► An immersion test machine was developed for simulation of thermal fatigue testing. ► A thermal fatigue resistance of tool steel and welded maraging steel was tested. ► A FEM was developed for ...prediction of stresses and optimization of test specimen. ► A phenomenon of thermal cracking of die casting dies is explained in detail. ► Crack growth promoted by changes in chemical composition (oxidation) is explained.
The investigation of aluminium alloy die casting die failures was done with the emphasis on thermal cracks. The aim of the study was to prolog the in-service die life by cladding with maraging steels, which would be economically beneficial. A vast analysis of thermal fatigue cracks in aluminium alloy die casting is done. Immersion test apparatus was developed, which enables simulation of conditions during aluminium alloy die casting and enables controlled thermal fatigue testing of materials. Special specimens made of the AISI H13 tool steel were differently heat treated. On the edges of some specimens, the maraging steel is cladded using gas tungsten arc (GTA) welding. These samples are tested in as-welded and in optimally aged condition. After completion of a particular number of cycles, the specimen edge surfaces were examined visually. The specimens were then sectioned and examined with light and scanning electron microscopy (SEM). The energy-dispersive X-ray spectroscopy (EDS) mapping of areas around the cracks was done. The number and length of thermal fatigue cracks were statistically evaluated and a Vickers hardness profiles were measured. The results confirmed a good thermal fatigue resistance of the properly hardened H13 hot work tool steel. The surface cracks growth is accelerated by surface oxidation.
A paper describes the most popular alloys for power plant application as well as the most promising alloys for future application in that technology. The components in power plants operate in severe ...conditions (high temperatures and pressures) and they are expected reliable service for 30 years and more. The correct choice of the material is, thus, of a very importance. The paper describes the development as well as advantages and disadvantages of convenient ferritic/martensitic steels, ferritic/bainitic steels, austenitic stainless steels and the new alloys for the application at temperatures of 650°C and more.
The presented work studied the response of new generation armored steel plates PROTAC 500 to the ballistic testing with armored piercing bullets with a core of tungsten carbide, charge 7,62 mm, and ...interactions between the piercing bullets and the armored steel plate were also investigated. The most obvious and significant phenomena in penetrating of the piercing bullets Nammo AP8 in steel target PROTAC 500 are strain hardening of steels, the appearance of cracks and local failure, adiabatic shear bands (ASB) with related phase transformations, and melting as well as alloying at the border of the bullet / the steel plate.
The effect of 10% carbamide peroxide on human enamel subsurface layers was examined. Microhardness, microstructure, and mineral content were studied in such a manner that control and test side were ...located on the same tooth. Longitudinally sectioned samples were obtained from six teeth and Vickers microhardness of the enamel was measured. Enamel microstructure was analyzed using a scanning electron microscope and subjected to electron probe microanalysis for chemical analysis of calcium (Ca) and phosphorus (P). The concentration of Ca in the bleaching gel was measured spectrophotometrically and the concentration of P was measured photometrically. Results showed that a bleaching gel of 10% carbamide peroxide did not significantly affect the microhardness of the enamel. Scanning electron microscopic analysis showed local changes in enamel microstructure similar to those of initial caries. Electron probe microanalysis showed lowered concentrations of Ca and P; in addition the Ca:P ratio was lowered. There was some Ca and P in the bleaching gel after use. It is concluded that 10% carbamide peroxide causes local microstructural and chemical changes in enamel that are likely not clinically significant.
The occurrence and formation sequence of secondary ledeburite in the heat affected zone of chromium ledeburitic tool steel W.Nr. 1.2379 (OCR12 VM) after welding with SAW, TIG, microplasma and laser ...welding techniques is presented in this paper. Special attention was paid on the behaviour of carbides. The occurrence of secondary ledeburite is a result of local enrichment of the austenite matrix with alloying elements, due to partial or complete dissolution of primary/eutectic carbides. The results show that the largest amount of secondary ledeburite is formed during submerged arc welding, followed by TIG and microplasma welding technique. Welding by laser technique, with appropriate technological parameters, could prevent secondary ledeburite formation.
The aim of this study is the investigation of micro-structural behaviour of a Mat. No. 1.2379 (EN-X160CrMoV121; AISI D2) cold work tool steel after remelting with a precise pulsed Nd:YAG laser. The ...investigated steel is one of the most hard to weld tool steels, due to large amount of alloying elements. The analysis was done on single spots remelted with specific laser pulse shape and parameters, assuring crack-less solidification. Re-solidified areas were investigated with microscopy, hardness measurements, X-ray spectroscopy and diffraction method. Laser treatment causes rapid solidification leading into a formation of a fine dendritic microstructures containing high amount of retained austenite causing a significant decrease of hardness.
The electrospark deposition is a process for surfacing of hard metal alloys, e.g. carbides and stellites, on the surfaces of new or old machine elements. In this process, a high current is conducted ...through an oscillating electrode and a substrate for a very short period of time. In the paper, the process is described and the thickness of deposited layer, chemical composition, dilution rate and the layer roughness are determined.
The subject of investigation was the effect of post-weld heat treatment (PWHT) on mechanical properties, hardness distribution across the welded joints, and on the microstructure of AISI 316L ...austenitic stainless steel weld metal. Steel plates of 15 mm thickness were welded by manual electric arc welding and treated at 600-900'C. The tensile strength increased and impact energy values decreased with the increasing annealing temperature. The hardness test results for the weld metal, which were approximately equal before PWHT and after it, were higher than those for the base metal and the heat-affected zone. The weld metal microstructure was examined by means of an optical microscope and a scanning electron microscope. It demonstrated the presence of austenite, ferrite and microslag inclusions before PWHT, and that of sigma phase after PWHT. Also, the presence of complex Mn-Cr-Si-Ti inclusions in small holes was observed in tensile and impact (Charpy) tested specimens.
The reduction of area in the through thickness direction is an essential mechanical property of thick steel heavy plates. By a routine control, a very small through thickness reduction of area was ...found for tensile specimen of a 90 mm plate. Careful investigations of the fracture and section of specimens cut from the as solidified continuously cast 250 mm thick slab showed that the cause was the presence of coarse particles of niobium carboni-tride as constituent of the quasi eutectic Fe-Nb(C, N) that form because of the centerline segregation of niobium.
Molybdenum disulphide (MOS2) might be a useful addition in the production of composite self-lubricating high-speed steel parts, which are used in different anti-wear applications. MoS2 might also has ...a favourable influence on the synthesis of sintered high-speed steels (HSSs) improving the compressibility of the metal powder mixture during its cold compaction, as well as acting as a sinterability enhancer of powder compacts during their sintering. In view of this, the compressibility and the sinterability of M3/2 and M35 types of HSS powder mixtures with MoS2 additions were investigated. In this article, the influence of MoS2 additions on the densification during cold compaction and vacuum sintering of selected HSSs is presented. It has been established that the MoS2 promotes a consolidation of HSS powders during automatic die compaction, as well as final densification during sintering. Sintering of HSS-MoS2 powder mixtures proceeds by the combination of a reactive and supersolidus liquid-phase sintering process. The added MoS2 reacts with the steel matrix, enhancing densification. Fine dispersion of complex sulfides (Cr, V, Fe)S is formed, which improves the machinability and tribological properties of sintered steel.
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