High strength low-alloyed (HSLA) Cr-Mn-Si steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Those properties depend both on the temperature and time of tempering. Knowing the tempering parameters, it is possible to reach the desired properties of the treated steel. Some results on investigating the Hollomon-Jaffe equation (in parametric form) application for tempering of HSLA steel, are shown in this paper. The experiments were performed in real production conditions, using a standard material. The quenching was performed at 870 °C, the heating period was always 30 min, with subsequent cooling into the oil bath. The tempering was carried out in temperature range from 480 to 680 °C, while tempering time varied from 15 min to 24 h. The degree of tempering is referred through the hardness values changing. The experimental results have shown a pretty well agreement to tempering parameters, included in Hollomon--Jaffe equation, for this kind of HSLA steel.Quenched steels, from a group of heat-treatable steels, always have high values of both hardness and strength, but pretty low values of impact properties. The residual stresses are also on a high level. So, any kind of tempering has to be done -depending of the steel type. However, the tempering [1-4] is provided in a wide temperature range (even up to Ac 1 point), and then a wide diapason of structures will appear: from the untransformed martensite (with differrent amounts of retained austenite) to the structure, which contains carbide globules into ferrite matrix.Although the tempering temperature shows a dominant influence on the structure changes, the tempering time also has a strong influence but is usually less investigated. One more reason for investigating the tempering time is a fully diffusion character of all processes which are involved in tempering processes [1,4]. In relation with the processes mentioned, many efforts are still made to find out one proper parameter, which will include both the temperature and time of tempering. Only in that way, i.e., on the equivalency of a simultaneous influence of tempering temperature
Hydroxyapatite is a widely used bioceramic material in implant coatings research because of its bioactive behavior when being deposited onto the metallic implant and compatibility with the human bones composition. The coating of nanosized hydroxyapatite was electrophoretically deposited on a blasted surface of stainless steel 316LVM samples at constant voltage, for different deposition times and subsequently sintered in both, vacuum and argon atmosphere, at 1040 and 1000 °C, respectively. Although sintering temperatures needed to achieve highly dense coatings can cause HAp coating phase changes, the possibility to obtain a bioactive coating on 316LVM substrate, without the coatings phase changes due to the nature of the used stoichiometric nanostructured hydroxyapatite is presented in this work. The thermal stability of the used HAp powder was assessed by DTA-TG analyses over the temperature range of 23-1000 °C, i.e., at the or nearby experimental sintering temperature. The microstructure characterization was accomplished using SEM, while phase composition was determined using XRD.
Co-Mo-Cr alloys for dentistry obtained by vacuum precise casting There are several biocompatible Co-Cr-Mo alloy compositions, as well as technological processes suitable for obtaining the tablet samples aimed to produce dental implants and orthodontic devices. Here presented Co-Cr-Mo alloy, besides its biocompatibility, corrosion resistance, and nickel absence, is favorable for its mechanical properties, such as hardness, tensile and fatigue strength. The technology for raw materials preparation and manufacturing of a Co-Cr-Mo alloy for dental implants vacuum precise casting is presented here. Besides the technological process characteristics, there are the chemical analysis of raw materials, alloy obtaining guidelines and microstructure of as-cast samples.
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