The main task for a ballast bed is to transmit the sleeper pressure in a form of stress cone to the subsoil, provide proper drainage and resist the sleeper displacement. Poorly maintained ballast ...could severely limit the maximum speed capacity and create further problems with the structural integrity, possibly leading to a complete failure of a given rail line. To prevent the unwanted corollaries, the ballast bed has to be periodically cleaned with an appropriate machinery. In this paper the authors investigated the effect of the chemical composition on the physical properties of the ballast excavating chains made of high-manganese steels. The authors focused on the wear mechanism, work hardening ability and hardness in the cross-sections areas. A microstructure analysis was performed as well, and observations revealed divergent morphology of precipitations at the grain boundaries, which influenced the size of austenite grains. The deformation twins formed as a result of operation were noticed in the samples. Research has shown that less carbon and chromium reduces the hardness of cast steel, and it specifically affects the ability to strain hardening. The authors explained the role of adjustments in chemical composition in the operational properties of high-manganese cast steels. It has been shown in the paper that different chemical compositions affect the properties of the alloys, and this causes different types of wear. The high content of chromium increases the hardness of materials before and after plastic deformation hardening, which in the conditions of selector chains results in greater dimensional stability during wear of holes in pin joints and will be more susceptible to abrasive wear in the presence of dusts from the ballast than creep.
Precipitation strengthening is a crucial method for enhancing the mechanical properties of steel. The bridgman directional solidification furnace, optical microscope (OM), scanning electron ...microscope (SEM), electron probe analyzer (EPMA) and transmission electron microscope (TEM) were used to investigate the effect of solidification cooling rate on the solidification microstructure, microsegregation, and nanoprecipitates in medium carbon CrMo cast steel. The results indicate that as the cooling rate increases, the solidification microstructure is significantly refined. The relationship between the cooling rate (CA) and primary dendrite arm spacing (PDAS, λ1) and secondary dendrite arm spacing (SDAS, λ2) are given by λ1 = 123.74 × C-0.4088A, λ2 = 66.63 × C-0.6532A. Solute elements like Cr, Mo, and V exhibit noticeable positive segregation in the inter-dendritic. When the cooling rate does not exceed 0.47 °C/s, the solute concentrations in the inter-dendritic increase with higher cooling rate, leading to a decrease in the effective solute partition coefficient. This phenomenon is primarily attributed to the back diffusion of solute elements during solidification. Following heat treatment, precipitation of M6C, V(C,N), and M23C6 occurs within the inter-dendritic regions. If the solidification cooling rate does not exceed 0.47 °C/s, the density and volume fraction of nanoprecipitates increase with higher cooling rate. This trend primarily results from the reduction in critical nucleation radius and critical nucleation energy, facilitating easier nucleation of nanoprecipitates.
Cast steel joints are widely used in engineering structures and exhibit different mechanical responses in service environments at elevated temperatures. Hence, the temperature-dependent mechanical ...properties in cast steel joint must be characterized to guide the engineering design and service life assessment at elevated temperatures. This study carried out a comprehensive, experimental investigation of the base materials of cast steel ZG300–500 H and vessel steel Q345R cut from a cast steel joint to obtain the reduction factors and stress–strain responses at elevated temperatures. The reduction factors of yield strength, elastic modulus, and ultimate strength were analyzed and compared with the code-recommended values and obtained test data. The material properties of ZG300–500 H and Q345R deteriorated significantly as the temperature increased, and the currently available reduction factors in the design codes and obtained test data were incapable of accurately describing their material performance degradation. Therefore, new predictive equations have been proposed to accurately describe the mechanical properties’ degradation and stress–strain responses of ZG300–500 H and Q345R at elevated temperatures of 20–700 °C. These research results also provide a strong base for the safety research and design of cast steel joint structures at elevated temperatures.
Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very ...rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.
•Cr-(Al, Sn)-B MAB phase solid solution was prepared by hot-dip aluminizing of Fe-Cr-B cast steel in AlSn alloy melt.•Sn whisker spontaneously grew on the Cr-(Al, Sn)-B MAB phase solid solution.•The spontaneous growth of Sn whisker observed in-situ by SEM.•The spontaneous growth of Sn whisker could grow from both the bottom and the tip.
Corrosion fatigue (CF) experiments of G20Mn5QT cast steel and Q355D steel butt-welded joint are conducted with loading frequencies of 1 Hz and 10 Hz. The decrease of loading frequency resulting in a ...reduction in the CF life of specimens. The average percentage of CF life reduction are 6.4% (S = 300 MPa), 53.5% (S = 260 MPa), 17.5% (S = 220 MPa), 34.3% (S = 190 MPa), 38.6% (S = 160 MPa) and 80.5% (S = 130 MPa), respectively. The CF failure mechanism remains unchanged regardless of the loading frequency. Based on continuum damage mechanics (CDM), a novel CF life prediction model is proposed, in which the effect of loading frequencies is introduced by the evolution of corrosion pits. The prediction model considers the coupling effect of fatigue and corrosion, and it achieves the prediction of CF life of the butt-welded joints using experiment data at higher loading frequency. The accuracy and universality of the prediction model are verified by predicting the CF life of other specimens.
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•The S–N curves of butt-welded joints under different loading frequencies is obtained.•The corrosion fatigue failure mechanism of butt-welded joints is analyzed.•A corrosion fatigue life prediction model considering loading frequency is proposed.•The prediction of corrosion fatigue life of the butt-welded joints is achieved.•The accuracy and universality of the prediction model are verified.
In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental ...analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was found that the addition of Ti in the higher concentrations refines the solidification macrostructure (dendritic pattern) for both cast part sizes evaluated. Regarding mechanical properties, the addition of Ti does not significantly vary the ultimate tensile strength but reduces the total elongation for cast part sizes
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.
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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