The role of shielded gas in welding of low-carbon low-alloyed steels

U radu je analizirana uloga zaštitnog gasa pri elektrolučnom zavarivanju niskougljeničnih niskolegiranih čelika. Posebno su razmotreni pojam ekvivalenta kiseonika, koji predstavlja uporedni uticaj sastava mešavina gasova, kao i uslovi za nastanak acikularnog ferita. Prikazani su rezultati ispitivanja žilavosti metala šava u zavisnosti od ekvivalenta kiseonika u zaštitnom gasu.The role of shielded gas In electric arc welding of lowcarbon low alloyed steels is analyzed. Special interest is paid to shielding gas oxygen equivalent, which shows a comparative influence of gas mixtures composition, and the conditions of acicular ferrite appearance. Results of weld metal toughness testing as a function of shielding gas oxygen equivalent are presented

The role of shielded gas in welding of low-carbon low-alloyed steels

U radu je analizirana uloga zaštitnog gasa pri elektrolučnom zavarivanju niskougljeničnih niskolegiranih čelika. Posebno su razmotreni pojam ekvivalenta kiseonika, koji predstavlja uporedni uticaj sastava mešavina gasova, kao i uslovi za nastanak acikularnog ferita. Prikazani su rezultati ispitivanja žilavosti metala šava u zavisnosti od ekvivalenta kiseonika u zaštitnom gasu.The role of shielded gas In electric arc welding of lowcarbon low alloyed steels is analyzed. Special interest is paid to shielding gas oxygen equivalent, which shows a comparative influence of gas mixtures composition, and the conditions of acicular ferrite appearance. Results of weld metal toughness testing as a function of shielding gas oxygen equivalent are presented

The effect of input energy on toughness of weld metal made by gas metal arc welding of microalloyed steel

Instrumentiranim Šarpijevim klatno je ispitana udarna žilavost metala šava dva valjana mikrolegirana čelika, zavarena elektrolučno u zaštiti mešavine gasova. Prethodno određena optimalna mešavina gasova (Ar+5%CO2+0.9%O2) je korišćena sa različitim vrednostima unete energije da bi se odredio njen uticaj na žilavost metala šava na različitim temperaturama. Optimalne vrednosti unete energije su određene za oba čelika, koje su davale najveću energiju rasta prsline u prisustvu acikularnog ferita, kao dominantne mikrostrukture.Impact toughness of weld metals of two hot rolled microalloyed steels, welded by gas shielded metal arc process, has been evaluated by using the instrumented Charpy pendulum. Previously determined optimum gas mixture (Ar+5%CO2+0.9%O2) was used with different energy inputs to determine its effect on weld metal toughness at different testing temperatures. For both steels the optimum energy input has been determined, providing maximum crack propagation energy due to presence of acicular ferrite, as a dominant microstructure

Massive Open Online Courses (MOOC) and Its Possibilities as Instrument of Formal, Nonformal, Informal and Lifelong Learning

In this chapter, we present the definition, development, and providers of massive open online courses (MOOC). We also explain the advantages and disadvantages of MOOC. We also present the structure of participants of MOOC, and also the motivation of participants is analyzed. Some basic statistics of realization and success of participants are also displayed. In one part of this chapter, the authors present case study of MOOC implementation in formal education in Belgrade Polytechnic (BP) College. For informal learning, a MOOC for welding is presented. This MOOC is planned to be organized on faculty of mechanical engineering at Belgrade University. During MOOC, participants also expanded their knowledge base and in that way they created possibilities for rerun of MOOC on a higher level. In that way, a participant can attend the same course after a couple of years and then will upgrade his knowledge. This attribute makes MOOC an instrument for lifelong learning

The effect of input energy on toughness of weld metal made by gas metal arc welding of microalloyed steel

Instrumentiranim Šarpijevim klatno je ispitana udarna žilavost metala šava dva valjana mikrolegirana čelika, zavarena elektrolučno u zaštiti mešavine gasova. Prethodno određena optimalna mešavina gasova (Ar+5%CO2+0.9%O2) je korišćena sa različitim vrednostima unete energije da bi se odredio njen uticaj na žilavost metala šava na različitim temperaturama. Optimalne vrednosti unete energije su određene za oba čelika, koje su davale najveću energiju rasta prsline u prisustvu acikularnog ferita, kao dominantne mikrostrukture.Impact toughness of weld metals of two hot rolled microalloyed steels, welded by gas shielded metal arc process, has been evaluated by using the instrumented Charpy pendulum. Previously determined optimum gas mixture (Ar+5%CO2+0.9%O2) was used with different energy inputs to determine its effect on weld metal toughness at different testing temperatures. For both steels the optimum energy input has been determined, providing maximum crack propagation energy due to presence of acicular ferrite, as a dominant microstructure

Mašinski materijali 1

Predgovor Ovaj udžbenik je namenjen studentima koji slušaju predmet Mašinski materijali 1, na osnovnim akademskim studijama u drugom semestru sa fondom časova 1+1, a napisan je prema nastavnom planu i programu. Osnovna namena ovog udžbenika je da pomogne studentima u savladavanju osnovnih znanja iz nauke o materija- lima, koja su im potrebna u toku daljeg studiranja. Pred autorima je bilo velikih dilema kako, da na jasan način izlože veoma komplikovanu i raznovrsnu materiju, imajući u vidu da prethodno stečeno srednjoškolsko znanje studenata, iz fizike i hemije, nije ujednačeno. Nakon uvodnih razmatranja o istorijskom razvoju i podeli materijala, prelazi se na strukturu atoma i veze između atoma, kao i na kristalnu strukturu materijala i greške u kristalnoj strukturi. Objašnjen je mehanizam difuzije u čvrstom stanju, mehanička svojstva materijala, kao i oštećenja i vrste lomova u materijalima. Takođe je razmatrana teorija legura i osnovne vrste dvokomponentnih dijagrama stanja. Nastavnim planom i programom je predviđeno da se osim metalnih materijala razmatraju, u manjoj meri, polimeri, keramike i kompozitni materijali. Imajući u vidu stalni razvoj materijala kao i pojavu novih inženjerskih materijala, svakako se vodilo računa da se i njima posveti odgovarajuća pažnja. Na kraju knjige navedena je i literatura koja može da se koristi u cilju proširenja znanja iz oblasti nauke o materijalima. Tokom pisanja ove knjige ideja je bila da se materija izloži u što jasnijem, a donekle, i popularnom stilu da bi bila dostupna i razumljiva studentima sa manjim obimom predznanja iz ove oblasti. Zbog toga, strogo se vodilo računa da se, gde god je to moguće, reči zamene dobrom slikom ili dijagramom. Ukoliko uspešno savladaju ovo gradivo studenti mogu biti sigurni da će imati solidnu osnovu za savladavanje gradiva iz određenih predmeta tokom studiranja, kao i da će u praksi primeniti stečeno znanje. Autori se zahvaljuju recenzentima i kolegama na korisnim primedbama i sugestijama. Posebno se zahvaljujemo profesorima dr Veri Šijački Žeravčić i dr Nenadu Radoviću koji su svojim korisnim predlozima i sugestijama doprineli poboljšanju kvaliteta knjige. Takođe se zahvaljujemo dr Draganu Cvetkoviću za pruženu moralnu podršku i nesebičnu pomoć pri tehničkoj obradi. Svojim studentima želimo puno uspeha u životu i daljem studiranju

Selecting hardfacing technologies for ventilation mill suction plates and extending its working life

This paper presents results of the suction plate surface modification by hardfacing, of the ventilation mill in the Kostolac B power plant. Before applying hardfaced suction plates to exploitation conditions, it is necessary to study model hardfaced samples for determining the optimal tech-nology and filler material for revitalization. Experimental tests of revitalized mill suction plates in real exploitation conditions show that the proposed modification, hardfacing technologies and filler materials give good results. The relative weight loss of the suction plates after 1440 h period of exploitation in real conditions is 1-3%. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Novel procedure to determine actual stress-strain curves

This paper presents a novel procedure for determining the actual stress- strain curves for undermatching rectangular welded joints made of martensitic armoured steel Armox 500T. The method is based on an analytical expression for true stress; digital image correlation (DIC) with two cameras, i.e. recording 3D deformations of samples; and finite element method (FEM) for stress state analysis of samples. Stresses obtained by dividing the force by the current cross-sectional area of the sample do not represent the actual stress occurring in the sample, because they do not take into account the stress concentration. In this paper we have analysed the stress concentration obtained numerically using Abaqus software in which the model's entered strain values are measured by DIC method

The effects of composition of shielding gas mixture on the microstructure and toughness of microalloyed steel weld metal

It has been established that the ferrite structure occurring in different morphologic forms dominates in weld metal of microalloyed steel. Acicular ferrite is the most desirable morphology of ferrite, so this paper analyses influence of the composition of gas mixture on the ferrite modification in the weld metal, specially on the morphology of acicular ferrite. At the same time, this morphological form of ferrite is very significant, because it has great influence on the mechanical properties, especially toughness. Five different gas mixtures (Ar, CO2, O2) were used to determine the optimal gas shielded metal arc process. For investigated microalloyed steel, the optimum gas mixture has been established (5% CO2, 0.91% O2, balance Ar), providing maximum impact energy due to microstructure, consisting predominately of acicular ferrite

Novel procedure to determine actual stress-strain curves

This paper presents a novel procedure for determining the actual stress- strain curves for undermatching rectangular welded joints made of martensitic armoured steel Armox 500T. The method is based on an analytical expression for true stress; digital image correlation (DIC) with two cameras, i.e. recording 3D deformations of samples; and finite element method (FEM) for stress state analysis of samples. Stresses obtained by dividing the force by the current cross-sectional area of the sample do not represent the actual stress occurring in the sample, because they do not take into account the stress concentration. In this paper we have analysed the stress concentration obtained numerically using Abaqus software in which the model's entered strain values are measured by DIC method