Search Results (38)

Straw as a building material alternative is in line with sustainable development goals. To make effective use of straw resources such as rice and corn stalks in rural areas, a kind of steel wire mesh-reinforced straw concrete sandwich panel (SCSP) was developed. The SCSP was composed of cold-drawn low-carbon steel-wire mesh (SWM), fine gravel concrete (FGC), and straw. The used type of FGC was shotcrete. A cold-drawn low-carbon SWM was arranged on the upper and lower sides of the SCSP, and a vertical wire tie was arranged between the upper and lower cold-drawn low-carbon SWMs. The FGC was sprayed on the SWM to make the SCSP layer work together. The loading process of the SCSP could be divided into three stages: elastic working state, cracking state, and failure state. The results of the four-point loading test show that the maximum flexural moment of the SCSP can be up to 7.5 kN·m in the elastic range. The ultimate bearing capacity of SCSP reaches 10.9 kN·m, and the maximum crack width can reach 3~4 mm. At the same time, based on the assumption of the flexural section of SCSP, two simplified calculation models of SCSP bearing capacity were established. The average error was 2.99% and 9.41%, respectively, by comparing the experimental values with the two calculated values. The results obtained by using the two models were in good agreement with the experimental results. Full article

This paper focuses on the study of the tensile fracture behaviour of prismatic notched specimens of cold drawn pearlitic steel, providing a macro- and micro-approach. Two types of notched samples with very different notch radius (sharp and blunt notches, PAA and PCC) and the same notch depth were studied, thereby allowing a study of the fracture behaviour under different levels of stress triaxiality (constraint) in the experimental specimen. The studied samples are machined from pearlitic steel wires taken from a real cold drawing chain, analysing the entire drawing process, from the initial base material (hot rolled bar; not cold drawn at all) to the final commercial product (prestressing steel wires; heavily cold drawn), including two intermediate stages in the manufacture chain. The aforesaid specimens were subjected to tensile fracture tests and analysed at macroscopic and microscopical level using the scanning electron microscope (SEM), thereby obtaining micrographs of the different areas appearing in the specimens under study and assembling full micro-fracture maps (MFMs) of the fractured area. The aim of the research is to analyse the macro- and microscopic changes produced by the variation in stress triaxiality state (constraint), along with the different fracture processes. The first relevant finding is the increase in fracture path deflection for higher drawing degrees, and for greater triaxiality levels associated with sharp notches. Another finding is the variation in area of the different fracture zones, i.e., outer crown (OC), fracture process zone (FPZ) and intermediate zone (Z_INT), which are characterised by their specific micro-mechanisms, micro-void coalescence (MVC), cleavage (C) and special (large) micro-void coalescence (MVC*). The higher the stress triaxiality level, the larger the area occupied by the Z_INT in the fracture process. The fracture behaviour tends to unify along with the degree of drawing, with less dependence on the state of triaxiality imposed on heavily drawn wires. Results have been obtained in which the increase in triaxiality, imposed by the smaller radius of curvature of the notch (sharp notch), as well as the greater degree of drawing of the wires, cause the fracture process to place the FPZ at the notch tip. It is demonstrated that the variation in stress triaxiality and the drawing degree can generate different locations of the fracture initiation zone (FPZ). 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 effect of plastic deformation induced by wire drawing on thermal properties in twinning-induced plasticity (TWIP) steel has been investigated. The investigation on the relationship between thermal conductivity (k) and the microstructure in the drawn TWIP steel wire was systematically performed to accurately understand the behavior of the k of a metal during wire drawing. The yield and tensile strengths linearly increased with drawing strain owing to the deformation twins and dislocations that were generated during wire drawing. However, the total elongation sharply decreased with drawing strain. The linear thermal expansion coefficient of the TWIP steel exhibited a similar value regardless of drawing strain. The density decreased linearly with temperature, and it was independent of the drawing strain. k increased initially and then decreased after reaching its maximum value with increasing drawing strains. At a nominal drawing strain of 0.26, k increased compared with the state of hot rolling because the increase in k due to grain elongation was greater than the decrease in k due to dislocations generated during wire drawing. However, as the amount of drawing step increased further, the influence of dislocations on k increased more than that of grain elongation, causing k to decrease. Full article

The hydrogen embrittlement (HE) phenomenon occurring in drawn pearlitic steel wires sometimes results in dangerous delayed fracture and has been an important issue for a long time. HE is very sensitive to the amount of plastic deformation applied in the drawing process. Hydrogen (H) atom diffusion is affected by ambient thermal and mechanical conditions such as stress, pressure, and temperature. In addition, the influence of stress gradient (SG) on atomic diffusion is supposed to be crucial but is still unclear. Metallic materials undergoing plastic deformation naturally have SG, such as residual stresses, especially in inhomogeneous regions (e.g., surface or grain boundary). In this study, we performed molecular dynamics (MD) simulation using EAM potentials for Fe and H atoms and investigated the behavior of H atoms diffusing in pure iron (α-Fe) with the SG condition. Two types of SG conditions were investigated: an overall gradient established by a bending deformation of the specimen and an atomic-scale local gradient caused by the grain boundary (GB) structure. A bi-crystal model with H atoms and a GB structure was subjected to bending deformation. For a moderate flexure, bending stress is distributed linearly along the thickness of the specimen. The diffusion coefficient of H atoms in the bulk region increased with an increase in the SG value. In addition, it was clearly observed that the direction of diffusion was affected by the existence of the SG. It was found that diffusivity of the H atom is promoted by the reduction in its cohesive energy. From these MD results, we recognize an exponential relationship between the amount of H atom diffusion and the intensity of the SG in nano-sized bending deformation. Full article

The final aim of this paper is to study the microstructural changes in the necking region of progressively cold-drawn pearlitic steel wires by means of a thorough and detailed analysis of pearlite interlamellar spacing and Vickers micro-hardness in this special region. To this end, a set of progressively cold-drawn pearlitic steel wires belonging to a real manufacturing chain were subjected to standard tension tests, in such a manner that the tests were interrupted before the final fracture, i.e., the test development was aborted just at the necking instant. The microstructural changes during necking were evaluated by measuring the pearlite interlamellar spacing in the necking region, as well as the Vickers micro-hardness in the different points of it. The study of the afore-said microstructural changes preceding the final fracture was the final aim of the research, intending to determine the local areas in the necking region of the specimens in which microstructural changes are most evident, thereby affecting the local mechanical response of a specific cold-drawn steel at the moment of instability under load control during the standard tension test. Full article

Cold drawing is a commonly used technique for manufacturing the prestressing steel wires used as structural elements in prestressed concrete structures. As a result of this manufacturing process, a non-uniform plastic strain and residual stress states are generated in the wire. These stress and strain fields play a relevant role as the main cause of the in-service failure of prestressing steel wires in the presence of an aggressive environment, hydrogen embrittlement (HE). In this paper, hydrogen susceptibility to HE is compared in two different commercial cold-drawn wires with the same dimensions at the beginning and at the end of manufacturing that follow different straining paths. To achieve this goal, numerical simulation with the finite element (FE) method is carried out for two different industrial cold-drawing chains. Later, the HE susceptibility of both prestressing steel wires was estimated in terms of the hydrogen accumulation given by FE numerical simulations of hydrogen diffusion assisted by stress and strain states, considering the previously obtained residual stress and plastic strain fields generated after each wire-drawing process. According to the obtained results, the hardening history modifies the residual stress and strain states in the wires, affecting their behavior in hydrogen environments. Full article

This paper studies the drawing-induced intercolonial microdamage (ICMD) in pearlitic microstructures. The analysis was performed from the direct observation of the microstructure of the progressively cold-drawn pearlitic steel wires associated with the distinct steps (cold-drawing passes) of a real cold-drawing manufacturing scheme, constituted by seven cold-drawing passes. Three types of ICMD were found in the pearlitic steel microstructures, all affecting two or more pearlite colonies, namely: (i) intercolonial tearing; (ii) multi-colonial tearing; and (iii) micro-decolonization. The ICMD evolution is quite relevant to the subsequent fracture process of cold-drawn pearlitic steel wires, since the drawing-induced intercolonial micro-defects act as weakest links or fracture promoters/initiators, thereby affecting the microstructural integrity of the wires. Full article

In this paper, the effects of the skin pass technique on the residual stress and plastic strain fields generated in cold drawn pearlitic steel wires are analyzed. The aim is to find out the optimal conditions to be used in the design of a manufacturing process for obtaining more reliable structural components in terms of the main cause of failure: the hydrogen embrittlement (HE). To achieve this goal, diverse numerical simulations were performed by using finite elements (FE) and considering, on one hand, the first step of a real cold drawing chain, using (i) a conventional drawing die and (ii) modified drawing dies with different soft diameter reductions, and, on the other hand, numerical simulations by FE of the hydrogen diffusion assisted by stress and strain states to estimate the hydrogen distributions. Obtained results revealed the secondary reduction degree as a key parameter in the die design for reducing the drawing-induced residual stress. According to the results, low values of the reduction ratio cause radial distributions of residual stress with significant reductions at both the wire core and at the wire surface. In addition, the hydrogen accumulation at the prospective damage zone (near the wire surface) given by FE simulations is lower in the wires drawn with modified drawing dies including a skin pass zone. Full article

The effects of contact conditions at the wire–die interface on the temperature distribution of the specimen and die are investigated to understand the wire drawing process. Finite element analysis and experiments are performed to analyze the temperature distribution of a drawn wire and die based on different contact conditions using a low-carbon steel wire. The maximum temperature (T_max) of the die decreases as the contact heat transfer coefficient at the wire–die interface increases, whereas that of the wire increases with the contact heat transfer coefficient. The T_max of the die and wire decreases with the thermal conductivity of the die. As the thermal conductivity of the die increases, the heat generated by friction is rapidly absorbed into the die, and the T_max of the die decreases, thus resulting in a decrease in the surface temperature of the wire. The T_max of both the die and wire linearly increases with the friction factor. In particular, the T_max of the die more sensitively changes with the friction factor compared with that of the wire. The T_max of the die linearly increases with the drawing velocity, whereas that of the wire parabolically increases with the drawing velocity. The influence of bearing length on the temperature increase in both the wire and die is insignificant. Full article

Corrosion fatigue is an important factor that limits the life of grid materials including wire clips. In order to study the effect of corrosion fatigue and to select suitable grid steels, this paper focuses on the corrosion fatigue properties of Q235 carbon steel, Q235 galvanized steel, and 316L stainless steel in the corrosive environments of air, 2wt% NaCl, 5wt% NaCl, and 8wt% NaCl. Through the fatigue test in the corrosive environment, and the surface morphology scanning and microstructure observation of the fracture, the following conclusions are drawn: the three materials are more susceptible to corrosion fatigue in the Cl⁻ environment, and the higher the Cl⁻ concentration, the greater the likelihood of fracture caused by corrosion fatigue for these three materials. By analyzing the surface roughness, dimples, and cracks in the microstructure, it is found that 316L stainless steel is highly sensitive to Cl⁻ corrosion under cyclic stress, and Q235 galvanized steel is more resistant to Cl⁻. By plotting the stress fatigue life curve of Q235 galvanized steel, it is found that the corrosion fatigue life decreases as the Cl⁻ concentration increases. For wire clips in areas with severe Cl⁻ pollution, Q235 galvanized steel should be selected to achieve the best anti-corrosion fatigue effect; at the same time, the original parts should be repaired or replaced in a timely manner based on the predicted corrosion fatigue life. Full article

The main cause of in-service failure of cold drawn wires in aggressive environments is hydrogen embrittlement (HE). The non-uniform plastic strains and residual stresses generated after cold drawing play a significant role in the matter of HE susceptibility of prestressing steels. In this paper, a new and innovative design of the drawing scheme is developed, geared towards the reduction in both manufacturing-induced residual stresses and plastic strains. To achieve this goal, three innovative cold drawing chains (consisting in diverse multi-step dies where multiple diameter reductions are progressively carried out in a single die) are numerically simulated by the finite element (FE) method. From the residual stress and plastic strain fields revealed from FE numerical simulations, hydrogen accumulation for diverse times of exposure is obtained by means of FE simulations of the hydrogen diffusion assisted by stress and strains. Thus, an estimation of the HE susceptibility of the cold drawn wires after each process was obtained. Results reveal that cold drawn wire using multi-step dies exhibits lower stress and strain states nearby the wire surface. This reduction causes a decrease in the hydrogen concentration at the prospective damage zones, thereby improving the performance of the prestressing steel wires in hydrogenating environments promoting HE. Thus, the optimal wire drawing process design is carried out using special dies with several reductions per die. Full article

The research presented in this article aimed to obtain a semi-finished product in the form of TRIP wires, which in further research will be used to produce fasteners in the form of KPS-6 screws used in the construction industry. At present, the process of manufacturing this type of fastener (from wire rod to the finished product) involves two technological lines: one for carrying out the drawing process and obtaining a semi-finished product in the form of a wire with appropriate properties, and the other for the production of fasteners. Semi-finished product wires with a ferritic-perlitic structure obtained after the drawing process are the starting product for the production of fasteners, the tensile strength of which is approximately 450 MPa. In order to be able to obtain fasteners characterized by an increased level of properties in 8.8 grade, after the screw manufacturing process, heat treatment should be carried out by hardening and tempering. The new technology proposed in the article includes: a drawing wire rod with a semi-finished product diameter, two-stage heat treatment on the line for pass-through heating and cooling, ensuring the obtaining of a TRIP-type structure in drawn wires, and calibration drawing. The product of this process was a wire whose tensile strength was in the range of 700–800 MPa with a TRIP structure. Thanks to obtaining a TRIP-type structure with the assumed amount of retained austenite, we obtained wires with higher strength properties and very high plasticity in relation to wires with the same chemical composition and ferritic and perlitic structure. The research carried out in the article also allowed us to obtain, in the semi-finished product wires, a favourable relationship between the strength properties and plasticity of the material, expressed by the value of the R_e/R_m coefficient (yield strength/tensile strength) and the so-called yield ratio, which determines the material′s susceptibility to cold deformation; the smaller these coefficients, the greater the yield strength. The subsequent stages of the research will include the development of forming fasteners in the form of KPS-6 screws used in the steel construction industry with TRIP structures, with increased properties of products in the 8.8 property class, without conducting heat treatment by hardening and tempering. It is assumed that the resulting product will have an additional usable feature: preserving a certain amount of retained austenite in the structure of the finished fasteners, which will be transformed into martensite during operation, and thus affect the longevity of the fasteners. Full article

The paper presents the impact of the drawing method on the microstructure and corrosion resistance of galvanized steel wires. The microstructural tests confirmed that, in the drawing speed range v = 5–20 m/s, the use of hydrodynamic dies creates more favorable conditions for the deformation of the soft zinc coating on the hard steel core. The increase in friction at the wire/die interface in the conventional method, as compared to the hydrodynamic method, contributed to the decrease in coating thickness and the increase in the diffusion layer, and the higher the drawing speed, the greater the differences between the analyzed drawing methods. In the conventional method, while drawing at high speeds v = 20 m/s, there was a two-way diffusion and complete remodeling of the ζ phase in δ₁. In the hydrodynamic method, at the speed of 20 m/s, in the analyzed micro-areas, places showing the presence of the ζ phase, partially dispersed in the layer with pure zinc, were observed. A corrosion tests comparison between conventionally and hydrodynamically drawn wires showed an improved behavior of the latter. The greater mass in the surface layer of pure zinc, a substrate for the corrosion product in hydrodynamically drawn wires, reacted, creating insulation from the white corrosion produced. The compressive stresses in the hydrodynamic dies caused by the high pressure of the lubricant on the circumference of the wire closed the microcracks on its surface, which additionally sealed the zinc coating. Full article

The different behaviors of the mechanical properties of drawn and caliber-rolled wires with applied strain were investigated to determine the appropriate process between wire drawing and caliber rolling with consideration of materials and process conditions. Ferritic, pearlitic, and TWIP steels were drawn and caliber-rolled under the same process conditions. Caliber-rolled wires exhibited a hardening behavior in the early deformation stage and softening behavior in the later deformation stage compared with the drawn wires, regardless of the steel. The hardening behavior of the caliber-rolled wires was explained by the higher strain induced by caliber rolling compared with wire drawing, especially the higher amount of redundant work in caliber-rolled wire. The caliber-rolled wire had approximately 36% higher strain than the drawn wire and approximately 85% higher strain than nominal strain. The softening behavior of the caliber-rolled wire in later deformation stages was related to the Bauschinger effect or low-cycle fatigue effect caused by the roll geometries and loading conditions during caliber rolling. The different intersection points of the tensile strength between drawn and caliber-rolled wires with the steels were attributed to the different strain hardening rates of each steel. Between the options of the caliber rolling and wire drawing processes, the appropriate process should be selected according to the strain hardening rate of the material and the amount of plastic deformation. For instance, when the wires need to deform at high levels, wire drawing is the better process because of the appearance of the Bauschinger effect in caliber-rolled wire. Full article