[en] Short communication

[en] Normalized 21/4Cr-1Mo steel has been tempered at 998 K for durations up to 50 h, and then oxidized in air at 773, 873 and 973 K for a maximum duration of 1000 h. The extent of the prior tempering treatment was found to influence the oxidation behaviour of the steel significantly. In general, the oxidation resistance of the steel decreased with increasing duration of prior tempering. However, a pronounced influence has been observed during oxidation at 973 K, when at the end of a 6h exposure the specimens with prior tempering for 50 h were found to have a weight gain 2.5 times more than the specimen without prior tempering. From the results of the pre-and post-oxidation analyses of the oxide-alloy matrix interfaces by SEM/EDAX, the observed oxidation behaviour could be attributed to the degree of depletion of free (effective) chromium from the alloy by the precipitation of secondary phases of chromium compounds during tempering for different durations. The secondary precipitates in the specimen tempered for 50 h at 998 K can become enriched in chromium by one order of magnitude more than that in the specimen with no prior tempering. Such a drastic depletion of chromium from the matrix causes the formation of a less protective inner oxide layer during oxidation. Acoustic emission tests carried out to assess the mechanical stability of the scale showed that the 50 h tempered specimen suffered cracking after about 4 h oxidation at 973 K, which results in subsequent enhanced oxidation. (author)

[en] The influences of temperature and duration of tempering on hardness and microstructure were investigated at high-temperature martensitic and low-carbon steels with 9% chrome and the further alloying elements molybdenium, vanadium, niobium and partially tungsten. After austenitizing and subsequent air cooling the steels were tempered at temperatures below, at and above Ac_1b for different times and finally a hardness test was performed. Making use of the temperature dependence of the hardness tempering diagrams were constructed and the Hollomon-Jaffe-Parameter on the three steels was determined within its application limits. Micrographs of the structure shows the formation of the carbides and the martensite. At tempering temperatures below Ac_1b a decrease of hardness occurs, above Ac_1b, a hardness rise due to the partial austenitizing was obtained. While hardening below Ac_1b, the tempering quality increases from P 91, NF 616 to E 911. (orig.)

[en] This paper discusses two deterministic quantities, mean first exit time and escape probability, for the anomalous processes having the tempered Lévy stable waiting times with the tempering index $\mathrm{\mu <!--\; ??\; -->}>0$ and the stability index $0<\mathrm{\alpha <!--\; ??\; -->}\le <!--\; ???\; -->1$. We derive the nonlocal elliptic partial differential equations (PDEs) governing the mean first exit time and escape probability. Based on the analysis of the derived PDEs, some interesting phenomena are observed. (letter)

[en] A direct method to calculate the tempering response of a tool steel (H13) that exhibits secondary hardening is presented. Based on the traditional method of presenting tempering response in terms of isothermal tempering, we show that the tempering response for a steel undergoing a non-isothermal tempering schedule can be predicted. Experiments comprised (1) isothermal tempering, (2) non-isothermal tempering pertaining to a relatively slow heating to process-temperature and (3) fast-heating cycles that are relevant to tempering by induction heating. After establishing the tempering response of the steel under simple isothermal conditions, the tempering response can be applied to non-isothermal tempering by using a numerical method to calculate the tempering parameter. Calculated results are verified by the experiments.

[en] The concept of 'Matrix Steel' developed by G.A. Roberts is used, to produce several High-Steels with matrix similar to M-2 steel and varying quantities of MC type carbide, NbC. The carbide was obtained by adding C and Nb stoichiometrically. The resultant steels exhibit hardness in the range of 63 to 64HRC when hardened at 1.200⁰C and double tempered at 540⁰C, which satisfies the requirements of ASTM Standard A-600. An upper limit of -3% is set in the allowed amount of Nb due to the size of the carbide particles. (Author)

[en] This work provides a novel method for increasing the mechanical strength of porcelain materials. To achieve this was used a ceramic powder prepared from sodium feldspar and clay. This powder was wetted up to 8wt.% with water and pieces of rectangular section are formed by uniaxial pressing at 21MPa. The dried specimens were then sintered in a laboratory furnace (1,218°C). These specimens were subjected to a chemical ion exchange treatment in order to increase their mechanical properties, also known chemical tempering. Temperature and time were varied during chemical treatment according to a factorial design. The results showed an increase of ∼74% in breaking force of porcelain material, providing a reduction of the material thickness greater than 15%. Therefore, the process of chemical tempering can be used to increase the breaking force and consequently decreasing the thickness, saving raw materials and energy in the production process.(Author)

[en] Retained austenite particles with nanometric dimensions in 9% nickel steels microstructures were observed after different intercritical tempering treatments ranged between 540 degree centigrade and 670 degree centigrade corresponding to the ( α +γ) two-phase field of Fe-Ni diagram. The thermal stability of particles turned out to be strongly influenced by its nickel contents and gradients of this element. The gradients were dependent on time and temperature of tempering. (Author) 14 refs

[en] This invention comprises a procedure for the dosimetry of ionizing radiation fields by means of analytic materials on the basis of polyethyleneterephthalate (PETP) foils which can be used also for the time domain < 24 h after irradiation. It was found that a immediate constancy of measured values (alterations of transmission) can be obtained by tempering the irradiated foils (temperatures between 80 ⁰C and 125 ⁰C, time up to 30 min)

[en] The behaviour of 4340 steel has been studied with respect to low cycle fatigue for the as quenched and tempered condition at temper temperatures of 200decC, 400degC and 600degC. All the tests wre accomplished with strain control at environment temperature. The obtained test results have shown different behaviours for each temper temperature. For all the temperatures a sofftening effect of the material related to the tension test was observed. (Author)