Some Effects of Low-Frequency Vibration During Solidification of Fe–28Mn–12Al–0.9Si–1.4C Steel As-Cast Ingots

Semenko A.Y., Parkhomchuk Z.V., Veis V.I., Likhatskyi R.F., Likhatskyi I.F.

Smirnov O., Ukhin V., Goryuk M., Semiriagin S., Yefimova V., Voron M., Semenko A.

Molds, which are used for largeingot castings, are operated under severe conditions that combine cyclic temperature loads with the mold metal interactions during mold filling. The paper presents a study of the main technological aspects that affect the durability of large octagonal ingot molds weighing 13000 kg with a wall thickness of 210–270 mm made of pig iron. An assessment of the liquid steel flow distribution in the ingot volume during the bottom casting and the features of their interaction with the walls of the mold was made by using mathematical modeling. The studies were carried out on the effect of vibration treatment on the physical and mechanical characteristics of blast furnace pig iron castings of various weights. It was shown that vibration treatment in a certain frequency range can provide an increase in the pig iron tensile strength and hardness by an average of 20–25% and fluidity by an average of 1.5–1.8 times. Application of an experimentally established vibration treatment mode in the production of industrial molds for 10000 kg ingot castings increased their durability by an average of 16–17%.

Bai S., Chen Y., Liu X., Lu H., Bai P., Li D., Huang Z., Li J.

The rapid development of automotive industry results in a series of increasingly serious problems such as energy consumption and environmental pollution, so that developing the automotive steels with high-strength and low-density is of great significance for energy conservation and emission reduction. Recently, Fe–Mn–C–Al system steel is favored by numerous researchers because of its low density and excellent combination of strength and ductility. However, too much Al addition inevitably triggers various changes of microstructure, deformation mechanism, and mechanical properties. In this paper, the composition design, production process, strengthening and strain hardening mechanism, and microstructure evolution are systematically expounded. The discussion mainly focuses on various strengthening (solid solution strengthening, grain refinement strengthening and precipitation strengthening) and strain hardening mechanisms (phase transformation-induced-plasticity (TRIP), twinning-induced-plasticity (TWIP), microband-induced-plasticity (MBIP), shear-band-induced-plasticity (SIP) and dynamic slip band refinement (DSBR), etc.). Also, the existing problems and future challenges in Fe–Mn–Al–C low-density steels are pointed out via analyzing the service performance (cryogenic performance, impact toughness, fatigue performance, hydrogen embrittlement, wear performance, and tensile properties). Finally, we look forward to the future development direction of Fe–Mn–Al–C low-density steels and provide the valuable ideas.

Vaz Penna R., Bartlett L.N., O’Malley R.

The potential of different inclusions to act as heterogeneous nucleation sites for primary austenite during solidification of a lightweight Fe–30Mn–5.5Al–1.5C–1.2Si steel was analyzed by thermodynamic calculations and experimental heats. Thermodynamic simulations and lattice disregistry calculations were utilized to predict the stability and nucleation potential of different inclusions. TiN was considered as the grain-refining addition because of the success of this inoculant in other austenitic steel castings. Addition of TiN was performed through the use of a pre-made master alloy containing a large volume fraction of fine TiN inclusions. Experimental castings were produced from cylindrical phenolic resin-bonded sand molds with a bottom chill to introduce directional solidification. Additions of 0.5 and 1.5% of the TiN containing master alloy, up to 0.29 wt% Ti addition to the melt, did not yield detectable grain refinement of the as-cast grain structure when compared to the steel castings without additions. Scanning electron microscopy revealed that the inclusions present in the resulting castings consisted mainly of Ti(C,N) with up to a 0.4% area fraction, and this suggests that the original TiN inclusions were at least partially dissolved. Thermodynamic modeling predicted the equilibrium stability of Ti4C2S2 at temperatures above 1440 °C. Although this phase was not observed experimentally, a nanoscale interface layer of Ti4C2S2 or sulfur adsorption on the surface of the Ti(C,N) inclusions may be responsible for poisoning of the nuclei.

Balasubramanian K., Bartlett L.N., O’Malley R., Chakraborty S., Xu M.

The efficiency of ceramic foam filters in removing different inclusion populations in a Fe–30Mn–9Al–1Si–0.9C–0.5Mo steel was investigated. A mold design was created utilizing fluid flow and solidification modeling software. The design utilized a common pouring cup attached to two different but balanced gating systems. One runner utilized a ceramic foam filter, while the other runner was unfiltered. Three molds were poured in sequence from a teapot-style ladle. Metallographic samples revealed extensive Al- and Mn-rich oxide bi-films in samples taken before the filter. Samples sectioned after the filter did not contain bi-films. AlN or complex AlN–MnS or AlN–MnO comprised more than 70% of all inclusions. Samples sectioned from the first two molds showed an inclusion removal efficiency of 38% and 39%, respectively. Larger inclusions greater than 3 µm were more efficiently filtered. The third mold with the greatest number of larger inclusions showed the highest inclusion removal efficiency of 55%.

Dubodelov V., Semenko A., Bogdan K., Goryuk M.

A new principle to control the temperature and mass flow rate of metal melt at its continuous casting has been proposed. It has been established that such control can be executed based on continuous monitoring of the mass of a liquid alloy in casting and metallurgical assemblies and at appropriate adjustment by the equipment systems. Using electromagnetic fields and magnetohydrodynamic (MHD) factors to influence a liquid-metal environment is an effective means to ensure the required technological and technical-economic indicators for the process of continuous casting. We have proposed an appropriate principal structural-functional circuit for the automated control system (ACS) over the process of continuous casting of alloys, based on the application of a magnetodynamic tundish (MD-T) and a magneto-weighting system. Their basic design features and functional capabilities have been defined that are related to the processes of continuous casting, compared both with existing equipment and systems for similar purposes. It has been proposed to implement MD-T in the form of a two-chamber assembly, which separates the functions of receiving the melt from a steel-casting ladle, heating the liquid metal, releasing it into the crystallizer of a continuous casting machine (CCM). Stabilization of the flow rate mode of casting, including low-head, is achieved by permanently controlling the mass of melt in the system and by tracking its level in the release chamber of MD-T and in the crystallizer of CCM.The devised technique and created assemblies, the system, as well as auxiliary devices, would make it possible to significantly improve modern technologies of continuous casting

Cho S., Thomas B.G.

This paper reviews the current state of the art in the application of electromagnetic forces to control fluid flow to improve quality in continuous casting of steel slabs. Many product defects are controlled by flow-related phenomena in the mold region, such as slag entrapment due to excessive surface velocity and level fluctuations, meniscus hook defects due to insufficient transport of flow and superheat to the meniscus region, and particle entrapment into the solidification front, which depends on transverse flow across the dendritic interface. Fluid flow also affects heat transfer, solidification, and solute transport, which greatly affect grain structure and internal quality of final steel products. Various electromagnetic systems can affect flow, including static magnetic fields and traveling fields which actively accelerate, slow down, or stir the flow in the mold or strand regions. Optimal electromagnetic effects to control flow depends greatly on the caster geometry and other operating conditions. Previous works on how to operate electromagnetic systems to reduce defects are discussed based on results from plant experiments, validated computational models, and lab scale model experiments.

Vaz Penna R., Bartlett L.N., Constance T.

High manganese lightweight steel alloys in the Fe–Mn–Al–C system are promising alternatives to quenched and tempered Cr and Mo steels for transportation and military applications. The understanding of nonmetallic inclusion formation and their effect on the mechanical properties is of extreme importance for further alloy development. Sharp and brittle AlN forms prior to the liquidus and has been shown to decrease notch toughness. Controlled additions of sulfur may promote soft and globular MnS that precipitates around AlN during solidification, thus mitigating their detrimental effect. The effect of controlled sulfur additions from 0.004 to 0.042%S was studied in a Fe–30%Mn–9%Al–1%Si–(0.9–1.2)%C–0.5%Mo steel. The main inclusions observed were AlN, MnS, and AlN-cored MnS. Charpy impact toughness was evaluated in the solution treated condition and in specimens aged to 329–340 HBN. Toughness is a function of the overall inclusion population. In aged specimens, same was true only for steels with 0.9% carbon; above 1%C the toughness was below 15 J for any sulfur content.

Chen S., Rana R., Haldar A., Ray R.K.

Fe-Mn-Al-C steels, previously developed in the 1950s for replacing Fe-Cr-Ni steels, are currently generating a lot of interest with potential applications for structural parts in the automotive industry because they are lighter. This paper provides a review on the physical metallurgy, processing strategies, strengthening mechanisms and mechanical properties of Fe-Mn-Al-C steels from the published literature over a period of many years, and suggests avenues for future applications of these alloys in the automotive sector. The addition of Al to Fe-C steels leads to a reduction in both density and Young’s modulus. A 1.3% reduction in density and a 2% reduction in Young’s modulus are obtained per 1 wt% addition of Al. Due to the addition of the high amounts of Al, together with Mn and C, the physical metallurgy, general processing, microstructural evolutions and deformation mechanisms of these steels are largely different from those of the conventional steels. The addition of Al to high-Mn austenitic steels brings two other important effects: increasing the stacking fault energy (SFE) and producing short-range ordering (SRO) and/or κ′-carbide precipitation. Plastic deformation of low-density Fe-Mn-Al-C steels with a high SFE, which involves SRO, is dominated by planar glide. New deformation mechanisms such as the microband induced plasticity (MBIP), the dynamic slip band refinement (DSBR) and the shear band induced plasticity (SIP) are introduced to describe plastic deformation of Fe-Mn-Al-C austenitic steels in addition to the transformation-induced plasticity (TRIP) and the twinning-induced plasticity (TWIP), which are often observed in Mn TWIP steels. These new deformation mechanisms are related to the formation and uniform arrangement of the SRO or nano-sized κ′-carbides which are coherent with the austenitic matrix. The κ′-carbide precipitation is a unique strengthening mechanism in the austenitic Fe-Mn-Al-C steels bearing high amounts of Al and C. The lightweight Fe-Mn–Al-C alloys can produce a variety of microstructures and achieve a wide range of properties. These alloys can be classified into four categories: ferritic steels, ferrite based duplex steels, austenite based duplex steels and austenitic steels. The austenitic steels are the most promising in terms of properties and processing. The tensile properties of the austenitic lightweight steels are similar to those of high Mn TWIP steels. The impact toughness of these steels in the solution treated condition is slightly lower than that of Cr-Ni stainless steels but is higher than that of the conventional high strength steels. The energy absorption at high strain rate is similar to that of high Mn TWIP steels and higher than that of conventional deep drawing steels. The ferrite based duplex low-density steels is another promising alternative. A bimodal microstructure can be obtained here through process control for steels with lower alloying contents, in which the plastic deformation of the ferrite and the TRIP and/or TWIP effects from the retained austenite can be profitably used. This type of Fe-Mn-Al-C steels exhibits an improved combination of strength and ductility compared with the first generation advanced high strength steels. The ferritic Fe-Al steels have tensile properties comparable with HSLA steels of 400–500 MPa strength level. The corrosion behaviour of Fe-Mn-Al-C steels is not improved in comparison with the conventional high strength steels. The application properties such as the fatigue behaviour and formability of Fe-Mn-Al-C steels cannot be properly understood at this stage, because of the limited experimental results so far. Some other application aspects such as weldability, coatability are not well documented. The applications of the Fe-Mn-Al-C steels in the automobiles is still not prevalent due to the lack of knowledge related to application properties so far. Above all, the reduced Young’s modulus of these steels and the processing problems as a result of the high Al and high Mn contents are the main issues. The future developments will therefore have to concentrate on the alloying and processing strategies and also on the methods to increase the Young's modulus. An improved processing strategy and a high value for the Young’s modulus will go a long way towards upscaling these steels to real automotive applications.

Sohn S.S., Song H., Jo M.C., Song T., Kim H.S., Lee S.

Needs for steel designs of ultra-high strength and excellent ductility have been an important issue in worldwide automotive industries to achieve energy conservation, improvement of safety, and crashworthiness qualities. Because of various drawbacks in existing 1.5-GPa-grade steels, new development of formable cold-rolled ultra-high-strength steels is essentially needed. Here we show a plausible method to achieve ultra-high strengths of 1.0~1.5 GPa together with excellent ductility above 50% by actively utilizing non-recrystallization region and TRansformation-Induced Plasticity (TRIP) mechanism in a cold-rolled and annealed Fe-Mn-Al-C-based steel. We adopt a duplex microstructure composed of austenite and ultra-fine ferrite in order to overcome low-yield-strength characteristics of austenite. Persistent elongation up to 50% as well as ultra-high yield strength over 1.4 GPa are attributed to well-balanced mechanical stability of non-crystallized austenite with critical strain for TRIP. Our results demonstrate how the non-recrystallized austenite can be a metamorphosis in 1.5-GPa-grade steel sheet design.

Tucker R.

New CAFE requirements stand to impact original equipment parts suppliers.

Campbell J.

Flemings M.C.

Interaction between theory and practice in the field of solidification has been strong in recent years, to the great benefit of both. Solution of important problems has required conceptualizing on greatly different size scales simultaneously, and has also required extensive experimentation to suggest and justify suitable approximations for theoretical analyses. Some areas of solidification where theory and practical application have advanced, or are advancing nicely together are dendrite arm spacing, grain size control, columnar structures, eutectic-like in-situ composites, inclusion formation, macrosegregation, and non-dendritic structures.