Origin of the Significant Impact of Ta on the Creep Resistance of FeCrNi Alloys

Heat resistant FeCrNi alloys are widely used in the petrochemical industry because they exhibit a unique combination of creep and oxidation resistance at temperatures exceeding 900$^\circ$C. Their creep properties are often optimized by micro-additions of carbide forming elements. In the present work, the influence of Ta micro-additions has been experimentally investigated both on as-cast and aged microstructures to understand the origin of the significant impact of this element on the creep resistance. Calculations with thermocal software were also carried out to support experimental data. It is shown that a small addition of Ta is beneficial as it increases the volume fraction of stable MC carbides. We demonstrate also that additions of Ta may have a dramatic effect on the thermal stability of microstructures. This is attributed to a smaller equilibrium volume fraction of M23C6 and more pronounced heterogeneous precipitation at MC/matrix interfaces. The influence on the creep properties in then discussed

Zaštitna aluminijska prevlaka izvedena izravno u ljevačkom kalupu na čeliku otpornom prema puzanju

The structure of coatings and their ability to protect the castings made of G-X25NiCrSi 36-17 (DIN 17006) cast steel against carburization have been described. Al-Cu and Al-Si protective coatings, produced directly in a casting mould, have a considerable thickness (400 - 2000 µm), and complex multiphase structure. Its main structural constituents are: (Fe, Ni, Cr), (Fe, Ni, Cr), Al(Ni, Fe), carbides M23C6 and M7C3. In Al-Si ferritic coatings are also present: (Ni, Fe), (Fe, Al, Ni, Cr) and (Cr, Si)3Ni2Si. Carburisation changes substantially the structure of coatings, what results in an increase of the amount of (Fe, Ni, Cr) or (Ni, Fe) and carbides, and a decrease of the amount of (Fe, Ni, Cr) and Al(Ni, Fe). Apart from above mentioned changes, the investigated coatings reduce the carbon diffusion by 20 - 65 % Al-Cu, about 55 % Al-Si (austenitic), and 75 % Al-Si (ferritic), so they can provide a temporary protection against high-temperature corrosion.U radu je opisana struktura prevlaka i njihova sposobnost lijevanja od G-X25NiCrSi 36-17 (DIN 17006) u svrhu zaštite protiv naugljičavanja. Zaštitne prevlake Al-Cu i Al-Si, napravljene izravno u ljevačkom kalupu, imaju znatnu debljinu (400 - 2000 µm) i složenu multifaznu strukturu. Glavni strukturni element su: g(Fe, Ni, Cr), a(Fe, Ni, Cr), bAl(Ni, Fe), karbidi M23C6 i M7C3. U feritnim prevlakama Al-Si prisutni su i: g(Ni, Fe), a(Fe, Al, Ni, Cr) i (Cr, S)3Ni2Si. Naugljičavanje mijenja suštinu strukture prevalaka, a to dovodi do povećanja količine g(Fe, Ni, Cr) ili g(Ni, Fe) i karbida, a smanjuje količinu a(Fe, Ni, Cr) i bAl(Ni, Fe). Neovisno o gore spomenutim promjenama prevlake smanjuju difuziju ugljika za 20-60 % Al-Cu, oko 55 % Al-Si (austenitni) i 75 % Al-Si (feritni) pa mogu osigurati privremenu zaštitu protiv korozije na visokoj temperaturi

Short term effect of air pollution on mortality in Polish urban populations--what is different?

STUDY OBJECTIVE: To assess, within the multinational European Community funded APHEA project, the relationship between daily ambient air pollution with sulphur dioxide (SO2) and black smoke (BS) and the daily number of deaths from all causes except external, from cardiovascular diseases, and from respiratory diseases taking into account several possible confounding factors. DESIGN: Time series analysis with the application of Poisson regression to the counts of daily number of deaths from selected causes over several years. Data were obtained from the computer files of individual death records in four Polish cities. Criteria developed for all the centres participating in the project were applied to the process of model building. SETTING: Four Polish cities - Cracow (period 1977-89), Lodz (1977-90), Poznan (1983-90), and Wroclaw (1979-89). SUBJECTS: Permanent residents of the cities who died in a city of residence or in a surrounding region during the study period. MAIN RESULTS: There were significant positive associations between mortality from all causes excluding external ones and SO2 and BS in Cracow and in Lodz and between mortality from cardiovascular diseases and SO2 in Cracow alone. In other cities the association was either non-significant or significant but in the opposite direction. No significant positive association was found between respiratory deaths and these pollutants. CONCLUSIONS: Short term effect of air pollution on mortality in Polish urban population cannot be ignored. However, differences observed between the cities suggest that the association may be not so straightforward and therefore there is a need of further studies to identify additional factors that may modify and confound the association

Svojstva stabiliziranog Ni-Cr čeličnog lijeva izloženog utjecaju atmosfere za naugljičavanje i toplinskom zamoru

In this paper results investigation of an effect of niobium and/ or titanium as well as silicon on the resistance of 0,3%C-30%Ni-18%Cr cast steel to the carburising effect and thermal shocks at a temperature of 900 °C under the carburising atmosphere of carbon potential equal to 0,9% are shown. Eight test alloys were manufactured in which the content of niobium was changing in a range of 0-1,75%, that of titanium in a range of 0,03-1,00%, and of silicon in a range of 1,34-2,48% (wt. - %). Quantitative relationships were plotted to describe the effect of stabilizing elements on an increase of specimen weight and volume content of carbide phases in the external layers of specimens. Also the susceptibility to crack formation and mechanical properties after carburising process are shown. It has been proved that, with exception of the resistance to carburising effect, the examined elements deteriorate the cast steel properties.U ovom radu prikazani su rezultati istraživanja utjecaja niobija i/ili titana te silicija na otpornost 0,3%C-30%Ni-18%Cr čeličnog lijeva u uvjetima naugljičenja i termalnih promjena kod temperature do 900 °C i potencijala ugljika do 0,9%. Izrađeno je osam legura kod kojih je sadržaj niobija od 0 do 1,75%, titana od 0,03 do 1,0% i silicija od 1,34 do 2,48% (mas. %). Prikazani su kvantitativni odnosi koji opisuju utjecaj stabilizirajućih elelmenata na porast mase uzorka i volumni sadržaj karbidnih faza u vanjskim slojevima uzoraka. Također je prikazana i osjetljivost na nastajanje pukotina kao i mehanička svojstva nakon procesa naugljičavanja. Utvrđeno je da, osim otpornosti na naugljičavanje, istraživani elementi pogoršavaju svojstva čeličnog lijeva

Utjecaj Nb i Ti na mikrostrukturu i mehanička svojstva lijevanog čelika 30 % Ni / 18 % Cr nakon žarenja

The study discusses the microstructure and mechanical properties of eight tested 0.3 % C -30 % Ni - 18 % Cr cast steels stabilized with niobium and titanium after annealing in the cycle of 900 °C / 300 h. The niobium content in the cast steels varied from 0.0 to 2.0 % and that of titanium from 0.0 to 1.2 % by weight. Microstructure was examined using both light microscope and a scanning electron microscope with Link IS-IS attachement as well as an X-ray diffractometer. Depending on the chemical composition of cast steel, the following phases were identified: carbides of MC and M23C6 type and a phase rich in silicon, nickel, niobium and / or titanium, which was supposed to be a phase G. Relationships between the microstructure and mechanical properties of cast steel at 20 and 900 °C were examined as well.Studija raspravlja o mikrostrukturi i svojstvima osam testiranih lijevanih čelika - 0,3% C, 30 % Ni, 18 % Cr stabiliziranih niobijem i titanijem nakon žarenja u ciklusu od 900 °C / 300 h. Težinski udio niobija u lijevanim čelicima je varirao od 0,0 do 2,0 % a titanija od 0,0 do 1,2 %. Mikrostruktura se ispitivala i svjetlosnim mikroskopom i skener-elektronskim mikroskopom s priključkom na link IS-IS kao i na rentgenski difraktometar. Ovisno o kemijskom sastavu lijevanog čelika, identificirane su slijedeće faze: karbidi tipa MC i M23C6 i faze bogate silicijem, niklom, niobijem i / ili titanijem, a koju se smatra da je faza G. Također se ispitivao i odnos između mikrostrukture i mehaničkih svojstava lijevanog čelika na temperaturi od 20 i 900 °C

Effect of base–acid properties of the mixtures of water with methanol on the solution enthalpy of selected cyclic ethers in this mixture at 298.15 K

The enthalpies of solution of cyclic ethers: 1,4- dioxane, 12-crown-4 and 18-crown-6 in the mixture of water and methanol have been measured within the whole mole fraction range at T = 298.15 K. Based on the obtained data, the effect of base–acid properties of water– methanol mixtures on the solution enthalpy of cyclic ethers in these mixtures has been analyzed. The solution enthalpy of cyclic ethers depends on acid properties of water– methanol mixtures in the range of high and medium water contents in the mixture. Based on the analysis performed, it can be assumed that in the mixtures of high methanol contents, cyclic ethe

Introductory background for Life Cycle Assessment (LCA) of pure silk fabric

The main goal of this study is to provide an introductory background to development of the Life Cycle Assessment studies of pure silk fabric. There are not studies available on the life cycle of pure silk fabric. In this sense, was developed a scenario model for LCA application, following the methodology established by the Standard BNR ISO 14040:2009, which establishes principles and framework for an LCA study. It was considered one of the first steps in ISO, being the definition of the purpose and scope. The limits considered for the system had as a starting point the wiring step within the company, and as a final limit the stage of the finishing of the fabric, where you get the finished product. The information used in this study was collected directly from the company entitled 'Fio de Seda', a Brazilian industry. In order to construct the scenario proposed, was used the software Umberto® 5.6 v. Acad and through it, it was possible to generate the scenario model for the production of the silk fabric. Based on this scenario, the accomplishment of the later stages is possible, as outlined in ISO 14040, thus obtaining the inventory of the LCA for the pure silk fabric, as well as its life cycle inventory assessment