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Kocijan A.,Slovenian Institute of Metals And Technology | Merl D.K.,Jozef Stefan Institute | Jenko M.,Slovenian Institute of Metals And Technology
Corrosion Science | Year: 2011

The evolution of the passive films on 2205 duplex stainless steel (2205 DSS) and AISI 316L stainless steel in artificial saliva, and with the addition of fluoride, was studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements. The extent of the passive range increased for the 2205 DSS compared to the AISI 316L in both solutions. The formation of the passive film was studied by EIS at the open-circuit potential (OCP). The passive layers were studied at the OCP by X-ray photoelectron spectroscopy (XPS). The passive films on both materials predominantly contained Cr-oxides, whereas the Fe species were markedly depleted. © 2010 Elsevier Ltd.


Podgornik B.,Slovenian Institute of Metals And Technology | Jerina J.,University of Ljubljana
Surface and Coatings Technology | Year: 2012

Tribological evaluation of the tool steel, focused on determining coefficient of friction and critical load for galling initiation against austenitic stainless steel as a function of surface topography was carried out in a load-scanning test rig. Surfaces investigated included turned, ground, polished, shot penned and laser surface textured cold work tool steel. Additionally, effect of surface roughness and post-polishing on galling resistance of TiN and DLC coated surfaces was investigated. Results of this investigation show that by removing sharp peaks polishing of the bearing surface gives plateau-like topography and improves galling properties of forming tool steel. This becomes even more important when using hard ceramic coatings (i.e. TiN). When superbly polished contact surfaces can give similar galling resistance as otherwise obtained through contact lubrication. However, application of low friction coatings or introduction of micro-dimples with proper density and contact lubrication will result in superior galling resistance of the surface. © 2011 Elsevier B.V.


Sedlacek M.,University of Ljubljana | Podgornik B.,Slovenian Institute of Metals And Technology | Vizintin J.,University of Ljubljana
Tribology International | Year: 2012

The aim of the present research was to investigate the correlation between surface roughness parameters and friction. For this purpose 100Cr6 steel plate samples were prepared using different grades and combinations of grinding and polishing in terms of similar S a but different S sk and S ku values. Dry and lubricated pin-on-disc tests, using different contact conditions, were carried out, using Al 2O 3 ball as counter-body. Test results show that surfaces with higher S ku and negative S sk values tend to reduce friction. © 2012 Elsevier Ltd. All rights reserved.


Kovacic M.,Store Steel Company | Kovacic M.,University of Nova Gorica | Sarler B.,University of Nova Gorica | Sarler B.,Slovenian Institute of Metals And Technology
Energy | Year: 2014

The Energy Agency of the Republic of Slovenia regulates and determines the operations of the natural-gas market, charges for related gas imbalances, decides on suppliers and controls penalty provisions relating to breaches of stipulated provisions. Each supplier regulates and determines the charges for the differences between the ordered (predicted) and the actually supplied quantities. Štore Steel Company is one of the major spring-steel producers in Europe. Its natural gas consumption represents approximately 1.1% of Slovenia's national natural gas consumption. The company is contractually bound to a supplier which exacts penalties according to the differences mentioned above. A successful approach to gas consumption prediction is elaborated in this paper, with the aim of minimizing associated costs. In the attempt to model and predict the gas consumption and, accordingly, to minimize ordered and supplied gas quantity error, we used linear regression and the genetic programming approach. The genetic programming model performs approximately two times more favorably. The developed gas consumption model has been used in practice since April 2005. The results show good agreement between the model-based ordered quantities and the actually supplied quantities, with savings amounting to approximately 100,000EUR per year. © 2014 Elsevier Ltd.


Conradi M.,Slovenian Institute of Metals And Technology
Materiali in Tehnologije | Year: 2013

In the fast growing field of nanotechnology, polymer nanocomposites have become a prominent area of current research and development. Silica/polymer nanocomposites are dominating the polymer and composite literature as well as a variety of applications, many industrial products and other significant areas of current and emerging interest. This review will give a general overview of the leading and most commonly used techniques and strategies for the preparation of both silica fillers and silica/polymer nanocomposites, followed by a discussion of the main characterization methods, mechanical testing, properties and applications. Typical examples of different systems will be reported and referred to the corresponding references for more detailed descriptions.


Petrovic D.S.,Slovenian Institute of Metals And Technology | Mandrino D.,Slovenian Institute of Metals And Technology
Materials Characterization | Year: 2011

An X-ray photoelectron spectroscopy analysis of the surface of fully processed, non-oriented, electrical steel sheet was performed in an attempt to elucidate the chemistry of the complex oxide scale. Ar+ sputtering was used to clean the surface contamination. Not only Fe2+, but also Fe0 states were detected in addition to the Fe3+ in the top several tens of nanometers of the 1-5-μm-thick complex oxide scales. This reduction of iron was explained as being due to the preferential sputtering of the oxygen atoms from the iron compounds in the Ar+ sputtering process. A fayalite reduction mechanism is proposed to account for the reduction of the iron down to Fe0. The results of the study indicate that X-ray photoelectron spectroscopy is limited to the determination of thick, complex oxides in multicomponent iron alloys. © 2011 Elsevier Inc.


Podgornik B.,Slovenian Institute of Metals And Technology | Leskovsek V.,Slovenian Institute of Metals And Technology
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

Dies and tools used in hot metal forming are exposed to elevated temperatures and high contact pressures, and therefore to wear and fatigue. Fracture toughness is thus one of the main material properties used when selecting and optimizing heat treatment of tools. However, fracture toughness data alone is not sufficient and need to be supported by other material properties and features. The aim of the present research work was to correlate fracture toughness properties of hot-work tool steel, especially its variation to the local microstructure, microhardness, and composition and to establish methodology for proper evaluation of tool steel's fracture toughness. Research was performed on H11-type hot-work tool steel specimens, heat treated under the same conditions but displaying greatly different fracture toughness. Results show that the presence of any weak point, either in a form of non-metallic inclusions and/or large undissolved eutectic carbide clusters, located in the region of positive segregation with high microhardness will lead to considerable reduction in fracture toughness. © The Minerals, Metals & Materials Society and ASM International 2013.


Petrovic D.S.,Slovenian Institute of Metals And Technology
ISIJ International | Year: 2011

The effect of selenium on the oxidation of Fe-Si-Al-C alloy during decarburization at 840°C in wet hydrogen was studied. Selenium was found to change the morphology of internal oxides of an Fe-Si-Al-C alloy. The long penetrating internal oxides of Si and Al in the alloy containing 0.034 at.% Se demonstrate an obvious preferential growth perpendicular to the steel substrate. FEG-SEM/EDX was performed to analyze the scale and the subscale. It was assumed that columnar morphology of internal oxides could be induced by selenium surface segregation. Therefore, in-situ AES analysis using a resistive heating of specimen in UHV was used to obtain more accurate data on temperature dependence of selenium surface segregation in silicon steel. Additionally, the kinetics of the selenium surface segregation was investigated in-situ during annealing at 840°C in the ultra-high vacuum chamber of a field-emission Auger electron spectrometer. © 2011 ISIJ.


Petrovic D.S.,Slovenian Institute of Metals And Technology
Materiali in Tehnologije | Year: 2010

Non-oriented electrical steel sheets are sheets tailored to produce specific properties and are produced from Fe-Si or Fe-Si-Al alloys. Non-oriented electrical steel sheets are incorporated into a wide range of equipment, from the simplest domestic appliances to hybrid and pure electric vehicles. Future efforts will be focused on controlling the residual elements in the steel, optimizing the hot and cold rolling, and optimizing the crystallographic texture development, with the aim to enhance the performance of the finished product.


Skobir D.A.,Slovenian Institute of Metals And Technology
Materiali in Tehnologije | Year: 2011

Micro-alloyed, high-strength, low-alloy (HSLA) steels are important structural materials and contain small amounts of alloying elements, such as niobium, titanium, vanadium, and aluminium, which enhance the strength through the formation of stable carbides, nitrides or carbonitrides and have an effect on the hardenability. Such steels contain less than 0.1 % of the alloying additions, used individually or in combination. Yield strength increments of two or three times that of plain carbon-manganese steel can be attained. Nowadays, also micro-alloyed cast steels have found many applications in the manufacturing of industrial parts that used to be produced by more expensive manufacturing processes.

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