The need of innovation in construction technology has driven involved parties within the industry to keep researching for new methods or materials in which could bring efficiency, yet more reliable. ...In this research, composite concrete panels which has become commonly used, is going to be modified by implementing lightweight steel as its concrete reinforcement. Three model of lightweight steel composite concrete panels were designed and tested for its compressing strength after 14 days. The proposed model was designed for low budget small housing and should be easily implemented. Moreover, all of the model used 1:2:3 concrete mix design without adding addictive solvent or other composite material. The tests result for model A is 5000 KN, for model B is 4600 KN and lastly for model C is 6000 KN. Based on these compressing strength test results, the designed models are able to be implemented for small housing construction.
The microstructure evolution and tensile properties of a newly designed Fe-21Mn-10Al-1C-5Ni (wt.%) lightweight steel subjected to two annealing conditions (inducing partial recrystallization and full ...recrystallization) and subsequent aging treatment have been investigated. In the as-annealed condition, the microstructure of the steel consists of polygonal B2 particles along grain boundaries of recrystallized austenite grains and plate-shape B2 particles within unrecrystallized austenite grains, with no B2 bands. In addition, there is a formation of nano-sized κ-carbide and D03 particles within austenite grains and B2 particles, respectively. Subsequent aging promotes the formation of intragranular κ-carbide and D03 nanoparticles within austenite grains and B2 particles, respectively. As a result, the present steel shows an ultrahigh yield strength of 1.6 GPa after aging, which is mainly due to the presence of fine B2 particles within austenite grains and along grain boundaries as well as the additional strengthening effect of nano-sized κ-carbide and D03 particles present in austenite grains and B2 particles, respectively. The steel possesses good ductility (total elongation of 20%) even at such an ultrahigh strength level in the as-aged condition, surpassing the tensile properties of other B2 and κ-carbide strengthened lightweight steels.
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The presence of δ-ferrite makes it challenging to achieve higher strength-ductility in low-Mn lightweight steels. In this study, a large deformation warm rolling process was used to construct a ...precursor enriched with Mn, nano-precipitations, ultra-fine grains, and high-density dislocations. The subsequent flash annealing process not only promotes the formation of multi-heterogeneous structures but also refines and reduces δ-ferrite while increasing the ultrafine-grained hard phase martensite. Additionally, this process enhances the retention of retained austenite, whose ultrafine grains contribute to improved mechanical stability. The synergistic effect of multiple strengthening mechanisms enables low-Mn lightweight steel to achieve outstanding comprehensive mechanical properties, with a tensile strength of 1423 MPa and a total elongation of 23.0 %.
In this study, warm rolling was applied to Fe–28Mn–11Al–1C–5Ni (wt.%) austenitic lightweight steel, which realized the higher dislocation density and finer dislocation-cell structures, achieving a ...better mechanical properties with ∼2.0 GPa of yield strength and ∼6.8 % of total elongation than cold rolling in the same conditions. In the subsequent partial recrystallization condition, the numerous dislocations and substructures existed in warm rolled steel provide more heterogeneous nucleation sites for grain refinement, resulting in the ultrafine-sized austenite and B2 with the size of 0.36 μm and 0.24 μm, respectively. Combined with grain refinement strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening in the unrecrystallized austenite, the present steel shows an ultimate tensile strength of 1734 MPa, a uniform elongation of 21.7 % and a specific tensile strength of 267 MPa g−1 cm3. Such an excellent combination of strength and ductility induced by simple warm rolling and annealing is much better than previously reported for lightweight steels.
•A novel dual-nanoprecipitation of intragranular “B2+κ′-carbides” strengthened austenitic lightweight steel is designed by coupling the pre-cold rolling and two-step aging process.•Typical K-S and ...N-W orientation relationships between the austenite matrix and intragranular B2 particles are confirmed.•Pre-cold rolling process effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations.•The balance of strength-ductility is enhanced via the nanoscale “planar slip and dislocation bow-out” multiple deformation mechanisms.
Strength-ductility trade-off is usually an inevitable scenario in κ′-carbides strengthened austenitic lightweight steel. The reduction of ductility is primarily attributed to the shearing of coherent κ′-carbides by dislocations, resulting in strain localization and ultimately leading to a low work hardening rate. Semi-coherent B2 particles, on the other hand, effectively enhance the work hardening capability due to the non-shearable feature. However, achieving a large volume fraction and uniform distribution of B2 particles within the austenite matrix, as well as optimizing their morphology as fine particles, remains a challenge for austenitic lightweight steel. In this study, we have addressed the above challenges by implementing the two-step aging process combined with pre-cold rolling process. The pre-cold rolling treatment, performed prior to the initial aging treatment at 900 °C, effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations, resulting in a more uniform distribution of B2 particles and a refinement in size (with an average length of 200–500 nm and a width of 50–80 nm). Furthermore, these intragranular B2 particles exhibit the typical K-S and N-W orientation relationships with the austenite matrix. Subsequently, after the second-step aging process at 450 °C, spherical nano-sized κ′-carbides (5 nm) are homogeneously dispersed within the austenite matrix. The above dual nanoparticles provide an approximate precipitation hardening effect of 400 MPa. Concurrently, the nanoscale “planar slip and dislocation bow-out” multiple deformation mechanisms contribute to an efficient source of work hardening capability, leading to a beneficial synergy of strength-ductility. This promising strategy is expected to expand the applications of dual-nanoprecipitation austenitic low-density steel in various lightweight structural materials.
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The current work investigated the mechanical behaviors of a novel austenitic lightweight Fe-Mn-Al-Si-C steel that combined the characteristics of lightweight steel and TWIP steel, due to ...compositional complexity. The critical design principle lay in the synergetic addition of Al and Si to obtain simultaneously a stacking fault energy of 49.5 mJ/m2, short-range ordering, and density reduction. The initial strain hardening in this steel proceeded by microband-induced plasticity slip featuring the substructure of Taylor lattices due to planar-slip dislocations. It contributed to a high Hall-Petch coefficient of 673 MPa·μm0.5. In the latter stage of deformation, even though the stacking fault energy was not low, stacking faults and deformation twins were triggered when the critical stress was achieved. This transition behavior was first observed in lightweight steel and the overall effects led to an outstanding work hardening rate of about 2.4 GPa. This lightweight TWIP steel with a density of 6.98 g/cm3 possessed ultimate tensile strength of 800-950 MPa and total elongation of 67-77%. This study focused on its mechanical behaviors and developed a confined dislocation model to clarify the transition from dislocation glide to mechanical twinning.
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Diverse microstructure and complex application environments increases the uncertainty of the corrosion resistance of lightweight steels. The effect of solution treatment on the corrosion behavior of ...Fe–16Mn–10Al–1.5C–0.1Ti lightweight steel in Cl−, HSO3− and Cl−–HSO3− environments was investigated using electrochemical measurement, scanning electron microscope (SEM) and X–ray photoelectron spectroscopy (XPS). The lightweight steels are dominated by austenite and contain a small amount of ferrite. The increase in solution treatment temperature leads to more ferrite formation, but it has less effect on grain size. The decrease in austenite content results in more corrosion microcells and a porous oxide film; therefore, the corrosion resistance of the steel deteriorates with increasing temperature. In addition, in the Cl−–HSO3− environment, the synergistic effect of Cl− and HSO3− leads to the formation of a weak protective oxide film, resulting in a significant increase in corrosion rate compared to the Cl−and HSO3− environment.
High strength and ductility and vehicle's weight reduction are key issues for improving fuel efficiency in automotive industries. In addition, structural reinforcement components require high yield ...strength because the prevention or minimization of deformation is more important than the absorption of impact energy. In this study, new ultra-high-strength duplex lightweight Fe-0.5C-12Mn-7Al-(0,3)Cu (wt%) steels have been developed by varying annealing temperature. Here, Cu, an austenite stabilizer, not only raises the austenite volume fraction but also delays the recrystallization due to a solute drag effect, while it promotes the formation of Cu-rich B2 particles and Cu-segregated interfacial layers. The steels show the planar slip and fine dislocation substructures (Taylor lattices) as desirable deformation mechanisms. Non-shearable Cu-rich B2 particles, solid solution hardening of Cu, and delayed recrystallization greatly improve the yield strength (∼1 GPa) and strain hardening. Through these unique and excellent tensile properties together with weight saving of 10.4%, the present work provides a desirable possibility for applications to automotive reinforcement components preferentially requiring an excellent yield-to-tensile ratio.
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A series of Fe-30 wt%Mn-10.5 wt%Al-1.1 wt%C steels with Mo addition from 0 to 5 wt% were prepared to investigate the effect of Mo on the microstructure and tensile deformation behavior of austenitic ...lightweight steel. When the Mo content was below 4 wt%, the microstructure of solution-treated samples consisted of austenite and κ–carbide, while Mo-enriched M6C and M23C6 carbides were additionally precipitated in samples containing Mo more than 4 wt% during a solution treatment at 1050 °C. These carbides inhibited austenite grain growth during the solution treatment, resulting in significant grain refinement in the samples containing more that 4 wt% of Mo. Tensile test results showed that the yield strength gradually decreased with an increase in the Mo content up to 3 wt% due to the suppression of κ–carbide precipitation, whereas it significantly increased when the Mo content exceeded 4 wt% due to grain refinement and precipitation strengthening caused by Mo-enriched carbides. During the tensile deformation, the strain hardening rates of all alloys increased and then the deformation mode subsequently changed with an increase in the Mo content from shearband-induced plasticity (SIP) to microband-induced plasticity (MBIP). Finally, the change in the κ-carbide precipitation behavior upon the addition of Mo and its effect on the deformation behavior were carefully analyzed and discussed through nanoindentation experiments, first-principles calculations and atom probe tomography analyses.
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Lightweight Fe–Mn–Al–C steels have become a topic of significant interest for the defense and automotive industries. These alloys can maintain high strength and ductility while also reducing weight ...in structural applications. Conventionally processed Fe–Mn–Al–C austenitic steels with high Al content (~9 wt%) demonstrate greater than 1.5 GPa strength with 35% elongation. Several recent studies have demonstrated success in fabricating steel parts using laser powder bed fusion (L-PBF) additive manufacturing (AM), which can generate near-net-shape components with complex geometries and is capable of local microstructural control. However, studies on L-PBF processing of Fe–Mn–Al–C alloys have focused on low Al content (<5 wt%) compositional regimes representing alloys that undergo transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). Here, in this study, we present the effects of L-PBF processing on the microstructure and mechanical properties of an Fe–30Mn–9Al–1Si-0.5Mo-0.9C austenitic steel. A process optimization framework is employed to determine an ideal L-PBF processing space that will result in >99% density parts. Implementing this framework resulted in near-fully dense specimens fabricated over a broad range of process parameters. Additionally, two bi-directional scan rotation strategies (90° and 67°) were applied to understand their effects on texture and anisotropy in this material. As-printed specimens displayed considerable work-hardening characteristics with average strengths of up to 1.3 GPa and 36% elongation in the build direction. However, solidification microcracks oriented in the build direction resulted in anisotropy in tensile strength and ductility resulting in average strengths of 1.1 GPa and 20% elongation perpendicular to the build direction. The successful L-PBF fabrication of Fe–30Mn–9Al–1Si-0.5Mo-0.9C presented here is expected to open new avenues for weight reduction in structural applications with a high degree of control over part topology.
