Jan Ketil Solberg

Observations on shear plug formation in Weldox 460 E steel plates impacted by blunt-nosed projectiles

Shear plug formation in circular Weldox 460 E steel plates impacted by blunt-nosed cylindrical projectiles with striking velocities between 100 and 500 m/s has been investigated. Target thickness and projectile impact velocity were the primary variables, and for each target thickness the ballistic limit curve of the material was precisely determined. The test at an impact velocity just below the ballistic limit for each target thickness was selected for a microscopic examination of shear localisation and fracture. In these tests, the plug was pushed only partway through the target, and the localised shear zones outlining the fracture were easily recognised both in the optical and scanning electron microscope. Clear evidence of adiabatic shear bands and material damage due to void growth was found in several of the target plates. Analytical models available in the literature were compared with the results from the experimental and microscopic studies. Reasonable agreement was found between calculations and experiments. 2001 Elsevier Science Ltd. All rights reserved.

Cleavage Fracture Initiation at M–A Constituents in Intercritically Coarse-Grained Heat-Affected Zone of a HSLA Steel

Local brittle zones, i.e., martensite–austenite (M–A) islands, are formed within the coarse-grained heat-affected zone (CGHAZ) and the intercritically reheated CGHAZ (ICCGHAZ) during welding of many HSLA steels. In the current study, the M–A constituents in the microstructure of simulated ICCGHAZ of an API X80 pipeline steel were investigated using transmission electron microscopy and scanning electron microscopy. The focused ion beam technique was applied to make TEM specimens of M–A constituents that were located in the initiation sites of cleavage cracks. The main purpose of the study was to identify crack-initiation sites of cleavage fracture in ICCGHAZ and to prove the presence of M–A constituents in such initiation sites. Twinned martensite was detected in all local brittle zones that were investigated in the current study, demonstrating that they are M–A constituents. It was also demonstrated that the fracture initiation occurred preferentially at M–A constituents by a debonding mechanism rather than cracking of the M–A constituents.

Formation of precipitates and recrystallization resistance in Al–Sc–Zr alloys

Al-x%Sc-0.11%Zr alloys (x=0, 0.02, 0.05, 0.08, 0.11, 0.15) were produced by a chill cast procedure. The effect of Sc content on the precipitation of Al3(Sc,Zr) during heat treatment at 475 °C for 12 h was studied. Nucleation, precipitation and distribution of Al3(Sc,Zr) precipitates were found to be strongly related to the Sc content. With increasing the Sc content, the average radius of the precipitates decreases, while the number density of the precipitates increases, as investigated by transmission electron microscopy (TEM). The distribution of the precipitates becomes more and more homogeneous when the Sc content is increased. The recrystallization resistance of samples that was 90% cold rolled and isothermal annealed for half an hour in the temperature range of 200-600 °C was investigated. The results show that the recrystallization temperature varies from 250 °C for the alloy without Sc to about 600 °C for the alloy containing 0.15% Sc because of the high density of Al3(Sc,Zr) precipitates.

The Effect of PWHT on the Material Properties and Micro Structure in Inconel 625 and Inconel 725 Buttered Joints

This report describes investigations performed on as welded and post weld heat treated samples of AISI 8630 steel, buttered with Inconel 625 and Inconel 725. The investigations have focused on the properties and microstructure in the partial mixed zone between the buttering and the steel before and after post weld heat treatment. The samples were heat treated for 4 1/2 hours at 640°C, 665° and 690°C and investigated with respect to mechanical properties and microstructure near the fusion line. A range of testing and analyses were performed including notch impact toughness testing, identification of fracture initiation and propagation in impact specimens, hydrogen measurements, examination of the micro structure in steel and Inconel using light microscope, hardness testing and electron micro-probe analysis of the alloying elements across the fusion line. Additional investigations in TEM on samples from an actual joint, post weld heat treated at 665°C were also performed. The results show that post weld heat treatment at 665°C and 690°C reduced the impact toughness in coarse grained heat affected zone, caused by decarburisation, ferrite formation and grain growth. The partially mixed zone (5–10μm) of the Inconel buttering, gained partly extremely high hardness caused by carbon enrichment, reaustenitization and formation of virgin martensite. As welded samples gave more favorable properties and microstructure than the post weld heat treated ones.Copyright

Application of combined EBSD and 3D-SEM technique on crystallographic facet analysis of steel at low temperature

Electron backscatter diffraction has been increasingly used to identify the crystallographic planes and orientation of cleavage facets with respect to the rolling direction in fracture surfaces. The crystallographic indices of cleavage planes can be determined either directly from the fracture surface or indirectly from metallographic sections perpendicular to the plane of the fracture surface. A combination of electron backscatter diffraction and 3D scanning electron microscopy imaging technique has been modified to determine crystallographic facet orientations. The main purpose of this work has been to identify the macroscopic crystallographic orientations of cleavage facets in the fracture surfaces of weld heat affected zones in a well‐known steel fractured at low temperatures. The material used for the work was an American Petroleum Institute (API) X80 grade steel developed for applications at low temperatures, and typical heat affected zone microstructures were obtained by carrying out weld thermal simulation. The fracture toughness was measured at different temperatures (0°C, −30°C, −60°C and −90°C) by using Crack Tip Opening Displacement testing. Fracture surfaces and changes in microstructure were analyzed by scanning electron microscopy and light microscopy. Crystallographic orientations were identified by electron backscatter diffraction, indirectly from a polished section perpendicular to the major fracture surface of the samples. Computer assisted 3D imaging was used to measure the angles between the cleavage facets and the adjacent polished surface, and then these angles were combined with electron backscatter diffraction measurements to determine the macroscopic crystallographic planes of the facets. The crystallographic indices of the macroscopic cleavage facet planes were identified to be {100}, {110}, {211} and {310} at all temperatures.

Effect of Magnesium on Segregation of Trace Element Lead and Anodic Activation in Aluminum Alloys

Anodic activation of aluminum alloys in chloride solution, as a result of segregation of the trace element Pb by heat-treatment, has recently been investigated extensively on commercial and model binary alloys. Certain commercial alloys are activated by heat-treatment at temperatures as low as 350°C, whereas others have to be heated to significantly higher temperatures (600°C) to obtain a similar effect. Activation by annealing at low temperature has often been attributed to the presence of the alloying element Mg. This work investigates the effect of Mg on the segregation of Pb in a ternary Al-Mg-Pb model alloy by use of electron-optical and electrochemical characterization. The presence of Mg in the alloy-enhanced Pb segregation to the surface at 450°C, which in turn resulted in a more activated surface in relation to the binary Al-Pb alloy. Magnesium segregated to the surface was oxidized as spinel MgAl 2 O 4 . By annealing at 600°C, both alloys exhibited increased activation since Pb segregated as both metallic particles and a continuous nanofilm at the oxide-metal interface. However, the Al-Pb alloy became more active than the Al-Mg-Pb alloy. This was attributed to the passivating effect of the spinel on alloy Al-Mg-Pb.

Wear of Inconel 718 die during aluminium extrusion—a case study

Abstract The wear analysis of an aluminium extrusion die made of Inconel 718 alloy has been performed. The highest degree of wear was observed in the middle of the contact surface with no or little wear in the adjoining regions. The wear mechanism was similar to that for steel dies and consisted in adhesive and abrasive modes. Strong adhesion of aluminium to the die led to the formation of Ni–Al–Si–Mo–Ti–Cr–Fe–Zn–O compounds that, along with aluminium oxides, acted abrasively and resulted in considerable material removal after 40 extrusion cycles.

Microstructural evolution of melt-spun Mg-10Ni-2Mm hydrogen storage alloy

The microstructural evolution of a Mg-10Ni-2Mm (molar fraction, %) (Mm=Ce, La-rich mischmetal) hydrogen storage alloys applied with various solidification rates was studied. The results show that the grain size of melt-spun ribbon is remarkably reduced by increasing the solidification rate. The microcrystalline, nanocrystalline and amorphous microstructures are obtained by applying the surface velocities of the graphite wheel of 3.1, 10.5 and 20.9 m/s, respectively. By applying the surface velocity of the graphite wheel of 3.1 m/s, the melt-spun specimen obtains full crystalline with a considerable amount of coarse microcrystalline Mg and Mg2Ni except for some Mm-rich particles. The amount of nanocrystalline phases significantly increases with increasing the surface velocity of the wheel to 10.5 m/s, and the microstructure is composed of a large amount of nanocrystalline phases of Mg and Mg2Ni particles. A mixed microstructure containing amorphous and nanocrystalline phases is obtained at a surface velocity of the wheel of 20.9 m/s. The optimal microstructure with a considerable amount of nanocrystalline Mg and Mg2Ni in an amorphous matrix is expected to have the maximum hydrogen absorption capacity and excellent hydrogenation kinetics.

Measurement of austenite-to-ferrite transformation temperature after multi-pass deformation of steels

Abstract The austenite-to-ferrite transformation temperature (Ar3) under multi-pass deformation has been studied using the continuous hot torsion testing method by monitoring the variation in the stress with temperature during the cooling period. The experimental results show that the effect of deformation on the Ar3 temperature decreases rapidly with decreasing cooling rate. This may be due to static recovery taking place within the deformed austenite during the cooling period, effectively reducing the nucleation of ferrite.

Nanostructured Metal Hydrides for Hydrogen Storage Studied by In Situ Synchrotron and Neutron Diffraction

This work was focused on studies of the metal hydride materials having a potential in building hydrogen storage systems with high gravimetric and volumetric efficiencies of H storage and formed / decomposed with high rates of hydrogen exchange. In situ diffraction studies of the metal-hydrogen systems were explored as a valuable tool in probing both the mechanism of the phase-structural transformations and their kinetics. Two complementary techniques, namely Neutron Powder Diffraction (NPD) and Synchrotron X-ray diffraction (SR XRD) were utilised. High pressure in situ NPD studies were performed at D 2 pressures reaching 1000 bar at the D1B diffractometer accommodated at Institute Laue Langevin, Grenoble. The data of the time resolved in situ SR XRD were collected at the Swiss Norwegian Beam Lines, ESRF, Grenoble in the pressure range up to 50 bar H 2 at temperatures 20-400°C. The systems studied by NPD at high pressures included deuterated Al-modified Laves-type C15 ZrFe 2-x Al x intermetallics with x = 0.02; 0.04 and 0.20 and the CeNi 5 -D 2 system. D content, hysteresis of H uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content. Deuteration exhibited a very fast kinetics; it resulted in increase of the unit cells volumes reaching 23.5 % for ZrFe 1.98 Al 0.02 D 2.9(1) and associated with exclusive occupancy of the Zr 2 (Fe,Al) 2 tetrahedra. For CeNi 5 deuteration yielded a hexahydride CeNi 5 D 6.2 (20°C, 776 bar D 2 ) and was accompanied by a nearly isotropic volume expansion reaching 30.1% (∆a/a=10.0%; ∆c/c=7.5%). Deuterium atoms fill three different interstitial sites including Ce 2 Ni 2 , Ce 2 Ni 3 and Ni 4 . Significant hysteresis was observed on the first absorption-desorption cycle. This hysteresis decreased on the absorption-desorption cycling. A different approach to the development of H storage systems is based on the hydrides of light elements, first of all the Mg-based ones. These systems were studied by SR XRD. Reactive ball milling in hydrogen (HRBM) allowed synthesis of the nanostructured Mg-based hydrides. The experimental parameters (P H2 , T, energy of milling, ball / sample ratio and balls size), significantly influence rate of hydrogenation. The studies confirmed (a) a completeness of hydrogenation of Mg into MgH 2 ; (b) indicated a partial transformation of the originally formed -MgH 2 into a metastable -MgH 2 (a ratio / was 3/1); (c) yielded the crystallite size for the main hydrogenation product, -MgH 2 , as close to 10 nm. Influence of the additives to Mg on the structure and hydrogen absorption/desorption properties and cycle behaviour of the composites was established and will be discussed in the paper.