metals Article Kinetics of Arsenic Surface Segregation in Scrap-Based Silicon Electrical Steel Darja Steiner Petroviˇc Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia; [email protected]; Tel.: +386-1470-1968 Abstract: The segregation kinetics of surface-active, residual elements are investigated in an in situ study of annealing scrap-based silicon electrical steel sheet where the arsenic (As) surface segregation is highlighted. During annealing in the temperature range of 300–950 ◦C, different kinds of interactions between the segregated residual elements were observed. Attractive interactions between the segregands produced co-segregation, e.g., between Sn and Sb, whereas repulsive interactions resulted in site competition, e.g., between Sn and As. These competing interactions are strongly time dependent. In spite of there being twice as much Sn compared to As in the bulk material, the As prevailed in the surface enrichments of the polycrystalline silicon steel at 950 ◦C. The intensity of the As surface segregation in the temperature range 800–950 ◦C is proportional to the calculated amount of γ-austenite phase in the (α + γ) steel matrix. The detected phenomenon of the As versus Sn site competition could be valuable for the texture design and surface engineering of silicon steels with a thermodynamically stable two-phase (α + γ) region. Keywords: arsenic; surface segregation; silicon steel; α-ferrite; γ-austenite; surface engineering; Auger electron spectroscopy 1. Introduction There is an increasing need for highly power-efficient electrical machines for a wide range of applications in which silicon electrical steel is the core material. For an optimal de- Citation: Steiner Petroviˇc,D. Kinet- sign of the electromagnetic properties, the chemical composition, and the recrystallization ics of Arsenic Surface Segregation in annealing of the steel are the most important influencing parameters [1–4]. Because the Scrap-Based Silicon Electrical Steel . interest will continue to grow for high-specific-power electrical machines, especially for Metals 2021, 11, 1. http://dx.doi.org/ various new and un-conventional applications, the development of new classes of high- 10.3390/met11010001 specific-power electrical machines and drives is required [4]. Recent studies reveal that a properly controlled phase transformation from γ-austenite Received: 26 November 2020 to α-ferrite provides a promising method to optimize the crystallographic texture of silicon Accepted: 15 December 2020 steels [5,6]. It is well known that the phase transformations in an alloy system are set Published: 22 December 2020 by the laws of thermodynamics. In Fe–Si alloys that are to be further processed into grain-oriented and non-oriented electrical steel sheets and coils, the metallurgy is relatively Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims complex. When secondary-metallurgy routes are involved, the steel’s cleanliness is an in published maps and institutional important factor. Efforts must be focused on the overall chemical composition of the steel, affiliations. and the control of the residual elements must be appropriate. In the electric-arc-furnace (EAF) steelmaking process, the main raw material is ferrous scrap, and an inspection of its quality is the first crucial step in producing a clean steel. Ferrous scrap is the most recycled material in the world, and through its utilization Copyright: © 2020 by the author. Li- CO2 emissions can be significantly reduced. According to the comprehensive statistical censee MDPI, Basel, Switzerland. This data of The World Steel Association [7], the imports and exports of scrap rose globally article is an open access article distributed to >200 million metric tonnes in total, and that value is still increasing. In Figure1, under the terms and conditions of the the importance of the ferrous-scrap trade flow in the global economy is demonstrated by Creative Commons Attribution (CC BY) imports being greater than exports. license (https://creativecommons.org/ licenses/by/4.0/). Metals 2021, 11, 1. https://dx.doi.org/10.3390/met11010001 https://www.mdpi.com/journal/metals Metals 2020, 10, x FOR PEER REVIEW 2 of 13 > 200 million metric tonnes in total, and that value is still increasing. In Figure 1, the im- portance of the ferrous-scrap trade flow in the global economy is demonstrated by imports being greater than exports. Metals 2021, 11, 1 2 of 12 Figure 1. Trade flow of ferrous scrap in the global economy, data from [7]. Figure 1. Trade flow of ferrous scrap in the global economy, data from [7]. The scrap received by steel plants comes from the recycling industries and should be pre-processed in several steps, including collecting, sorting and mechanical preparation The scrap received by steel plants comes from the recycling industries and should be via magnetic separation, fragmentation, physical separation, etc. Currently, the steel pre-processed in several steps, including collecting, sorting and mechanical preparation industry uses predominantly visual inspection to specify the ferrous scrap and its quality. via magnetic separation, fragmentation, physical separation, etc. Currently, the steel in- The concentration of impurities and residual elements is generally identified after the dustry uses predominantly visual inspection to specify the ferrous scrap and its quality. melting process, rather than before or during the selection of the scrap [8]. The concentration of impurities and residual elements is generally identified after the It is well known that routinely manufactured steel using recycled scrap leads to an melting process, rather than before or during the selection of the scrap [8]. overall increase in the impurity concentrations of Cu and Sn, in particular, though the presence of other impurities,It is well known like As that and routinely Sb, is not manufactured negligible [9– steel12]. Although using recycled there isscrap a leads to an great deal of knowledgeoverall increase about in residual the impurity Cu and concentratio Sn in steel, ans shortage of Cu and of recent Sn, in studies particular, on though the other, less commonpresence elements of other at impurities, residual levels like has As beenand Sb, identified is not negligible [8]. [9–12]. Although there is a Arsenic (As)great can deal originate of knowledge from several about resources, residual Cu such and as complexSn in steel, iron a shortage ore, scrap of steel, recent studies on ferroalloys, andother, other less furnace common charges elements [9–11 at]. residu The effectsal levels of has residual been identified element As [8]. on the properties of steelsArsenic are receiving (As) morecan originate and more from attention several [9,11 resources,–17]. In a such micro-alloyed as complex steel iron ore, scrap resulting fromsteel, a compact ferroalloys, strip productionand other furnace (CSP) process, charges As [9–1 was1]. foundThe effects to segregate of residual at the element As on grain boundariesthe whenproperties the steel of steels was annealedare receiving in the more temperature and more range attention 950–1100 [9,11–17].◦C[18 In,19 a]. micro-alloyed Macroscopic segregationsteel resulting studies from showeda compact that strip As production segregated (CSP) in regions process, near As the was top found and to segregate bottom surfacesat the of the grain strip boundaries [20]. Moreover, when Asthe was steel found was annealed to segregate in the to the temperature interface be- range 950–1100 tween the matrix°C [18,19]. and the Macroscopic oxide scale of segregation the micro-alloyed studies steelshowed [21]. that It was As alsosegregated reported in [regions9] near the that As and (Astop + and Cu) bottom accelerate surfaces the oxidation of the strip of C–Mn [20]. steelsMoreover, and induceAs was hot found shortness. to segregate to the Surface crackinginterface is most between severe atthe 1050 matrix◦C. and As promotesthe oxide internalscale of the oxidation micro-alloyed and facilitates steel [21]. It was also the grain-boundaryreported oxidation [9] that atAs temperatures and (As + Cu) above accelerate 1000 ◦ theC[9 oxidation]. In Fe-0.3 of wt C–Mn % Cu steels alloys, and induce hot the presence ofshortness. up to 0.1 Surface wt % As cracking did not is induce most grain-boundarysevere at 1050 °C. cracking As promotes [12]. internal oxidation and A studyfacilitates of the literature the grain-boundary [9–25] shows oxidation that the at effects temperatures of As on above the properties 1000 °C [9]. of In Fe-0.3 wt % iron alloys andCu steels alloys, have the beenpresence studied of up for to contents 0.1 wt % ranging As did not from induce 0.002 grain-boundary to 10.0 wt % As, cracking [12]. whereas surface-science investigations on As segregation behavior were predominantly focused on As contents ranging from 0.005 to 0.05 wt % As in polycrystalline samples and single crystals. High temperature annealing studies have shown that the segregation of S is highly favored over the segregation of As [23,24]. Metals 2021, 11, 1 3 of 12 In the research field of silicon electrical steels, the search for the microstructure and texture optimization of electrical steels that can reduce magnetic losses is of great relevance. Therefore, the aim of this study is to provide more accurate data on the temperature- time dependency of As surface segregation in the scrap-based silicon steel produced by secondary metallurgy. The results derive from a methodology using in situ Auger electron spectroscopy (AES) during isothermal annealing at temperatures from 300 ◦C up to 950 ◦C. 2. Material and Methodology 2.1. Material In this study, a specimen of semi-processed, non-oriented silicon steel sheet with dimensions of 15.0 mm × 5.0 mm × 0.1 mm was used. The alloy’s chemical composition is given in Table1. Table 1. Chemical composition of the scrap-based silicon steel (wt %). Fe C Si Al Mn P S N O Cu Sb Cr Ni Sn As Bal.