Temperature Embrittlement Research Articles

Prediction of radiation embrittlement of VVER-1000 RPV welded seam material at lifetime extension up to 60 years and more

The correctness of the model assumption about additivity of the contributions of hardening (formation of dislocation loops and radiation-induced precipitates) and non-hardening (formation and accumulation of grain boundary segregations) mechanisms to the final radiation embrittlement of VVER-1000 RPV weld materials has been verified. The paper presents the results of the experiment to obtain predicted values of the critical embrittlement temperature of weld metal with nickel content of 1.59–1.88% using accelerated irradiation in the IR-8 research reactor from states characterized by different starting level of grain boundary segregation. The procedure of accounting for the flux effect for the values of critical embrittlement temperature obtained using accelerated irradiation has been proposed. The conservativity of the weld metal radiation embrittlement dependence has been verified based on the modal assumption of additivity of the contributions of the strengthening and non-strengthening mechanisms up to the values of fast neutron fluence ~75–1022 neutrons/m2.

Experimental Study on Liquid Metal Embrittlement of Al-Zn-Mg Aluminum Alloy (7075): From Macromechanical Property Experiment to Microscopic Characterization.

This study is a multiscale experimental investigation into the embrittlement of Al-Zn-Mg aluminum alloy (7075-T6) caused by liquid metal gallium. The results of the experiment demonstrate that the tensile strength of the 7075-T6 aluminum alloy significantly weakens with an increase in the embrittlement temperature and a prolonged embrittlement time, whereas it improves with an increase in the strain rate. On the basis of the analysis of the experimental data, the sensitivity of the embrittlement of 7075-T6 aluminum alloy by liquid gallium to the loading strain rate is significantly higher compared to other environmental factors. In addition, this study also includes several experiments for microscopic observation, such as Scanning Electron Microscope (SEM) observation, Energy-Dispersive Spectrometer (EDS) spectroscopy, and Electron Back Scatter Diffraction (EBSD) analysis. The experimental observations confirmed the following: (1) gallium is enriched in the intergranular space of aluminum; (2) the fracture mode of 7075-T6 aluminum alloy changes from ductile to brittle fracture; and (3) the infiltration of liquid gallium into aluminum alloys and its enrichment in the intergranular space result in the formation of new dislocation nucleation sites, in addition to the original dislocations cutting and entanglement. This reduces the material's ability to undergo plastic deformation, intensifies stress concentration at the dislocation nucleation point, and, ultimately, leads to the evolution of dislocations into cracks.

Regulation Law of Tempering Cooling Rate on Toughness of Medium-Carbon Medium-Alloy Steel.

Temper embrittlement is a major challenge encountered during the heat treatment of high-performance steels for large forgings. This study investigates the microstructural evolution and mechanical properties of Cr-Ni-Mo-V thick-walled steel, designed for large forgings with a tensile strength of 1500 MPa, under different tempering cooling rates. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural features. The results demonstrate that the embrittlement occurring during air cooling after tempering is attributed to the concentration of impurities near Fe3C at the grain boundaries. The low-temperature impact toughness at -40 °C after water quenching reaches 29 J due to the accelerated cooling rate during tempering, which slows down the diffusion of impurity elements towards the grain boundaries, resulting in a reduced concentration and dislocation density and an increased stability of the grain boundaries, thereby enhancing toughness. The bainite content decreases and the interface between martensite and bainite undergoes changes after water quenching during tempering. These alterations influence the crack propagation direction within the two-phase microstructure, further modifying the toughness. These findings contribute to the understanding of temper embrittlement and provide valuable guidance for optimizing heat treatment processes to enhance the performance of high-performance steels in large forgings.

Novel Approach in Fracture Characterization of Soft Adhesive Materials Using Spiral Cracking Patterns

A novel approach for the fracture characterization of soft adhesive materials using spiral cracking patterns is presented in this study. This research particularly focuses on hydrocarbon polymeric materials, such as asphalt binders. Ten different asphalt materials with distinct fracture characteristics were investigated. An innovative integrated experimental–computational framework coupling acoustic emissions (AE) approach in conjunction with a machine learning-based Digital Image Analysis (DIA) method was employed to precisely determine the crack geometry and characterize the material fracture behavior. Cylindrical-shaped samples (25 mm in diameter and 20 mm in height) bonded to a rigid substrate were employed as the testing specimens. A cooling rate of −1 °C/min was applied to produce the spiral cracks. Various image processing techniques and machine learning algorithms such as Convolutional Neural Networks (CNNs) and regression were utilized in the DIA to automatically analyze the spiral patterns. A new parameter, “Spiral Cracking Energy (ESpiral)”, was introduced to assess the fracture performance of soft adhesives. The compact tension (CT) test was conducted at −20 °C with a loading rate of 0.2 mm/min to determine the material’s fracture energy (Gf). The embrittlement temperature (TEMB) of the material was measured by performing an AE test. This study explored the relationship between the spiral tightness parameter (“b”), ESpiral, Gf, and TEMB of the material. The findings of this study showed a strong positive correlation between the ESpiral and fracture energies of the asphalt materials. Furthermore, the results indicated that both the spiral tightness parameter (“b”) and the embrittlement temperature (TEMB) were negatively correlated with the ESpiral and Gf parameters.

Effects of Intercritical Heat Treatment on the Temper Embrittlement of SA508 Gr.4N Ni-Cr-Mo High Strength Low Alloy Steels for Reactor Pressure Vessels

To analyze the effects of intercritical heat treatment on the temper embrittlement of SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was heat treated by applying a conventional heat treatment process (quenching-tempering) with/without an intercritical heat treatment process (IHT) and a step-cooling heat treatment for temper embrittlement. Then their microstructure and mechanical properties were evaluated. The microstructure of the SA508 Gr.4N model alloy was composed of tempered lower bainite and martensite, and nano-sized precipitates formed both inside and at boundaries. The grain size was reduced when IHT was applied. There was a small difference in tensile properties according to the heat-treatment conditions and P contents, but the difference in Charpy impact properties was large. The heat treatment for temper embrittlement (TE) increased the impact transition temperature, and a very significant increase was observed in steels with a high P content. The increase in transition temperature owing to TE was reduced when IHT was applied. The fractograph analysis of Charpy fractured specimens at transition temperatures showed that an increase in intergranular fracture was main reason for the TE, and that IHT reduced the formation of intergranular fracture. The AES results showed that P-Ni was segregated at grain boundaries, and the level of segregation was reduced by applying IHT. This occurred because the formation of prior austenite grain boundaries by IHT dispersed the P at grain boundaries, and reduced the amount of P segregation.

Hot Ductility Evolution Mechanism of Titanium‐Bearing Microalloyed Steels

Titanium‐bearing (Ti‐bearing) microalloyed steels have high strength and toughness by grain refinement effect of carbonitride precipitates. However, they can induce surface cracks of continuous casting slab when the Ti alloyed content is high. A microalloyed steel with Ti content (0.10–0.15 wt%) is carried out by thermalmechanical simulator over 600–1350 °C to analyze hot ductility evolution mechanism. Fracture surface morphology, phase transition, and behavior of precipitates of the tensile samples are investigated by experimental detection and thermodynamic calculation. The ductility–temperature curves show that the third brittle temperature range is 600–890 °C, which is mainly attributed to the thin proeutectoid ferrite film and precipitated titanium carbonitride particles, widening the embrittlement temperature ranges through of steel. In addition, the tensile samples at 890–1350 °C have good hot ductility, indicating the dynamic recrystallization of deformed austenite can trigger grain boundaries migration away from cracks and avoid the side effect of the Ti (C,N) particles on hot ductility. The first brittle temperature range of 1350 °C‐melting point is mainly ascribed to the partial melting of the grain boundaries with element segregation of sulfur and phosphorus, and microporosity loose among dendrites.

Cold tolerance and mechanical properties of thermoplastic polymer based composite for the marine cables operating in polar regions

Cold tolerance of a thermoplastic polymer largely depends on the type and content of about 20 or more additives used to make the polymer. Observing the change of dynamic viscoelasticity as a function of the temperature change through glass transition temperature measurement is a representative method for evaluating cold resistance. In this study, mechanical properties of composite materials prepared by mixing various types of thermoplastic polymers and various additive components were evaluated to improve their cold tolerance performances. The cold tolerance was improved by blending resin having an embrittlement temperature lower than the operating temperature.

Temper embrittlement in HY-80 steel: Microstructure, magnetic and microhardness properties

Temper embrittlement is characterized by the migration of impurity elements and carbides towards the grain boundaries of alloy steels, such as HY-80 steel. The accumulation of inclusions at grain boundaries causes dramatic reductions in impact toughness due to the increased susceptibility of intergranular fracture. This kind of failure can be catastrophic for submarines under high pressure with hulls constructed of HY-80 steel. The detection of temper embrittlement is crucial for the safety of the crew. Currently, the most common method of detecting temper embrittlement is destructive, which is costly and inefficient. Non-destructive methods of temper embrittlement detection are more desirable, however, there are no widespread methods currently in use. One possible non-destructive method utilizes Magnetic Barkhausen Noise (MBN). This method was investigated by testing eight HY-80 samples for MBN energy, microhardness, and microstructural changes before and after a heat treatment at 525 °C for a variety of holding times. Scanning electron microscopy showed carbide migration to the grain boundary and spheroidization with increased holding time. Microstructural quantification was performed using computer vision to extract useful data on precipitate behavior during heat treatment. The microhardness of each sample was measured using Vickers microhardness testing before and after heat treatment to further characterize the level of temper embrittlement. Microhardness changes with holding time were attributed to the change in precipitate density and the migration of the precipitates to the grain boundary during temper embrittlement.

The influence of phosphorus on the temper embrittlement and hydrogen embrittlement of some dual-phase steels

The temper embrittlement (TE) and hydrogen embrittlement (HE) of some dual-phase (DP) steels were investigated, focusing on the influence of the phosphorus (P) content. An increased P content of 0.02 wt% caused little TE and enhancement of HE susceptibility in DP steels. Hydrogen had little influence on strength, but caused a significant decrease in ductility. For the DP steels with the different microstructures, the hydrogen-induced cracks initiated at the specimen surface, and hydrogen-induced micro-crack initiation was mainly martensite related. The increased martensite related cracking and the tendency of interface cracking was attributed by the enhanced element segregation (by both increased tendency of P segregation and promoted by other element segregation like Mn). The increased P content can enhance HE susceptibility through both interface weakening related HE mechanisms (HESIV, HEDE, or defactant) and ferrite ductility loss related HELP mechanism.

Understanding temperature and dwell time dependence of liquid metal embrittlement in austenitic stainless steel by liquid zinc and copper

Austenitic stainless steels are known to be susceptible to LME-induced cracking when exposed to various liquid metals, including zinc and copper. However, the conditions under which LME cracking occurs are only vaguely defined. The effect of temperature and dwell time are investigated in this study using Gleeble hot tensile testing. Liquid zinc embrittlement is most severe at 800 °C and decreases towards lower or higher test temperatures. The lower temperature limit for copper embrittlement is defined by the melting temperature of copper (1085 °C); significant embrittlement is observed up to a test temperature of 1300 °C, at which ductility largely recovers. The observed zinc and copper induced LME behavior in Type 304L austenitic stainless steel are discussed based on the thermodynamics of the 304-Zn and 304-Cu systems which suggest that liquid metal embrittlement occurs in a temperature range where the phase diagrams display a two phase liquid zinc (or copper) + solid region that extends over a wide compositional range. Diffusion calculations across the stainless steel to liquid zinc interface and results from electron microscopy analysis indicate that liquid zinc availability due to isothermal solidification of BCC ferrite at the stainless steel to liquid zinc interface is a limiting factor for LME in the 304-Zn system during Gleeble hot tensile testing.

The Influence of Phosphorus on the Temper Embrittlement and Hydrogen Embrittlement of Some Dual-Phase Steels

The Influence of Phosphorus on the Temper Embrittlement and Hydrogen Embrittlement of Some Dual-Phase Steels

Understanding Temperature and Dwell Time Dependence of Liquid Metal Embrittlement in Austenitic Stainless Steel by Liquid Zinc and Copper

Understanding Temperature and Dwell Time Dependence of Liquid Metal Embrittlement in Austenitic Stainless Steel by Liquid Zinc and Copper

PDMS material embrittlement and its effect on machinability characteristics by cryogenic abrasive air-jet machining

Abstract The use of cryogenic abrasive jet machining (CAJM) technology for polydimethylsiloxane (PDMS) materials is increasing rapidly due to its high material removal rate and high surface quality. However, how the material properties of PDMS affect the machining properties under cryogenic conditions is still an unsolved problem. Firstly, the thermodynamic and mechanical properties of PDMS materials are studied by dynamic thermo-mechanical analysis and universal material testing. The results show that the PDMS material’s embrittlement temperature is 126 K. Secondly, evaluation of cooling temperature of PDMS during CAJM shows that the machined area has reached embrittled state. Thirdly, the effect of PDMS material’s embrittlement on the machining behaviour is studied. The experimental results show that the PDMS material exhibit increased abrasive erosion at medium-angle under cryogenic conditions and shows a semi-brittle wear mechanism. Furthermore, the erode surface’s roughness is evaluated. The result shows that the roughness decreases with decreasing air pressure at the same impact angle; with increasing impact angle, the roughness shows a trend of increase initially and then decreases. This work shows that the PDMS material’s embrittlement and the erosion response behaviour during CAJM are due to the combined effects of thermo-mechanical properties and material removal mechanisms, providing a better understanding of CAJM technology.

Low-Temperature Micro-Fracture Toughness Testing of Grain Boundaries in Steel

Temper embrittlement in high-strength steel occurs due to the segregation of impurity elements along prior austenite (γ) grain boundaries, resulting in a decrease in intergranular strength. However, the grain boundary properties have not yet been experimentally investigated. In this study, we developed a micro testing method to selectively process micro-cantilever specimens based on a specific prior γ-grain boundary to measure the grain boundary fracture toughness. Fracture toughness tests using micro-cantilever specimens with side grooves and notch were carried out at 183 K and brittle fracture behavior was successfully obtained. The fracture surface showed almost flat and brittle crack propagation along the prior γ-grain boundary. The derived fracture toughness value, KQ, is lower than that from previous values. By employing this method for the evaluation of intergranular fractures in steel, we believe that we can evaluate more intrinsic prior γ-grain boundary properties compared with conventional methods.

Temper embrittlement of 9%Ni low carbon steel and nondestructive inspection by magnetic Barkhausen noise

9% Ni and low carbon steel is used in cryogenic services in oil and gas industries. The final mechanical properties are adjusted by quenching and tempering heat treatments. However, the un-correct tempering may cause temper embrittlement, with drastic decrease of toughness at cryogenic temperatures. In this study, specimens tempered at 350°C, 400°C and 450°C showed very low toughness at low temperature (-196°C) due to temper embrittlement. Specimens slowly cooled from the tempering temperature (565°C, 585°C and 605°C) also showed toughness reduction in comparison with specimens tempered at the same temperature and cooled in water. The brittle fracture was characterized by intergranular cracks and cleavage. Magnetic Barkhausen Noise (MBN) inspection was conducted to verify if this technique can be used to detect the temper embrittlement in 9Ni steels. The root mean square (RMS) of the MBN signal was higher in specimens as quenched and in specimens tempered in the temper embrittlement range (350°C-500°C) than in specimens which were correctly tempered (565°C-605°C and water cooled). Comparing specimens tempered at 565 and 585°C range and slowly cooled with those which were water cooled, the RMS(MBN) was higher in the former group, which presented the lower toughness. However, the MBN inspection could not separate specimens tempered at 605°C slowly and rapidly, which can be related to the higher austenite volume fraction measured in the specimen slowly cooled.

Deterioration of HAZ toughness by residual Sn and Determination of its Allowable Content for Electric Furnace Steels

One promising direction in steelmaking to respond to global climate change issue is to increase the use of electric furnace manufacturing methods using zero-carbon electricity, which have received more and more attention recently. Considering the replacement from blast furnace steel, the temper embrittlement problem induced by some tramp elements, which is unique behavior for electric furnace methods, must be resolved.Sn is considered as a tramp element that cannot be removed in steel refining process, and it has been reported that the toughness of the base metal and the welded heat affected zone can be significantly degraded. In the case of electric furnace steels with degraded toughness, segregation of Sn is observed at grain boundaries and the resulting fracture mode shifts to intergranular fracture mode. In this study, in order to quantify the allowable amount of Sn added to thick steel plates that is used for large-heat input welding, experiments were conducted on specimens with different amounts of Sn and heat-treated for different holding times at 400℃, which is a typical embrittlement temperature and investigated the effect of the amount of Sn on the change in low-temperature fracture toughness. As a result of fracture toughness tests, clear evidence of temper embrittlement was observed. Apart from previous famous study by McMahon, there was no intergranular fracture in fracture surface but transgranular and cleavage fracture was observed. Therefore, the mechanism by which Sn tends to cause cleavage fracture in the weld heat affected zone was proposed. Based on our newly proposed mechanism, a model was developed to estimate the transition temperature change for various conditions of tempering time, tempering temperature and Sn content.Finally, the authors propose allowable maximum content of Sn based on the model for the establishment of the rational ore sorting system from scraps in near future society.

Tempered Bainite and Martensite Embrittlement in Microalloyed Steel for Forged Railroad Wheel to Heavy Haul Application

Abstract This research shows two new microalloyed steels with niobium (Nb) for railroad wheels (Nb1 and Nb2) applied on heavy haul transportation (load over 30 tons/axle). The steels have mixed microstructure composed of pearlite and bainite (finished wheel rim section), and another one composed of martensite with bainite (black wheel section removed on machining) obtained by continuous cooling quenching heat treatment followed by tempering. The bainitic and martensitic microstructure are sensitive to the temper embrittlement phenomenon; therefore, knowing the embrittlement temperature range of these steels is mandatory in order to avoid such an event in the tempering process. Charpy specimens were extracted from the rim of railroad wheels, austenitized (860 oC), quenched in water for four minutes, and tempered at different temperatures to obtain the embrittlement curve. Three materials were compared: AAR (Association of American Railroads) Class C steel with pearlitic microstructure (not sensitive to embrittlement), Nb1, and Nb2 microalloyed steels with martensitic, bainitic, and pearlitic microstructures. The microalloyed steels have niobium (Nb), molybdenum (Mo), and silicon (Si) addition. The effect of Si content and the microstructure (analyzed by Scanning Electronic Microscope (SEM)), regarding the embrittlement phenomenon, was also studied. The microstructure of Nb2 steel was analyzed by with Transmission Electronic Microscope (TEM) for improving its characterization.

Investigation on Temper Embrittlement of TS1100 MPa Grade Ultra-High Strength Steel

Temper embrittlement is one of the major challenges encountered during the heat treatment of ultra-high strength steels. In this work, the microstructural evolution and mechanical properties during the austenite region quenching and tempering (Q-T) and the intercritical quenching and tempering (IQ-T) processes in a tensile strength (TS) 1100 MPa grade steel targeted for the manufacturing of a mooring chain were investigated. The temper embrittlement presented in the Q-T sample was attributed to the carbide network decorating the prior austenite grain and martensitic lath boundaries. In contrast, the IQ-T sample, where intercritical holding before quenching at the temperature of 12 °C lower than Ac3 was applied, exhibited a reasonable CVN impact energy of 188 J at − 20 °C with a slightly reduced strength. The ferrite formed during intercritical holding not only added extra interphase boundaries, but also refined the substructure of the quenched martensite. These increased boundary areas provided more nucleation sites for carbide precipitation during tempering. Meanwhile, the refined martensitic substructure promoted the diffusion of Cr, encouraging the fast coarsening of Cr-rich carbides. The formation of a carbide network was eventually prevented in the IQ-T sample. Thus, the IQ-T process was an effective approach to eliminate temper embrittlement caused by the carbide network.

Magnetic Barkhausen Noise Measurements to Assess Temper Embrittlement in HY-80 Steels

Magnetic Barkhausen noise (MBN) can result from abrupt motion of domain walls due to their interaction with pinning sites during magnetization of ferromagnetic steel. However, understanding domain structure interactions with pinning site density is limited. In this article, the effect of density of pinning sites within grains of HY80 steel, on generation of MBN, was investigated. Pinning site density was modified by a heat treatment that produces temper embrittlement. Temper embrittlement refers to the reduction of fracture toughness of alloy steels when heated or slowly cooled through the embrittling temperature range and arises due to migration of impurity elements to grain boundaries. Samples, machined from a casting, were held at a constant temperature (525 °C) for different holding times, to generate varying degrees of temper embrittlement. MBN signal response was observed to decrease exponentially as a function of holding time with decay constants (relaxation time) in the range of 160-190 h. A reduction in the MBN signal along each sample's easy axis was attributed to different densities of impurity elements, which act as pinning sites for domain wall movement within grains. Samples were also characterized using a scanning electron microscope (SEM), hardness testing, and impact toughness testing. Hardness was observed to increase with holding time and MBN energy decreased linearly with increasing hardness. Furthermore, a linear relationship between impact energy and MBN energy was observed. This implies that MBN signal analysis can be used as an indirect measure of the change in material properties of the sample.

The influence of the moisture content of raw materials on the structuring of the extrudates

The article presents the results of studies on the model systems of extrudates conducted with a view to determining the function of moisture during the process of forming the structure of starch pastes. There was studied the influence of the moisture content of raw materials on a starch gelatinization point. Studies showed that 15% moisture content in raw materials is sufficient for its constituent phase - starch gelatinization, as well as for the transition of the whole mass to a fluid-viscous state. Further increase in the moisture content is accompanied by a decrease in a gelatinization point. In order to study the influence of moisture on the formation of a porous structure of extrudates, we studied the relationship between the different-type starch pastes and the degree of its transparency and its embrittlement temperature. It has been found that during the process of thermal and mechanical impacts, there occurs the process of the formation of a structure of starch pastes, in particular, samples with the different moisture contents can have an amorphous or crystalline structure. There has been established the relationship between the moisture content of raw materials on the modulus of elasticity of starch pastes based on them. The modulus of elasticity of samples was determined one hour (cooling time to room temperature) and one week after obtaining the starch paste. The above studies showed that minimal physico-chemical and mechanical transformations occur in starch pastes, which are in an amorphous state, that is, in the conditions of a low moisture content. We have established that the moisture content of raw materials, on the one hand, ensures the transition of a high-dispersive phase to a fluid state, or implementing the ex process of extrusion, and on the other hand, influences on the formation of a porous structure in the extrudates.