Increase In Impact Toughness Research Articles

Microstructure, mechanical properties and corrosion behavior of Al–Si–Cu–Zn–X (X=Bi, Sb, Sr) die cast alloy

The microstructure evolution, mechanical and corrosion properties of Al–11Si–2Cu–0.8Zn die cast alloy treated with Bi, Sb and Sr additions were investigated. The results of mechanical testing showed that all additions increased impact toughness, ultimate tensile strength, and elongation of the alloy as a result of change in eutectic Si morphology. The analysis of fracture surfaces revealed that with addition of Sr and to lesser extent Bi and Sb, the alloy exhibited a predominantly ductile fracture rather than quasi-cleavage brittle fracture. Moreover, with the additions of Sr, Bi and Sb, the quality index increased to 164.7 MPa, 156.3 MPa and 152.6 MPa respectively from 102 MPa for the base alloy. Polarization corrosion tests conducted in sodium chloride solution showed that the corrosion potential shifted to more negative values with additions of Sb, Bi and Sr, respectively. Corrosion immersion tests also revealed that the element additions have a detrimental effect on the corrosion rate of alloys, due to the increase of boundaries between the Al and eutectic Si phases.

Mechanical properties of carbon nanotube/carbon fiber reinforced thermoplastic polymer composite

Carbon nanotube (CNT)/carbon fiber (CF) hybrid fiber was fabricated by sizing unsized CF tow with a sizing agent containing CNT. The hybrid fiber was used to reinforce a thermoplastic polymer to prepare multiscale composite. The mechanical properties of the multiscale composite were characterized. Compared with the base composite (traditional commercial CF), the multiscale composite reinforced by the CNT/CF hybrid fiber shows increases in interlaminar shear strength (ILSS) and impact toughness. Laminate containing CNTs showed a 115.4% increase in ILSS and 27.0% increase in impact toughness. The reinforcing mechanism was also discussed by observing the impact fracture morphology. POLYM. COMPOS., 38:2001–2008, 2017. © 2015 Society of Plastics Engineers

The formation of delamination cracks in impact-toughness tests as a cause of the increase in the impact toughness of steels with bcc structure

The role of weakened surfaces parallel to the plane of rolling in the formation of delamination cracks in the course of impact-toughness testing of steels with the bcc structure subjected to high-temperature thermomechanical treatment has been theoretically substantiated. A mechanism of increasing impact toughness during the formation of delamination cracks has been described using 08Kh18T1 steel as an example. It has been shown that the stress state that arises in a material with weakened surfaces can be modeled using composite specimens.

Impact toughness of a gradient hardened layer of Cr5Mo1V steel treated by laser shock peening

Laser shock peening (LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts. Cr5Mo1V steel exhibits a gradient hardened layer after a LSP process. A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer. Assuming a linearly gradient distribution of impact toughness, the parameters controlling the impact toughness of the gradient hardened layer were given. The influences of laser power densities and the number of laser shots on the impact toughness were investigated. The impact toughness of the laser peened layer improves compared with an untreated specimen, and the impact toughness increases with the laser power densities and decreases with the number of laser shots. Through the fracture morphology analysis by a scanning electron microscope, we established that the Cr5Mo1V steel was fractured by the cleavage fracture mechanism combined with a few dimples. The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.

Mechanism of improvement on strength and toughness of H13 die steel by nitrogen

The mechanism of nitrogen addition to AISI H13 die steel is proposed and supported using thermodynamic calculations in addition to observed changes in precipitate, microstructure, crystal structure, and macroproperties. The results indicate that the average impact toughness ak of the novel nitrogen H13 steel is maximally 17.6Jcm−2 and minimally 13.4Jcm−2. These values result in die steel that reaches premium grade and approximate the superior grade as specified in NADCA#207-2003, additionally the hardness is improved 3–5HRC. Experimental findings indicate that the residual V(C,N) particles undissolved during nitrogen H13 steel austenitizing by quenching helps to suppress growth of original austenitic crystal grains, this in turn results in finer martensitic structures after quenching. In the subsequent tempering process all N atoms are dissolved in the solid state matrix a result of C atoms displacing N atoms in V(C,N). Solid dissolution of N atoms produces a distorted lattice of Fe matrix which results in an increase in the hardness of the steel. Additionally this displacement reaction is important for slow growth of secondary particles in nitrogen H13 steel during the tempering process which helps to increase impact toughness compared to its nitrogen-free counterpart given the same condition of heat-treatment.

Modification of microstructure to increase impact toughness of nanostructured bainite–austenite steel

To improve impact toughness of the nanostructured bainite–austenite steel, a heat treatment operation was developed to divide prior austenite grains by plates of martensite directly before isothermal transformation. In the investigation, nanostructured steel containing 0·55%C, 1·95%Mn, 1·82%Si, 1·29%Cr and 0·72%Mo was used. It was found that a partial transformation to martensite achieved by cooling to 160°C followed by direct isothermal transformation to bainite at 225°C was the most promising treatment to improve Charpy impact energy of the investigated steel. For each testing temperature: ambient, 0, −20, −40 and −60°C, the specimens subjected to the developed treatment showed a higher averaged impact energy than the specimens subjected to the standard treatment.

Effect of Heat Treatment Processing Parameters on the Microstructure and Properties of Low-Carbon Cr-Ni-Mo Carburizing Bearing Steels

The low-carbon Cr-Ni-Mo carburizing bearing steel was tested with different heat treatment processes. Quenching-tempering temperature and cryogenic treatment (-73°C) wasstudied respectively onthe mechanical properties and microstructure.Results show thatthe increase of quenching temperature causes the micron-sized Cr-rich carbide re-dissolution and smaller quantity of retained austenite, makingthe strength and hardness of the tested steel increase and the impact toughness decrease. The tempering temperaturerising causesthe reduction of micro-residual stresses and smallerdegree of lattice distortion andlower dislocation density, resulting in the decrease of strength and the increase of impact toughness. Cryogenic treatment contributes to the refinement of martensite lath and precipitation of nanosized carbide and lowest quantity of retained austenite, improving the strength and impact toughness of the steel.The good comprehensive mechanical propertieswith the hardness of HRC41.3, tensile strength of 1413MPa,yield strength of 1168MPa, and impact toughness of 162J/cm2 can be obtainedby optimizing the heat treatment process parameters.

Effect of Tempering Temperature and Time on Strength and Hardness of Ductile Cast Iron

The effects of tempering temperature and time on the mechanical properties of ductile cast iron is investigated in the current work. The specimens were austenitized at 900°C for 120 minutes and then quenched in mineral oil at room temperature. Immediately after quenching the specimens were tempered at 400°C and 200°C for 60min, 90min, and 120min. In the tempering temperature range of 200°C-400°C, there is sudden increase in impact strength, ductility and toughness of the materials, as the temperature and time increase. The UTS drops initially, and hardness of materials will depends on amount of phase of martensitic and retained austenitic and graphite nodules. In this work alloying elements also effected the microstructure of the specimen. And due to increase tempering time the amount of martensitic phase will decrease and retained austenitic phase will increase, retained austenitic phase is softer then martensitic so hardness will decrease.

Effect of Tempering Temperature on Microstructure Evolution and Mechanical Properties of 5% Cr Steel via Electro‐Slag Casting

The newly designed 5% Cr steel processed by electro‐slag casting can be a candidate material as components in blast furnace top gas recovery turbine unit (TRT). The present study focuses on the evolution of the microstructure, strength and toughness with increasing tempering temperature from 550 to 700 °C. Typical tempered martensitic structure was achieved after quenching and tempering for the 5% Cr steel. The microstructure characterization shows that M3C in the matrix after 550 °C tempering was not stable and transformed to M7C3 during tempering above 600 °C. After tempered at the temperature higher than 600 °C, only M7C3 existed in the specimens. The M7C3 carbides along the boundaries were significantly larger than those in the matrix due to the effect of direct nucleation as well as the greater mobility of alloy elements. The size and Cr content of M7C3 increased considerably with increasing tempering temperature. With the increase of tempering temperature, both tensile and yield strength decreased, which can be attributed to the recovery of martensitic laths and the decrease of the quantity of interstitial carbon atoms in the matrix as well as the coarsening of carbides. The softening of matrix and increase of the length of high angle grain boundaries were responsible for the increase of impact toughness. The integrated effects of the softening of matrix and coarsening of carbides resulted in the slight decrease of the impact absorbed energy after 700 °C tempering.

Effect of interpass temperature on microstructure, impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.

Influence of equal-channel angular extrusion on impact toughness of aluminum and brass at room and low temperatures

Abstract Background Equal-channel angular extrusion is a severe plastic deformation process that can be used for grain refinement to improve material properties of bulk metals. In this paper, the effect of equal-channel angular extrusion on the impact toughness of aluminum 1100 and brass C26000 was investigated. Methods Brass and aluminum materials were extruded in two and four passes using two equal-channel angular extrusion processing routes. Specimens were tested for hardness and Charpy impact toughness. Microstructure and fractography were examined. Results The results showed the hardness remained almost constant after two passes for both brass and aluminum. Impact energy of brass after two passes decreased due to increase in dislocation density whereas for aluminum it remained almost constant after four passes due to the formation of ultrafine grains in addition to deformation/dislocation structures. Impact energies of specimens tested at room temperature and low temperature (−70°C) were almost the same due to their face-centered crystal structure. It was also found that the impact toughness of a specimen with a non-distorted notch surface is higher than that of a specimen with a distorted notch surface. Conclusions It is evident from the present study that the number of passes determines the extent of ultrafine grain structure that is known to increase impact toughness of equal-channel angular extrusion processed materials. All of these observed characteristics can influence material and process selections in practical design applications.

Long Term High-Temperature Environmental Effect on Impact Toughness in Austenitic Alloys

Structural integrity is crucial for the safety of power plants with higher efficiency to meet the increasing global energy consumption. High-temperature environment will demand not only improved high-temperature corrosion resistance but also a maintained sufficient toughness. This study investigates how long term high-temperature environment influence the impact toughness of two austenitic stainless steels (AISI 304 and Sandvik SanicroTM 28) and one nickel-bas alloy (Alloy 617). Alloy 617 has shown increasing impact toughness with both increasing temperature and time, up to 700°C and 3 000 hours, while the two austenitic stainless steels have shown the opposite for the same conditions. At 10 000 hours the impact toughness of Alloy 617 has decreased but the alloy still possess great toughness. Both austenitic stainless steels show embrittlement due to brittle σ-phase and Alloy 617 seems to gain good impact toughness performance from small evenly distributed precipitates.

Effects of Laser Quenching on Impact Toughness and Fracture Morphologies of 40CrNiMo High Strength Steel

The surface of 40CrNiMo steel was quenched with a CO2 laser, Charpy impact test was conducted at temperatures of 20, 0, and −20 °C, and the impact absorption energies were measured. The fracture morphologies were observed with SEM, and the influence of microhardness, residual stress, and retained austenite on mechanical behavior of impact fracture after laser quenching was discussed. The results show that the hardened layer depth is more than 1 mm after laser quenching, and hardness is about 480-500 HV. The fracture morphology of the sample is dimple rupture at a temperature of 20 °C; with the lower temperature the fracture dimples become smaller. At a temperature of −20 °C, the fracture morphologies change from ductile to brittle, which is mainly cleavage fracture. The increase in surface hardness, production of compressive residual stress, and existence of retained austenite after laser quenching are the main mechanisms of increasing impact toughness.

Effect of microstructure evolution on strength and impact toughness of G18CrMo2-6 heat-resistant steel during tempering

G18CrMo2-6 steel is one kind of low alloy CrMo steel with ferrite/bainite phase constituent. It is widely adopted in the large casting parts of pressure vessels. This paper aims at investigating evolution of G18CrMo2-6 steel microstructure, tensile strength and impact toughness during the tempering (680°C). The tempered microstructure characterization shows that the tempering time mainly affects the precipitation of three kinds of carbides, naming MC, M3C and M23C6. Both tensile strength and impact toughness do not obey the monotonic evolution with the tempering time but the complex changes. The shift of mechanical properties results from the interaction among matrix phases and the evolution of three different kinds of carbides. The softening of matrix due to the dislocation recovery and the decrease of the amout of carbon and other alloy elements in matrix lattice due to the precipitation of M23C6 cause the decreasing tensile strength for the whole tempering except for that an increase during the short-term tempering controlled by the precipitation of MC and the spheroidization and refinement of M3C carbide. On the other hand, both the softening of matrix and the spheroidization and refinement of M3C carbide are responsible for the increasing impact toughness. However, the precipitation and coarsening of M23C6 at ferrite grain boundaries during long-term tempering results in the sharp deterioration of impact toughness. It attributes to the larger grain boundary carbides result in the lower critical fracture stress of a carbide-ferrite interface.

Fabrication and mechanical properties of phenolic foam reinforced with graphene oxide

In this article, samples of phenolic foam reinforced with graphene oxide were prepared. Gel time of resole was tested to choose the appropriate foaming agent. Friability and Mechanical properties of the composite were tested. Dynamic mechanical analysis (DMA) was employed to study the mechanical properties in varied temperatures. The results show that gel time is increased 68.2% by using of 0.5% graphene oxide; n‐hexane is more fitting as blowing agent for graphene oxide reinforced phenolic foam; Impact toughness increase along with the graphene oxide content. It is not obvious when the amount is lower than 0.3% and there is a sudden enhancement when the amount reaches 0.5%. There is a 26.7% reduction in mass loss by reinforcing with 0.5% graphene oxide. Ester bonds between graphene oxide and phenolic foam matrix may be considered as “nails,” while graphene oxide may be considered as a “net.” The “net” mantle up the matrix tightly with those “nails” and stops separating of particles whose size is smaller than the “net.” POLYM. COMPOS., 35:581–586, 2014. © 2013 Society of Plastics Engineers

Microstructure and Mechanical Properties of 16Cr-2Ni Stainless Steel Fusion and Solid State Welds-Influence of Post Weld Treatments

Many critical applications in chemical equipment, aircraft and ordinance demand a material of construction with high strength and good corrosion resistance. Frequently the strength requirement exceeds that obtainable with austenitic or ferritic stainless steel and it is necessary to use one of the martensitic stainless steels. Since martensitic stainless steels are structural materials, weldability has been an important consideration in their development. AISI 431 is one of the most potentially attractive steels in this class used extensively for parts requiring a combination of high tensile strength, good toughness and corrosion resistance. Although this material has been used for many years, little information is available on the welding behavior of these steels. Further, data on electron beam (EB) welding and solid state welding process like friction welding are scarce. The lack of knowledge constitutes a potential drawback to the more widespread use of these steels. Hence, a study has been taken up to develop an understanding on the electron beam welding and friction welding aspects of martensitic stainless steel type AISI 431. Various kinds of post weld heat treatments (PWHT) were investigated to determine their influence on microstructure and mechanical properties. Weld center in EB welding resulted a cast structure consists of dendritic structure with ferrite network in a matrix of un-tempered martensite. In friction welding, the weld center exhibited thermo-mechanical effected structure consists of fine intragranular acicular martensite in equiaxed prior austenite grains. In both the welding processes, post weld tempering treatment resulted in coarsening of the martensite which increases with increase in tempering temperature. In the as-weld condition, welds exhibited high strength and hardness and poor impact toughness. Increase in impact toughness and decrease in strength and hardness is observed with an increase in tempering temperature. The hardness of EB welds increased with increase in the austenitizing temperature up to 1100 °C and a marginal decrease thereafter was observed. Double austenitization after double tempering resulted in optical mechanical properties i.e., strength, hardness and toughness.

Toughening plastics by crack growth inhibition through unidirectionally deformed soft inclusions

We demonstrate that without changing the filler content mechanical properties of commodity plastics with immiscible soft inclusions can be decisively enhanced, simply by pressure induced flow processing in the solid state. As an example, we have chosen acrylonitrile-butadiene-styrene (ABS), where shape and orientation of the soft fillers were changed by processing, resulting in an array of aligned and oriented nanosize deformed rubber domains. These deformed domains effectively controlled the propagation of cracks inside the solid matrix and were responsible for a multifold increase of tensile and impact toughness. Thus, appropriate processing allows manufacturing plastics with high impact resistance in accordance with engineering needs.

Efeito da temperatura interpasse na microestrutura, tenacidade ao impacto e propagação de trinca por fadiga de uniões soldadas por GTAW do aço ASTM A743-CA6NM

Atualmente os aços inoxidáveis martensíticos tem sido utilizados para a fabricação de turbinas hidráulicas, devido principalmente a sua elevada tenacidade. Entretanto, estes aços apresentam algumas restrições com relação à regiões recuperadas por soldagem, principalmente em razão da formação de martensita não revenida, a qual gera redução na tenacidade. Considerando as aplicações de reparo de turbinas hidráulicas, há grande interesse em desenvolver procedimentos de soldagem que elevem a tenacidade ao impacto e evitem os tratamentos térmicos pós-soldagem (TTPS). O presente trabalho busca analisar a influência da temperatura de interpasse na microestrutura, tenacidade ao impacto e propagação de trincas por fadiga nas uniões soldadas multipasse do aço inoxidável martensitico CA6NM usando AWS410NiMo como metal de adição, e processo TIG (tungsten inert gas). Observou-se a influência da temperatura de interpasse na formação de ferrita d, com formação intergranular no campo bifásico δ+γ, na amostra com temperatura interpasse de 80ºC, enquanto que na amostra soldada a 150ºC a formação de ferrita d ocorreu principalmente no campo monofásico. A alteração na formação da ferrita d, com a menor temperatura, promoveu um aumento na tenacidade ao impacto e uma diminuição na velocidade de propagação de trinca, quando comparada com a amostra soldada com maior temperatura de soldagem. Os resultados obtidos indicam que o processo TIG apresenta-se como uma excelente alternativa para o reparo do aço CA6NM, observando-se também uma influência significativa da temperatura de interpasse.

Effect of equal channel angular pressing on microstructural and mechanical properties of as cast Al–20 wt-%Zn alloy

The microstructural and mechanical properties, mainly the hardness, tensile properties and impact toughness of two phase Al–20 wt-%Zn alloy subjected to severe plastic deformation via equal channel angular pressing (ECAP) up to two passes, were studied. High cycle fatigue behaviour of ECAP processed alloy was investigated for the first time. The ECAP almost completely eliminated the as cast dendritic microstructure including casting defects such as microporosities and formed a refined microstructure consisting of elongated microconstituents, aluminium rich α and zinc rich α+η eutectoid phases. As a result of this microstructural change, the tensile response, impact toughness and fatigue performance of the alloy improved significantly. The rates of increase in endurance limit and impact toughness after ECAP are 89 and 122% respectively. In addition, a relationship represented by an equation between the stress amplitude σa and number of cycles to failure N values was determined to express the fatigue behaviour of the alloy in all states. It was also observed that the nature of fatigue fracture characteristics of the as cast Al–20 wt-%Zn alloy changed after ECAP.

Dynamic compressive behavior of ceramic fiber reinforced concrete under impact load

Dynamic properties of ceramic fiber reinforced concrete (CRFRC) are investigated using a 100-mm-diameter split Hopkinson pressure bar (SHPB) system. Different ways of choosing strain rate were adopted to express the strain rate effects on dynamic compressive stress, elastic modulus and impact toughness of CRFRC. The results show that the dynamic compressive strength and impact toughness increase with strain rate, while the elastic modulus decrease with strain rate. The addition of ceramic fiber can significantly improve the dynamic strength and elastic modulus of concrete. 0.1% and 0.2% volume fraction of ceramic fiber improve the impact toughness at higher strain rate. And the optimum volume fraction of ceramic fiber is 0.2%. The dynamic damage model was established based on the improved parallel bar system (IPBS) model. The result reveals that the model can well describe the relation between stress and strain of CRFRC.