer embrittlement times. In the step-cooling embrittlement, phosphorus is still found to be the main embrittling element, but heavy segregation of sulfur in some isolated intergranular facets was also observed. For P segregation, a Mo-C-P interaction is observed, while sulfur segregation is attributed to site competition between sulfur and carbon atoms.

Influence of Prior Austenite Grain Size on the Degree of Temper Embrittlement in Cr-Mo Steel

Reversible temper embrittlement has been frequently observed in many different low alloy steels serving at high temperature, e.g. order of 500 °C. This type of embrittlement can change the brittle transgranular fracture mode to intergranular decohesion with subsequent change in fracture stress and fracture toughness. The present paper deals with the influence of the prior austenite grain size and isothermal aging time on the degree of embrittlement of 2.25Cr-1Mo steel, which is very popular for its use in power generating and other petrochemical industries. In this research work, the specimens of 2.25Cr-1Mo steel were treated in three different austenitizing temperatures along with different isothermal embrittling time periods. Then the induced degree of embrittlement was characterized by the fracture stress values at −196 °C and area fraction of intergranular failure. The outcome of the experimental results shows that the increase in austenite grain size and/or isothermal embrittling time severely weakens the grain boundary cohesive strength leading to brittle intergranular failures and thus to a greater degree of temper embrittlement.

Temper Embrittlement Sensitivities of 3Cr-1Mo and 2.25Cr-1Mo Low Alloy Steels

Contradicted results have been reported on sensitivities of Cr‐Mo low alloy steels to fracture toughness, so it seems further investigations is required in order to establish the reasons for this contradictions. This study tried to rationalize the causes of contradiction and establishes the reasons for variations in the observed changes in fracture toughness of two types of low alloy steels namely 3Cr‐1Mo and 2.25Cr‐1Mo steels. For investigating the embrittlement sensitivity in this research, a factor called J used since there are some clams that Cr‐Mo low alloy steels with higher J-Factor are more sensitive to temper embrittlement. For inducing temper embrittlement on these alloys, a step-cooling operation from high temperature to room temperature for a period of 234 h was employed. Then some of the mechanical properties of the embrittled sample and unembrittled alloys were determined and compared. The results showed that step cooling operation had no noticeable effect on tensile and hardness properties of the steels but strongly affected their resistance to impact. In the alloy having a low J-Factor of equivalent to 107, changes in both FATT and TT54J were about 11°C, this was relatively low, while in the alloy having a high J -Factor equivalent to 224, these changes were 70°C and 78°C respectively which indicated this alloy was highly sensitive to temper embrittlement. Changes in temper embrittlement of the two alloys used in this research were found and we tried to justify these changes in this article.