Specialty Steels Research Articles

Theoretical precipitation modeling and multidimensional characterization of sulfide inclusions in tellurium-containing steels

This study investigates the precipitation characteristics of sulfide inclusions during the solidification of alloy steels under the combined influence of sulfur (S), manganese (Mn), and tellurium (Te). A multidimensional characterization and comparison of sulfide inclusions in Te-containing steels with varying sulfur content and cooling conditions were performed using X-ray Micro-CT, Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM). Both 2D and 3D analyses confirmed that increasing the S content in Te-containing steels leads to a higher overall number of sulfide inclusions. In particular, the rise in the proportion of small-sized inclusions was analyzed from the perspectives of interfacial dynamics and equilibrium thermodynamics. Regarding inclusion morphology, 2D characterization exhibited significant inaccuracies in assessing large inclusions in high-S, Te-containing steels, while X-ray Micro-CT proved advantageous for evaluating both the spatial distribution and morphology of inclusions. In addition, X-ray Micro-CT was used for the first time in this study to perform a non-destructive analysis of the layered MnS-MnTe structure, expanding the method's application in the metallurgical field. A predictive model based on inter-element activity interaction coefficients was employed to determine the first-order activity interaction coefficient of Te for Mn. Furthermore, a thermodynamic model for sulfide precipitation in Te-containing steels was developed. This study lays a theoretical foundation for better control of sulfide inclusions in future Te-containing specialty steels.

Investigation of Non-Metallic Inclusions During Primary Melting of Specialty Steels

Investigation of Non-Metallic Inclusions During Primary Melting of Specialty Steels

Influence of thermally grown oxide layers thickness on temperature evolution during the forging of large size steel ingots

Medium carbon low alloy specialty steels are preheated in gas-fired furnaces before undergoing open die forging operation. Oxide layers with different thicknesses and compositions are formed on the surface and significantly influence the temperature evolution during the forging process. In the present work, the kinetics of oxide growth of two high-strength medium carbon steels with different Ni concentrations, were determined. Four oxidation temperatures and five oxidation times were used to simulate various forging and intermediate heat treatment conditions. Three distinct oxide layers with different thicknesses were identified and correlated with the applied thermal cycles. The results indicated that the kinetics of oxidation varied with the Ni concentration of the alloys, but interestingly the fractions of different layers were the same at different oxidation temperatures. A 3D finite element model (3D-FEM) was developed, and the effect of the oxide layer investigated on the temperature evolution of the ingots. Correlations are made between the thickness of the oxide layers and the cooling pattern of the ingots, as well as their impact on the forging die temperature. The 3D-FEM predicted critical temperatures were validated by experimental temperature measurements on the ingot during the forging process.

Rapid Prototyping of Carbon‐Bonded Alumina Filters with Flame‐Sprayed Alumina Coating for Bottom‐Teeming Steel Ingot Casting

Although continuous casting is the state‐of‐the‐art casting method in steelmaking, ingot casting by bottom teeming has kept its relevance, for example, in the area of specialty steels. The main challenge is to meet the ever‐increasing quality requirements demanded by the customers. Regarding high‐performance steel applications, the purity with respect to the content of nonmetallic inclusions thereby is of special interest. Herein, foam templates with tailored geometry are designed and manufactured by selective laser sintering. Different coating techniques based on carbon‐bonded alumina slurries are applied to replicate foam structures with miniature cube geometry and cylindrical geometry. The techniques are evaluated regarding the porosity, pore size distribution, bulk density, mechanical strength, and shrinkage of the resulting filters. Suitable processing routes are selected to manufacture prototype batches with near‐net‐shape geometry. Finally, the feasibility of applying a flame spray coating is tested. First samples of the prototype batch are tested in industrial bottom‐teeming ingot casting.

Corrosion-resistance evaluation of coated and specialty bars

The reduction in service-life of reinforced concrete structures caused by corrosion of reinforcing steel is a major problem to the construction industry. The use of specialty steels is one of the strategies suggested to minimize this deterioration phenomenon. In this study, the corrosion-resistance of epoxy-coated and selected specialty steel bars embedded in concrete and exposed to chloride environment was evaluated. The specialty bars considered included two types of epoxy-coated bars with varying degrees of damage, stainless steel bars, stainless clad bars, and a low-carbon chromium steel bar. The corrosion resistance of the investigated reinforcing bars was investigated by measuring corrosion potentials and corrosion current density over a period of about 32 months. As expected, the corrosion resistance of specialty bars was better than that of the black (normal) bars. The corrosion resistance of the epoxy-coated bars decreased with the degree of surface damage. Further, the corrosion-resistance of epoxy-coated bars with up to 1% damage was better than that of the other specialty bars. Additionally, the low corrosion rate noted in the epoxy-coated bars suggests longer service-life of structures built with these bars compared to structures incorporating specialty steel bars considered in the study. The relatively low initial cost of epoxy-coated bars, compared to other specialty steel bars, and their longer life results in a considerable cost saving. Also, the decreased corrosion damage of concrete results in technical (long service-life and safety), environmental (aesthetics) and economic (less overall cost of construction) benefits.

Effect of martensite volume fraction on the mechanical behavior of an UNS S41003 dual-phase stainless steel

UNS S41003 (410D) steel is a relatively low chromium unstabilized ferritic stainless steel. It has superior mechanical and corrosion resistance than ordinary low carbon steels. Therefore, and for its relatively low cost among specialty steels, it is a strong candidate for replacement of low carbon common steels in many applications. In order to enable new applications for this steel, it is important to ensure good performance in relation to its mechanical strength, so the development of hardening mechanisms without significant loss of ductility is desirable. Dual-phase microstructures are an example that fits in this context, because they tend to increase mechanical strength and are favorable to the fracture toughness and fatigue resistance of steels. This research evaluated the influence of quenching heat treatments after intercritical austenitizing on the microstructure, tensile strength, hardness, fracture toughness (J x Δa curves) and fatigue crack growth resistance (da/dN x ΔK curves) of a 410D ferritic stainless steel. The used intercritical austenitization temperatures were defined based on its critical temperatures Ac1 and Ac3 measured by dilatometry. Ten different quenching heat treatments were performed, varying the austenitizing temperature and time, in order to obtain dual-phase microstructures (ferrite and martensite) with different volume fractions of constituents. The obtained results revealed that the increase of the austenitizing temperature and time favor the increase of the martensite volume fraction in the microstructure. Higher martensite volume fractions imply greater hardness and mechanical tensile and fatigue strength of the steel, but with loss of ductility and fracture toughness. The best balance among the studied mechanical properties was presented by steel treated at 825 °C for 15min, containing 57% of martensite.

Assessing the Long-Term Global Sustainability of the Production and Supply for Stainless Steel

The integrated systems dynamics model WORLD6 was used to assess long-term supply of stainless steel to society with consideration of the available extractable amount of raw materials. This was done handling four metals simultaneously (iron, chromium, manganese, nickel). We assessed amounts of stainless steel that can be produced in response to demand and for how long, considering the supply of the alloying metals manganese, chromium and nickel. The extractable amounts of nickel are modest, and this puts a limit on how much stainless steel of different qualities can be produced. The simulations indicate that nickel is the key element for stainless steel production, and the issue of scarcity or not depends on how well the nickel supply and recycling systems are managed. The study shows that there is a significant risk that the stainless steel production will reach its maximum capacity around 2055 and slowly decline after that. The model indicates that stainless steel of the type containing Mn–Cr–Ni will have a production peak in about 2040, and the production will decline after 2045 because of nickel supply limitations. Production rates of metals like cobalt, molybdenum, tantalum or vanadium are too small to be viable substitutes for the missing nickel. These metals are limiting on their own as important ingredients for super-alloys and specialty steels and other technological applications. With increased stainless steel price because of scarcity, we may expect recycling to go up and soften the decline somewhat. At recycling degrees above 80%, the supply of nickel, chromium and manganese will be sufficient for several centuries.

Finding true north: Design and implementation of a strategic sourcing framework

This study investigates the evolution of the design, development and implementation of a strategic sourcing framework able to support decision-makers in formulating differentiated, rather than generic supplier base strategies. These strategies are in turn implemented through specific action plans, assuring the coherence and alignment between the different strategic hierarchical levels, beginning with business strategy, through category strategy to specific tactical sourcing levers. The proposed framework is the result of a longitudinal study executed through two action research cycles engaging in a strategic sourcing project in a leading European specialty steels manufacturer. By integrating and refining in our framework three dominant purchasing portfolio models - i.e. Kraljic, Olsen & Ellram, and Scott & Westbrook - we highlight the importance of adopting multiple perspectives to manage the complexity of formulating a purchasing strategy and its related implementation decisions. The proposed framework has been designed to facilitate dynamic learning mechanisms through a feedback loop to continuously update the three integrated models and in turn allow managers to gain a strategic perspective of the evolution of buyer-supplier relationships, the influence of previous decisions and external factors. A critical discussion explores the proposed solution through the main theoretical lenses emerged throughout the research process.

A System Dynamics Assessment of the Supply of Molybdenum and Rhenium Used for Super-alloys and Specialty Steels, Using the WORLD6 Model

The extraction, supply, market price and recycling of the metals molybdenum and rhenium were modelled using an integrated system dynamics model. The resource estimates made here resulted in significantly larger estimates than earlier studies for molybdenum. Present molybdenum resources are about 75–80 million ton and about 7 million ton has been mined to date. The ultimately recoverable resources (URR) for molybdenum are about 65 million in primary resources and about 45 million ton in secondary sources, a total of about 111 million ton, and after considering technical extractability, evaluating several hundred different geological deposits, the extractable amount is about 90 million ton. For rhenium, URR is about 21,000 ton contained in mostly in molybdenum and copper, but some come from nickel, wolfram and platinum group metal ores. The model outputs show that molybdenum and rhenium are finite resources, and that they may become exhausted unless the degree of recycling will be significantly improved. Peak production is estimated to take place in 2060 for molybdenum and rhenium, with peak in stocks-in-use around 2090. The molybdenum and rhenium recycling rates are generally low. Both market intervention mechanisms and governance incentives should be used to increase recycling. The metal extraction and ore grades were modelled with good success when tested against observed data. The model predicts a significant decline in molybdenum supply after 2100 under the present demand combined with the present regime of recycling. The supply situation for rhenium is dependent on the situation applicable for molybdenum ore availability and rhenium recycling rate.

Recent developments in steel products for automotive applications

This paper reviews recent developments in steels for motor car manufacture and the applications of these steels in the automotive industry. The following items are discussed: hot and cold rolled steel sheets including high strength steel sheets, vibration damping steel sheets, laminated steel sheets, various coated steel sheets and structural specialty steels such as free cutting steel and wire rods for suspension springs.

USO DE AGENTES OXIDANTES/PRECIPITANTES PERMANGANATO/CARBONATO E PERÓXIDO/URÉIA PARA PRECIPITAÇÃO SELETIVA DO ÍON CÉRIO

In this work there are presented some examples of the use of thermodynamic modeling to development of new alloys for different segments and applications. By the use of thermodynamic modeling coupled with numerical simulations of heat transport and mechanical simulations, it was possible to optimize the rolling and heat treatment routes in order to improve the properties of specialty steels and alloys. The use of the thermodynamic modeling it is also important to the development of new alloys which consider from its conception the process variables, simplifying the development of the new materials in the pilot and industrial scale

Coupling of CFD and PBE Calculations to Simulate the Behavior of an Inclusion Population in a Gas-Stirring Ladle

Gas-stirring ladle treatment of liquid metal has been pointed out for a long time as the processing stage is mainly responsible for the inclusion population of specialty steels. A steel ladle is a complex three-phase reactor, where strongly dispersed inclusions are transported by the turbulent liquid metal/bubbles flow. We have coupled a population balance model with CFD in order to simulate the mechanisms of transport, aggregation, flotation, and surface entrapment of inclusions. The simulation results, when applied to an industrial gas-stirring ladle operation, show the efficiency of this modeling approach and allow us to compare the respective roles of these mechanisms on the inclusion removal rate. The comparison with literature reporting data emphasizes the good prediction of deoxidating rate of the ladle. On parallel, a simplified zero-dimensional model has been set-up incorporating the same kinetics law for the aggregation rate and all the removal mechanisms. A particular attention has been paid on the averaging method of the hydrodynamics parameters introduced in the flotation and kinetics kernels.

Manufacturing and Critical Applications of Stainless Steel – An Overview

This paper presents an overview of development of stainless steel for critical applications and its metallurgical aspects in general. Novel emerging methods of processing of stainless steel are also discussed. Advances in steel making aspects with respect to stainless steel and other specialty steels especially in nuclear applications are presented. Overview of alloy design, physical metallurgical aspects of steel for critical applications is discussed. Advances in manufacturing of stainless steel, strengthening mechanisms, corrosion resistance, challenges in stainless steel applications have also been elaborated.

Comparative Behaviour of Specialty Austenitic Stainless Steels in High Temperature Environments

Two different alloying strategies may be utilised to improve the high temperature performance of austenitic stainless steels: increasing the chromium content, sometimes in combination with a higher nickel level; and alloying with silicon, nitrogen and rare earth metals. The relative merits of the two approaches are explored by comparing the performance of commercial alloys in oxidation tests in air–water vapour, corrosion tests in an oxidising-sulphidising atmosphere and with applied deposits, and creep and fatigue testing. Significant increases in high temperature performance are achieved by selecting specialty heat-resisting austenitic stainless steels, and it will be shown that the choice of grade should be governed by the dominant operative degradation mechanisms.

Mechanisms governing cyclic fracture behavior of two high-strength steels: role of composition and microstructure

In this article, the cyclic fatigue fracture behavior of two high-strength specialty steels denoted as Tenax 310 and 300 M, is presented and discussed. The two chosen specialty steels have noticeably improved properties to offer than most steels in this category and even other competing high-strength steels. The observed improvement can be ascribed to be because of the synergistic and mutually interactive influences of chemical composition and secondary processing technique used for the two steels. The two chosen high-strength steels, designated by the manufacturer as Tenax 310 and 300 M, were produced by initial melting using vacuum arc remelting and then casting to obtain ingots. The cast ingots were mechanically deformed by hot working to get the starting blocks. At the fine microscopic level, cyclic fatigue fracture of these two steels revealed features reminiscent of the occurrence of “locally” ductile and brittle failure mechanisms. Over the range of maximum stress and at the two different load ratios, the two steels were cyclically deformed. It was observed that the cyclic fatigue resistance of the candidate steels was noticeably higher than their high-strength steels counterparts for which data are available in the literature. The key mechanisms responsible for the observed fracture behavior of the two steels, cyclically deformed over a range of maximum stress, are presented and discussed.

The Tensile Response and Fracture Behavior of Four High Strength Specialty Steels

AbstractIn this technical paper the role of alloy chemistry and secondary processing on tensile response and final fracture behavior of four high strength steels is presented and discussed. The conjoint influence of composition, secondary processing and intrinsic microstructural features in governing stress versus strain response and tensile properties is highlighted. The macroscopic mode and intrinsic microscopic features that result from final fracture of the four high strength steels is discussed. The intrinsic microscopic mechanisms governing tensile deformation and final fracture behavior of the high strength steels are outlined in light of the specific role played by composition, intrinsic microstructural effects and nature of loading.

An Advanced Dynamic Secondary Cooling Control Model for Bloom Castings

For bloom casting, typical quality defects such as midway crack usually occur upon improper cooling control during non-steady casting conditions specially for the production specialty steels,. A key measure to eliminate the defects formation has been presented by the adoption of more sophisticated secondary cooling strategies to balance the surface reheating due to casting speed fluctuation. With the consideration of the complex casting conditions and the characteristics of bloom casters, a dynamic control model for the secondary cooling has been developed in the paper to obtain a reasonable temperature profile and solidification progress for the bloom casting process, which is based on a slice residence time method combined with a multi-level control strategy. The feedback system, based on the difference between the calculated surface temperatures and the predetermined or measured surface temperatures, has been integrated into two-dimensional thermal model. The interlocking protection system between level-1 and level-2 is included in the model together with the data diagnosis and processing. Furthermore, the control model also offers technological interface for the introduction of new steel grades in production and the related modification to the secondary cooling parameters. It is shown from online application that the dynamic control system of secondary cooling for bloom casting is robust during operation and adaptable to any change of real casting conditions. Sound quality bloom castings according to acid etched tests have been obtained from the caster accordingly.

Liquid Metal Processing and Casting

Liquid Metal Processing and Casting, represents a key stage in the development of many metallic materials, providing the final product with many of its intrinsic properties. During the last thirty years, an increasingly large number of scientific papers have been devoted to the characterization of the various processes involved, detailing both sophisticated experimental measurements and the mathematical modeling and numerical simulation of processes. LMPC2003 Conference, held in Nancy, France, in September 2003 under the auspices of Societe Francaise de Metallurgie et des Materiaux (SF2M), was the fifth in the series of “International Symposium on Liquid Metal Processing and Casting,” previously held in Santa Fe, New Mexico. The presentations and ensuing discussions covered a range of topics from theoretical mathematical models of microstructural evolution to industrial-scale experimental investigations. Although many metallic systems were studied, the focus was on specialty steels, nickel-base superalloys, and titanium alloys. From the 48 papers presented at the conference, 21 were selected and reviewed for publication in this special issue of the Journal of Materials Science to highlight the key scientific and engineering advances in the field. This selection shows the intense interest in the advanced modeling of the processes with most studies including results from industrial trials for validation. The significant advances in computational fluid dynamics (CFD) methods to include the additional physics of solidification, segregation and electromagnetic forces are illustrated by their application to simulation of processes ranging from consumable electrode remelting (VAR-ESR) to induction skull melting, nucleated casting and spray deposition. As with all modeling exercises, the quality of the output is dependent on the accuracy of the input parameters. Since our knowledge of both the physical and chemical properties of hightemperature systems is still very sparse, a few papers address this problem with approaches ranging from high temperature experimental measurements to “first principle” computations.

Aluminothermic studies of a liquid partial reduced ilmenite

A non-traditional method for ferrotitanium production using aluminothermic reduction of ilmenite was investigated. It included preliminary melting of ilmenite in mixture with lime and anthracite for production of a liquid titanium slag. The liquid phase generated was reacted with Al in a separate reactor. Preliminary thermo-analytical investigations (DTA/TG) of the reduction were performed. These investigations were instrumental for finding out the start temperature of the reactions for different compositions of the charges. These experiments for ferrotitanium production were carried out using the novel application of electroslag crucible remelting (ESCR) furnaces of the portable and the stationary types. The ferrotitanium produced, which had a composition (wt.%) 25–28 Ti, 4 Si, 46–50 Fe, 14 Al and was also of high purity with respect to other detrimental elements, has an industrial application in specialty steels production. The safety and the cost effectiveness of the process were demonstrated as compared to the traditional technologies.

Cyclic response of plate steels under large inelastic strains

In structures subjected to extreme loading, plate steels are relied upon to plastically deform under large repeated strains. Nevertheless, limited data exists on the hysteretic stress–strain response and low-cycle fatigue life of these steels. In the study described in this paper, axial coupons were tested for five types of plate steel, including conventional and high performance A709 steel as well as specialty low yield point steels, to investigate the material response under repeated inelastic demands of constant amplitude between 1% and 7% strain. Parameters for analytical models were established for cyclic stress–strain and low-cycle fatigue life relationships. Based on this study, it was found that the low-cycle fatigue life of the different types of plate steels was similar and that the effect of increased strain rate was minimal. However, the maximum cyclic stress was found to exceed the yield strength by a factor of 2.0 for the conventional grade steel and up to 4.8 times for the low yield point steels, within just a few reversals in the considered strain ranges. The maximum cyclic stress behavior was not related to the yield strength as much as it was to the manufacturing specifications. This behavior should be considered when using these materials in the limit state design of structures for extreme events such as earthquakes.