Super invar cast steel, Fe–32%Ni–5%Co by mass%, with excellent low coefficient of thermal expansion has disadvantages in the both of Young’s modulus and strength, because of coarse columnar ...solidification structure having texture. To simultaneously overcome these disadvantages, the variations of microstructure and mechanical properties through the novel heat treatment referred to as cryo-annealing, which is consisting of subzero treatment and subsequent annealing, were investigated in a super invar cast steel. The cryo-annealing promoted fcc-bcc martensitic transformation and then bcc-fcc martensitic reversion. The bidirectional martensitic transformations led to the formation of duplex austenitic structure consisting of untransformed and reversed austenite with a coarse-grained structure similar to solidification structure. Furthermore, it is found that the austenitic structure was varied depending on the annealing temperature of the cryo-annealing; reversed austenite was remained at lower annealing temperature, while it recrystallized to fine-grained structure as increasing annealing temperature. The high-density dislocations in reversed austenite and the randomized orientation of recrystallized austenite contributed to the development of strength and Young’s modulus, respectively. Therefore, the simultaneous development of rigidity and strength is not achieved by single cryo-annealing, but can be achieved by two-cycle cryo-annealing. Increasing the first annealing temperature and lowering the second annealing temperature in the two-cycle cryo-annealing are appropriate to randomize crystal orientation through austenite recrystallization and to make volume fraction of reversed austenite higher, respectively. As a result, Young’s modulus and 0.2% strength were simultaneously optimized.
•A new shape optimization method for cast steel tubular (CST) joints is proposed.•Flexible shape control of CST joints with a few parameters is attained.•Versatile selection of optimization ...objectives is achieved.•Significant reductions in material usage and structural stress are acquired.•Joint design with smooth surfaces is obtained, improving the manufacturability.
Cast steel tubular (CST) joints are extensively employed in steel structures for their excellent integrity and mechanical performance. However, the diverse configurations of CST joints result in the absence of standard verification formulas, leading to inefficient trial-and-error design approaches. To tackle this issue, this paper introduces a novel shape optimization method for CST joints that integrates subdivision surface techniques with genetic algorithms. The method comprises three key components: geometric modeling, structural analysis, and optimization algorithm, with shape optimization achieved through their collaborative operation. Applied to two types of CST joints, this approach resulted in significant reductions in joint volume by 39.2 % and structural stress by 49.0 %, respectively. The shape-optimized joints were compared with topology-optimized joints from published literatures, and demonstrated enhanced mechanical performance while presenting superior manufacturability. The proposed method offers considerable advantages over traditional trial-and-error approaches and topology optimization methods. It generates designs with continuous and smooth boundaries, better suited for the conventional casting process, and overcomes manufacturability issues of topology optimization. Additionally, the genetic algorithm allows for flexible selections of optimization objectives, addressing the restrictions of topology optimization methods. Furthermore, the methodʼs high level of automation is anticipated to expedite the joint design process, significantly reducing the requirement for manual intervention.
Currently, steel products are manufactured by continuous casting or large-sized ingot casting, and macrosegregation that occurs during the manufacturing process significantly impacts product quality ...in terms of cracks and deterioration of mechanical properties. To clarify the principle of casting defects, such as shrinkage porosity and macrosegregation due to the formation of bridging of the columnar dendrite of the medium-carbon steel, in this experiment, a laboratory-scale local-chilled mold in which the middle part was forcedly cooled was designed to cause bridging, shrinkage porosities, and macrosegregation. Enough risers were also designed to simulate realistic gravity casting as much as possible. The solidification structure morphology was observed, concentration analysis of alloying elements was performed, and the effect of bridging on macrosegregation was investigated. Solidification proceeded preferentially from the chill plate, and the bridging was formed successfully at a high casting temperature. The high casting temperature condition could cause bridging, but large shrinkage porosities would be formed as well. On the contrary, the lower casting temperature condition could increase the grain density and form shrinkage porosities that are smaller in size but larger in number and more dispersed, compared with the case cast with no chill plate mold. Due to the formation of bridging, macrosegregation was formed, and the difference between positive and negative segregation was increased from the longitudinal center of the sample.
In the industrial steel manufacturing process, such as continuous casting and ingot casting, macrosegregation occurs due to the effect of bridging and contraction flow during the middle and end ...periods of solidification. Since the macrosegregation results in a nonuniform structure and eventually cracks, there has been a demand for technological development that does not cause macrosegregation in the casting process. In this study, model experiments using the medium-carbon steel cast with a laboratory-scale local-chilled mold at different superheating have been carried out to investigate the relationship between solidified structure and macrosegregation occurred by local bridging during casting. The morphology of shrinkage porosities and dendrite structures was observed. The concentrations of the alloying elements were analyzed for macrosegregation by an electron probe micro-analyzer. Chill plates successfully formed the columnar dendrite bridging area and the columnar dendrite shell in the sample with high superheating. During solidification, the negative pressure of the region below the bridging increased, and the concentrated contraction flow flowed into the bottom of the large shrinkage porosity. Finally, V segregation was formed in the bridging area, large shrinkage porosities remained below the bridging area, and point-like or band-like positive macrosegregation occurred in the interdendritic region between columnar dendrites and equiaxed dendrites below the bridging. In comparison, a lower casting temperature increased the grain density and formed shrinkage porosities that were smaller in size but larger in number and more dispersed.
A new type of wear resistant low carbon Fe–B cast steel with granular borides can be obtained by alloying with titanium and cerium rare earth (RE). As a result, the as-cast eutectic boride structures ...of Fe–B cast steel are greatly refined and a blocky, less interconnected boride network is obtained from continuous ledeburite. After heat treatment, the boride eutectic in the modified Fe–B cast steel is in the form of a granular boride structure that appears to be isolated particles The guide rollers made of modified low carbon Fe–B cast steel show excellent wear resistance and thermal fatigue resistance in high speed wire mills.
The inhibition action of environmentally sustainable inhibitor Cycas revoluta leaves extract (CRLE) for corrosion protection of soft‐cast steel in a solution of HCl was assessed with electrochemical ...and chemical methods. The eco‐friendly inhibitor forms a thin coating on soft‐cast steel and slows the corrosion in acid media. The percent inhibition performance, corrosion current density, corrosion potential, and both anodic and cathodic slopes for Tafel were calculated. The results for electrochemical and chemical research are in beneficial correlation with each other. The inhibitor's inhibitory ability was well illustrated by the CRLE adsorption on soft‐cast steel followed the Langmuir isotherm. The investigations reveal that CRLE is a mixed form of inhibitor. Studies were performed with varying inhibitor amounts and temperatures. Thermodynamic parameters were calculated, and it shows that the corrosion inhibition effect is spontaneous and exothermic. The interaction of the plant extract was characterized by SEM, FTIR, contact angle measurements, and AFM techniques.
In previous studies, we reported a cryo-annealing process consisting of subzero treatment and subsequent annealing as a novel heat treatment to overcome the low rigidity and strength caused by the ...coarse solidified texture in super invar cast steel. In the present study, aging was added to the cryo-annealing process of Ti and Si-bearing super invar cast steels for further strengthening. By aging at 723 K after the subzero treatment, the intermetallic compounds L12–Ni3Ti and Ni3Si were finely precipitated within lenticular martensite, but not within untransformed austenite. This is because of the higher driving force for precipitation and faster atomic diffusion in the body-centered cubic matrix of martensite, as well as the high-density lattice defects that acted as preferential nucleation sites. The precipitated intermetallic compounds remained even after the matrix reverted from martensite to austenite, which led to significant strengthening of the reversed austenite. The high-strength reversed austenite contributed to the enhanced strain hardenability in the duplex structure composed of untransformed and reversed austenite, and consequently, the tensile strength was enhanced to over 800 MPa while maintaining an excellent low thermal expansion coefficient. Furthermore, an analysis of the strength mechanism based on the Orowan and Ashby-Orowan models reveals that the intermetallic compounds precipitated in reversed austenite acted as weak obstacles against dislocation motion.
The effect of tempering process on the microstructure and properties of low alloyed cast steel was studied. The results show that tempered at (200~400)°C, the M/A island of the granular bainite ...decomposes and carbide precipitates. When the tempering temperature rises to (500~600)°C, the M/A island is completely decomposed, and the carbide aggregates and gradually spheroidizes. With the increasing of tempering temperature, the tensile strength increases first and then decreases, elongation and impact energy show a trend of increasing at first, then decreasing and then increasing. The tempering brittleness occurs at 400°C.
•This paper presents a state-of-the-art cast-steel connector to be used in HSS modular construction.•This study ensures satisfactory performance of the HSS modular connection under axial design ...loads.•Two significant design improvements are recommended based on a parametric study.•The connector weight can be reduced up to 20% without compromising the design load requirements.•The location of the screws can be adjusted to significantly increase axial tension load capacity.
The popularity of steel modular construction is on the rise. This paper presents a new and innovative modular steel construction which uses state-of-the-art cast-steel connectors and hollow structural steel members. Structural behavior of a typical corner connection of this modular construction to be used in an assisted living facility was studied when the connection is subject to axial tension and axial compression loads. The study was completed using both experimental method and a numerical method. Six full-scale specimens were built and tested under axial compression and axial tension. It was found that this innovative modular connection satisfactorily carries the design loads. Based on the parametric study completed using finite element method, two significant design improvements are recommended. The cast-steel connector can be made 20% lighter without compromising the strength needed to satisfy the design loads. The locations of the connecting screws can be adjusted to achieve a higher stiffness and load carrying capacity of the connection when subjected to axial tension. This paper presents the new modular construction method in brief, the test method and test results, development of finite element model, and parametric study.
The mass‐loss, polarization tests, and electrochemical impedance spectroscopic strategies were applied to assess the inhibition performance of the environmentally friendly inhibitor Araucaria ...heterophylla leaves extract (AHLE) for soft‐cast steel corrosion safety in 1 M HCl at 300 ± 1 K. The environmentally friendly inhibitor creates a protective coat on soft‐cast steel that decelerates the corrosion process in acidic environments. The percentage inhibition effectiveness, corrosion current density, corrosion potential, cathodic and anodic Tafel slopes are being assessed. The outcomes of chemical and electrochemical research are almost similar. The inhibitor's inhibition activity was well illustrated by the AHLE adsorption on soft‐cast steel follows the Langmuir adsorption isotherm. According to the study, AHLE is a mixed kind of inhibitor. Experiments were conducted with varying inhibitor amounts and temperatures. The calculated ΔGadso$\Delta G_{{\rm{ads}}}^o$ values were in the range of −33.75 to −34.40 kJ/mol, which discloses the corrosion inhibitory action is exothermic and spontaneous. Scanning electron microscopy, Fourier transform infrared spectroscopy, and contact angle techniques were used to determine the association of the AHLE on the metal surface.
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