Tramp Elements Research Articles

Evaporation of As and Sn from Liquid Iron: Experiments and a Kinetic Model during Top-Blown Oxygen Steelmaking Process.

Evaporation kinetics of tramp elements (M = As and Sn) in liquid iron were investigated by high-temperature gas–liquid reaction experiments and a phenomenological kinetic model. Residual content of As or Sn in the liquid iron ([pct M]) during the evaporation was measured in the temperature range of 1680 C to 1760 C. [pct As] and [pct Sn] decreased faster as the reaction temperature and [pct C] increased. Assuming first-order reaction kinetics, the apparent rate constants () were obtained at each reaction temperature and [pct C]. [pct M] in a liquid iron during the top-blown oxygen steelmaking process was simulated, with an emphasis on enlarging the reaction surface area by forming a large number of liquid iron droplets. The surface area and the droplet generation rate were obtained based on the oxygen-blowing condition. The whole surface area increased up to ∼163 times the initial liquid iron (bath) surface area, due to the generation of the droplets. Using the obtained in the present study, the evaporation of M during the top-blown oxygen steelmaking process for 200 tonnes of liquid iron was simulated. For a condition of [pct M] = 0.005 (M = As and Sn), As and Sn could be removed from the liquid iron, which was seen to be much improved by the consideration of the droplet generation. However, additional actions are required to improve the evaporation rate, as the evaporation rate in the BOF process was not fast enough to be practically considered.

Effect of initial solidification characteristics on longitudinal crack formation in thin slab caster

ABSTRACT Longitudinal surface crack has been one of the serious problems of thin slab casting (TSC). The present study was undertaken to comprehend the characteristics of longitudinal facial crack (LFC) and minimise the same in hot rolled low carbon steel sheets produced through thin slab casting and rolling (TSCR). Macro-structural characteristics of solidified shell has been investigated and correlated with plant observations. The centre and edges of funnel region showed maximum propensity of LFCs. TSC solidification is initiated with fine columnar dendrites which gradually coarsened towards the slab centre. This has been attributed to the characteristics of liquid steel flow instability in the upper mould region. Meniscus flow instability may lead to non-uniform heat transfer besides mould flux entrapment in the solidifying shell. Examination revealed that the mould hot faces ware covered with brass containing voids and cracks. Brass formation was found to be the most prominent around the meniscus of the wide hot face, which gradually faded out towards the mould exit. Tramp elements (zinc and lead) in liquid steel were found to be responsible for harmful brass formation during casting. The present findings were implemented in plant operation to minimise its concentration.

Effect of Intermetallics and Tramp Elements on Porosity Formation and Hardness of Al–Si–Mg and Al–Si–Cu–Mg Alloys

Effect of Intermetallics and Tramp Elements on Porosity Formation and Hardness of Al–Si–Mg and Al–Si–Cu–Mg Alloys

Effect of tinplated scraps surface-to-volume ratio on the efficiency of the electrolytic detinning process

Recycling of steel scrap is a more competitive practice than steelmaking from iron ores. However, the presence of tramp elements within steel scrap affects the quality of the new steel produced. Tinplating of cans for drinks and food contains a high quantity of tin, which is responsible for adverse phenomena such as surface hot shortness and temper embrittlement. Thus, the development and application of a detinning process is necessary. This investigation focuses on studying an electrolytic detinning process performed in a 2.5M NaOH solution to decrease the tin content in tin-plated scrap. The process's performance was evaluated by varying input variables such as the process time, the applied current density, the operating temperature, and the material size (surface to volume ratio, S/V). The best process time for electrolytic de-tinning was estimated. The effect of the applied current density and S/V ratio on the process time and on the energy consumed by the process was evaluated at both room temperature and at 70 °C. The results showed that the tin content in tinned plates can be reduced to a negligible level (<0.01 wt-%) at 70 °C and the efficiency of de-tinning tin-plated scrap proved to increase with the S/V ratio.

How will tramp elements affect future steel recycling in Europe? – A dynamic material flow model for steel in the EU-28 for the period 1910 to 2050

Global steel production has undergone massive growth since WWII. In recent decades, however, affluent regions such as the US and the EU-28 have been experiencing a saturation of the steel market. Stagnant steel production volumes and increased post-consumer scrap volumes are the consequence. The increasing shares of post-consumer scrap provide the opportunity to increase the scrap rate (share of utilized scrap) in crude steel production. However, steel recycling has a major limiting factor: the content of specific tramp elements.In the present study, a dynamic material flow model for steel is used to compare available scrap with crude steel demand on a quantitative and qualitative level (tramp element content of Cu, Ni, Mo, Cr and Sn). The results show that post-consumer scrap increases from 80 Mt/yr (65% of all scrap available) in 2020 to more than 100 Mt/yr (75% of all scrap available) in 2050. Based on the model, the development of the yearly surplus of low purity scrap (for which there is a higher supply than demand) was assessed via material pinch analysis. The low purity scrap surplus rises further, from today's 20 Mt/yr (2020) to 43 Mt/yr in 2050. Assuming that the current handling of scrap continues, the maximal scrap rate is shown to lie at around 55%, while the potential scrap rate (without quality constraints) could reach 75%. The dilution of low purity scrap with high purity resources would allow the utilization of all scrap until 2040 if the current collection scheme remains in place.

Steel scrap generation in the EU-28 since 1946 – Sources and composition

A detailed understanding of scrap generation and utilization is needed to target increased material efficiencies and circular economy in the steel industry. In the present paper, the generation and composition of steel scrap (production & forming scrap, fabrication scrap and post-consumer scrap and their composition) in the former territory of the EU-28 have been assessed from 1946 to 2017 by means of Material Flow Analysis. The results reveal that the steel scrap composition in the EU-28 has changed significantly since 1946. Until 1980 scrap generation was dominated by new scrap (mostly production & forming scrap). Today, most of the overall steel scrap is post-consumer scrap. Most of the new scrap consists of fabrication scrap. Taking the presence and tolerance levels of major tramp elements in steel (Cu, Sn, Cr, Ni and Mo) into consideration, a material pinch analysis reveals a surplus of steel scrap with higher levels of tramp elements since the 1990ies. This scrap could only be utilized in the European steel industry by dilution with primary iron sources. At present, this surplus scrap seems to be largely exported as its quantity corresponds well to the net-exports of steel scrap from the EU-28. Transplanting the observed trends of steel scrap generation to emerging economies implies a significant increase in fabrication and post-consumer scrap in these countries in the near future. However, the utilization of scrap at higher rates, particularly post-consumer scrap, will challenge the local steel industry as tramp elements significantly increase along the production, use and end-of-life chain.

Model Development to Study Uncertainties in Electric Arc Furnace Plants to Improve Their Economic and Environmental Performance

A statistical model is developed in order to simulate the melt composition in electric arc furnaces (EAFs) with respect to uncertainties in (1) scrap composition, (2) scrap weighing and (3) element distribution factors. The tramp element Cu and alloying element Cr are taken into account. The model enables simulations of a charge program as well as backwards estimations of the element concentrations and their variance in scrap. In the backwards calculation, the maximum likelihood method is solved by considering three cases corresponding to the involved uncertainties. It is shown that the model can estimate standard deviations for elements so that the real values lie within the estimated 95% confidence interval. Moreover, the results of the model application in each target product show that the estimated scrap composition results in a melt composition, which is in good agreement with the measured one. The model can be applied to increase our understanding of scrap chemical composition and lower the charged material cost and carbon footprint of the products.

Deterioration of HAZ toughness by residual Sn and Determination of its Allowable Content for Electric Furnace Steels

One promising direction in steelmaking to respond to global climate change issue is to increase the use of electric furnace manufacturing methods using zero-carbon electricity, which have received more and more attention recently. Considering the replacement from blast furnace steel, the temper embrittlement problem induced by some tramp elements, which is unique behavior for electric furnace methods, must be resolved.Sn is considered as a tramp element that cannot be removed in steel refining process, and it has been reported that the toughness of the base metal and the welded heat affected zone can be significantly degraded. In the case of electric furnace steels with degraded toughness, segregation of Sn is observed at grain boundaries and the resulting fracture mode shifts to intergranular fracture mode. In this study, in order to quantify the allowable amount of Sn added to thick steel plates that is used for large-heat input welding, experiments were conducted on specimens with different amounts of Sn and heat-treated for different holding times at 400℃, which is a typical embrittlement temperature and investigated the effect of the amount of Sn on the change in low-temperature fracture toughness. As a result of fracture toughness tests, clear evidence of temper embrittlement was observed. Apart from previous famous study by McMahon, there was no intergranular fracture in fracture surface but transgranular and cleavage fracture was observed. Therefore, the mechanism by which Sn tends to cause cleavage fracture in the weld heat affected zone was proposed. Based on our newly proposed mechanism, a model was developed to estimate the transition temperature change for various conditions of tempering time, tempering temperature and Sn content.Finally, the authors propose allowable maximum content of Sn based on the model for the establishment of the rational ore sorting system from scraps in near future society.

Optimization of Production of Blast Furnace Ferromanganese in Conditions of Non-Integrated Iron Works

Production of high carbon blast furnace ferromanganese (HC FeMn) in conditions of Russian non-integrated iron works stipulates use of various combinations of permanently changed sorts of manganese ores with different mineralogy, manganese content and granulometric composition. Operation complexity is caused by challenge to satisfy with customers’ stringent requirements specific to percentage of manganese, silicon and maximum permissible content of tramp elements in produced alloy as well as by necessity to recycle fine fraction formed at the stage of crushing of solidified large-sized ferromanganese. Fluxless technological regime is defined as a most efficient mode to achieve high technical and economic indices. Special attention is given to methods of increase of manganese recovery in every stage of technological process. The largest losses of manganese are related to losses with slag and top gas, and developed techniques to minimize these losses are described with taking ecological aspects into consideration.

The coming wave of aluminum sheet scrap from vehicle recycling in the United States

The emergence of mass-produced aluminum sheet intensive vehicles presents an opportunity for recyclers to shift towards high value recycling into wrought alloys. We use dynamic material flow analyses (2015–2050) to estimate the timing, scale, and composition of U.S. aluminum automotive body sheet (ABS) scrap generated from the aluminum ABS intensive vehicles with the highest U.S. sales: Ford F-150, Super Duty, Expedition, and Lincoln Navigator. Lifespan distribution models are derived for each vehicle, and 5xxx and 6xxx series sheet alloys are aggregated according to their copper and magnesium content. A Markov chain model is used to estimate the fraction of deregistered vehicles scrapped domestically versus exported.It is found that the above four vehicles account for around 1,200 kt of aluminum ABS embedded within the 2020 U.S. fleet. The aluminum ABS intensive construction of these vehicles presents a unique opportunity to U.S. recyclers. If production continues at the current volumes, aluminum ABS scrap from these vehicles will increase to approximately 125 kt/year in 2035 and 246 kt/year in 2050. The majority of this scrap will be available for U.S. processing with <<10% of deregistered vehicles exported or achieving vintage status. For comparison, only 121 kt of aluminum auto shred (containing negligible aluminum ABS) was domestically consumed in the U.S. in 2017. We analyze the composition of the future potential scrap streams, revealing the need for alloy separation and tramp element removal if closed loop aluminum ABS recycling is to be achieved.

Potential Influences of Impurities on Properties of Recycled Carbon Steel

Contamination with tramp elements is a major concern in steel recycling. This study aimed to identify the influence of impurity elements on the major properties of carbon steel. The content of impurity elements in recycled steel was determined via elemental analysis of randomly sampled steel bars. Of the 23 impurity elements considered, 15 were found to be mixed in the recycled steel. Industrial standards stipulate that the six major properties of carbon steel are tensile strength, elongation, yield point or proof stress, soundness in the welding area, fracture toughness, and bendability. The influence of the fifteen impurity elements on all of these properties except bendability was investigated by reviewing previous academic reports. Properties related to strength and stress were found to be enhanced by the presence of almost any impurity, while elongation and welding soundness were often compromised. The influence of impurities on the other properties remains largely unknown. The negative effects of impurities on the workability and weldability can be minimized by adjusting the steelmaking, casting, and annealing processes, or rethinking the design of products and manufacturing processes. Further, the incorporation of impurities may be prevented during the recovery of steel scrap from end-of-life products. A useful approach to the prevention of the negative influence of impurities is a new concept termed R-PSPP, which stands for recovery, process, structure, property, and performance.

Partitioning of tramp elements Cu and Si in a Ni-based superalloy and their effect on creep properties

An alloy's processing history, including melting, remelting or the choice of stock material, affects its purity and eventually involves tramp element pickup or retention. In this investigation, variants of a novel Ni-based superalloy were manufactured with different levels of purity. The so-called low purity alloys contained 0.138 wt. % Cu and 0.019 wt. % Si while the Cu and Si levels were below x-ray fluorescence (XRF) detection limits of 0.003 and 0.010 wt. %, respectively, in the high purity ingots. Atom-probe tomography (APT) was carried out and revealed Si partitioning at the following interfaces: grain boundaries, MC carbide/γ, M3B2 boride/γ and M3B2 boride/γ′. Copper was found to primarily segregate to the γ′ precipitates. An average of 2.4 × decrease in creep life and 4.3 × decrease in creep ductility was measured in the low purity alloys, which was attributed to the embrittlement caused by Si segregation to grain boundaries. Furthermore, the positive effect of B on the creep properties was mitigated by the presence of Si. Thermodynamic predictions for the matrix and γ′ precipitate compositions represented the trends observed experimentally although the extent of preferential partitioning lacks accuracy. Monte Carlo simulations were performed to describe the partitioning of Cu and Si atoms to either γ or γ′ phases.

Toughening of AISI 410 Stainless Steel Through Quenching and Partitioning and Effect of Prolonged Aging on Microstructure and Mechanical Properties

AISI 410SS is one of the widely used martensitic steels. Tramp elements present in this steel segregate during tempering at prior austenite grain boundaries, which reduces the cohesive strength and results in intergranular cracking. Quenching and partitioning heat treatments stabilize minutes of austenite at room temperature. This reduces the segregation of tramp elements after prolonged aging and yields four to five times higher toughness compared with normalized and tempered steels. Thus, it provides resistance to cracking.

Removal of Tramp Elements from Molten Iron for Recycling Ferrous Scraps

The possibilities of removing impurities in molten iron by oxidation and evaporation, which are usual methods in metal refining, are firstly investigated. Of all the elements which are dissolved in molten iron, Cu, Sn Ni, Co, Mo and W are found to be difficult to be removed by such usual methods as oxidation and evaporation. The elements which are difficult to be removed in steel making when they are once dissolved into molten iron are called “tramp elements”. In recycling ferrous scraps, to begin with, it is important to keep iron from being mixed with tramp elements. But, it is necessary to develop a method to remove tramp elements, because it is impossible to avoid the contamination of these elements completely. In this work, several prospective methods to remove such tramp elements are discussed. Copper, which is one of the most important tramp elements in iron, can be removed by evaporation or by sulfurization, although it is not enough to apply them in practical use. As other methods, in this work, the possibilities to remove copper in molten iron by oxidation and by the use of calcium are proposed. It is found that copper and tin in iron can be decreased at the content of 0.2 to 0.4mass% and under 0.001mass%, respectively by oxidation. If pure calcium is equilibrated with iron directly at 1823K, the high distribution ratios, LSn(mass) (=(mass%Sn)in Ca-Pb/[mass%Sn]in Fe) = 3400 and LCu(mass) (=(mass%Cu)in Ca-Pb/[mass%Cu]in Fe) = 200 are expected.

High-temperature oxidation kinetics of Cu bearing carbon steel

In this article, oxidation kinetics of carbon steel is investigated with respect to the existence of copper (Cu). It is aimed to figure out the high-temperature oxidation behaviours of Cu bearing steel. Cu induced hot shortness is the main problem of recycling of tramp element containing steels. The experimental temperature range was decided according to the steel deformation process’. Oxidation experiments were conducted between 900 and 1200 °C with 100 °C intervals in an electrical resistance furnace. High-temperature oxidation kinetics of Cu bearing carbon steel was examined. Topographical surface analysis’ of samples were carried out via X-ray diffraction, scanning electron microscopy, optical microscopy. Mass gain rate and kinetical results were algebraically evaluated. Cu segregation on steel surface at elevated temperatures and its behaviour against oxygen were observed.

Recycling of Ferrous Scraps

This work provides an overview of the steel production process, pretreatment and tramp elements of scraps and recycling technology of dust generated from steelmaking process. Steel is the most common metal used by mankind, with the world production of crude steel in 2018 exceeding 1.8 billion tonnes. Recycling of ferrous scraps reduces CO2 emissions by about 42 % and saves about 60 % of energy, compared to production steel from iron ore. Steel scraps are usually recycled to both an electric arc furnace (EAF), scrap-based steelmaking and the basic oxygen furnace (BOF), in ore-based steelmaking. EAF steelmaking, which uses iron scrap as a main raw material, is changing to an energy-saving type with a device for preheating scrap. Dust generated from the steelmaking process is recycled in various ways in the steel mill to recover iron and zinc.

Grain boundary engineering to overcome temper embrittlement in martensitic steel

Grain boundary engineering (GBE) approach has been introduced in martensitic steel through quenching and partitioning (Q&P) heat treatment to overcome temper embrittlement. This heat treatment increases fraction of low energy coincidence site lattice (CSL) boundary from 0.12 in Q&P specimen to 0.22 in Q&P-tempered specimen through transformation of retained austenite to martensite. Presence of austenite in martensitic matrix produces different interfaces. Low energy austenite / austenite and austenite / martensite interfaces reduces segregation of tramp elements during tempering leading to increased toughness compared to normalized and tempered specimen having high energy martensite / martensite interface. Increased toughness is accompanied by a change in fracture morphology from intergranular fracture to typical dimple fracture.

Microscopic Distribution and Coexistence States of Tramp Elements and Valuable Metals in Recycled Steel Material by a Statistical Analysis

Microscopic Distribution and Coexistence States of Tramp Elements and Valuable Metals in Recycled Steel Material by a Statistical Analysis

Estimating increasing diversity and dissipative loss of critical metals in the aluminum automotive sector

As the demand for and consumption of products and services grow in the US, so does the concern for sustainable material usage. In the automotive industry, major sustainability issues revolve around advocating for improved fuel economy and the incorporation of materials with higher recyclability in order to reduce greenhouse gas (GHG) emissions. A popular strategy to achieve this in the automotive industry is light-weighting. Many studies in this field are focused on the environmental benefits of light-weighting, that is, how replacement of traditional steel in the automotive industry with aluminum, for instance, will help reduce the amount of CO2-eq emissions in the environment. The increasing use of aluminum in the industry for differing automotive applications broadens the range of alloying elements. Unfortunately, many of these elements are dissipatively lost and also deemed critical. Furthermore, some of the alloying elements accumulate as tramp (unwanted) elements in the secondary aluminum stream, hence posing as a barrier to effective recycling, thus leading to material and economic losses. We quantified the material losses and analyzed the economic losses attributed to the dissipation of critical metals and also examined the attendant accumulation of tramp elements in the recycled aluminum stream. Our results indicate that to achieve a more circular economy requires investment and further development of a) operational blending and batching strategies that comprehend alloying additions and the inherent variability of their actual composition, and b) economically feasible material identification and sorting technologies that will help in abating these material losses and associated economic losses.

Review: Possibilities of Steel Scrap Decopperization

Copper is one of the most common tramp elements in steel scrap. It originates from recycling of copper-alloyed steels, such as weather-resistant construction steel (up to 0.3 mass% Cu) or austenitic stainless steels (up to 3 mass% Cu). In both cases, corrosion resistance is increased. Certainsteels, on the other hand, be alloyed with Cu to influence the Ms point, ductility and/or antiseptic properties. However, copper increases the risk of hot shortness and cold work hardening in low-alloyed steels, which is even more pronounced if Sn is also present in the alloy. Furthermore, Cu is frequentlyintroduced into the scrap melt unintentionally, when steel scrap contains undiscovered parts or components of Cu or its alloys. Because the oxygen affinity of copper is lower than that of iron, selective oxidization of Cu from steel melts is not possible. Therefore, various alternative decopperization methods have been proposed by researchers, starting from the mid-1950s, up to the present. Among those are, apart from scrap pre-treatment, sortation and physical separation, melt dilution, treatment with chemical elements, carrier-metal equilibration, distillation/volatilization, slag treatment, melt filtration and oxide powder blowing. In this paper, various methods for decopperization of steel scrap melts, as reported in available literature, are being reviewed. This is complemented by pretest results from the Institute of Iron and Steel Technology at TU Bergakademie Freiberg (IIST).