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[en] The hardness reference slabs used for the calibration of Rockwell hardness testing devices will deform by buckling due to increasingly deep marks left on the slab surfaces during the hardness tests, the buckling becoming more significant with lower degrees of hardness and highly dense structure of testing patterns. The article presented here illustrates the results of a study using a modified, computer-automated hardness testing device with high-precision penetration depth measurement using a LASER interferometer, showing that the effect of buckling on the hardness data to be measured may not be neglected. (orig.)
[de]Die zur Kalibrierung von Rockwell-Haertepruefgeraeten als Pruefnormal verwandten Haertevergleichsplatten unterliegen bei zunehmender Eindrucksbesetzung infolge der durch die Pruefeindruecke induzierten Eigenspannungen einer Aufwoelbung, die besonders bei intensiver Belegung und niedrigen Haertegraden ausgepraegt ist. In der beschriebenen Untersuchung, bei dem ein modifiziertes, rechnerautomatisiertes Haertepruefgeraet mit hochgenauer Eindringtiefenmessung mittels LASER-Interferometer verwandt wurde, wird nachgewiesen, dass diese Aufwoelbung einen nicht zu vernachlaessigenden Einfluss auf die Haertewertermittlung besitzt. (orig.)
[en] The article presents a status report on standardisation efforts in the field of hardness testing, with particular regard to the Vickers hardness test. Here, standardisation work was carried out under German leadership in SSO/TC 164?SC 3. Further, information is presented on the Brinell and Rockwell hardness tests and on universal hardness
[en] Highlights: • Nitrogen refines M7C3 carbides in high chromium cast iron. • Ti(C,N) precipitates were identified in high chromium cast iron with joint addition of Ti and N. • Ti(C,N) precipitates can act as the heterogeneous nuclei substrate for M7C3 carbides. • Impact toughness was improved with increasing nitrogen content. In this work, the effect of nitrogen on the as-cast microstructure and impact toughness of high chromium cast irons(HCCIs) mainly containing 2.2%C, 25.0%Cr and 0.8%Ti was studied (all compositions are in wt.% in this work). The experimental results showed that with the addition of N(0.028%, 0.075%, 0.2%, respectively), Ti(C,N) precipitates were formed in the high chromium cast irons, and dispersedly distributed in M7C3 carbides and austenite matrix. With the increase of nitrogen content, the microstructure was significantly refined, especially the M7C3 carbides, which was related to the heterogeneous nucleation of M7C3 carbide where Ti(C,N) precipitates act as the heterogeneous nuclei substrates. The Rockwell hardness of the specimen with 0.2% nitrogen increased to 49HRC in comparison to the specimen with 0.028% nitrogen (47HRC). The impact toughness of the specimen reached its peak value of 20.79 J/cm2 with 0.075% nitrogen, improving almost 80% compared with the specimen with 0.028% nitrogen (11.80 J/cm2).
[en] The alloy JBK-75, an age-hardenable austenitic stainless steel, is similar to commercial A-286, but has certain chemistry modifications to improve weldability and hydrogen compatibility. The principal changes are an increase in nickel and a decrease in manganese with lower limits on carbon, phosphorus, sulfur, silicon, and boron. In this study, the effects of solutionizing time and temperature, quench rate, cold working, and the effects of cold working on precipitation kinetics were examined. Findings show that the solutionizing temperature has a moderate effect on the as-quenched hardness, while times greater than that required for solutionizing do not significantly affect hardness. Quench rate was found to have a small effect on as-quenched hardness, however, hardness gradients did not develop in small bars. It was found that JBK-75 can be significantly strengthened by cold working. Cold working alone produced hardness increases from Rockwell-A 49 to R/sub A/ 68. A recovery-related hardness change was noted on heat treating at 300 and 4000C for both as-quenched and as-worked JBK-75. Significant age-hardening was observed at temperatures as low as 5000C for as-worked metal. Aging at 6000C resulted in maximum hardness in the 75 percent worked sample at about 6 hours (R/sub A/ 73.5) while the 50 percent worked sample was near maximum hardness (R/sub A 72.5) after seven days. THE 25 and 0 percent worked samples were considerably underaged after seven days. Similar type kinetic data were obtained for worked and nonworked metal at 650, 700, 800, 850, 900, 1000, and 11000C for times from 10 minutes to 10,000 minutes (6.7 days). The overall purpose of the hardness survey was to better define the effects of cold work on the stress-relieving range, coherent precipitation range, incoherent precipitation range, recrystallization range, solutionizing range, and grain-growth range
[en] Seventeen different Araldite-hardener specimens are irradiated by thermal neutrons, in three steps at regular intervals of increasing exposure corresponding to 0.2776 x 1012 nvt for each successive exposure. The effect of irradiation on the elastic moduli of these specimens has been investigated by determining the moduli before and after irradiation, by the ultrasonic rotating plate method. The results indicate that low flux irradiation improves the elastic moduli of the specimens containing low proportion of hardener and cast at low temperature. Further exposure is found to introduce deleterious effects. No further change is observed at and beyond 0.5552 x 1012 nvt. Specimens of high hardener proportions and those cured at high temperatures are found to be radiation resistant. Unmodified Araldites have shown comparatively higher radiation resistance than the plasticized ones. (author)
[en] Cylindrical samples having different theoretical coefficients of tension concentration and different initial hardnesses (HRC of 20 and 50) have been used to study the effect of the surface plastic deformation upon the sensitivity of steel 40KH to notching in the course of cyclic-impact loading. The surface plastic deformation raises the limited fatigue strength of steel and the higher the initial hardness of steel the greater will be the fatigue limit. For samples with HRC of 50, the increase of sigma sub(-1) amounts to 25 to 30%. The surface plastic deformation substantially reduces the notch sensitivity of steel during the cyclic-impact loading. The higher the initial hardness of steel and the effective coefficient of tension concentration Ksub(t), the greater is the reduction in the sensitivity of steel to notching with the increasing durability
[en] The case depth of induction-hardened steel rods has been determined using multi-frequency alternating current potential-drop measurements. Experimental results are analyzed using a model which approximates the variation in the material properties of a hardened rod by assuming that a homogeneous core is surrounded by a homogeneous case-hardened layer of uniform thickness. Experimental measurements on an untreated rod are used to estimate the core conductivity and permeability of similar hardened rods. The implicit assumption is that the material parameters in the core region are unchanged in the hardening process. The case depth is found by parameter fitting to minimize a penalty function representing the overall difference between multi-frequency potential-drop measurements and theoretical predictions. Case-depth values found nondestructively show reasonable agreement with those found using Rockwell hardness measurements on sectioned rods
[en] Gamma-ray or electron beam irradiation at high temperature and at a small dose improved the Rockwell hardness and resistance to wear for polycarbonate and polysulfone. The effective temperature during irradiation was the glass transition temperature (Tg) of respective polymer, and the dose at maximum hardness was only 3-5 kGy. The effect for hardness was same between 60 Co-gamma ray and electron beam and the main chain scission was predominant for both the polymers. The improvement of hardness and wear resistance was supposed to be dense molecular packing in matrix by rearrangement of molecules with synergistic effect of radiation and temperature.
[en] In this paper we developed two types of chitosan-based microspheres with and without biomimetic apatite coatings and compared their potential as injectable scaffolds for bone regeneration. The microspheres were obtained by emulsion cross-linking (E0) and coacervate precipitation (C0), respectively. They were then biomimetically coated with apatite to become E1 and C1 microspheres. The physicochemical properties and biocompatibility of the microspheres were characterized. Both E0 and C0 microspheres presented favorable ranges of diameter, density and Rockwell hardness. However, there were differences in the degree of cross-linking, shape, morphology, degradation rate, swelling rate, pH value after PBS immersion and the biocompatibility between E0 and C0. The apatite coating was successfully prepared for both C0 and E0, which enhanced the attachment, proliferation and differentiation of MC3T3-E1 cells. In conclusion, our results suggest the feasibility of using chitosan microspheres as a potential injectable scaffold. Both the preparation method and the biomimetic apatite coating contribute to their biological properties. (paper)
[en] The most critical metal forming component is usually considered to be the die. Its high cost is based on special material and processing, very fine tolerances, and high demands on repeated thermo-mechanical performance. The most common modes of die failure are fatigue fracture, gradual wear, and plastic deformation, fracture being the most dominant mode. Plane-strain fracture toughness (K/sub 1c)/ is perhaps the most important material property in the prediction and prevention of fracture, and in damage tolerance assessment. Hot metal forming is carried out at elevated temperatures, making the use of room temperature material properties invalid. Also, heat treatment and surface hardening change the properties of the die material. Traditional methods of K/sub 1c/ determination are therefore not generally feasible at elevated temperatures due to the cost of the experimental setup. Material properties such as hardness, yield strength and impact energy are quite sensitive to temperature and to strain-rate changes. Some data is available in literature relating material properties of certain tool steels to temperature. Attempts have also been made to develop correlations between Charry impact energy (CVN) and K/sub 1c/ for different steels. This paper attempts to propose a strategy for K/sub IC/ prediction (through fundamental material properties) of hot working tool steels at different tempering and operating temperatures. Focus will be on H-13 steel, the most favored hot working die material, especially in commercial extrusion. Data on material properties be fun at different tempering and specimen temperatures has been generated through exhaustive commercial and technical literature search, and by judicious interpolation and extrapolation of available experimental data. (author)