Decrease In Impact Energy Research Articles

Evaluation of Microstructural, Mechanical Properties and Corrosion Behavior of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel Exposed in a Dynamic Bimetallic Sodium Loop at 798 K (525 °C) for 16,000 Hours

Changes occurring in the chemical composition, microstructure, mechanical properties, and carburization behavior of type 316LN stainless steel and modified 9Cr-1Mo steel on exposure to flowing sodium at 798 K (525 °C) for 16,000 hours in a bimetallic loop are discussed in this article. Type 316LN stainless steel revealed a degraded layer of approximately 5 μm depth. No significant microstructural changes were observed in the case of modified 9Cr-1Mo steel exposed to sodium. The carburization depth in type 316LN stainless steel was approximately 100 μm and the surface carbon concentration was 0.374 wt pct. In the case of modified 9Cr-1Mo steel, the carbon concentration at the surface was approximately 3.50 wt pct and the depth of carburization was nearly 75 μm. The concentration of nickel and chromium decreased from the bulk to the surface of type 316LN stainless steel, leading to the formation of a ferrite layer. The concentration of these two elements reached the original matrix concentration at around 30 μm. Sodium-exposed material indicated an increase in yield strength by 10 pct and reduction in ductility by 34 pct vis-a-vis annealed material. No such changes in strength and ductility were observed in the case of modified 9Cr-1Mo steel. A decrease in impact energy was noticed for sodium-exposed type 316LN stainless steel and modified 9Cr-1Mo steel vis-a-vis as-received material.

Effect of Manganese Addition and Sintering Conditions on Mechanical Properties of Low Carbon 3Cr Prealloyed Steels

Mechanical properties, microstructure and fracture of Fe-3Cr-0.5Mo-xMn steels sintered laboratory at 1250°C and industrially at 1180°C, and of Fe-3Cr-0.3Mo-0.3V-xMn steels laboratory sintered at 1200°C are presented; all steels with 0.24% C. The highest tensile strength of 806 and 856 MPa attained the steels with 2% Mn based on Fe-3Cr-0.5Mo powder and of 929 MPa the Fe-3Cr-0.3Mo-0.3V-1.5Mn-0.24C steels. Linear increase of hardness and relatively linear decrease of impact energy in dependence on Mn addition was recorded. Tested steels exhibited lower heterogeneity of the microstructures. The fracture of steel containing vanadium with 2% Mn showed more metallic inclusions adversely affecting the strength properties.

Stainless Steels Sintered Form the Mixture of Prealloyed Stainless Steel and Alloying Element Powders

The aim of the presented paper is to describe the sintered duplex stainless steels manufactured in sinter-hardening process and their structural and mechanical properties. Duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed base powders by controlled addition of alloying elements powder. Prepared mixes were compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at temperature of 1240°C for 1h. After sintering different cooling cycles were applied: rapid cooling (6°C/s) using nitrogen under pressure and slow cooling (0.1°C/s) with furnace in argon atmosphere. Produced sintered duplex stainless steels were studied by scanning and optical microscopy and EDS chemical analysis of microstructure components as well as X-ray analysis. Mechanical properties were studied through tensile and three-point bending tests and Charpy impact test. It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Produced sintered duplex steels show good mechanical properties which depend on austenite/ferrite ratio in the microstructure and elements partitioning (Cr/Ni) between phases. The optimal mechanical properties were obtained for compositions based on ferritic 410L powder where the balanced distribution of α and γ is present and the tensile strength can reach value about 500MPa with 16% of elongation and impact energy about 120J. The precipitations of hard intermetallic σ-FeCr phase take place when sintering with slow cooling cycle what cause substantial decrease of plastic properties, including reduce of elongation to 7% and in particular decrease of impact energy to 68 J.

L x-ray production cross sections from 50-300 keV proton impact on selected 4d transition elements

L x-rays were measured from the impact on thick targets of protons in the 50-300 keV energy range. The derived L sub-shell cross sections were compared with the ECPSSR theory and with measurements by others. It was found that ECPSSR over-predicts the measurements as the impact energy decreases.

Pinning of size-selected Co clusters on highly ordered pyrolytic graphite

Deposition and implantation of size-selected Co+ 50±5 cluster ions on/in highly ordered pyrolytic graphite (HOPG) have been performed. Cobalt clusters were produced by laser ablation using the second harmonic (532 nm) of a Nd:YAG laser. They were deposited/implanted with energies of 250–4850 eV/cluster and examined using scanning tunneling microscopy (STM). For the highest energies the clusters created craters and wells with residual clusters at the bottom of the wells. Decrease of the impact energy led to formation of bumps whichconsist of damaged graphite areas mixed with fragmented cobalt clusters. Further decrease of the impact energy to 250–450 eV/cluster probably corresponds to the so-called pinning regime, when the impacting cluster creates defects in the surface layer and becomes bound to them. The transition from implantation to pinning with a decrease of impact energy was confirmed by etching experiments showing the depth of the damage introduced by the cluster collisions with HOPG.

Stress Corrosion Cracking Crack Growth Behavior of Type 316L Stainless Steel Weld Metals in Boiling Water Reactor Environments

Abstract Thermal aging and consequent embrittlement of materials are ongoing issues in cast and duplex stainless steels. Spinodal decomposition is largely responsible for the well-known “475°C” embrittlement that results in drastic reductions in ductility and toughness in cast materials. This process is also operative in welds in cast or wrought stainless steels where delta ferrite is present. While the embrittlement can occur after several hundred hours of aging at 475°C, it can also occur at lower temperatures where ductility reductions have been observed after tens of thousands of hours at 300°C. The effect of thermal aging on mechanical properties, including tensile, toughness, fatigue, and static crack growth, has been investigated at room temperature and in 288°C high-purity water simulating boiling water reactor (BWR) operating conditions. The measurements of tensile, microhardness, and Charpy-impact energy show an increase in strength and a decrease in impact energy after aging for up to 10,000 h ...

Effect of ageing on precipitation and impact energy of 2101 economical duplex stainless steel

The impact energy and microstructure of a thermally aged 2101 duplex stainless steel with composition of Fe–21.4Cr–1.2Ni–5.7Mn–0.23 N–0.31Mo were studied. The results showed that the room temperature impact energy of specimens decreased gradually with ageing temperature up to 700 °C and then increased with aging over 700 °C. The minimum value of impact energy was 37 J after 700 °C aging, which was only 34% of that for as-annealed specimens. For specimens aged at 700 °C, the room temperature impact energy decreased significantly after 3 min and was halved after 10 min. Fractographs showed that, with increasing aging time, the fracture morphology changed from fibrous fracture to transgranular and intragranular fracture. Scanning electron micrographs revealed that many precipitates were distributed along α/γ and α/α interfaces. The precipitates were extracted and confirmed by X-ray diffraction to be Cr 2N. Therefore, it can be concluded that precipitation of Cr 2N is the main reason for the decrease of impact energy in aged 2101 duplex stainless steel.

Off-shell continuum distorted wave theory for positronium formation from noble gas atoms

The formation of ground-state positronium in collisions of positrons on noble gas atoms is considered. We report results obtained by means of the eikonal final state–continuum distorted wave (EFS–CDW) approximation for which off-shell distortion effects were taken into account. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important as the impact energy decreases.

Continuum distorted wave theory for positronium formation reactions

The formation of ground-state positronium in collisions of positrons on hydrogen atoms is considered. In previous theoretical works, two-center distorted wave functions were employed to approximate either the initial or the final channel. Here we report results obtained by means of the eikonal final state-continuum distorted wave (EFS-CDW) approximation for which asymptotically correct distorted wave functions are used for both the initial and final states of the scattering system. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important in both channels as the impact energy decreases. This work also shows that the EFS-CDW model is suitable for capture process in the scattering system at unexpected low energies.

Effect of aging at 700 °C on precipitation and toughness of AISI 321 and AISI 347 austenitic stainless steel welds

A detailed knowledge of changes in microstructures and mechanical behaviour that occur in austenitic stainless steels with or without Nb/Ti-stabilized weld during heat treatment is of great interest, since the ductility and toughness of the material may change drastically after long aging times. Two kinds of materials, i.e. AISI 321 base and without Ti-stabilized weld steel and AISI 347 base with Nb-stabilized weld steel, were compared during aging at 700 °C up to 6000 h. Both materials present increased amount of precipitate and decreased impact energy as the aging time increases. The decreased extent of impact energy with aging is almost the same for both base materials. However, it presents differences for 347 and 321 weld samples. The latter shows a more drastic decrease of impact energy than the former due to the different amount of precipitates. 321 weld sample precipitates more numerously than 347 weld sample due to the absence of stabilized Ti/Nb on the former. Large amount of carbides is formed on 321 weld sample immediately after welding. The carbides are transformed to sigma phase, which is mainly responsible for the much more sigma phase precipitation compared with other samples, after high-temperature aging. The fractographs showed, in general, brittle fracture mode in 321 weld impact-fractured specimens after aging at 700 °C for 6000 h. However, other samples show ductile fracture mode in general. Several approaches should be employed to control sigma phase precipitation in weld material. These approaches include: decreasing content of ferrite and M 23C 6 carbide in weld and selecting Nb added weld wire during welding.

Collision mechanisms in one-electron capture by slow H and He-like ions of C, N and O in H andH2

Translational energy spectroscopy (TES) has been used to study state-selectiveone-electron capture by H and He-like ions of C, N and O in both H and H2within the range 250–900 eV amu−1.The main collision mechanisms leading to state-selective electron capture havebeen identified, their relative importance assessed and compared, where possible,with theoretical predictions and with any previous measurements basedon photon emission spectroscopy. For one-electron capture in H2,the relative importance of contributions from non-dissociative and dissociativecapture as well as from two-electron capture into autoionizing states isfound to be strikingly different for the cases considered. Our TESmeasurements in atomic hydrogen provide an important extension of previousmeasurements to energies below 1000 eV amu−1 andshow that, as the impact energy decreases, electron capture becomes more selective untilonly a single nproduct channel is significant. These product main channels are well described byreaction windows calculated using a Landau–Zener approach. However, the sameapproach applied to the more complex energy-change spectra observed in H2is found to be less successful.

Effects of aging on impact behaviour of different stainless steel weldments

Instrumented impact testing was used to investigate the effects of aging on the impact deformation and fracture of different weldments of an AISI type 316L stainless steel plate and a superduplex stainless steel plate. Aging at 800C of metal inert gas MIG and laser beam LB weldments of the 316L stainless steel plate produced a precipitation of sigma phase, which was more intense in the MIG weldments. Correspondingly, the MIG weldments showed a noticeable decrease in impact energy and in impact yield and maximum loads as the aging time was increased. The LB weldments, on the other hand, showed an initial decrease in absorbed energy followed by a noticeable increase, because of the appearance of delaminations during the fracture event. Aging at 900C of the parent metal and of LB and plasma arc PA weldments of the superduplex stainless steel plate produced a precipitation of sigma phase which was much more intense in the parent metal. Both the parent metal and the weldments showed a noticeable decrease in impact energy and in impact yield and maximum loads as the aging time was increased. These weldments were found to be more sensitive to the precipitation of sigma phase than the austenitic stainless steel weldments.

Impact fatigue of a polycarbonate/acrylonitrile‐butadiene‐styrene blend

AbstractThis study analyzes the impact properties of a polycarbonate/acrylanitrile‐butadiene‐styrene (PC/ABS) blend. The specimens were prepared under various injection molding conditions, including filling time, melting temperature, and mold temperature. Impact tests were performed with a Dynatup drop weight impact tester at different impact energies (10, 15, 20, 25 J). The fracture mechanism was examined with a scanning electron microscopy. The results indicated that the load‐time history of the PC/ABS blend has approximately a sinusoidal form in impact. The best injection molding conditions are a filling time of 12 s, a melting temperature of 260°C and a mold temperature of 80°C. In this case, the specimen shows the highest energy absorbed in single impact, together with the highest impact number in impact fatigue. The impact number and the accumulation energy seem to follow an exponential curve as the impact energy decreases. The PC/ABS blend material clearly exhibited ductile fracture with a continuous reduction in strength by viscoplastic deformation. The higher the impact number, the higher the accumulation energy. The accumulation energy of impact fatigue with impact energy 10 J is about 35–45 times greater than the energy absorbed in single impact. Tearing, shear fracture, and plastic deformation are the major fracture mechanisms of the PC/ABS blend matrix in single impact and repeated impact conditions.

FTIR and DSC study of HDPE structural changes and mechanical properties variation when exposed to weathering aging during Canadian winter

The aging of high-density polyethylene (HDPE) when exposed to drastic climatic conditions (Canadian winter, characterized by low temperature and abrupt temperature variations between the night and the day) was studied. The importance of degradation was determined by evaluating the microstructural changes in HDPE (i.e., oxidations, ramifications, and polymeric chain breaking) by means of FTIR spectrophotometry. The crystallinity variation in HDPE by FTIR and DSC was also studied. Both techniques led to coherent results: there was a loss of crystallinity due to weathering degradation. This crystallinity reduction produced a drastic decrease in impact energy. However, the other properties evaluated were not significantly affected. © 1996 John Wiley & Sons, Inc.

Tensile, flexural and impact properties of a thermoplastic matrix reinforced by glass fiber and glass bead hybrids

The tensile and flexural properties, together with the unnotched and notched impact strengths of acrylonitrile butadiene styrene (ABS), glass bead (GB) and glass fiber (GF) ternary composites have been studied. The tensile strengths of the hybrid composites were predicted, from a theory formulated in this study, by using the strengths of the ABS/GB and ABS/GF composites alone. The addition of even a small quantity of glass fiber to ABS or ABS/GB composites changes the mode of deformation from one which shows vacuole growth and crazing to brittle failure. Thus, the elongation at break, the area under the stress/strain curve and the impact energy decrease sharply with the introduction of glass fiber to ABS or ABS/GB composites.

Microstructural and Property Changes During Short-Term Ageing of Cast Austenitic Stainless Steels

ABSTRACTThe Charpy ν-notch impact properties at -196°C of casts of Type 316 austenitic stainless steel have been compared, after ageing at 650°C for time periods up to 90 minutes. The impact energy of all steels depends on ageing time; the degree of response to ageing depends on original delta ferrite content, which varied from −0.5% to 5.0% in the steels studied. For steels with delta ferrite content in the lower half of this range the impact energy, during ageing, initially decreases to a minimum, subsequently rises to a maximum and finally decreases. Steels with delta ferrite contents near 5% suffer a continuous decrease in impact energy as ageing time increases.Microstructural investigation reveals, during early stages of ageing, the rapid formation of sigma phase, at the ferrite-austenite interphase boundaries. Some delta concurrently transforms to new austenite. Microfractographs indicate a change in the nature of the fracture as ageing progresses. Initially, fractures have large dimples, but as ageing progresses, a finer dimpling appears and extends in area. These dimples contain fine particles, identified mainly as MnS. The variations in impact behaviour are explained on the basis of the structural changes observed.

On the effects of intercritical tempering on the impact energy of Fe-9Ni-0.1C

The effects of intercritical tempering on the impact energy of Fe-9Ni-0.1C have been investigated. The Charpy V-notch energy at all test temperatures between 77 and 300 K increased with increasing precipitated and retained austenite up to concentrations of austenite of ≈ 14% and then decreased. Evidence for a mechanically-induced austenite → martensite transformation in the plastic zone preceding the crack tip was obtained using Mössbauer effect scattering from the fracture surface. The contribution to the impact energy from this localized TRIP mechanism is shown to be negligible compared with the scavenging effect of the austenite, removing deleterious impurities from the martensite and increasing its toughness. The decrease in impact energy for austenite concentrations in excess of ≈ 14% is attributed to the development of a nearly continuous network of austenite in interlath and prior austenite boundaries. In the plastic zone ahead of the crack, this network is transformed into brittle, untempered martensite, providing a low energy path for the advancing crack.

Comparison of experimental and theoretical electron ejection cross sections in helium by proton impact from 5 to 100 keV

Absolute values of doubly differential cross sections are obtained for electron production in helium by 5- to 100-keV proton impact. The measured values along with earlier data at higher energies are compared with theoretical plane-wave Born-approximation functions obtained from a Hartree-Fock potential. Not only is good agreement obtained at high impact energies (above 300 keV), but fairly good agreement is found at low energies (below about 20 keV). For electrons ejected in the backward hemisphere, unexpectedly poor agreement is noted at intermediate energies where the measured cross sections dip to 50% of the calculated values in some cases. Singly differential cross sections integrated over all angles agree quite well with the theoretical calculations over all ranges of parameters studied. Singly differential cross sections integrated over all electron energies tend to be more isotropic in angle as the proton energy is decreased from 100 to 5 keV. Total cross sections for electron production are also obtained which compare reasonably well with those of Solov'ev et al. but which are higher than those of de Heer et al. It is shown that the contribution to the cross section by the mechanism of charge transfer to the continuum decreases as the impact energy decreases, contrary to the prediction of Salin's treatment.

Excitation of Ne, Ar, Kr and Xe by He + impact (0.3–10 keV)

Impact radiation from He + in Ne, Ar, Kr and Xe is studied in the wavelength region between 500 Å and 2000 Å. This work forms a continuation of the measurements between 3000 Å and 6000 Å, which have been published in a preceding article. There we have discussed the relatively strong production of spectral ion lines of the target atom, whose emission cross sections in many cases show a striking increase with decrease in impact energy. The deviation from the normal adiabatic behaviour in the lower energy range was explained by the effect of pseudo-crossing of the potential curves of the collision complexes before and after the reaction. In the present experiment the same behaviour is found for many ion spectral lines in the vacuum ultraviolet region. The experimental results indicate that the upper levels of these spectral lines are populated not only by the collision process, but for a large part via cascade from higher excited ion levels formed in the collision process. There is strong evidence that in the low-energy region (∼300eV) most of the electron capture processes go in combination with the formation of the excited ion states of the target atom, considered in this article. Further we find that the deviation from the normal adiabatic behaviour is not only confined to the emission of the ion spectral lines, but also occurs for atomic spectral lines of the target atom.

Excitation of Ne, Ar, Kr and Xe by He+ impact (0.3–35 KeV; 3000Å–6000Å)

Impact radiation resulting from collisions of He + with Ne, Ar, Kr and Xe for He + kinetic energies in the range 0.3–35 KeV is studied in the wavelength region between 3000 Å and 6000 Å. Particular attention is paid to the relatively strong production of ion lines of the target atom, whose emission cross sections in many cases show a remarkable increase with decrease in impact energy. These spectral lines are produced when the helium ion captures an electron from the target atom with a simultaneous excitation of the resultant ion. The unexpectedly high emission cross sections at low impact energies may be explained in terms of pseudocrossing of the two potential curves of the interacting atomic systems before and after the reaction. For comparison, some measurements have been taken with H + and H + 2, where the effect of pseudocrossing does not seem to be present. For He + incident on Ne, atomic lines are observed which also show an increase in intensity with decreasing impact energies. Similar lines for Ar, Kr and Xe could not be studied, because most of these lines are present above 6000 Å, outside the spectral range of the apparatus.