Showing papers on "Charpy impact test published in 1998"

Fracture resistance of unfilled and calcite-particle-filled ABS composites reinforced by short glass fibers (SGF) under impact load

Abstract: Acrylonitrile-butadiene-styrene (ABS) terpolymer, unfilled and filled with calcium carbonate (calcite) particles, was used as a matrix for reinforcement with short glass fibers (SGF). All of the materials were prepared by injection molding and the fibers in the specimens were oriented preferentially in the flow direction (i.e. the axial direction of the specimens). The composites were studied with respect to the work of fracture (WOF), here the notched Charpy impact energy, determined by the Charpy V-notch impact test. The fracture surfaces of the composites were studied by scanning electron microscopy. The total WOF theory for short-fiber-reinforced composites was used to evaluate the interface energy and the matrix fracture work, whereby the fiber fracture work was neglected because of the brittleness of glass fibers, only a small amount of broken fibers being observed experimentally. It was shown that the interface energy is much higher than the matrix fracture work in the presence of fibers. The results showed that the reduction in WOF caused by adding SGF to pure ABS resin matrix is the consequence of a significant reduction in the matrix fracture work; on the other hand, the incorporation of SGF into calcite-filled ABS resulted to some extent in an increase in the WOF, this is being due to the relatively large interface energy contribution to the WOF of the composite. Moreover, it was observed experimentally that the treated case showed a higher WOF for SGF/ABS composites than for the as-received case, whereas this was not observed for hybrid SGF/calcite/ABS composites. This behavior was explained in terms of the changes in fiber length distribution by using the total WOF theory and the fiber pull-out energy theory. Furthermore, it was pointed out that when investigating the influence of the fiber/matrix interface on the WOF of short-fiber composites, the fiber length distribution must be taken into consideration.

Ultra-high strength, weldable steels with excellent ultra-low temperature toughness

Abstract: A steel plate having a tensile strength of at least about 930 MPa (135Ksi), a toughness as measured by Charpy V-notch impact test at -40 °C (-40 °F) of at least about 120 joules (88 ft-lb), and a microstructure comprising at least about 90 volume percent of a mixture of fine-grained lower bainite and fine-grained lath martensite, wherein at least about 2/3 of said mixture consists of fine-grained lower bainite transformed from unrecrystallized austenite having an average grain size of less than about 10 microns and comprising iron and specified weight percentages of the additives: carbon, silicon, manganese, copper, nickel, niobium, titanium, aluminum, calcium, Rare Earth Metals, and magnesium, is prepared by heating a steel slab to a suitable temperature; reducing the slab to form plate in one or more hot rolling passes (10) in a first temperature range in which austenite recrystallizes; further reducing said plate in one or more hot rolling passes (10) in a second temperature range in which austenite does not recrystallize, quenching (12) said plate to a suitable Quench Stop Temperature (16); and stopping said quenching and allowing said plate to air cool (18) to ambient temperature.

Effect of direct quenching on microstructure and mechanical properties of copper-bearing high-strength alloy steels

Abstract: This study aims to investigate the effects of direct quenching on microstructural modification and mechanical properties of copper-bearing high-strength alloy steels. Two direct quenched and tempered (DQ&T) steel plates were rolled at different finish rolling temperatures, and their microstructures and mechanical properties were compared with those of a reheat quenched and tempered (RQ&T) steel plate. The as-quenched microstructure of the DQ plates consisted of refined lath martensite with high density of dislocations, which acted as preferred precipitation sites for NbC or e -Cu particles during tempering. These fine precipitates were not coarsened much up to the tempering temperature of about 650°C, and thus played a role in improving the tempering resistance. Especially in the DQ&T plate quenched at 760°C and tempered at 660°C, yield strength reached 1050 MPa, and Charpy impact energy at −18°C showed 140 J, indicating the potent effect of the DQ&T process. These findings indicated that the copper addition and the application of the DQ&T process to low-carbon alloy steels contributed to the production of steel plates with excellent strength and toughness.

Steel material having high ductility and high strength and process for production thereof

Abstract: A process for the production of a steel material comprising rolling a steel material having a structure mainly comprising ferrite or ferrite plus pearlite or ferrite plus cementite at a percentage reduction of area of at least 20 % in a ferrite recrystallization temperature region to achieve such characteristics as a crystal particle diameter of not greater than 3 νm, preferably not greater than 1 νm, an elongation of at least 20 %, a value of tensile strength (TS: MPa) x elongation (El: %) of at least 10,000 or a percent ductile fracture of at least 95 %, preferably 100 %, in an actual pipe Charpy impact test at -100 °C. Particularly, this process yields a steel material containing 0.05 to 0.30 wt.% of C, 0.01 to 3.0 wt.% of Si, 0.01 to 2.0 wt.% of Mn and 0.001 to 0.10 wt.% of Al and having a structure comprising ferrite alone or ferrite and a second phase, wherein the ferrite particle diameter is not greater than 3 νm and the areal ratio of the second phase is not greater than 30 %. An untreated steel pipe having the composition described above is heated to (Acl + 50 °C) to 400 °C and subjected to stretch reduction at a cumulative diameter reduction ratio of at least 20 % in a rolling temperature range of (Acl + 50 °C) to 400 °C. In this case, the rolling process preferably contains at least one rolling pass having a diameter reduction ratio of at least 6 % in the stretch reduction. When the contents of C, Si, Mn and other alloy elements are kept at low levels and stretch reduction is carried out in the temperature range described above, a steel pipe having high ductility and strength and improved toughness and stress corrosion crack resistance can be manufactured and the resulting pipe can be used as a line pipe. The fatigue resistance can be improved, too.

Method for producing ultra-high strength, weldable steels with superior toughness

Abstract: A method is provided for producing an ultra-high strength steel having a tensile strength of at least about 900 MPa (130 Ksi), a toughness as measured by Charpy V-notch impact test at -40 °C (-40 °F) of at least about 120 joules (90 ft-lbs), and a microstructure comprising predominantly fine-grained lower bainite, fine-grained lath martensite, or mixtures thereof, transformed from substantially unrecrystallized austenite grains and comprising iron and specified weight percentages of the additives: carbon, silicon, manganese, copper, nickel, niobium, vanadium, molybdenum, chromium, titanium, aluminium, calcium, Rare Earth Metals, and magnesium A steel slab is heated to a suitable temperature; the slab is reduced to form plate in one or more hot rolling passes in a first temperature range in which austenite recrystallizes; said plate is further reduced in one or more hot rolling passes (10) in a second temperature range below said first temperature range and above the temperature at which austenite begins to transform to ferrite during cooling; said plate is quenched (12) to a suitable Quench Stop Temperature (16); and said quenching is stopped and said plate is allowed to air cool (18) to ambient temperature

Impact Strength of Fiber Pre-Stressed Composites:

Abstract: By applying the appropriate tension to the fibers during the curing process, the impact strength of glass-epoxy composites is improved up to 33%. Charpy tests show that the increase of the fiber pr...

Mechanical Properties of Zr-Ti-Al-Ni-Cu Bulk Amorphous Sheets Prepared by Squeeze Casting

Abstract: Tensile fracture strength (σ f ) and Vickers hardness (H Y ) of Zr-Al-Ni-Cu amorphous sheets with a thickness of 2.5 mm prepared by squeeze casting were found to increase by the addition of 2.5-5 at%Ti and the increase of Al content to 12.5-15 at%. The σ f and H v of the amorphous alloy sheets with the new compositions are 1800 to 1850 MPa and 500 to 520, respectively, which are higher than those (σ f =1650 to 1790 MPa and H v =470 to 480) for the Zr-10%Al-Ni-Cu amorphous cylinders prepared by copper mold casting. The Young's modulus, elastic elongation and Charpy impact fracture energy are 86 to 92 GPa, 2.0 to 2.2% and 90 to 160 kJ/m 2 , respectively. The highest value of the three point-bending flexural strength is 3900 MPa for Zr 55 Al 15 Ni 10 Cu 20 . The high impact fracture energy indicates that the cast amorphous alloy sheets have good ductility. Furthermore, the improvement of σ f and H v by the simultaneous addition of Ti and Al is presumably due to the increase of the bonding force of the constituent elements resulting from the increase of Zr-Al and Ti-Al pairs with larger negative heats of mixing. The synthesis of the high Al concentration Zr-Al-Ni-Cu and Zr-Ti-Al-Ni-Cu amorphous alloys with higher mechanical strength, higher impact fracture energy and lower density is important for the future progress of high-strength bulk amorphous alloys because the Zr-Al-Ni-Cu amorphous alloys with the 10 at% Al concentration have already been used as new engineering materials.

Ultra-high strength, weldable, boron-containing steels with superior toughness

Abstract: An ultra-high strength boron-containing steel having a tensile strength of at least about 900 MPa (130 Ksi), a toughness as measured by Charpy V-notch impact test at -40 °F of at least 120 joules (90 ft-lbs), and a microstructure comprising predominantly fine-grained lower bainite, fine-grained lath martensite, or mixtures thereof, transformed from substantially unrecrystallized austenite grains and is prepared by heating a steel slab to a suitable temperature; reducing the slab to form plate in one or more hot rolling passes in a first temperature range in which austenite recrystallizes; further reducing said plate in one or more hot rolling passes in a second temperature range below said first temperature range and above the temperature at which austenite begins to transform to ferrite during cooling (10); quenching (12) said plate to a suitable Quench Stop Temperature (16); and stopping said quenching and allowing said plate to air cool (18) to ambient temperature.

Ultra-high strength, weldable, essentially boron-free steels wit h superior toughness

Abstract: An ultra-high strength essentially boron-free steel having a tensile strength of at least about 900 MPa (130 Ksi), a toughness as measured by Charpy V-notch impact test at -40 °C (-40 °F) of at least about 120 joules (90ft-lbs), and a microstructure comprising predominantly fine-grained lower bainite, fine-grained lath martensite, or mixtures thereof, transformed from substantially unrecrystallized austenite grains and comprising iron and specified weight percentages of the additives: carbon, silicon, manganese, copper, nickel, niobium, vanadium, molybdenum, chromium, titanium, aluminum, calcium, Rare Earth Metals, and magnesium, is prepared by heating a steel slab to a suitable temperature; reducing the slab to form plate in one or more hot rolling (10) passes in a first temperature range in which austenite recrystallizes; further reducing said plate in one or more hot rolling (10) passes in a second temperature range below said first temperature range and above the temperature at which austenite begins to transform to ferrite during cooling; quenching (12) said plate to a suitable Quench Stop Temperature (16); and stopping said quenching and allowing said plate to air cool (18) to ambient temperature.

Relationship Between Apparent (Total) Charpy Vee-Notch Toughness and the Corresponding Dynamic Crack-Propagation Resistance

Abstract: The consequences of a dynamic fracture in a gas-transmission pipeline require that pipelines be designed to avoid such incidents at a high level of certainty. For this reason, the related phenomonology has been studied since the early 1970s when the possibility of a dynamic ductile fracture was recognized. Full-scale experiments were done to characterize the fracture and gas dynamics associated with this process and empirical models were developed as a means to represent these experiments in a design or analysis setting. Such experiments focused on pure methane gas, and in the early days used steels with toughnesses less than 100 J, consistent with the steel making capabilities of the 1970s. Subsequently, interest shifted to larger diameter, higher pressure, higher BTU “rich” gases requiring higher toughness steels. The full-scale tests conducted to validate the arrest toughness levels determined that these empirical models were non-conservative.This paper presents a relationship between the dynamic crack propagation resistance and the apparent crack propagation resistance as measured by Charpy vee-notch (CVN) test specimens. This relationship is used in conjunction with the existing Battelle empirical criterion for dynamic-fracture arrest to determine the apparent toughness required to arrest a propagating ductile fracture in gas-transmission pipelines. The validity of this relationship is illustrated by successful predictions of arrest toughness in pipelines under a range of conditions including rich gases and high-toughness steels, including those showing a rising upper-shelf behavior.Copyright © 1998 by ASME

Statistical modelling of intergranular brittle fracture in a low alloy steel

Abstract: The intergranular brittle fracture (IBF) behaviour of a low alloy steel 16MND5 (A508 Cl. 3) was investigated. A temper embrittlement heat treatment was applied to the material to simulate the effect of local brittle zones (ghost lines) which can be found in the as-received material condition. An increase in the Charpy V toughness transition temperature and a significant decrease in the fracture toughness measured on CT-type specimens were observed in the embrittled material, as compared to the reference material which was submitted to the same austenitizing and tempering heat treatment, but which was not subjected to the temper embrittlement treatment. Tensile tests on notched specimens were carried out to measure the Weibull stress and scatter in the results. A statistical model, the Beremin model, originally proposed for brittle cleavage fracture was applied to IBF. It is shown that this model is not able to fully account for the results, in particular for the existence of two slopes in a Weibull plot. Systematic fractographic observations showed that the low slope regime in this representation was associated with the existence of MnS inclusions initiating brittle fracture, while the larger slope was related to microstructural defects. Initiation of IBF from MnS inclusions can occur when the material is still elastically deformed while the second population of microstructural defects is active in the plastic regime. A modified statistical model based on the Beremin model and taking into account these specific aspects is proposed in the framework of the weakest link theory. The parameters of this model are identified from test results on notched specimens. It is shown that this model is able to predict the temperature dependence of fracture toughness and the scatter in the experimental results.

Small Punch Tests on Steels for Steam Power Plant ( I ) - Ductile-Brittle Transition Temperature -

Abstract: Conventional test methods for measuring fracture toughness require the removal of large material samples from in-service component. However, recent developments of small punch test technique using miniature specimens have proved its usefulness and accuracy to evaluate the mechanical properties of components. Correlations have been obtained between mechanical characteristics determined from small punch test and uniaxial tensile test. Furthermore, the study showed that an appropriate empirical based-approach could be used to evaluate the Charpy-FATT of as-received and ex-service materials from small punch test.

Charpy V-notch properties and microstructures of narrow gap ferritic welds of a quenched and tempered steel plate

Abstract: Multipass welds of quenched and tempered 50-mm-thick steel plate have been deposited by a single wire narrow gap process using both gas metal arc welding (GMAW) and submerged arc welding (SAW). Of the five welds, two reported much lower Charpy V-notch (CVN) values when tested at −20 °C. The CVN toughness did not correlate with either the welding process or whether the power source was pulsed or nonpulsed. The only difference in the ferritic microstructure between the two welds of low Charpy values and the three of high values was the percentage of acicular ferrite. There was no effect of the percentage of as-deposited reheated zones intersected by the Charpy notch or the microhardness of the intercellular-dendritic regions. In all welds, austenite was the microconstituent between the ferrite laths. The percentage of acicular ferrite correlated with the presence of MnO, TiO2, γ Al2O3, or MnO. Al2O3 as the predominant crystalline compound in the oxide inclusions. In turn, the crystalline compound depended on the aluminum-to-titanium ratio in both the weld deposits and the oxide inclusions. In addition to the presence of less acicular ferrite, the two welds that showed lower Charpy values also reported more oxide inclusions greater than 1 µm in diameter. The combination of more oxide inclusions greater than 1 µm and less acicular ferrite is considered to be the explanation for the lower Charpy values.

The effect of segregation on the austemper transformation and toughness of ductile irons

Abstract: The effect of segregation of alloying elements on the phase transformation of ductile iron during austempering was investigated. Four heats, each containing 0.4%Mn, 1% Cu, 1.5% Ni, or 0.4% Mo (wt%) separately, were melted; then three different sizes of casting bars (3,15, and 75 mm diameter) were poured from each heat. The distribution and the degree of segregation of certain elements were quantitatively analyzed using an electron microprobe. A personal computer (PC)-controlled heat treating system was used to measure electrical resistivity, and the information on resistivity variations was used to analyze the effect of segregation on phase transformations during austempering. Also, Charpy impact and Rockwell hardness tests were performed to determine the effect of segregation on properties.

Carburisation of nickel‐base alloys and its effects on the mechanical properties

Abstract: The effect of carburisation on the ductility in terms of Charpy V-notch impact energy of five nickel-base alloys (alloy 45-TM, alloy 600H, alloy 617, alloy 601 and alloy 602CA) and three iron-nickel-chromium alloys (alloy 800H, alloy AC66, alloy DS) with different concentrations of aluminium, chromium and silicon was investigated in CH 4 - H 2 at a carbon activity of a c = 0.8 at 850°C and 1000°C. All chromia-forming materials suffer carbon pick-up, formation of internal carbides and a severe loss of ductility during exposure. The loss of Charpy V-notch impact energy after exposure is directly correlated to the carbon pick-up. The susceptibility to carburisation increases with increasing iron concentration and decreasing nickel concentration of the alloy. Silicon was found to decrease the carbon pick-up and the loss of ductility. Alumina-forming alloys do not suffer any significant ductility loss by carburisation.