Charpy Impact Properties Research Articles

The Charpy Impact Properties of Oxide Dispersion-Strengthened FeCrAl Alloys with Different Cr Contents

The Charpy Impact Properties of Oxide Dispersion-Strengthened FeCrAl Alloys with Different Cr Contents

Effect of Welding Heat Input on the Simulated Heat-Affected-Zone Toughness for Yield Strength 390MPa Class TMCP Steel Plate

In this study, the influence of heat input on the microstructure and toughness of the simulated heat-affected zone (HAZ) of YP390 MPa grade steel with a thickness of 80 mm was investigated. The weld coarse-grained HAZ was simulated using a Gleeble 3500 simulator, with heat input levels ranging from 30 to 650 kJ/cm. Following the HAZ simulation test, the microstructures and Charpy impact properties were examined. For heat inputs ranging from 30 to 50 kJ/cm, the microstructure consisted of bainitic ferrite/acicular ferrite, resulting in an impact toughness exceeding 200 J at -20 ℃. Conversely, in the higher heat input range of 130 to 650 kJ/cm, the simulated HAZ exhibited a lower impact toughness value due to the formation of coarse grain boundary ferrite. A high proportion of acicular ferrite with minimal grain growth was found to be the key metallurgical factor contributing to the improvement of impact toughness.

Investigation on Cracking Cause of Drill Pipe Joint Used in an Ultra Deep Well

The drill pipe joint cracked during service, resulting in joint failure. The geometric dimensions of thread, chemical composition and microstructure of the drill pipe joint were tested. The geometric dimensions, chemical composition and microstructure were found to comply with the standard requirements. The whole macroscopic fracture didn’t show obvious corrosion product. The tensile properties, Charpy impact properties, and Brinell hardness met the standard requirements. Microstructure of fracture was analyzed, which showed a typical erosion micromorphology with parallel arranged fatigue strips. Through simulation analysis, it was found that the location of cracking was the stress concentration area. The failure mechanism of the drill pipe joint was revealed. The stress concentration led to fatigue cracking at the drill pipe joint. After the fatigue crack penetrated through the wall thickness, the drilling fluid leaked from the inner wall to the outer wall. The flow rate of the leaking drilling fluid is significantly increased. And it is sprayingly leaked, which further leads to fan-shaped erosion damage of the cracked surface from the inner wall to the outer wall.

Effects of B Doping and Quenching Rate on Charpy Impact Properties in AISI 4130 Steels

Effects of B Doping and Quenching Rate on Charpy Impact Properties in AISI 4130 Steels

Effect of Austenite Reversion and Its Stability on the Tensile and Impact Transition Behavior of High‐Strength Naval Steel

The present investigation correlates the austenite reversion and its stability during intercritical annealing (IA) with the tensile and Charpy impact properties of a low‐C naval grade steel. The as‐received steel is subjected to water quenching after austenitization at 950 °C, followed by IA at 620, 650, and 680 °C for 2 h. DICTRA simulation is used to predict the austenite reversion kinetics during the IA. Incorporation of cementite phase in the simulation correlates well with the experimental dilatometry results on the austenite growth kinetics. DICTRA simulation predicts a continuous rise in the reverted austenite fraction with increasing IA temperature. However, the percentage of reverted austenite, that gets retained after the subsequent quenching, decreases with increasing annealing temperature due to the reduction of austenite stability at elevated IA temperature. In other words, the amount of fresh untempered martensite increases rapidly with increasing IA temperature. Consequently, the sample annealed at an intermediate temperature of 650 °C (IA650) shows the best combination of strength, elongation, and low‐temperature impact properties as compared to the IA620 and IA680 steels due to an optimum balance of mechanically stable austenite and relatively lower untempered martensite fractions.

Effect of hydrogen embrittlement on the safety assessment of low-strength hydrogen transmission pipeline

Currently, no systematic approach exists for the safety assessment method of hydrogen transmission low-strength pipeline, it is necessary to study the effect of hydrogen embrittlement (HE) on the method of failure assessment diagram (FAD) for the defective pipe. The hydrogen charging experiments of tensile and Charpy impact specimens for the L245 pipe steel were carried out with charging time of 0, 30, 90, and 120 h, and then the tensile and Charpy impact tests were immediately conducted. The HE indexes of tensile and Charpy impact properties were presented to quantitatively analyze the effect of HE under tensile and impact deformation processes. Subsequently, the FAD method coupled with the effect of HE was investigated to analyze the difference in the safety assessment method between hydrogen and non-hydrogen environments. Finally, the fracture morphology of tensile and Charpy impact specimens was observed to analyze the responses of microscopic fracture modes between hydrogen and non-hydrogen environments. The results show that the effect of HE on the tensile properties of the base material is more sensitive than that of the weld joint. The FAC with the effect of HE for safety assessment of defective pipes shrinks by reducing the safe zone. The decrease ratio of safety factors affected by HE presents an increasing tendency as the increase of crack depth while showing a decreasing tendency as the increase of internal pressure.

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.

The Correlation Between Bending, Tensile and Charpy Impact Properties of Ultra-high-Strength Strip Steels

The Correlation Between Bending, Tensile and Charpy Impact Properties of Ultra-high-Strength Strip Steels

Effect of B and N Content and Austenitization Temperature on the Tensile and Impact Properties of Modified 9Cr-1Mo Steels

The present study investigates the relative effect of B and N concentrations and the austenitization temperature on the microstructure and mechanical properties (tensile and Charpy impact) of modified 9Cr-1Mo (P91) steels. Initially, a B-free P91 steel (with 500 ppm N) and four different B-containing steels (25–100 ppm) with varying N concentrations (20–108 ppm) were hot-rolled, normalized from different austenitization temperatures (1000–1100 °C/1 h) and finally tempered at 760 °C for 1 h. A Charpy impact test shows that the ductile–brittle transition temperature (DBTT) of all the B-added steels decreases with an increase in the austenitization temperature, where the 100 ppm B steel offers the lowest DBTT (−85 °C). Similarly, the strength increases with the increase in the austenitization temperature (1100 °C), with a slight drop in ductility. The influence of precipitates on the microstructure and mechanical properties is explained considering the B enrichment at the precipitates and the thermodynamic stability of the precipitates. The 100 ppm B steel (containing the maximum B and minimum N), normalized from 1100 °C austenitization, shows the best combination of tensile and Charpy impact properties, owing to the effective dissolution of coarse M23C6 and MX precipitates during the normalization treatment and the formation of fine B-rich (Fe,Cr)23(B,C)6 precipitates during the subsequent tempering.

Comparative study on the effect of test temperature on tensile and charpy impact properties of Ti–5Al–1V–1Sn–1Zr-0.8Mo alloy

Impact toughness is a critical indicator to prevent catastrophic failure, especially at low service temperature. At present, most strategies to strengthen and toughen Ti alloys are proposed under the quasi-static tensile deformation condition. In fact, whether these strategies can be directly extended to improve impact toughness is still controversial due to the high loading rate and the existing of pre-notch during Charpy impact deformation condition. In this work, we found that, even though the yield strength and elongation of Ti–5Al–1V–1Sn–1Zr-0.8Mo alloy increase simultaneously with the decrease of test temperature under tensile deformation condition, the impact toughness still decreases gradually with the decreasing of deformation temperature under Charpy impact deformation condition. This phenomenon indicates that the successful strengthening and toughening strategies under quasi-static tensile deformation may fail under impact deformation. Finally, the reasons behind this phenomenon are explained based on the comparison of surface deformation morphologies under different deformation conditions, and the corresponding deformation mechanisms are established.

Dependence of Charpy Impact Properties of Fe-30Mn-0.05C Steel on Microstructure

Fe-30Mn-0.05C steel specimens with cold-rolled, partially recrystallized, fine-grained, and coarse-grained microstructures were fabricated by means of 80% cold rolling followed by annealing at 550–1000 °C. The initial and deformed microstructures were characterized, and the Charpy impact properties were tested at room temperature (RT) and liquid nitrogen temperature (LNT). It was found that the Charpy absorbed energy increased with the annealing temperature, while the specimens showed different trends: parabolic increase at RT and exponential increase at LNT, respectively. Compared with the fully recrystallized specimens, those with a partially recrystallized microstructure exhibited lower impact energy, especially at LNT. This was because cracks tended to nucleate and propagate along the recovery microstructure where stress concentration existed. The grain size played an important role in the twinning behavior and impact properties. High Charpy impact energy (~320 J) was obtained in the coarse-grained specimen having the grain size of 42.1 μm at both RT and LNT, which was attributed to the activation of high-density deformation twinning. However, deformation twinning was inhibited in the specimen with the average grain size of 3.1 μm, resulting in limited work hardening and lower impact energy.

Simulated Coarse Grain Heat‐Affected Zone Transformation Behavior of Newly Developed Zr–Ti–RE Deoxidized High‐Strength Low‐Alloy Steels with Extremely High Impact Toughness

The continuous cooling transformation behavior of the Zr–Ti–RE deoxidized high‐strength low‐alloy steel in the simulated coarse grain heat‐affected zone at different cooling rates (corresponding to different t8/5) is investigated by a Gleeble 3800 thermomechanical simulator in combination with microstructure and mechanical properties analysis. The continuous cooling transformation curve in the simulated heat‐affected zone is plotted, and the transformation law of M/A constituents is systematically investigated. It is found that with the increase of the cooling rate, the dominated microstructure is transformed from pearlite + ferrite into granular bainite and, finally, into lath bainite with the further refinement of M/A constituents. The steel exhibits excellent V‐notch Charpy impact properties at −20 °C under typical heat inputs (20, 100, 500 kJ cm−1). Moreover, acicular ferrite formed on spherical Zr–Ti–RE composite inclusions are observed at the heat input of 100 kJ cm−1. The low‐temperature impact absorbed energy gradually decreases with the increasing heat input due to the coarsening of the microstructure, larger effective grain size, and the reduction in the number of high‐angle variant pairs.

Influence of Grain Size and Its Distribution on Charpy Impact Properties of TA3 Alloy

In practice, most components often receive impact loads during service. In order to ensure the service safety of components, impact toughness evaluation is essential. To the best of our knowledge, the previous studies were mainly focused on the quasi-static tensile deformation, and the impact toughness of bimodal grain structured metals have rarely been reported. Three different grain size characteristics TA3 alloy, i.e., fine grained sample (FG Ti), the mixture of coarse and fine grained sample (MG Ti), and coarse grained (CG Ti), were produced, and their tensile and Charpy impact properties were comparatively investigated. Owing to the strengthening of retained β phase and the twining inducing plasticity effect, MG Ti display the highest tensile strength and impact absorbed energy, together with an intermediate tensile elongation. The impact deformed microstructures revealed that the primary deformation modes of FG Ti, MG Ti and CG Ti sample are: dislocation slips, a combination of dislocation slip in fine grained region and {101¯2} deformation twins in coarse grained region, and {112¯1} deformation twins in sequence.

Simultaneously improve the mode II interlaminar fracture toughness, flexural properties, and impact strength of CFRP composites with short aramid fiber interlaminar toughening

AbstractThis work mainly focuses on the mode II interlaminar fracture behavior of carbon fiber composite that was interlaminar toughened by short aramid fiber modified epoxy resin. The short fibers were first dispersed in the epoxy matrix and then in the laminate interlayer area during the lamination process. The ENF test evaluated the Mode II interlaminar fracture toughness of laminates. The results show that mode II interlaminar fracture toughness increases with the addition of short fibers. When the fiber content is 10 g/m2, the toughening effect is the best at 2437.72 J/m2, which is about 61.8% higher than the untoughened sample. The toughening mechanism of CFRP laminates by adding short fibers was observed by mode II fracture surface SEM images. In addition, flexural properties and Charpy impact properties of short fiber modified resin interlayer toughened laminates were also studied. The results showed that with this method, flexural properties and impact strength were improved to a certain extent, proving that this method is an effective interlaminar toughening method.

Curaua-Aramid Hybrid Laminated Composites for Impact Applications: Flexural, Charpy Impact and Elastic Properties.

Curaua, as a leaf-based natural fiber, appears to be a promising component with aramid fabric reinforcement of hybrid composites. This work deals with the investigation of flexural, impact and elastic properties of non-woven curaua–aramid fabric hybrid epoxy composites. Five configurations of hybrid composites in a curaua non-woven mat with an increasing quantity of layers, up to four layers, were laminated through the conventional hand lay-up method. The proposed configurations were idealized with at least 60 wt% reinforcement in the non-alternating configuration. As a result, it was observed that the flexural strength decreased by 33% and the flexural modulus by 56%. In addition, the energy absorbed in the Charpy impact also decreased in the same proportion as the replaced amount of aramid. Through the impulse excitation technique, it was possible observe that the replacement of the aramid layers with the curaua layers resulted in decreased elastic properties. However, reduction maps revealed proportional advantages in hybridizing the curaua with the aramid fiber. Moreover, the hybrid composite produced an almost continuous and homogeneous material, reducing the possibility of delamination and transverse deformation, which revealed an impact-resistant performance.

An investigation on the plane-strain fracture toughness of a water atomized 4130 low-alloy steel processed by laser powder bed fusion

A water atomized 4130 steel powder was processed by Laser powder bed fusion and investigated both in as-built condition and after quench and tempering thermal treatment. Analyses were focused on the different microstructures developed and on steel fracture behavior in terms of tensile fracture elongation, Charpy impact properties, and linear elastic fracture toughness. Comparisons were also drawn by testing a reference 4130 steel fabricated from a gas atomized powder. The slightly higher oxygen content found in the water atomized powder led to the formation of finely dispersed nano-size oxide particles in the steel matrix. It was found that these inclusions have a minor effect on the tensile properties, but a significant influence on the impact toughness response. The fracture toughness tests showed that the orientation leading to propagation of cracks along the inter-layer planes represented the most critical situation, and the steel toughness could be significantly improved after the quench and tempering treatment owing to the achievement of a more homogeneous microstructure. The results suggest that the investigated water atomized low-alloy steel powder feedstock can be considered as a suitable and cheaper alternative for structural parts produced by additive manufacturing, which could replace the more popular gas atomized steel grades.

Charpy impact properties of uni-directional carbon fiber-reinforced polymer tendons with protective layers

The present study explored potential forms of impact protection for carbon fiber-reinforced polymer (CFRP) tendons. Charpy impact tests were performed on CFRP rods and strands under protections of polyvinyl chloride (PVC) and poly-ethylen (PE). In the experimental program, the impact damage pattern and absorbed energy of CFRP tendons with and without external protection were obtained. The results show that the energy absorption capacity of CFRP tendons was improved under the protection of surface layers; and PE layers exhibited the highest protection effectiveness among all protection forms in terms of the increased absorbed energy and caused additional structural weight. Besides, two empirical expressions were established to quantify the relationship between the thickness of PE layers and the energy absorption capacity of the protected CFRP tendons, which may provide a simple tool to estimate the thickness of the layer required for the protection of a specific CFRP tendon in practical applications.

Tensile and Charpy impact properties of heat-treated high manganese steel at cryogenic temperatures

The structural materials for the superconductor in next generation DEMO fusion reactor are in great demanded with excellent nonmagnetic and mechanical properties such as strength, toughness, and ductility at the cryogenic temperature. High-Mn steels, newly developed for application to cryogenic industry, including DEMO fusion reactor, can change its deformation mechanism by twinning, martensite transformation and dislocation slip according to the range of stacking fault energy (SFE). Therefore, it is very important to investigate the mechanism of deformation behavior at cryogenic temperatures. In this study, tensile tests and Charpy impact tests were performed to investigate the effects of heat treatment on mechanical properties of high-Mn steels at cryogenic temperatures. In addition, the deformation mechanism of high-Mn steels at room temperature and cryogenic temperature was investigated through various analysis such as microstructure, XRD, EBSD and TEM. As a result, phase transformation from austenite to ε and α'-martensite was generated in the tensile test with a slow loading rate at cryogenic temperatures, while ε and α'-martensite was not observed in the Charpy impact test with a high loading rate.

Effects of thermal history on sensitization behavior and Charpy impact property of type 316L and 316 stainless steels for applications in a fired heater

Type 316L stainless steel (SS) reveals its superior corrosion resistance against uniform and localized corrosion. But, it might be prone to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) due to detrimental Cr-rich carbides formed along the grain boundaries. The present investigation was aimed to study the sensitization behavior and Charpy impact property of type 316L SS experienced isothermally aging at 650, 750 and 850 °C for 2 h to compare with type 316 SS exposed to the actual service at temperature between 800 and 900 °C for nearly 20 years. The results indicated that the degree of sensitization (DOS) values of below 0.5 % were obtained for type 316L SS, whereas type 316 SS revealed its DOS value of around 48 %. The presence of σ-phase transformed from δ-ferrite was a predominant factor to lower the Charpy impact energy of type 316L SS. The grain boundary Cr-rich carbide network played a key role in decreasing the Charpy impact energy of type 316 SS with indicating an intergranular fracture mode.

Influence of W concentration on the Charpy impact property and corrosion behavior of reduced activation ferritic-martensitic steels for fusion reactor

Fe-9Cr-0.4Mn-0.2V-0.1Ta-0.02Ti-0.1C-W (all in wt%) alloys with different W additions of 1 and 2 wt% were prepared to investigate the effects of W content on the mechanical properties and corrosion behavior of reduced activation ferritic–martensitic steels. The base steel samples were made through a heat treatment involving normalizing and tempering after hot rolling. When the W content was 1 wt%, the microstructure of the base steel consisted of tempered martensite with two types of precipitates, intergranular Cr-enriched M23C6 carbide and Ta/Ti-enriched MC carbide, while δ-ferrite additionally formed in an alloy containing W at 2 wt%. The results of Charpy impact tests showed that the ductile-to-brittle transition temperature slightly increased with an increase in W concentration without degrading the upper shelf energy, implying that the impact property slightly deteriorated. In addition, potentiodynamic polarization tests showed that the resistance to pitting corrosion also decreased when the W concentration was increased from 1 to 2wt%. This unexpected degradation of the impact property and corrosion resistance in alloy containing 2 wt% W was caused by the formation of δ-ferrite. That is, the δ-ferrite provided a relatively easy path for crack propagation during the impact tests. Also, since the δ-ferrite is a W-enriched phase, the matrix adjacent to the δ-ferrite was electrochemically active and acted as a local anode and the δ-ferrite formation then decreased the resistance to pitting corrosion.