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This review presents part of scientific research in the development of shape memory alloys (SMA) based on copper at the Faculty of Metallurgy of the University of Zagreb in the period from 2006 to 2022, in cooperation with a number of universities and scientific institutions in the region. The following SMA alloys were studied: CuAlNi, CuAlMn, etc. Physical modelling, including numerical simulation of microstructure evolution and thermal analysis were performed. The SMA alloys were produced in arc, high-frequency, and induction furnaces by means of three different technologies: melt spinning, casting in metallic and/or graphite moulds, and continuous casting in bars. The selected SMA alloys were then hot and cold rolled. The heat treatment (quenching and tempering) and the characterisation of the functional properties of the SMA alloys under the different conditions were carried out. Numerous sophisticated methods were used to characterise the functional properties, in addition to testing the mechanical properties: optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), etc. According to several parameters (ductility, corrosion resistance, etc.), it could be concluded that CuAlMn was the best alloy. As results of this investigation on SMA alloys, according to the CROSBI database (by December 23, 2022), the research team has published 33 articles in journals (including 23 articles in journals indexed in the Web of Science database), 74 papers in proceedings of international conferences, 18 abstracts in proceedings of conferences, and 5 other papers. In addition, 1 doctoral thesis, 12 bachelor theses, and 25 master theses were prepared and defended in the field of technical sciences in the areas of metallurgy and chemical engineering. [ABSTRACT FROM AUTHOR]

This work presents a brief review of mass crude steel production technology in the 1954–2020 period, with an accent on steel production in the Republic of Croatia in the 1992–2020 period. Steel producers in Croatia were Ironworks in Sisak and Split. Steel was produced using Siemens-Martin (Sisak) and electric arc furnaces (Sisak and Split). Today, steel is produced only by ABS Sisak Ltd., using contemporary electric arc furnaces including steelmaking processes (ladle-furnace and vacuum degasser). Due to the devastation of the working capacities of Sisak Ironworks (before 2012), and shutdown of steel production at Split Ironworks, today Croatia has no possibility of processing its own steel by plastic deformation processes into semi-finished products and/or finished products. In Croatia, during the 1954–2020 period, about 9.3 Mt of crude steels were produced (carbon and low alloyed steels). Also shown is the role of higher education and scientific-research work in steelmaking in the Republic of Croatia. [ABSTRACT FROM AUTHOR]

This paper shows the trend of the world crude steel production in the first two decades of the 21st century. From 2000 to 2020, the world steelmaking continuously increased (total production of 28.5 billion t steel), but decreased in 2008 (1,6 %) and 2009 (7,7 %) because of the global financial and economic crises. For more than fifty years, the primary steelmaking processes are those by means of two technologies: oxidation of pig iron (product from blast furnace) in basic oxygen converters by means of technical oxygen, and smelting of old ferrous (steel scrap) in the electro arc furnaces. For the production of quality steel, the secondary metallurgy procedures (treatment of steel in ladle) play a greater role. In 2000, global steel production was 847.2 million t (basic oxygen converters share was 58.2 % and the electro arc furnaces 33.8 %), while in 2020, production reached 1.8775 billion t steel, which is an increase of 2.2 times. By 2020, the production of steel by steelmaking processes was 73.2 % by basic oxygen converters, 26.3 % by electro arc furnaces, 0.3 % by Siemens-Martin furnaces, and 0.2 % by other procedures of steel production. Primacy in steelmaking is in countries and companies from Asia (73.9 % of the world’s output). The recycling degree of steel in the period from 2011 to 2019 was 34–37 %. China is the largest world steelmaking country (since 1996). China had an increase in steelmaking of 8.3 times in the period from 2000 to 2020 (from 127.2 Mt up to 1.064 Gt). China produced 56.6 % of the world’s steel. From 2000 to 2020, a share of continuous casting was increased by about 10 % (from 87 to 96.6 %). [ABSTRACT FROM AUTHOR]

The Sisak Ironworks Metallurgical Combine arose from the former Caprag Smelter (1938). The technological process of Sisak Ironworks had characteristics of integrated ironworks, including mass production of coke, pig iron, and crude steel, as well as rolled semi-finished and finished products, along with its own significant metalworking industry. The primary, and globally recognized, products of Sisak Ironworks were welded and seamless pipes. Sisak Ironworks was characterized by continuous reconstruction and modernization with the desire to expand the product range and improve the quality system of final products. Sisak Ironworks gained 16th place out of the 200 largest companies in former Yugoslavia according to journal „Ekonomska politika“ in 1986. Sisak Ironworks was the largest metallurgical company in the Republic of Croatia, and the third (after Zenica Ironworks and Associated Slovenian Ironworks), and the only producer of seamless pipes in former Yugoslavia. Sisak Ironworks was of great significance for today’ s Sisak-Moslavina County, because in 1978, for example, more than 90 % of the total revenue came from the ironworks, and at the end of 1989, it employed 13,992 workers and produced around 2.07 million tons of metallurgical products (coke, pig iron, crude steel, pipes etc.). Sisak Ironworks always nurtured solidarity; after World War II, it built more than 3,600 apartments, and approved over 4,000 loans for individual construction of houses, participated in the co-financing of numerous infractructural and communal projects, educational, cultural, sports-recreational, and other activities etc. The City of Sisak is not the same without the Sisak Ironworks, which we are still witnessing today. The development of the Sisak Ironworks improved the social and cultural life of Sisak and contributed to its urbanization. In 1939, at the time of the opening of the Caprag Smelter (the forerunner of Sisak Ironworks), the population of Sisak was 12,920, and in 1971, about 40,000, while in 1991, the city of Sisak had 45,992 inhabitants. There has always been a symbiosis between the metallurgical industry and the city of Sisak. Unfortunately, the Sisak Ironworks disappeared a long time ago due to several reasons (war afflictions, three unsuccessful privatizations, negligence of the relevant state institutions, etc.), so that the metallurgical production of the remains of the original Ironworks in 2019 had reduced to crude steel production (69 kt) to the level between 1955 (46.9 kt) and 1956 (82.5 kt). [ABSTRACT FROM AUTHOR]

This work presents the development of the scientific field of metallurgy in technical sciences of the Republic of Croatia from 1960 to 2020. Development of the scientific field of metallurgy was accomplished through the Department of Metallurgy (1960–1974), and Metallurgical Engineering Department of the Faculty of Technology, University of Zagreb (1974–1978), Zagreb Institute for Light Metals (1949–1968), Sisak Institute for Metallurgy (1961–1978), Faculty of Metallurgy of the Sisak Iron and Steel Works (1979–1991), and Faculty of Metallurgy as part of the University of Zagreb (1991–). Development of the scientific field of metallurgy is closely connected to the metallurgical industry of the Republic of Croatia (Sisak Iron and Steel Works, Šibenik Light Metals Factory, numerous foundries, etc.) and professional libraries. Presented are the education, scientific research, professional, publishing, and journalistic activities in the scientific field of metallurgy. In addition, the contribution of other higher school institutions and professional societies is presented. Up to December 31, 2019, achieved were 763 academic titles and 34 doctor-of-science degrees in the field of metallurgy at the University of Zagreb. During the 1960–2020 period, published were over 3000 scientific and professional papers in domestic and international journals, as well as in proceedings of international and domestic conferences. As a result of professional activities, produced were over 1000 studies, numerous professional reports for metallurgy and similar companies, about twenty patents registered, etc. During this period, published were also several monographies from the field of metallurgy, over fifty books and university textbooks, seven proceedings (1999–2006), and eleven books of abstracts from international casting conferences, as well as numerous university and internal scripts, etc. [ABSTRACT FROM AUTHOR]

This work reviews the development of the scientific field of metallurgy within the domain of technical science – from the High Technical School to the formation of the Department for Metallurgy, Zagreb Technology Faculty. Also presented is the development of teaching, scientific, and professional activities, including metallurgy teachers in the Republic of Croatia during the 1919–1960 period. The contribution of the metallurgical industry to the development of metallurgy as a scientific field in the Republic of Croatia is shown. [ABSTRACT FROM AUTHOR]

The corrosion behavior of NiTi alloy and stainless steels (AISI 316L and X2CrNiMoN22-5-3) in 0.9% sodium chloride (0.154 moll-1) solution was investigated using open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Microstructural analyses before and after electrochemical tests were performed with the scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The lowest corrosion current density has NiTi alloy and the extent of the passive range increased in the order AISI 316L stainless steel < NiTi alloy X2CrNiMoN22-5-3 duplex stainless steel. The oxide film formed on all samples has a double-layer structure consisting of a barrier-type inner layer and a porous outer layer. Oxide films formed on the surface of steels mainly contains iron oxides and chromium oxide, while the surface film of the NiTi alloy mainly contains TiO2 oxide. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) have been extensively investigated because of their unique shape memory behaviour, i.e. their ability to recover their original shape they had before deformation. Shape memory effect is related to the thermoelastic martensitic transformation. Austenite to martensite phase transformation can be obtained by mechanical (loading) and thermal methods (heating and cooling). Depending on thermomechanical conditions, SMAs demonstrate several thermomechanical phenomena, such as pseudoelasticity, superelasticity, shape memory effect (one-way and two-way) and rubber-like behaviour. Numerous alloys show shape memory effect (NiTi-based alloys, Cu-based alloys, Fe-based alloys etc.). Nitinol (NiTi) is the most popular and the most commonly used SMA due to its superior thermomechanical and thermoelectrical properties. NiTi alloys have greater shape memory strain and excellent corrosion resistance compared to Cu -- based alloys. However, they are very costly. On the other hand, copper-based alloys (CuZn and CuAl based alloys) are much less expensive, easier to manufacture and have a wider range of potential transformation temperatures. The characteristic transformation temperatures of martensitic transformation of CuAlNi alloys can lie between -200 and 200 °C, and these temperatures depend on Al and Ni content. Among the Cu -- based SMAs, the most frequently applied are CuZnAl and CuAlNi alloys. Although CuZnAl alloys with better mechanical properties are the most popular among the Cu-based SMAs, they lack sufficient thermal stability, while CuAlNi shape memory alloys, in spite of their better thermal stability, have found only limited applications due to insufficient formability owing to the brittle γ2 precipitates. The most important disadvantage of polycrystalline CuAlNi alloys is a small reversible deformation (one-way shape memory effect: up to 4 %; two-way shape memory effect: only approximately 1.5 %) due to intergranular breakdown at low stress levels. The technologies for production of shape memory alloys are induction melting, vacuum melting, vacuum arc melting, following hot and cold working (forging, rolling, wire drawing). In addition, rapid solidification methods, like melt spinning and continuous casting have been developed. These methods are characterized by high cooling rates. High cooling rates allow very short time for diffusion processes and may lead to extremely fine microstructure, better homogeneity etc. SMAs have found applications in many areas due to their thermomechanical and thermoelectrical properties (biomedical applications, engineering industry, electrical industry). In this paper, a review of shape memory alloys, properties and applications of mentioned materials is presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] As yet, continuous casting of Cu–Al–Ni SMAs with a cold mould was not reported. [•] 16mm strands were successfully cast via this technique. [•] The castability was found to be good. [•] No cracks or other casting flaws occurred. [•] Microstructures were martensitic already in as-cast condition. [ABSTRACT FROM AUTHOR]

The paper deals with results of thermal analysis of low-alloyed chromium-molybdenum steel. The methods of analysis were dilatometry, differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The Ac1 and Ac3 temperatures of the steel samples measured by dilatometry and DTA during the heating period were in good agreement. Generated by cooling a martensitic structure first became apparent at 503 K. Tempering of the as-quenched samples showed the presence of the second tempering stage in the region between 473 and 573 K. At that stage heat capacity decreased from 0.48 to 0.32 J g-1 K-1, as a result of conversion of transition carbide due to heat consumption. After normalization of the as-quenched samples the heat capacity values were restored to between 0.42 and 0.47 J g-1 K-1 in the temperature range from 373 to 673 K. [ABSTRACT FROM AUTHOR]

This work describes the hydrogen embrittlement damage of tubing made from a commercial low alloy manganese steel containing vanadium. Hydrogen charging of steels was carried out in 0.5 M H2SO4 solution which contained 10 mg/l As2O3 for 2 h under static load. Fractography was carried out using a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometry (EDXS). Normalizing the tubing increased the yield strength. Tubing normalized at 900 °C is more resistant to hydrogen embrittlement (HE) compared to that in the as-received condition. The improved behaviour of steels when normalized at 900 °C can be attributed to a fine ferrite-pearlite microstructure (mean area of pearlite colonies 2.5 times smaller than in the as-received condition) and a beneficial variation in hydrogen trapping behaviour. Initiation of fracture occurred at complex inclusion/matrix interfaces. The size of the inclusions that caused fracture was 2 to 5 μm. [Copyright &y& Elsevier]

In this work the failure of a mandrel and pipe during cold rolling of pipes ise presented. The effect of heat treatment on microstructure and hardness of mandrels made from X38CrMoV51 steel was investigated. A new heat treatment of mandrels was proposed. They are hardened at 1030 °C and quenched in oil. A triple tempering process was carried out in the temperature range from 530 to 560 °C. It was found that both fine carbide precipitation in the matrix and the dimensional stability of mandrels were obtained by this procedure. The obtained results are confirmed in industrial practice during the rolling of pipes in the cold pilger procedure. [Copyright &y& Elsevier]

This paper presents the results of thermal and microstructural analysis of Cu-Al-Ni shape memory alloy before and after heat treatment. After casting, a bar of Cu-12.8 Al-4.1 Ni (wt.%) alloy, obtained by the vertical continuous casting technique, was subjected to a certain heat treatment procedure. Solution annealing was performed at 850 °C for 60 min, followed by water quenching. Tempering was then performed at four different temperatures (150 °C, 200 °C, 250 °C and 300 °C). The microstructural results were obtained by optical and scanning electron microscopy. Thermodynamic calculation of ternary Cu-Al-Ni system under equilibrium was performed using Thermo-Calc 5 software. Phase transformation temperatures were determined by differential scanning calorimetry (DSC). The DSC results show the highest values of transformation temperatures in as-cast state. After solution annealing and tempering, the transformation temperatures show lower values with exceptional stability of Ms temperature (martensite start temperature). [ABSTRACT FROM AUTHOR]

Four Cu-rich alloys from the ternary Cu-Al-Mn system were prepared in the electric-arc furnace and casted in cylindrical moulds with dimensions: ϕ=8 mm and length 12 mm. Microstructural investigations of the prepared samples were performed by using optical microscopy (OM) and scanning electron microscopy, equipped by energy dispersive spectroscopy (SEM-EDS). Assignation of crystalline phases was confirmed by XRD analysis. Phase transition temperatures were determined using simultaneous thermal analyzer STA DSC/TG. Phase equilibria calculation of the ternary Cu-Al-Mn system was performed using optimized thermodynamic parameters from literature. Microstructure and phase transitions of the prepared as-cast alloys were investigated and experimental results were compared with the results of thermodynamic calculations. [ABSTRACT FROM AUTHOR]