Search Results (10)

The crucial point for obtaining high-strength wire is controlling the microstructure, and the refinement of the interlamellar spacing between 80 and 150 nm gives sorbite excellent tensile strength and plastic deformation ability. To realize sorbitization, the fastest possible cooling rate should be used to avoid austenite being transformed into coarse pearlite. In this article, the main production processes, advantages, and disadvantages of wire rods for bridges are discussed, and the relationship between microstructure and mechanical characteristics of wire rods is argued. On this basis, the research works of simulation and experiments for heat treatment of wire rods in a salt bath, together with the convection and boiling heat exchange mechanism of wire rods in a salt bath, are discussed and provided. The salt bath quenching course is capable of cooling the wire rapidly from the austenitizing temperature to the sorbite temperature region and also dissipates the latent heat, thus reducing the reheating temperature of the wires. It can realize precise control over the microstructure and characteristics of wire and has advantages in improving the wire strength, hardness, wear, and corrosion resistance. The process parameters are highly adjustable, with strong adaptability and flexibility. To obtain ultra-high-strength sorbite steel wire, the key technical problems to be solved include selecting the suitable coolant, controlling the internal microstructure, and precisely controlling the cooling effect. Full article

In civil engineering, stress corrosion cracking (SCC) is a common cause of premature failure in steel wires, and effective solutions are currently limited. Investigating the SCC behavior of steel wires with different strength levels is crucial for understanding its fracture mechanism and developing potential solutions. This study examines the SCC behavior of wire rods with three strength grades (Steel A, B, and C) through stress corrosion experiments. The results show that high-strength wire rods have smaller pearlite interlamellar spacing. Steel C has the highest tensile strength (2303 MPa), while Steel A has the lowest (1830 MPa). Regarding stress corrosion sensitivity, the SCC mechanism of Steel C is dominated by hydrogen embrittlement, while Steels A and B primarily exhibit anodic dissolution as the cracking mechanism. Although Steel C has the smallest pearlite interlamellar spacing and superior corrosion resistance, its SCC failure time is the shortest due to hydrogen embrittlement. In contrast, for the anodic dissolution cracking mechanism, Steel B has a smaller pearlite interlamellar spacing, which enhances its corrosion resistance, and exhibits higher local stress stability due to its higher strength, resulting in the best SCC resistance (failure time: 3.81 h). This study reveals the synergistic effects of microstructure and strength on the SCC behavior of wire rods, offering theoretical guidance for the application of high-strength wire rods. Full article

Pearlitic steel rods are subjected to cold-drawing processes to produce pearlitic steel wires with true strains ranging from 0.81 to 2.18. Tensile tests are utilized to attain mechanical properties of cold-drawn pearlitic steel wires. TEM and XRD investigations were performed on the microstructure of the cold-drawn steel wires. With an increasing cold-drawn strain, both the interlamellar spacing and cementite lamellae thickness decrease, while the dislocation density significantly increases. The drawn wire has a tensile strength of 2170 MPa when the true stain reaches 2.18. Deformation-induced cementite dissolution occurs during cold-drawing progress, which releases many C atoms. The findings indicate that the supersaturation of C is heterogeneously distributed in the ferrite matrix. The ordered distribution of the released C in ferrite phases creates short-range order (SRO). SRO clusters and disordered Cottrell atmospheres contribute to solution strengthening, which, together with dislocation strengthening and interlamellar boundary strengthening, form an effective strengthening mechanism in cold-drawn pearlitic steel wires. Our work provides new insights into carbon redistribution and the mechanism of solution strengthening within ferrous phases. Full article

The microstructural evolution of SCM435 cold heading steel at different cooling rates was investigated by means of scanning electron microscopy, TEM, XRD, and electron backscatter diffraction. The results show that the cooling rate has a significant effect on the microstructure of the experimental steel. With an acceleration in the cooling, the microstructure of the steel gradually changed from ferrite and pearlite to ferrite, pearlite, and granular bainite; finally, the pearlite disappeared, and the microstructure changed to acicular ferrite, bainite, and martensite. With an increase in the cooling rate, the morphology of the carbide underwent an evolution from sheet carbide to short-rod carbide, granular carbide, and ultimately thin-strip carbide. With the acceleration in cooling, the proportion of large-angle grain boundaries gradually decreased, and the area of small-angle grain boundaries gradually increased. When the cooling rate was 0.1 °C/s, the proportion of large-angle grain boundaries was as high as 52.8%, and the dislocation density was only 1.91 × 10¹² cm⁻². When the cooling rate was 2.0 °C/s, the proportion of large-angle grain boundaries was only 27.1%, and the dislocation density increased to 5.38 × 10¹² cm⁻². With the increase in the cooling rate, the depth of the decarbonization layer and the thickness of the scale oxide gradually decreased, the proportion of the FeO phase in the scale phase gradually decreased, and the proportion of the Fe₃O₄ phase and Fe₂O₃ phase gradually increased. The tensile strength increased monotonously with the increase in cooling rate, whereas the elongation and area reduction first decreased, then increased, and then decreased. When the cooling rate was 1.0 m/s, the short rod and granular bainite in the material structure endowed the SCM435 steel with excellent strength and toughness matching, and the tensile strength and elongation of the steel reached 895 MPa and 24%, respectively. Full article

The application of Nb microalloying to high-carbon pearlite bridge cable wire rod steel has always been controversial, especially in the actual production process, which will be affected by the cooling rate, holding temperature and final bonding temperature. In this paper, the experimental characterization, finite element simulation and phase diagram calculation of the test steel were carried out, then the microstructure and properties of different parts of Nb microalloying of bridge cable wire rods were compared and analyzed. The phase transition interval of pearlite during the water-cooling process of bridge cable wire rods is increased due to the refinement of austenite grains, and the significant increase in the end temperature of the phase transition makes the average interlamellar spacing of pearlite increase. The cooling rate of different parts of bridge cable wire rods simulated by Abaqus has little difference. At the same time, Nb microalloying effectively increases the proportion of low-angle grain boundaries, so that the overall average misorientation representing the surface defects is reduced. This helps to reduce the surface energy and increase the stability of the microstructure. Combined with the mechanical properties of microtensile rods, it is found that the grain refinement effect of Nb is greater than that of coarsening interlamellar spacing during hot rolling deformation in actual production, which makes the tensile strength at the 1/4 section increase significantly. The overall tensile strength and area shrinkage of the steel wire have also been effectively improved. Full article

Steel tire cord and steel saw wire represent typical precision pearlitic steel wire rods of wire products; it is a very important solar energy material with a diameter about 50 μm. This paper mainly discusses the research progress of the wire rod drawing process, and its main contents are as follows: First section—the control of the wire rod surface quality is summarized, including the thickness of the surface decarburization layer, the phase composition and thickness of the surface iron oxide scale, and the removal of surface iron oxide scale. Then, the research progress of the wire rod water bath treatment process during sorbitization is summarized. In addition, the development of brass plating technology for steel wire is summarized, including copper plating technology, coating phase composition, etc. Furthermore, the development of steel wire drawing methods is summarized. Finally, the development of the dies used in steel wire drawings is summarized. Full article

A coupled thermal-microstructural simulation model was developed to estimate the thermal history in a eutectoid steel wire rod under continuous cooling and forced-convection. The model coupled the phenomena of heat transfer, phase transformation and estimation of the cooling boundary condition. The thermal histories were analyzed at different cooling rates to emulate the forced-convection conditions by air-jet as in the controlled cooling conveyor. The thermal histories were acquired and used to calculate the forced-convection heat transfer coefficients through the solution of the Inverse Heat Conduction Problem, while the phase transformation was approximated with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic model. From the heat transfer coefficients and the kinetic parameters, a user-defined function (UDF) was coded and employed in the ANSYS Fluent^® software. The model results were compared and validated with the experimental histories, obtaining a good agreement between both responses, while the microstructural evolution of the pearlite was validated using Scanning Electron Microscopy (SEM) and Vickers microhardness. It was found that specimen diameter and air velocity are the main variables to modify the undercooling and therefore the pearlite interlamellar spacing. Full article

Forming processes influence the mechanical properties of manufactured workpieces in general and by means of forming-induced initial damage in particular. The effect of the latter on performance capability is the underlying research aspect for the investigations conducted. In order to address this aspect, fatigue tests under compressive, tensile and compressive-tensile loads were set-up with discrete block-by-block increased amplitudes and constant amplitudes, and performed up to fracture or distinct lifetimes. Aiming at the correlation of the macroscale mechanical testing results at the mesoscale, intensive metallographic investigations of cross-sections using the microscopical methods of secondary electron analysis, energy dispersive spectroscopy and electron backscatter diffraction were performed. Thereby, the correlation of forming-induced initial damage and fatigue performance was determined, the relevance of compressive loads for the cyclic damage evolution was shown, and material anisotropy under compressive loads was indicated. Finally, the need was addressed to perform further investigations regarding crack propagations and crack arrest investigations in order to clarify the mechanism by which initial damage affects cyclic damage evolution. The relevance of the principal stress axis relative to the extrusion direction was emphasized and used as the basis of an argument for investigations under load paths with different stress directions. Full article

The microstructure evolution and the corrosion behavior of welding heat affected zone (HAZ) of Q315NS steel in 50 wt % H₂SO₄ at 20 °C was investigated with thermal simulation technique, surface analysis and electrochemical tests. The microstructure of ferrite and pearlite was observed in base metal (BM), fine grained region (FGHAZ) and inter critical region (ICHAZ) while coarse grained region (CGHAZ) consisted of granular bainite. The CGHAZ exhibited the highest microhardness and the largest average grain size. The passivation process occurred on the surface of all specimens. Different microstructure give birth to different corrosion behaviors between CGHAZ and BM, FGHAZ, ICHAZ. The dense oxide film were formed on the surface of ferrite while oxide film with micro voids were formed on the surface of pearlite in BM, FGHAZ and ICHAZ after immersion in 50 wt % H₂SO₄ solution for 12 h. The rod-shaped corrosion product was formed on the surface of CGHAZ while the porous-structured corrosion product was formed on the surface of BM, FGHAZ and ICHAZ after immersion in 50 wt % H₂SO₄ solution for 72 h. The corrosion resistance of BM, CGHAZ, FGHAZ and ICHAZ increased during the first 12 h and then declined slowly with increasing immersion time. The BM had the best corrosion resistance while the CGHAZ had the lowest corrosion resistance throughout the corrosion process. Full article

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress. Full article