Physical and Powder Metallurgy

W artykule zaprezentowano zastosowanie metody WebQuest w wyższym szkolnictwie technicznym. Metodę wykorzystano do nauczania inżynierii materiałowej – temat: „Analiza układów równowagi fazowej”. Przedstawiono szczegółowy opis materiałów do metody oraz uwagi metodyczne związane z wdrożeniem projektu.

The effects of processing parameters on the microstructure and mechanical properties of Fe-Mn-Cr- Mo-C PM steels are described. Pre-alloyed Astaloy CrM and Astaloy CrL, low-carbon ferromanganese and graphite powders were used as the starting materials. After pressing in rigid die, the compacts were conventionally and high temperature sintered at 1120 and 1250°C, respectively. Sintering was carried out for 60 minutes in atmospheres with different H2/N2 ratios. Cooling rate from sintering temperature was 65°C min-1 (convective cooling). The specimens were subsequently tempered at 200°C for 60 minutes in air. All specimens were tested for tensile strength (UTS), elongation (A), offset yield strength (R0:2), transverse rupture strength (TRS), impact toughness and apparent surface hardness (HV 30). After mechanical tests the microstructure of Fe-Mn-Cr-Mo-C PM steels was studied by optical microscopy. These investigations have shown that, by sintering in inexpensive and safe nitrogen-rich...

The paper presents the effect of sintering conditions on the microstructure and mechanical properties of low-carbon Mn-Cr-Mo PM steels. It was proved there is no effect of tempering temperature on the properties of Astaloy CrL-base steels, sintered at 1250°C in 5%H2-95%N2 mixture as compared with the properties of those sintered at 1120°C. The properties of Astaloy CrM-based steels, sintered at 1250°C in air were comparable or higher to Astaloy CrL-based steels. The addition of lump of ferromanganese was not sufficient for metal oxides reduction. The structure investigation confirmed the earlier observations that Mn-Cr-Mo PM steels have predominantly martensitic or martensitic/bainitic microstructure.

Electrochemical chromium coatings on steel, modified with diamond nanoparticles (NDDS), were produced by detonation synthesis. Their particle size was from 10 to 50 nm. Galvanization conditions, current density, etc., concentration of NDDS, were studied in relation to the characteristics of the chromium coatings. The optimal conditions were determined to attain the maximal values of the physical and mechanical properties of the coating. Surface topography after wear testing was examined. Compared to unmodified chromium coating, microhardness of the surface increased to 1100 kg/mm2, wear resistance, expressed as % of mass loss, increased from 3 to 10 times.

The object of the study was the evaluation of the effect of production parameters on the microstructure and mechanical properties of Cr and Cr-Mo PM steels. The steels were processed from commercial Höganäs pre-alloyed powders: Astaloy CrA, Astaloy CrL and Astaloy CrM with carbon, added in the form of grade C-UF graphite powder in amounts of 0.4 and 0.8 wt. %. Following Turbula mixing for 30 minutes, green compacts were single pressed at 660 MPa according to PN-EN ISO 2740 standard. Sintering was carried out in a laboratory horizontal furnace at 1120°C and 1250°C for 60 minutes in a 5%-95% hydrogen-nitrogen atmosphere. After sintering, the samples were tempered at 200°C for 60 minutes in air. Mechanical tests indicate that the steel based on Astaloy CrA pre-alloyed powder could be an alternative material to steels based on Astaloy CrM. Steels sintered at the higher temperature revealed better mechanical properties.

The effect of processing variables on the structure and the properties of PM Ni-free steels was investigated. Two groups of steels have been examined: one was based on sponge iron powder with a carbon and ferromanganese addition, and the second – based on Cr and Mo pre-alloyed iron powder with a carbon and ferromanganese addition. The pressing of rectangular and ISO 2740 specimens was carried out in steel rigid dies to achieve the same level of density. Green compacts were conventionally (1120°C) and at high temperature (1250°C) sintered in the atmosphere consisting of hydrogen, nitrogen and the mixture thereof, and cooled at a cooling rate of 65°C/min. Convective cooled specimens were subsequently tempered in the air at 200°C for 60 min. To investigate the mechanical properties: UTS, elongation, R 0.2 yield offset, TRS, impact toughness and hardness measurements results were examined. After the mechanical examination, the microstructures of steels were studied by optical and SEM mi...

Ni and Cu and in some cases Mo are the alloying elements which have traditionally been used in sintered steels. High performance of PM heavy duty structural parts made from Fe powders is reached mainly by the alloying of Ni. The use of Mn in Fe-base PM structural parts have been avoided because of the high affinity of this element to oxygen. It makes it difficult to sinter steels containing Mn, without oxidation, in industrial atmospheres. However, the powder metallurgy industry also follows possibilities in order to develop Ni-free sintered steels which render as high mechanical properties as diffusion alloyed Ni-containing sintered steels and further fulfil the requirements of health protection. In recent years Mn has been introduced as an alloying element in Fe based structural parts, on a laboratory scale and also for pilot scale production. In this paper the factors that contribute to the structure and mechanical properties of PM Mn steels are summarised. INTRODUCTION Most powd...

Dilatometric data for Astaloy CrM (3% Cr-0.5% Mo) and Astaloy CrL (1.5% Cr-0.2% Mo) powders with additions of 0.3% carbon and 3.0% manganese during sintering cycles up to 1120 and 1250°C in different atmospheres are reported. For comparison, also Astaloy CrM and Astaloy CrL powders were investigated. Starting with green densities of approx. 6.8 g/cm3, the final density of sintered compacts was influenced mainly by the sintering temperature, while the results showed the only minor effect of the sintering atmosphere on the final dimensional changes. However, the sintering atmosphere influences the sintering behaviour, microstructure and the final chemical composition of sintered compacts. In sintered and in the dilatometer cooled Mn-Cr-Mo-C steels predominantly bainitic structures were obtained.

The aim of the study was to investigate the influence of sintering parameters on the microstructure and mechanical properties of Fe-(1.5-2.5)%Mn-0.6%Si-0.8%C steels based on commercial Höganäs sponge iron powder NC 100.24. Manganese was added in the form of Elkem ferromanganese powder (89% Mn, 1.18% C), carbon in the form of graphite C-UF and silicon in the form of ferrosilicon (55% Fe, 45% Si). Powder mixes were prepared in a Turbula type mixer for 30 minutes. “Dog bone” tensile samples (PN-EN ISO 2740) were cold pressed in a steel die. The green compacts were sintered at 1250°C for 60 minutes in 5% H2-95% N2 atmosphere. The heating and cooling rates were 75 and 60°C/min, respectively. After sintering, the specimens were examined metalographically and subjected to tensile and 3-point bend test. Microhardness was also determined on metallographic crosssections. Chemical composition influenced mechanical properties and the best combination of strength and ductility was obtained for t...

Low carbon ferro-manganese and graphite powders were admixed to Höganäs sponge, NC100.24, and water atomised, ABC 100.30 and ASC 100.29, iron powders – to produce three variants of sintered Fe-3Mn-0.8C steel. These were pressed into tensile and bend specimens at 660 MPa, sintered in semi-closed containers for 1 hour in dry nitrogen or hydrogen at 1120 or 1250 • C and cooled at 64 • C/min. Both tensile strength and transverse rupture strength were examined using Weibull statistics. This paper presents the results of a study to develop and evaluate goodness of fit tests for the two-and three-parameter Weibull distributions. The study was initiated because of discrepancies in published critical values for two-parameter Weibull distribution goodness of fit tests and the lack of general three-parameter Weibull distribution goodness of fit tests for properties of PM steels. Keywords: strength of sintered steels, Weibull statistics, goodness of fit tests Aby uzyskać trzy warianty spiekanej stali Fe-3Mn-0.8C wytworzono mieszanki proszków: niskowęglowego żelazoman-ganu, grafitu oraz proszków żelaza firmy Höganäs: gąbczastego – NC100.24 i rozpylanych – ABC 100.30 oraz ASC 100.29. Z proszków tych zostały sprasowane, przy ciśnieniu 660MPa, kształtki próbek wytrzymałościowych przeznaczonych do wykonania prób rozciągania i zginania, spieczone następnie w półhermetycznych pojemnikach, w czasie 1 godziny, w suchym azocie lub wodorze, w temperaturze 1120 lub 1250 • C, po czym chłodzone z szybkością 64 • C/min. Zbadano wytrzymałość na rozciąganie i zginanie otrzymanych próbek przy zastosowaniu statystyki Weibulla. W artykule zaprezentowano wyniki badań mających na celu wykorzystanie i ocenę testów zgodności dla dwu-i trzyparametrowych rozkładów Weibulla. Badania podjęto z powodu rozbieżności publikowanych krytycznych wartości testów zgodności dla dwuparametrowego rozkładu Weibulla oraz ogólnego braku testów zgodności dla trzyparametrowego rozkładu Weibulla, w odniesieniu do własności stali wytworzonych techniką metalurgii proszków.

The fabrication of P/M structural steels currently suffers from the occurrence of pores in the final part. In addition for a given type of microstructure, the stereometric parameters of the pores such as shape and distribution decisively affect the properties. Indeed, the magnitude of key material properties such as ten-sile and transverse rupture strength and tensile elongation is directly related to the level of porosity. This study deals primarily with the experimental measurements and analysis of the porosity of the Fe-3Mn-0.8C alloys prepared with a ferromanganese and iron powders. Sintered alloys have been investigated by using single-pressing and sintering technique. The influence of sintering temperature and cooling rate on porosity and mechanical properties is discussed. The nature of porosity, porosity evolution and its control is explored. The trends in the sintering data are rationalised in terms of two effects: manganese transport through sublimation and vapour adsorpti...

A gearbox is a complex system comprised of several gears. The failure of a gearbox is due to the failure of one gear (one gear tooth). As such, one can model the gearbox failures at the gear tooth level. This approach was applied to the investigation of spur gears sintered from manganese steel Fe-3Mn-0.8C. In order to compare the relevant properties of the new PM steels with those of presently used commercial PM materials, failure load measurements on gears of Hoganas DC-1+0.5% C and Fe-1.5Cu were also performed. Weibull plots were made and the survival probability, Sj, was estimated. For 99% survival probability heat-treated DC-1 alloy barely outperformed the Mn steel, which was significantly better than Fe1.5Cu. Improvements in composition and processing of Mn steels should ensure that these easily outperform DC-1 alloy.

To interpret nitrogen sintering of chromium and manganese steels without the formation of deleterious oxides, but with manganese and carbon modifying the local microclimate, the role of the volatile Mn and carbothermic reactions were considered. Reduction of Cr2O3 by Mn vapour is always favourable. CO is an effective reducing agent, however, whereas at atmospheric pressure it will reduce FeO at ~730°C, temperatures some 500 and 700°C higher, i.e. above those for conventional sintering, are necessary for reducing Cr2O3 and MnO, respectively. Accordingly partial pressures must be considered and the sintering process is modelled at a conglomerate of several surface oxidised alloy particles surrounding a pore with graphite present and a tortuous access to the nitrogen-rich atmosphere containing some water vapour and oxygen. The relevant partial pressures were calculated and reduction reactions become thermodynamically favourable from ~200°C. Kinetics, however, dictates availability of C...

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