Thin Steel Sheets Research Articles

Effects of yttrium on the microstructure, texture, and magnetic properties of non-oriented 6.5 wt% Si steel sheets by a rolling process

Non-oriented 6.5 wt% Si steel thin sheets with three different yttrium (Y) contents (0, 0.012, and 0.03 wt%) were prepared by hot rolling, warm rolling, intermediate annealing, cold rolling and final annealing processes. The effects of the Y content on the microstructure, texture, and magnetic properties of cold-rolled 6.5 wt% Si steel sheets were studied by optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and electron backscattered diffraction. The results showed that the sample with 0.012 wt% Y had the lowest volume fraction of inclusions, and Y played a role in purifying steel. The final average grain size of sheets decreased upon increasing the Y content. As the Y content increased, the {100} texture continuously weakened, and the overall intensity of the η (〈100〉//RD) texture increased first and then decreased, while the intensity of the detrimental γ (〈111〉//ND) texture decreased first and then increased. Adding an appropriate amount of Y optimized the recrystallization texture by promoting the occurrence of shear bands, which provided more nucleation sites for η - fiber oriented grains. When the Y content was 0.012 wt%, the magnetic induction B 50 reached the maximum (1.64655 T) due to the enhanced η texture and weakened γ texture. The sample with 0.012 wt% Y showed the lowest core loss at high frequencies (>5 kHz) because of the favorable grain size. The addition of excess Y increased the number of inclusions and increased γ -fiber oriented grain nucleation, which deteriorated the magnetic properties of non-oriented 6.5 wt%Si steel.

Metallurgical and Mechanical Characterization of Low Carbon Steel—Stainless Steel Dissimilar Joints Made by Laser Autogenous Welding

This paper addresses the metallurgical and mechanical characterization of dissimilar joints made by laser autogenous welding between thin sheets of low-carbon steel (CS) and austenitic stainless steel (SS). The welding technology applied, previously optimized to produce sound dissimilar joints, is based on the heat source displacement from the weld gap centerline towards CS, in order to reduce the SS overheating. The research includes optical microscopy observations, energy dispersive X-ray analysis (EDX) to assess the wt% of Cr, Ni, and Fe in all regions of the dissimilar welded joint, hardness measurements, and tensile tests of transverse-welded flat specimens. In comparison with classical determination of the joint overall mechanical characteristics, the novelty of this research consists of experimental assessment of the local mechanical behavior of the fusion and heat affected zones by using a digital image correlation technique (VIC-2D). This is an efficient tool for determining the constitutive properties of the joint, useful for modelling the mechanical behavior of materials and for verifying the engineering predictions. The results show that the positive difference in yielding between the weld metal and the base materials protects the joint from being plastically deformed. As a consequence, the tensile loading of flat transverse specimens generates the strain localization and failure in CS, far away from the weld.

Fatigue Strength of Rivet Resistance Spot Welding Technique in Comparison with Self-Piercing Riveting for Multi-material Body-in-White Structure

Cost-efficient multi-material design requires suitable joining techniques, ideally with low investment cost by re-using existing assembling lines. The recently developed resistance rivet spot welding (RRSW) technique combines mechanical joining with spot welding and enables cost-efficient joining of aluminum (Al) to steel for multi-material body-in-white structures. Here, the static and fatigue strengths of different hybrid Al-steel specimens made by RRSW were measured and compared to other state-of-the-art joining techniques, such as self-piercing riveting (SPR) and RSW. The static strength of RRSW matched or exceeded that of SPR regardless of the sheet thickness, whereas the fatigue strength of the RRSW joints showed a strong dependency on the thickness of the steel sheets. For thinner steel sheets, the fatigue of the RRSW-joined metal sheets was lower in comparison with SPR. Fatigue cracks were initiated in thin steel sheets around the weld nugget. By contrast, for thicker steel sheets, the fatigue strength of RRSW matched or exceeded that of SPR. With a thicker material combination of 1.5 mm steel and 1.0 mm Al, fatigue cracks occurred only in the Al sheet in both SPR and RRSW. For suitable steel sheet thickness, RRSW is thus a durable technique to join steel and Al.

Strength of Shear Nailed Connections in Thin Steel Sheets

AbstractThis paper investigated the potential applicability of the specification equation for the shear pull-out strength of a power-actuated fastener (PAF) connection to nail connections between s...

Butt welding of thin sheets of S960MC steel

The paper presents the application of MAG welding to TMCP steels (thermo-mechanically controlled processed) grade S960MC and 3 mm thick. In the analyzed joints, the research focused on their mechanical properties and changes in the heat-affected zone (HAZ) that occur in this type of steels. The hardness and tensile strength tests carried out showed a significant decrease in the properties of the joint compared to the declared values of the base material and the filler material used in the tests. In the case of hardness, it was a decrease of 34% in HAZ and by 15-21% in relation to the strength limit. Changes in HAZ properties of a joint correlate with changes in its structure.

Experimental studies on screw connections between cold-formed steel framing and sandwich sheathing

Cold formed steel (CFS) framed wall panels with sheathing is one of the main lateral load resisting systems in light gauge structures. The nonlinear behavior of the CFS wall panel under in-plane shear loading is dictated by the nonlinear behavior of the screw connections between CFS framing and sheathing. Necessity for new and high performance CFS shear wall configurations is clearly felt by the engineering community in order to cater for the increased seismic demands in mid-rise CFS buildings. To this end the experimental studies on screw connections are essential to understand the behavior of full scale wall panels by phenomenological models. This paper presents the experimental studies on the screw connection between CFS framing and new sheathing configuration with screw subjected to shear parallel to the free edge of the sheathing. This setup mimics shear experienced by the screw as a component in full scale wall panel tests. The proposed new sheathing configuration consists of a brittle sheathing material (one of cement particle board, fiber cement board and gypsum wallboard) sandwiched between two thin steel sheets. The experiments are performed for both monotonic and cyclic loading protocols and the stiffness, ultimate strength and ductility showed a significant increase due to the sandwich steel sheets. Ultimately, the configuration with sheathing material which provides higher strength as well as ductility has been proposed for future study by full scale experiments.

Physical-based methodology for prediction of weld bead characteristics in the Laser Edge Welding process

A comprehensive physical-based methodology is introduced to predict weld bead properties in the Laser Edge Welding (LEW) process. Laser edge welding of AISI 316L stainless steel thin sheets are conducted to investigate the behavior of geometrical, mechanical and metallurgical properties of the weld bead. The effect of significant processing parameters including the laser power, speed and focal distance are considered. The method however, utilizes a set of physical-based contour plots to predict the trend of weld characteristics using the heat input and power density. A novel combined physical parameter is also introduced and optimized to indicate the exact quantitative effectiveness of each physical and processing parameter. The developed approach is utilized to analyze a broad range of weld bead characteristics. First, weld bead geometrical characteristics such as weld width, penetration and distortion are studied. The physical-based method revealed that the power density has a significant effect on the weld penetration-to-width ratio while distortion is governed by the heat input. Variations of the fracture load are analyzed based on the corresponding combined parameter. Interestingly, a greater penetration-to-width ratio results in a higher fracture load. Finally, microstructural evolutions are investigated in three main regions, including the top, middle and bottom of the weld bead. A skeletal ferrite phase is observed in the mid-zone, which increases with increase of power density. The presented methodology can be applied to a broad range of other laser materials processing techniques to obtain insightful process design tips in order to achieve tailor-made properties.

Testing the Cross-Sectional Microhardness in Sheets with A 0.08% Carbon Concentration

The research team studied the hardness of cold-rolled sheets of varying thicknesses containing 0.08% carbon. Greater thickness correlated with lower mean hardness. The hardness was found to drop in the middle of a plate and to increase gradually towards the edges. This pattern was observed regardless of the thickness of thin cold-rolled sheet steel. The change in hardness may indicate uneven accumulated strain in the sheets rolled to a desired value. Pre-hardened sheets were analyzed to find whether the hardness was homogeneous through the thickness. The material was hardened by axial tensioning. Analysis showed that at greater accumulated strain, the through-thickness hardness was affected as well. However, the difference was less pronounced at the edge as well as in the middle of sheets. The paper shows graphs of the hardness distribution through thickness.

Investigations on Magnetic and Corrosive Characteristics of Thin Cold-Rolled Nonoriented Electrical Steel Sheets Post Gas Tungsten Arc and Laser Welding

Abstract Thin sheets (0.5 × 10−3 m) of cold-rolled nonoriented (CRNO) electrical steel are widely used for rotating electrical machines. Gas tungsten arc (GTA) and, recently, laser welding are used for welding M-43 grade CRNO steel. The performance of CRNO is thus explored because of changes in low-carbon, high-silicon content and thin insulation coatings post welding. The welding current for GTA varied from 30 to 110 A, whereas a laser of 800 W was used to estimate the heat affected zone (HAZ), fusion zone (FZ), and weld characteristic ratio. Ferritic phases with polygonal grain size, percent silicon content, magnetic losses, and welded corrosive samples corrosion rate (in mils penetration per year) are compared with the base material (average grain size 55 ± 12 μm). Five different corrodent (NaCl, NaOH, HCl, H2O, H2CO3) environments were created for 2,000 h as per ASTM B895-16(2020)e1, Standard Test Methods for Evaluating the Corrosion Resistance of Stainless Steel Powder Metallurgy (PM) Parts/Specimens by Immersion in a Sodium Chloride Solution, and ASTM G31-72(1999), Standard Practice for Laboratory Immersion Corrosion Testing of Metals standards. The GTA weld samples revealed much-increased weld geometry with welding current, and a significant increase in grain sizes up to 189.2 ± 4 μm for GTA and 187 ± 3 μm for the laser sample near the weld zone is observed. Microhardness variation is found to be in the range of 55 HV for GTA and 51 HV for laser samples in the FZ region with reference to the base metal hardness of 227 HV. In addition, the increase in core loss of 58.72 % for GTA and 39.82 % for laser samples with reference to nonwelded samples is observed.

Experimental and modeling study of cyclic plasticity and ductile fracture of thin structural steel sheets

The cyclic material properties of thin steel sheets are critical for accurate prediction of the structural response of the thin-walled steel elements. For the experimental study of the cyclic behaviors of thin steel sheets, we proposed a new anti-buckling device equipped with the disc-springs. This improvement aims to compensate the potential gaps between the fixtures and specimens under large plastic deformation so as to avoid the out-of-plane buckling. Furthermore, the negative influences derived from the transverse pressure and friction can be greatly minimized through the implementation of the disc-springs and the lubricated Teflon sheet, as indicated by the percentage errors of 0.31% and 0.08% for the external load and internal stress respectively. By virtue of this improved device, we perform 8 regular and 1 random cyclic testing with the Q345 steel sheet of the 6 mm thickness. It is noted that the smooth hysteresis loops feature no decrease in force under compression applied. Moreover, the sizes of hysteresis loops are dependent upon the current and maximum strain amplitude. The current strain amplitude controls the re-yielding rate, while the maximum value determines the saturated hardening stress. As for the ductile fracture initiation, the similar nominal stress–strain curves in the final tension stage among all cases and the considerably larger accumulated plastic strain than the one under monotonic loading imply the contribution of negative triaxiality to the decrease in the damage variable. Based on these observations, we develop a new cyclic plasticity and ductile fracture model, which is also programmed into the UMAT subroutine compatible with ABAQUS/Standard. By the comparison with the experimental results, the remarkable agreement of the predicted results demonstrates its validity in terms of the constitutive relationship, deformed shape of necking region and the fracture initiation under regular and particularly random cyclic loading.

Fatigue behaviour of thin Fe-Si steel sheets for electric motor production

The on-going evolution toward electric/hybrid traction requires the development of high-performance electric motors. The rotor of electric motors is made from a stack of thin steel sheets and a complex configuration of magnets. Electric steels are typically Fe-Si alloys where Si addition controls grain size. Mechanical durability assessment of electric motors is based on the fatigue performance of Fe-Si steels.This contribution reports a thorough mechanical characterisation of a Fe-Si alloy in the form of thin (i.e. 0.2 mm) sheets. Numerous tensile tests were performed to characterize the reference static properties and their respective scatter. A suitable fatigue testing procedure for thin sheets was developed and used in an extensive campaign aimed at investigating the directional fatigue behaviour of the Fe-Si steel. Comparison with literature data confirms that the fatigue response of thin sheets is affected by different factors related especially to the method of extraction.

Design of a non-destructive test for validating models of hydrogen migration

High-strength steels, despite their excellent mechanical properties in normal conditions, can be susceptible to hydrogen embrittlement. Due to the service loads or residual stresses, hydrogen migrates within the component and accumulates in the regions where the highest tensile hydrostatic stress occurs. As a consequence, component brittle failure can occur even if the initial or mean hydrogen concentration is lower than the critical value. The availability of models predicting the hydrogen diffusion within the component is a crucial task for the design. Several diffusive models have been presented in the literature and some general-purpose finite element codes have already implemented some of them. However, the validation of those models is still an open issue due to the difficulty in performing accurate local measurements of the hydrogen concentration. This study deals with the design of a test potentially able to validate hydrogen migration models. In the test, a four-point bending configuration is applied to a properly shaped hourglass specimen, previously charged with hydrogen, extracted from thin high-strength steel sheets. The specimen geometry and the loading configuration were designed to obtain a central region in which the stress and strain field is uniform in plane and exhibits a quasi-uniform gradient in the thickness direction. As a consequence, it is expected a large enough central region of the specimen in which the Hydrogen can migrate only in the thickness direction during the typical duration of the test. The local hydrogen concentration is evaluated by measuring the flux leaving the tensile surface of the specimen by a solid-state hydrogen sensor.

Study of Corrosion Behavior in Resistance Spot Welds of Thin Sheets of Zinc-Coated Interstitial-Free Steel

The aim of this research is to investigate the corrosion behavior of the resistance spot-welded joints of the zinc-coated interstitial free steel (IF steel) in contrast to the steel. For this purpose, the corrosion behavior of the welds and base interstitial-free steel (IF steel) was investigated in two solutions including 0.1 M NaCl + 0.1 M NaOH and 0.1 M NaCl + 0.1 M H2SO4. Potentiodynamic polarization curves and electrochemical impedance spectroscopy test results showed that the corrosion resistance of the base metal and welds in 0.1 M NaCl + 0.1 M NaOH solution is higher than their corrosion resistance in 0.1 M NaCl + 0.1 M H2SO4 solution. It was found that the corrosion resistance of the IF steel base metal in both solutions is higher than that of the welds obtained by the steel. According to the cyclic polarization curves, it can be said that the passive film formed on the specimens in 0.1 M NaCl + 0.1 M NaOH solution is highly susceptible to pitting corrosion while the specimens do not show any passivation behavior in 0.1 M NaCl + 0.1 M H2SO4 solution and undergo severe uniform corrosion.

Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry

The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface.

Modeling thin-walled elements with regard to steel hardening

Today in Russia 13% of buildings are built on the basis of a metal frame. To increase the energy efficiency of the industry, the use of thin-walled steel structures is one of the most technologically advanced and efficient solutions. To ensure the bearing capacity and reduce the risks of failure of buildings and structures at the design stage, it is important to correctly assess the reliability of the system, taking into account all influencing factors. The technology for the production of thin-walled profiles determines the factors that affect their stress-strain state. Uneven distribution of mechanical properties over the cross-section of the profile: hardening in the bending corners and adjacent zones leads to an increase in the strength of the metal. The article presents the results of numerical modeling of samples from thin sheet steel with and without the effect of hardening. The object of research is a thin-walled sigma profile with a section height of 300 mm, an element length of 4500 mm, operating under compression with bending. Metal hardening values are based on experimental data obtained by the authors. The stresses and displacements obtained as a result of the simulation were analyzed in four sections along the profile length: at a distance of 0.5 m, 2.3 m, 3.0 m and 4.0 m from the support. It is concluded that the supercritical work of the element without hardening of the material occurs earlier than in the element with hardening. The maximum stresses in the element without hardening exceed the stresses in the element with hardening by more than 30%. The maximum displacements in hardening are more than three times.

A Study of Mesh Sheets of 3-kW Stirling Engine

In recent years, the interest in low-pollution and high-efficiency heat engines has been increasing due to the growing awareness of environmental protection, and power generation at relatively low temperatures, such as use of exhaust heat and sunlight, has been attracting attention. Compared with other heat engines, Stirling engine is very important because it can be driven by any heat source at low temperatures, such as exhaust heat, and it does not emit exhaust gas. In order to realize a more efficient Stirling engine, it is essential to design a heat exchange system that is suitable for each component. Performance measurement and analysis on a new mesh regenerator material at low temperature difference using a 2-piston alpha-type 3-kW Stirling engine, NS03T are carried out. Mesh sheets developed for high performance Stirling engines can be designed with CAD and CAM technologies by etching process. For this study, M5 and M7 mesh sheets which are thin sheets of stainless steel with square holes in a grid arrangement, are used. With nitrogen and helium as the working fluid, the engine performance is measured by changing the charge pressure, heating temperature, and engine speed to clarify the flow resistance and heat transfer characteristics of the M5 and M7.

Dissimilar resistance spot welding of mild steel and stainless steel metal sheets for optimum weld nugget size

Different grades of steels are regularly used for various structural applications and it is always a difficult task to produce dissimilar welded joints. An attempt is made to weld thin sheets of mild steel (MS) and stainless steel (SS) materials by spot welding process by varying the different process parameters such as welding current, sheet thickness and different combinations of mild steel and stainless steel like MS with SS, MS with MS and SS with SS. The electrode is used as a copper and chromium alloy of 6 mm diameter. The experiment is designed as per the Taguchi L9 orthogonal approach by varying the three factors at three levels. The optimization of chosen factors and obtained weld nugget diameters as response values are performed to testify the statistical significance of the model terms by using R-square, analysis of variance (ANOVA), t and F tests, and desirability function. The outcomes will be useful in choosing the exact combinations of process parameters to achieve the desired quality spot-welded joints for automotive applications.

Mechanical characterization of lightweight foam-based sandwich panels

Foam-based composite structures are widely used in the field of construction market for roofing and closing walls. This paper presents a mechanical characterization of a lightweight sandwich panels with foam core. The faces of the panels are made of thin steel sheets, and for the core, closed-cell polyurethane foam with a density of 40 kg/m3 was used. Mechanical testing consists of quasi-static four-point bending, transversal tensile and compression tests. All experimental tests were conducted at room temperature in accordance to EN 14509:2013 Standard. With the data obtained from experimental tests, load–displacement curves and mechanical properties are presented. Following the experimental tests, the elastic characteristics (shear modulus, tensile E-modulus, compression modulus), strength properties (ultimate shear strength, transverse tensile strength, compression strength) and energy absorption performances were determined.

Effect of the strength of steel sheets and wires on residual stress of thin steel sheet lap-fillet GMA weld joint

Effect of the strength of steel sheets and wires on residual stress of thin steel sheet lap-fillet GMA weld joint

Laser dissimilar welding of copper and steel thin sheets for battery production

Laser processing of metallic thin sheets has gained undoubted industrial interest in the last decade especially due to its implications in the e-mobility field. In particular, dissimilar welding of thin sheets made of different materials, such as aluminum, copper, and steel is nowadays recognized as an effective solution for many joining applications in battery and related component production. According to these considerations, the present paper is aimed at evaluating the possibility to perform a sound joining of thin copper sheets on thin steel ones in a lap-welding configuration. This application is of particular interest especially when cylindrical cells have to be electrically connected to any of the elements constituting the battery, such as printed circuit boards, busbars, etc. By means of a continuous wave fiber laser and a galvo scanner, an experimental campaign was carried out in order to define a process window for characterizing the above-mentioned welding application. The results were characterized by means of metallographic analyses, microhardness measurements, electrical conductivity tests, and scanning electron microscopy-energy dispersive system analyses. Particular attention was placed on the role of process parameters in controlling the penetration depth on the lower steel layer, since it constitutes the external housing of the single cell and a drop through can seriously damage the cell itself.