Development of Direct Reduction Process and Smelting Reduction Processes for the Steel Production

Iako će proizvodnja čelika u visokim pećima i kisikovim konvertorima i nadalje biti primaran način izradbe čelika u narednom razdoblju, proizvodnja čelika u elektrolučnim pećima nastavit će se uveličavati. Međutim, povećava se važnost proizvodnje visokokvalitetnih čeličnih proizvoda dobivenih izravnom redukcijom željezne rude i/ili redukcijskim taljenjem. Zadnjih deset godina proizvodnja izravnom redukcijom povećala se za 140 %, od 20 do 49,5 MTg a -1. U ovom radu analizirani su glavni industrijski primijenjeni procesi izravne redukcije i redukcijskog taljenja kao i njihovi razvojni procesi.Although the blast furnace and basic oxygen furnace are going to be primary routes for steel production in future, the steelmaking industry using the electric arc furnace route will continue to grow. The importance of high-quality steel products manufactured by direct reduction of iron ore and/or by smelting reduction processes has been increasing. In the past decade the world steel production by direct reduction rose by 140 per cent, from about 20 to about 49.5 Mt/year. In this paper major industrial processes involving direct reduction and smelting reduction of iron ore are described, and their development is analysed

Današnje stanje i razvoj postupaka proizvodnje čelika

During 2003 year a total world’s crude steel production was 945,1 Mt, which is for 6,7 % higher than in 2002. The paper shows current state steelmaking processes (Basic Oxygen Converter and Electric Arc Furnace) including a short review of secondary metallurgy, steel casting and environmental protective as well as the development of a new steelmaking processes.Tijekom 2003. godine ukupna svjetska proizvodnja sirovog čelika iznosila je 945,1 Mt, što je za 6,7 % više nego u 2002 godini. Rad prikazuje današnje stanje postupaka proizvodnje čelika (bazični kisikov konvertor i elektrolučna peć), uključujući kratki pregled sekundarne metalurgije, lijevanje čelika i zaštitu okoliša, te razvoj novih postupaka proizvodnje čelika

The Effect of PWHT on Electrochemical Behaviour of AISI 316L Weld Metal

The subject of investigation was the corrosion behaviour of AISI 316L austenitic stainless steel weld metal as dependent on a protective passive film formed on the steel surface following exposure to w = 3.5 % NaCl. The corrosion properties were examined before PWHT and after it by means of cyclic polarization, electrochemical impedance spectroscopy, and chronoamperometric measurements. Cyclic polarization curves clearly indicated a decrease in the pitting potential following PWHT. Passivity was observed over a broad potential region. Charge transfer resistance associated with the corrosion resistance of the passive film as determined by electrochemical impedance spectroscopy indicated that high temperature PWHT acted by increasing the thickness of the passive film

Analiza međupovršine eksplozijski zavarenih ploča iz niskougljičnog čelika i titana

On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness approximately 1 to 2 mm. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.Na osnovi eksperimentalnih rezultata utvrđeno je da pri eksplozijskom zavarivanju dvaju metala na međupovršini spoja nastaje veoma tanki sloj rastaljenog metala unutar kojeg dolazi do istjecanja nečistoća tijekom taljenja. Velika brzina hlađenja nakon sudara dovodi do nastanka sitnozrnate legure drugačije strukture s proječnom veličinom od 1 do 2 mm. Zapaženo nastajanje amorfnog sloja na području spoja kod različitih kombinacija metalnih materijala predstavlja temeljni mehanizam eksplozijskog zavarivanja metala. Primjenom rezultata metalografske analize u radu je opisan razvoj vrtloga koji su nastali eksplozijskim zavarivanjem ploča iz niskougljičnog čelika i titana

Shape Memory Alloys (Part I): Significant Properties

U ovom radu naveden je pregled termomehaničkih svojstava slitina s prisjetljivosti oblika i opća obilježja martenzitne transformacije. Slitine s prisjetljivosti oblika pripadaju skupini relativno novih metalnih materijala te se od drugih slitina (npr. dentalnih slitina) razlikuju po pseudoelastičnosti i efektu prisjetljivosti oblika. Pseudoelastičnost je povezana s nastankom martenzita transformacijom austenita. Austenitno-martenzitna transformacija može se inducirati mehaničkim (naprezanje) ili toplinskim (zagrijavanje i hlađenje) metodama. Tijekom martenzitne transformacije ne odvijaju se procesi difuzije, nego dolazi do neelastične deformacije kristalne strukture. Austenitno-martenzitnu transformaciju karakteriziraju temperature početka te završetka austenitne i martenzitne transformacije (As i Af, Ms i Mf). Također su detaljno objašnjeni jednosmjerni, dvosmjerni i višestruki efekt prisjetljivosti oblika, te je uočeno da je jednosmjerni efekt prisjetljivosti oblika još uvijek najčešće primjenjivan efekt.Shape memory alloys (SMAs) belong to a group of functional materials with the unique property of “remembering” the shape they had before pseudoplastic deformation. Such an effect is based on crystallographic reversible thermo-elastic martensitic transformation. There are two crystal phases in SMAs: the austenite phase (stable at high temperature) and the martensite phase (stable at low temperature). Austenite to martensite phase transformation can be obtained by mechanical (loading) and thermal methods (heating and cooling). During martensitic transformation, no diffusive process is involved, only inelastic deformation of the crystal structure. When the shape memory alloy passes through the phase transformation, the alloy transforms from high ordered phase (austenite) to low ordered phase (martensite). There are two types of martensite transformations. First is temperature-induced martensite, which is also called self-accommodating (twinned) martensite. The second is stress-induced martensite, also called detwinned martensite. The entire austenite to martensite transformation cycle can be described with four characteristic temperatures: Ms – martensite start temperature, Mf – martensite finish temperature, As – austenite start temperature, and Af – austenite finish temperature. The main factors influencing transformation temperatures are chemical composition, heat treatment procedure, cooling speed, grain size, and number of transformation cycles. As a result of martensitic transformation in SMAs, several thermomechanical phenomena may occur: pseudoelasticity, shape memory effect (one-way and two-way SME) and rubber-like behavior. Pseudoelasticity occurs when the SMA is subjected to a mechanical loading at a constant temperature above Af. The second thermomechanical behaviour that can be observed in SMA is the shape memory effect (SME), mainly one-way SME, which is the most commonly used SME. When the sample is subjected to a mechanical loading, the stress reaches a critical value and the transformation of twinned martensite into detwinned martensite begins and finishes when the loading process is finished. When the loading-unloading process is finished, the SMA presents a residual strain recoverable by alloy heating, which induces the reverse phase transformation. As a result, the alloy recovers to its original shape. In this paper, a review of thermomechanical properties of shape memory alloys and general characteristics of martensite transformations is shown

Analiza međupovršine niskougljičnog čelika/tantal nakon eksplozivnog zavarivanja

The article discusses the morphology, microstructure and chemical composition of the boundary layer in explosive welding of low-carbon steel and tantalum plates. Pools of melt composed of both metals and having a heterogeneous chemical composition appear on the boundary layer. This phenomenon is the result of incomplete mixing of both: molten metals due to rapid cooling and solidification. Within the pools of alloy, a large number of non-metallic oxide inclusions, products of deoxidation of molten alloys, can be found. The non-metal inclusions are round (0.1 to 2 µm in diameter) and vary in both: size and chemical composition. The main component of the non-metal inclusions is Ta2O5, which also contains iron, manganese, and aluminium oxides. The number of non-metal inclusions is unusually high for low-carbon steel and comparable to the number of non-metal inclusions in welds. Oxygen which causes the large number of deoxidised products does not originate in the low-carbon steel, as this steel is relatively clean. The most probable source of oxygen is the oxide scale from the surface of the low-carbon steel, which was poorly cleaned prior to welding.Članak raspravlja o morfologiji, mikrostrukturi i kemijskom sastavu pograničnog sloja pri eksplozivnom zavarivanju traka niskougljičnog čelika i tantala. Područje zone taljenja sastavljeno je od oba metala i na graničnom sloju pojavljuje se heterogeni kemijski sastav. Ova pojava je posljedica nepotpunog miješanja oba rastaljena metala, zbog naglog hlađenja i očvršćivanja. Unutar područja spajanja legure može se utvrditi veliki broj nemetalnih oksidnih uključaka, produkata dezoksidacije rastaljenih legura. Nemetalni uključci su okrugli (0.1 do 2 µm) i variraju u veličini i kemijskom sastavu. Glavna komponenta nemetalnih uključaka je Ta2O5, koji također sadrži željezne, manganove i aluminijeve okside. Broj nemetalnih uključaka je neouobičajeno velik za niskougljični čelik i usporediv je s brojem nemetalnih uključaka u zavarima. Kisik koji dovodi do nastanka velikog broja produkata dezoksidacije ne potiče iz niskougljičnog čelika jer je čelik relativno čist. Najvjerojatniji izvor kisika je površinski oksidni sloj niskougljičnog čelika koji je slabo očišćen prije procesa zavarivanja

Secondary ledeburite formation during various welding techniques

The occurrence and formation sequence of secondary ledeburite in the heat affected zone of chromium ledeburitic tool steel W.Nr. 1.2379 (OCR12 VM) after welding with SAW, TIG, microplasma and laser welding techniques is presented in this paper. Special attention was paid on the behaviour of carbides. The occurrence of secondary ledeburite is a result of local enrichment of the austenite matrix with alloying elements, due to partial or complete dissolution of primary/eutectic carbides. The results show that the largest amount of secondary ledeburite is formed during submerged arc welding, followed by TIG and microplasma welding technique. Welding by laser technique, with appropriate technological parameters, could prevent secondary ledeburite formation

Ponašanje čelika AISI 316L izloženog demineraliziranoj vodi

The subject of investigation was the passivation of AISI 316L austenitic stainless steel. The effectiveness of various passivation media was tested by means of the potentiodynamic polarization technique. Potentiodynamic polarization was carried out in demineralized water before and after passivation treatment. Comparative analysis of the potentiodynamic curves for different passivation media showed that the best protection of the steel surface was provided by a HNO3 solution, φ= 6.0 %, containing CuSO4 · 5H2O, w = 2.0 %. The satisfactory protective properties were found to agree with the high value of the pitting potential.Predmet istraživanja rada bila je pasivizacija austenitnog nehrđajućeg čelika AISI 316L. Djelotvornost različitih sredstava za pasivizaciju ispitivana je potenciodinamičkom polarizacijom. Potenciodinamička polarizacija provedena je u demineraliziranoj vodi prije i nakon pasivizacije. Uočeno je da demineralizirana voda pri 80 °C prouzroči oštećenje površine čelika. Vodena otopina limunske kiseline, w(limunske kiseline) = 5 %, i amonijaka, w(amonijaka) = 25 %, ne djeluje povoljno kao sredstvo za pasivizaciju. Dobivene vrijednosti potencijala početka jamičaste korozije upućuju na to da otopina koja sadrži CuSO4 • 5H2O kao inhibitor korozije ima znatno veću sposobnost pasivizacije nego otopina koja sadrži K2Cr2O7. Usporedna analiza potenciodinamičkih krivulja snimljenih u različitim sredstvima za pasivizaciju pokazala je da se najbolja zaštita površine čelika postiže s otopinom HNO3, w = 6,0 %, i CuSO4 • 5H2O, w(CuSO4 • 5H2O) = 2,0%. Zadovoljavajuća zaštitna svojstva podudaraju se s visokom vrijednošću potencijala početka jamičaste korozije

Investigation of the washing conditions of domestic types of wool

The wool fibers that are obtained in the Republic of Serbs have not been systematically analyzed. Also, they are only used in domestic crafts production, not for industrial means. This study is the beginning of a project with the aim of determining how to replace a quantity of imported wool by domestic wool in the process of industrial manufacturing.The washing of two types of domestic wool was investigated, namely pramen-ka and polumerino. The parameters used to wash this wool were varied, such as materials for washing (from clean water to surfactants and additives), as well as the temperature and length of the washing process.The effects of washing the wool were tested with respect to the content of clean wool, the content of organic materials soluble in ethanol, the content of herbal components insoluble in sodium-hydroxide solutions and mineral substances represented as ash quantities. The optimal conditions for washing wool were defined, as well as recommendations for the more economic usage of materials used in washing