A LOW TEMPERATURE ALUMINIZING TREATMENT OF HOT WORK TOOL STEEL

Conventional aluminizing processes by pack cementation are typically carried out at elevated temperatures. A low temperature powder aluminizing technology was applied to the X40CrMoV5-1 hot tool steel. The aluminizing temperature was from 550 °C to 620 °C. Effects of temperature and time on the microstructure and phase evolution were investigated. Also, the intermetallic layer thickness was measured in the aluminized layer of a steel substrate. The cross-sectional microstructures, the aluminized layer thickness, and the oxide layer were studied. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and glow discharge optical spectroscopy (GDOS) were applied to observe the cross-sections and the distribution of elements

Institutional trust, political participation, and corruption: A European comparative perspective

Despite the theoretical and political importance of the relationship between institutional trust and different forms of political participation in Europe, theoretical and empirical focus on post-industrial economies leave the literature wanting of explanations of cross-national variation in political participation. In this article, we test whether levels of corruption influence the relationship between institutional trust and participation. We rely on the 9th wave of the European Social Survey results for an in-depth analysis of the relationship between institutional trust, political participation, and perceived corruption in 27 countries. The multilevel regression analysis results show that the effect of institutional trust on institutionalised political participation (including voting) is moderated by corruption. However, corruption does not moderate the relationship between institutional trust and non-institutionalised forms of participation

Utjecaj sastava sredstava za gašenje na brzinu ohlađivanja

Correct selection of quenching media decreases the risk of tensile stresses, and also cracking and workpiece distortion. High-performance quenching oil must have excellent oxidation and thermal resistance and low sludge formation, must be non-staining and have an elevated flash point and acceptable heat-transfer characteristics. The quenching media contain base oil and different types of additives according to application requirements. As the base oil, it is possible to use mineral oils, synthetic and natural oils separately or in combination. Mineral base oils are widely used because of their advantages in stability in comparison to natural oils, or lower prices in comparison to synthetic oils. There are numerous compounds available for use but, besides functional properties, the environmental and safety requirements have a strong influence on components selection. Based on that the barium additives must be replaced with less harmful compounds. Petroleum derivatives should be changed with renewable base stocks that are biodegradable, as the general trend in lubricant development. By changing the composition of quenching oils, base oils and additives, heat transfer characteristics are also changed. In this study the examination results of physical-chemical properties and also cooling characteristics of new quenching oils with different compositions are presented. Cooling curves for different compositions have been evaluated according to ISO 9950 standard.Ispravnim odabirom sredstva za gašenje smanjuje se rizik od nastajanja napetosti kao i pojave pukotina i deformacija obratka. Visokovrijedna ulja za kaljenje moraju imati odlična svojstva otpornosti na oksidaciju i postojanost pri povišenoj temperaturi, niski stupanj stvaranja taloga, što više plamište i prihvatljiva svojstva prijenosa topline. Ulja za kaljenje sastoje se od baznog ulja i različitih vrsta aditiva prema zahtjevima primjene. Kao bazno ulje mogu se primijeniti mineralna ulja, sintetička i prirodna ulja kao i njihove mješavine. Mineralna ulja su u najširoj primjeni zbog bolje stabilnosti u odnosu na prirodna ulja ili zbog niže cijene u odnosu na sintetička ulja. Postoji cijeli niz tvari koje se mogu primijeniti, ali osim radnih svojstava, ekološki i sigurnosni zahtjevi imaju velik utjecaj na izbor sastava ulja za kaljenje. Temeljem toga aditivi na osnovi barija moraju se zamijeniti manje štetnim spojevima. Slijedom općenitog trenda razvitka maziva, mineralna bazna ulja treba zamijeniti baznim uljima iz obnovljivih izvora koja su biorazgradljiva. Promjenom sastava ulja za kaljenje, baznog ulja i aditiva, svojstva prijenosa topline također se mijenjaju. U ovome radu prikazani su rezultati ispitivanja fizikalno kemijskih svojstava a također i svojstva sposobnosti ohlađivanja novih ulja za kaljenje s različitim sastavima. Ispitivanim uljima za kaljenje snimljene su krivulje hlađenja prema normi ISO 9950

EFFECTS OF CONCENTRATION WATERMISCIBLE METALWORKING FLUIDS ON COOLING RATE

Kaljenje je najrašireniji postupak toplinske obradbe metala a sastoji se od odgovarajućeg gašenja s određene temperature austenitizacije da bi se postigla martenzitna struktura. Sposobnost ohlađivanja sredstva za gašenje uglavnom ovisi o toplinskim svojstvima metala, debljini oblika obradaka te o svojstvima odvođenja topline sredstva za gašenje. Pravilnim izborom odgovarajućeg sredstva za gašenje smanjuje se opasnost od nastajanja napetosti, eventualnih pukotina i deformacija obratka. Za gašenje čelika najčešće se primjenjuju voda, biljna i mineralna ulja, otopine polimera, solne kupke, fluidizirane kupke, inertni plinovi te zrak. Voda je oštro sredstvo za gašenje dok ulja hlade znatno sporije od vode ali je njihov glavni nedostatak opasnost od požara. Primjenom vodomješivih tekućina za gašenje kombiniraju se pozitivna svojstva ova dva tipa sredstava za gašenje, vode i ulja. U ovom radu prikazana su fizikalno kemijska svojstva vodomješivih tekućina kao sredstva za gašenje kod toplinske obradbe metala. Pripremljeno je više vrsta tekućina s vodom u različitim koncentracijama. Za pojedine koncentracije ispitivanih sredstava za gašenje snimljene su krivulje hlađenja, određene brzine ohlađivanja i značajke H sredstva za gašenje prema standardu ISO 9950.Quenching is the most common procedure of metal heat treatment, which involves adequate cooling from given austenite temperature to achieve full transformation into martenzite structure. The cooling rate of quenching media mainly depends on thermal characteristics of the metals, section thickness of the workpieces, and the quenching medium heat-removal properties. Correct selection of adequate cooling media decreases risk of tension formation, possible cracking, and deformation of workpieces. The most commonly used cooling media for quenching steel are water, vegetable and mineral oils, polymer solutions, molten salts, fluidized baths, gases, and air. Water is a severe quenchant while oils cool more slowly than water but their main disadvantage is high fire hazard. Using watermiscible fluids combines positive properties of those two types of quenchant media, the water and the oils. In this work are presented physical and chemical properties of watermiscible metalworking fluids as cooling media. Several fluid mixtures were prepared with water in different concentrations. Cooling curves for every concentration of test cooling fluids are plotted with determined cooling rates and H-values using ISO 9950 standard

Effect of heat treatment parameters on the mechanical properties and microstructure of aluminium bronze

Aluminium bronzes are used for their combination of high strength, excellent corrosion and wear resistance. This paper presents the research of heat treatment parameters of two different chemical compositions of aluminium bronze (Cu-Al-Fe- Ni alloy) on microstructure and mechanical properties. The heat treatment employed in this research were solutionizing and tempering. The solution treatment was carried out at a temperature of 950 °C and the duration in the range of two hours. Similarly, tempering was carried out at 300 °C and 400 °C, wherein the duration was maintained at two hours. The heat treated samples were subjected to the cold water quenching in order to bring them to an ambient temperature. Metallographic studies were performed on samples in order to determine the changes in the microstructure of the hardened bronze, on the metallographic microscope OLYMPUS GX51 with a digital image analysis and the scanning electron microscope TESCAN VEGA 5136MM with EDX along with the digital recording on the computer. Moreover, the Glow Discharge Spectroscopy-GDS was done to determine the chemical composition of the samples. The results of the chemical composition for the aluminium bronze AK2 were: Cu- 78,37%; Al- 10,52%; Fe- 4,44%; Ni- 5,16% and for AK3 alloy: Cu- 78,95%, Al- 10,97%; Fe- 4,16%; Ni- 4,8%. The behavior of the alloy has been assessed in terms of the influence of the temperature and duration of the heat treatment on the microstructural and mechanical properties of the samples. The hardness of samples was measured by using a Vickers hardness tester at an applied load of one kg. The samples were polished metallographically prior to their hardness measurement and an average of three observations has been considered. The hardness of the AK2 alloy increased from 320 HV1 to 425 HV1 after quenching and to 500 HV1 after tempering on 300 °C or 540 on 400 °C. The hardness of the AK3 alloy increased from 300 HV1 to 400 HV1 after quenching and to 475 HV1 after tempering on 300 °C or 470 on 400 °C