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By Mariana Carla Mendes Rodrigues

The present study deals with the effects of strain rate on the functional behavior of NiTi thin wires. The samples, in the austenitic condition at room temperature, were mechanically cycled 20 times by loading up to 6% strain followed by complete unloading, at 25°C. Four different quasi-static strain rates were assessed: 1x10-4, 1x10-3, 1x10-2 and 5x10-2s-1. The functional properties are described by means of critical stress to induce martensite, stress at maximum strain, energy dissipated per cycle and residual strain. The sensitivity of repeated cyclic deformation to strain rate is also analyzed in terms of phase stability. The results show that the fluctuation in the loading plateau, due to non-homogeneous transformation, increases with increasing strain rate. During cycling, it is observed that higher strain rates result in lower critical stress to induce martensite after the 5th cycle. However, the stress at maximum strain is higher at high strain rates, regardless the number of cycles. The accumulation of residual strain also increases with the strain rate due to the higher applied stress. During unloading, both the elastic deformation of stress-induced martensite and the reverse transformation seem to overlap at high strain rates. The dissipated energy behavior changes between the 1st and 20th cycle. No martensite is stabilized after training, but the intensity of the X-ray diffraction peaks of austenite increases with strain rate, as a result of stress relaxation.

Aug 17, 2017

By Guilherme Corrêa Soares

The effects of temperature and strain rate on the mechanical behavior of a superelastic NiTi wire were investigated by uniaxial tensile testing. A universal testing machine with an attached heating chamber was used for the tensile tests. Temperature influence was studied through straining of samples until rupture at a fixed strain rate and temperatures of 25, 50, 75, 100, 125, 150, 175 and 200 °C. Strain rate effects were investigated by straining samples until rupture at room temperature and strain rates of 10-2, 5 x10-3 , 10-3, 5 x 10-4 and 10-4 s-1. The effects of temperature and strain rate on NiTi mechanical behavior were discussed in terms of critical stress to induce martensite and austenite yield strength, when applicable; upper plateau stress, transformation plateau length and ultimate plateau stress. It was found that increasing test temperature and strain rate shifted the stress-strain curve upwards, albeit temperature displayed a greater influence. Plateau length increased with temperature, but no significant changes were detected as a result of different strain rates.

Aug 17, 2017

By Ivo Filipovic

The steel melting process in an Electric Arc Furnace is a complex set of tasks, coping with highly dangerous hazards as fire, explosions, uncontrolled reactions, hot metal projections and gas or dust emissions. Melt shops are dangerous working areas for operators, recording statistics with a high frequency of injuries. In the past years, without dedicated safety equipment, there wasn't a real attitude to the risk prevention. The paper describes the available technological packages to eliminate the manned activities on the melting floor, with the aim to prevent accidents and keep furnace operators safe. The technological packages suite extends the automatic control of the EAF melting process to all the operations from charging phase to tapping. Plus, the integration of the most frequent operations by automated specialized tools effectively minimizes power-off times, enhancing reliability and improving the transformation costs.

Aug 17, 2017

By Douglas Glenn Stalheim

Hot strip structural steel coil used in construction, engineering, transport, structural applications and other applications are widely used in yield strengths from 300 – 700 MPa. However, structural design engineers are now not only requiring various strength levels but also other mechanical properties, primarily good formability, toughness and weldability. To produce a balanced approach to a cost effective structural steel, hot strip coil requires an understanding of utilization of an optimized alloy composition designed for the layout/equipment capabilities of a given hot strip mill to produce the desired metallurgy for optimum mechanical property performance. The term “cost effective” does not just focus on alloy design, but also ease of overall processing from steelmaking, casting, rolling and cooling, stable mechanical properties with a statistically normal distribution, no downgrades/rejections and a product that the end user recognizes as being superior to others. The desired metallurgy is simply understanding what will be the optimum microstructure and cross sectional grain size/distribution needed to meet the mechanical property requirements. This paper is a follow up paper that previously described optimum base alloy designs along with steelmaking/casting processing considerations and will focus on proper reheating, rolling and cooling metallurgy/processing strategies to produce quality cost effective hot strip structural steel coil.

Aug 17, 2017

By Enif Gutiérrez Guerrero

Inclusion deposition is still a standing problem in the continuous casting of steel since the deposition of alumina inclusions inside the SEN affects the productivity and the product quality. The present work studies the factors involved in the inclusion deposition at the nozzle and the effects of inertial, gravitational, buoyant, pressure gradient, and Saffman forces on the inclusion trajectories. The results show that the inclusions reaching the nozzle, only 30% get deposited along its walls mainly at the Upper Tundish Nozzle (UTN). This area of higher deposition is identified close to a low static pressure and a high turbulent kinetic energy dissipation zones where the effects of the gravitational and buoyant forces do not promote a significant inclusion radial movement since these are aligned with the direction of the flow stream lines. In contrast, in this zone, the Saffman force shows an important effect on the deposited inclusions, slowing down the inclusions in the vertical axis and increasing their radial movement.

Aug 17, 2017

By Saul Garcia Hernandez

The research work objective is to study a new ladle shroud internal design to reduce the slag emulsification in the tundish during ladle transient periods. A 3D mathematical model of the tundish was created to solve the fundamental equations, a turbulence model, and a multiphase model. The results show that using a conventional ladle shroud, the fluid is delivered with an excessive amount of kinetic energy being dissipated inside the tundish bath, generating strong mixing flow patterns and entrapping a massive amount of slag. In the other hand, the proposed ladle shroud dissipates the kinetic energy before the fluid enters the tundish promoting less intense mixing patterns; thus, the amount of slag emulsification is reduced significantly. Consequently, if the internal design of the ladle shroud is able to dissipate the kinetic energy before the fluid enters the tundish, it shall be possible to reduce considerable the slag emulsification and the slag opening area.

Aug 17, 2017

By Alberto Lainati

The Bar Reducing and Sizing Technology has a core function in the value-chain for the production of rolled SBQ (Special Bar Quality) products. The EVO 2+4-roll is based on the compact combination of a 2-roll high-reduction module followed by a 4- roll low-reduction module for precise sizing. The EVO 2+4-roll mill, allows to gain significant technical and economical advantages in the hot- and post-rolling process routes: dimensional and surface accuracy, quick adaptability to processing variances and to small lots requirements, superior technological features of as-rolled product, competitive capex and opex. The EVO 2+4 unit has a very compact design, which makes it suitable both for new mills and upgrade applications.

Aug 17, 2017

By Gergö Rimaszéki

Due the fast growing of pig iron and steel in the last years associate with some mineral resources changes (Hematite?Itabirite), has been checking the sinter feed degradation. The typical sinter feed (0.15;-6.3 mm) has become limited and the rapid growing production resulted in more and more fine ore (< 150 µm) availability in the market. The sinter plant operators are facing several new challenges since the mixing and granulation- and the sintering behavior of the fines containing mixtures often differs from the traditional sinter feed´s behavior. The utilization of fines in the sinter plants might increase the process water consumption required for the mixing and granulation process or even the solid fuel consumption, which effects the operational cost of the plant significantly. The current study presents an overview about Outotec´s laboratory facilities and competence regarding the mixing and granulation of fines in different equipments. The usage of high intensity mixers (HIM) – vertical and horizontal as well – showed to be the most effective, based in cold agglomeration tests in small scale, in case of fine ore handling. Permeability and particle size distribution curves are used to evaluate and demonstrate the efficiency of the different equipments. Outotec´s ”Know-How” with the different type of mixer and the modern laboratory facilities provide an excellent opportunities to optimize the mixing and granulation procedure and utilize up to 100 % pellet feed

Aug 17, 2017

By Márcia Maria da Silva Monteiro Pereira

Tundish is the last reactor where significant metallurgical operations can still be done. Calcium aluminate slags are able to positively contribute to metallurgy considering oxide separation, protection against reoxidation and preclusion of resulphurisation. However, these are poor insulators. When using low melting point slags it is necessary to use another covering material. The deviation from saturation can be used as a measure of absorption capacity. By utilizing computerized construction of ternary and quaternary diagrams it is possible to compare different slags and to find proper slag compositions with reasonable capacity to dissolve inclusions. Objective of the present technical contribution is to evaluate tundish slag capacity to absorb inclusions, considering a particular tundish industrial slag and the changes in its chemical composition during continuous casting of steel. It was observed that slag composition changed during the continuous casting process; this variation is possibly related to interaction between the CaO-Al2O3 liquid slag and the rice hull ash layer which is used above it. Computational thermodynamics was used to determine activity of alumina dissolved in liquid slag; it was observed that the variation in slag composition did not change slag capacity to absorb inclusions, since precipitation of Al2O3 solid phases is not predicted.

Aug 17, 2017

By Andrea Taurino

Innovation means implementing a new product or a product that has undergone significant improvement over time, in terms of method, form and performance. Innovation encompasses all the scientific, technological, organizational, financial and commercial steps that need to be taken to put it into operation. Innovation combined with research and development makes it possible to perfect the product with consistency over time. Taking inspiration from the bases developed by the Austrian economist Joseph A. Schumpeter back in 1911, Danieli came up with the concept of “Innovaction” – a combination of Innovation and Action, to refer to the development and advancement of various products for the steelmaking industry, including the loop laying head for wire rod.

Aug 17, 2017

By Qingwen Dai

The Marangoni effect is an important phenomenon where a surface tension gradient drives liquid towards high surface tension regions. Temperature gradient, evaporation, disparity of viscosity, and surface roughness and topography are all significant factors that can affect this thermo-capillary migration. The purpose of this study was to investigate the influence of micro-groove patterns on the migration of paraffin oil, and obtain a well-designed texture of micro-grooves to prevent the thermo-capillary migration. Patterns of micro-grooves with differing orientations and geometric parameters were fabricated on the surface of SUS 316 stainless steel substrates. Experiments on the migration behavior with different viscosities of paraffin oils were carried out various temperature gradients. The experimental phenomena indicated that the surface with the micro-grooves perpendicular or parallel to the temperature gradient have a strong impact on the migration performance of paraffin oil. Micro-grooves perpendicular to the temperature gradient exhibited extraordinary slower migration velocity than that of the parallel one. Width and depth of micro-grooves had an obvious influence on the behavior of temperature-driven migration and detail discussions on the effects of these geometric parameters were carried out.

Jul 31, 2018

By Marcelo Rebellato, Leonardo Silvestre, Zhang Yongqing, Felipe Bastos, Zhang Weiqiang

This work reviews the new version of GB1499.2-2018 Chinese national standard and specification, which governs the production of high-strength reinforcing hot rolled ribbed bars in China. In addition, it discusses the main concerns from Chinese rebar makers that might affect production and application of Nb-bearing rebars, like reheating temperature required to dissolve given niobium additions, the promotion of bainite microstructure and continuous yielding, as well as Nb strengthening effects. Through extensive investigation involving both thermomechanical laboratory simulations and industrial trial, the existing state and effects of Niobium along the reheating, rolling and cooling are illustrated. At the end, optimum processing conditions have been established to produce high strength rebars for the specified requirements. The adoption of new process conditions reflected in an amount of about 20.0 million tons of Nb-bearing rebar being produced in China in 2018 with required tensile properties and microstructure, and helped rebar makers to reduce production costs considerably. Based on production data, Niobium demonstrated positive strengthening effect for high strength rebars, in particular for small diameter rebars with earthquake resistant performance. What is more, the results of the research enrich the knowledge of the application of Niobium in steels when TMCP rolling is not used.

Oct 1, 2019

By Thiago Pinto Silva, Leandro Rocha Lemos, Luiz Fernando Andrade de Castro

This paper shows an evaluation about effect of dispersant sodium silicate along to limestone, in the form of pulp, on the cold agglomeration process for iron ore sintering. Before that, it was verified the effect of pH, solids content and amount of dispersant on the stability of the system (limestone, water and sodium silicate). It was found that the lower the solids content, the more alkaline pH and the amount of sodium silicate equal to 20 l for each 1t of limestone, was the level of dispersion of the system. The influence of the limestone pulp with dispersant depended on the granulometry of the ore mixture and the type of technological route. For the thinner type (42,8% <0.15mm), the limestone pulp with dispersant reduced the resistance of the adherent layer of the cold agglomerates, regardless of the technological route. However, for the coarser type (24,7% <0.15mm), the limestone pulp with dispersant increased the average size of the aggregates, preserving the resistance of the adherent layer when manufacturing with two intensive mixers in series.

Oct 1, 2019

By Steven G. Jansto

Nearly one third of the globally produced structural flat and long structural products are in the 0.11 to 0.16% carbon range. By definition, numerous steelmakers globally define this approximate carbon range as peritectic in their melting grade family within their organization. The metallurgical consequence is the result of numerous global structural specifications which allow carbon to wide carbon ranges resulting in quality issues. For example, such specifications as ASTM A588 set no minimum carbon and a 0.15 to 0.19%C maximum depending on the specific grade designated within the specification. This peritectic region is specifically challenging in production compared to less than 0.10%C because of solidification issues and a higher propensity for slab or billet cracking during continuous casting. During hot rolling, rejects and/or deviates are increased as well. The relative steelmaking operational cost of production is compared between peritectic and non-peritectic carbon compositions for a given specification.

Aug 17, 2017

By Ernst Lindemann

The SMS group has developed the ultrasound technology “HD scan” for inspection of the internal quality of as-cast products. This method of sample analysis requires less preparation work and is safer than the current, most common technique of etching and/or sulphur printing. Furthermore, this technology offers a three-dimensional view into the sample of the cast product and thus more representative information for a better quality evaluation. The internal quality evaluation can be performed automatically and objectively by software based on clear statistical methods. A quantitative centerline segregation rating can be assigned to each sample, based on the size and distribution of segregates detected by the unit. Internal crack statistic (length, position, orientation, etc.) and narrow side profile can also be measured. Grain macrostructure can also be visualized which allows for a potential optimization of casting parameters like strand cooling, soft reduction or electromagnetic stirring. The accuracy of the new method was proven by parallel metallographic investigations of more than 100 samples of different steel grades and sample shapes. Automatic defect evaluation and classification was compared against macroetching results. It was found that HD scan identified more defects and the visualization of the macro structure could be performed in more cases than with macro etching. All tests, comparisons, further developments and analyses for various steel producers and steel treatment companies have been conducted at the HD scan unit, located at the SMS group headquarters in Düsseldorf, Germany (Figure 1). Based on the results, SMS group has designed a unit which can be used in industrial scale.

Aug 17, 2017

By Thomas Schanz

Current steel market conditions require small investments only to lower operational cost. SMS Concast has developed new products which optimize continuous casting process cost for long product steel production. This paper describes a selection of three products. All three systems are patented (patent pending for CONDRIVE). CONSAFE, a non-radioactive mould level measurement system for reliable mould level measuring on open stream casting CCM’s; CONSTIR-MWS, an improved control software for electromagnetic stirrers which lowers energy cost by 35%; CONDRIVE, a brand new oscillation drive system which provides the features of a hydraulic oscillator, however with a cost efficient electric drive.

Aug 17, 2017

By Marco Antonio Meggiolaro

Most cyclic plasticity models used in multiaxial fatigue life predictions are based on a concept of a yield surface, which divides the elastic and plastic domains. Plastic straining occurs when the stress state reaches the surface and tries to move outward. Subsequent plastic straining causes the stress state to remain on the yield surface, which will translate to prevent the stress point from moving outside it according to a kinematic hardening rule that models the Bauschinger effect. The accurate modeling of the yield surface shape is fundamental to predict stress-strain relations. In this work, the main yield surface equations for isotropic materials are compared. Even though most materials can be modeled using Mises and Tresca surfaces, other need to consider the effect on the yield strength of the hydrostatic stress or the normal stress acting on a critical plane. It is shown that pressure-sensitive models originally devised for concrete can be applied to predict yielding in some materials, and even fatigue life for metallic structures with short cracks.

Aug 8, 2018

By Stanislas Mauuary

Price pressure is a real challenge on the stainless steel market. With market globalization, increase production capacity and exorbitant raw material, the margins are squeezing for stainless strip producers. Primetals Technologies offers a wide range of advanced technological solutions to secure the margins of our customers. Our solutions, implemented with professional project management, allow an optimum coil to market time, securing then the return on investment for the investor. Among the possible lever used to optimize the production route, one drastic step can be made to cut rolling time and cost by replacing the common 20-Hi mill stand reversing process by state of art high capacity X-HI® stands in continuous rolling line. Other source of savings can be implemented by integrated several process steps together (rolling, annealing, pickling, skin passing), achieving then savings on stocks and logistics while coil processing is reduced to fraction of hour. Additional solutions can also be implemented on the new, as well as existing line, like maintenance free solid state laser welder, skin-pass and tension levelers, in-line inspection system coupled with process and quality management system.

Aug 17, 2017

By Milena Kellen Oliveira Mendes

O entendimento mais aprofundado dos parâmetros que afetam a temperabilidade dos aços carbono permitiu atingir propriedades antes alcançadas apenas por aços microligados. Assim, este trabalho teve como objetivo avaliar o efeito dos teores de C e Mn, assim como da temperatura de austenitização sobre a temperabilidade de aços baixo carbono, possíveis candidatos para aplicação na fabricação de vergalhões de grau 50. Três aços com composições químicas diferentes foram submetidos a ensaios de temperabilidade Jominy, considerando temperaturas de austenitização de 850ºC, 920ºC e 1050ºC. Curvas de dureza em função da distância Jominy foram construídas e análises microestruturais por microscopia óptica foram realizadas em toda a extensão dos corpos de prova. Os resultados obtidos mostraram que tanto o C quanto o Mn aumentam a temperabilidade dos aços. O Mn, por ser um elemento de liga estabilizador da austenita, dificulta a nucleação e crescimento de constituintes difusionais. O C mostrou ter maior influência sobre a temperabilidade, pois além de também ser um elemento gamagêneo, é responsável pelo cisalhamento da rede da austenita que resulta na formação da martensita. A temperatura de austenitização influenciou a temperabilidade dos aços estudados, porém seus efeitos devem ser estudados com maior profundidade.

Aug 16, 2017

By Ernst Lindemann

Steel suppliers are required to deliver sheets with particular qualities and with lightweight-potential to the automotive industry. New types of steel call for new production processes. SMS group has developed a new micro-mill-concept, the core of which is the belt caster. This was first built on an industrial scale and has been put into operation and developed together with Salzgitter Flachstahl GmbH. The robustness in industrial-scale operation could be verified. The full use of the belt casting technology, mainly related to energy efficiency and CO2 reduction, is realized with the micro-mill-concept. This is an in-line-process, casting and rolling in one line.

Aug 17, 2017