Cold-rolled Steel Sheets Research Articles

Effect of non-linear tension-compression loading reversal on the hardening behavior and initiation fracture strain of a cold-rolled TRIP780 steel sheet

This work examines the influences of non-linear pre-forming paths on the ductile behavior and damage evolution of a cold-rolled transformation-induced plasticity (TRIP) steel. Two non-linear pre-forming paths, i.e. tension followed by compression (TC) and compression followed by tension (CT), were designed to reveal the Bauschinger effect and fracture ductility. The experimental results demonstrated that the fracture strain was strongly affected by the loading path and magnitude of pre-forming. A single-surface plasticity model accounting for a non-associated Hill’ 48 plastic flow potential was developed by combining a Voce-Swift isotropic hardening law and a mixed non-linear kinematic (NLK) hardening rule. The experimental strain-stress curves of pre-formed specimens were utilized to calibrate the model parameters. The proposed model well predicted the hardening anisotropy, Bauschinger effect, permanent softening and transient behavior of specimens undergoing TC and CT pre-forming strategies. In addition, the influence of non-linear TC and CT pre-forming loading paths on the initiation fracture strain were modeled and investigated through a Hosford-Coulomb fracture criterion. The results showed that the proposed non-associated and mixed hardening model can describe the hardening behavior under TC and CT non-linear deformation. It is also found that the Hosford-Coulomb fracture model is capable to provide reasonable prediction on the fracture strain under different non-linear pre-forming loading paths even though a larger scatter for the TC deformation. These results also confirm that the ductility of the TRIP780 increases under a TC or CT non-linear pre-forming.

Recognition of surface defects of rolled steel in sheets by application micro-X-ray spectral analysis

Surface defects of sheet rolled products have a significant impact on its quality, performance and further processing of products, for example, on application of a protective anticorrosive coating. Therefore, the elimination of such defects and their accurate identification is an important aspect of sheet rolling production. Reducing the rejection of metal for surface defects enables to get a significant technical and economic effect. Investigation of the causes of defectiveness of the surface of sheet rolled products will make it possible to determine the source of the appearance of the defects and methods to prevent them. Determination of the nature and morphology of surface defects, the sources of which being metallic and non-metallic inclusions, as well as remnants of slag surface layer, scales from metallurgical and rolling stages, rolled into the surface of a hot-rolled sheet, is often difficult, since the appearance of the defects is very similar. It was shown that application of a scanning electron microscope (SEM) with micro-X-ray spectral analysis (MXSA), thermodynamic analysis makes it possible to determine the chemical composition of micro-areas and associate it with the end-to-end technology of sheet production. The article presents the results of identifying surface defects of cold-rolled sheet steel.

Optimization of the formation technology of tripolyphosphate coating on mild steel

Tripolyphosphate conversion coatings are promising due to the active type of anti-corrosion protection. However, to be introduced into production, it is necessary to optimize the technology of tripolyphosphate coating deposition. Coatings were deposited to samples of st05kp cold-rolled sheet steel (analogs G10050, G10060, 1CR, 2CR, D6-2, DG-2) from aqueous solutions of sodium tripolyphosphate (4 %, 6 %, 10 %, 12 %, 14 %) at t=80 °C by dip coating and sputtering. The specific weight and morphology of the coating were determined. The corrosion-protective capability was studied in the G-4 climatic chamber at 90 °C and 100 % humidity using Akimov's test. The prospects of the dip coating and sputtering methods were shown. It was revealed that in the dip coating method, the specific weight of the coating was 1–4 g/m2 and increased linearly at a rate of 0.3–0.35 g/m2 by 1 % (wt.) Na5P3O10. For the sputtering coating method, it was revealed that at 4–8 % Na5P3O10, the growth rate of the specific weight was 0.2 g/m2 by 1 % Na5P3O10 and the specific weight exceeded that of the coating obtained by the dip coating method, due to accelerated oxygen access and increased coating formation rate. At 10–14 % Na5P3O10, the growth rate of the specific weight was 0.55–0.65 g/m2 by 1 % Na5P3O10. However, the specific weight was lower than that of the coating obtained by the dip coating method, due to the self-compaction of the iron tripolyphosphate matrix and decreased mass of the Na5P3O10 filler. Using accelerated corrosion testing methods, the optimum Na5P3O10 concentration to obtain a coating with the highest corrosion-protective capability was 6 %–10 % (wt.). The correlation of the protective capability of the coating samples with the coating defects and cracks was revealed

A simulation and experimental study on the deep drawing process of SPCC sheet using the graphical method

This study presents a method for finite element (FE) simulation of a deep drawing process of a cold-rolled carbon steel (SPCC) sheet material based on the graphical method. First, uniaxial tensile specimens were prepared and experimental tests were conducted to determine the flow stress curves. The calculation of the fracture points at special strain modes (plane strain, uniaxial tensile strain, and biaxial tensile strain) was presented using the modified maximum force criterion (MMFC). After that, the graphical method was adopted for the estimation of the forming limit curve (FLC) based on several hardening laws. FE models for a deep drawing process of the SPCC sheet were then built using the calculated FLCs. Using FE simulations, the fracture heights of cylinder cups formed by the deep drawing process were finally determined and compared with those from experiments. The results showed a good agreement between simulated and measured fracture height with a maximum of 3.6 % deviation. Additionally, simulations and corresponding experiments were performed to investigate the effects of the blank holder force, punch corner radius, and drawing ratio on the fracture height of cylinder cups.

An Improved Transmissive Method of Stress Nondestructive Measurement Based on Inverse Magnetostrictive Theory for the Ferromagnetic Material

In order to meet the technical requirements of non-destructive measurement for the internal stress of ferromagnetic materials represented by cold-rolled steel sheets during the rolling control process, the paper presents a novel method for the nondestructive measurement of ferromagnetic materials based on inverse magnetostrictive principle. By improving the traditional U-shaped sensor, a transmissive quadrapole layout is proposed. The corresponding excitation module and fast signal processing system for dynamic measurement were developed and the test system for detecting innerstress of ferromagnetic material was constructed in the laboratory. The relationship between the magnetic flux with the principal stress was found by experimental investigation and the sensitive correlation of the two was verified under the laboratory measurement conditions without strong electromagnetic interference. The influence of measurement results by sensor parameters such as sensor angle, amplitude of excitation current, variation of air gap were discussed in detail and a method was proposed to decrease the power supply instability caused by the change of the airgap. The experimental results show that the transmission quadrupole layout makes the test system exhibit a good linear response to the internal stress in the specimen. The feasibility of the magnetic detection method of internal stresses in ferromagnetic material was verified through the experiment.

Effects of Excess C on New Grain Formation and Static Recrystallization Behavior at Shear Bands in Cold-Rolled Ultra-Low Carbon Steel Sheets

Effects of Excess C on New Grain Formation and Static Recrystallization Behavior at Shear Bands in Cold-Rolled Ultra-Low Carbon Steel Sheets

Abrasion Resistance and Corrosion Resistance of Chromium-Free Fingerprint-Resistant Zn and Zn-Al-Mg Coating Cold-Rolled Steel Sheets

The wear resistance and corrosion resistance of chromium-free fingerprint-resistant pure zinc and Zn-Al-Mg coated cold-rolled steel sheets were studied by micro-friction wear experiments and neutral salt spray experiments. Two products are worn for a long time with a large load (5N load, 50 times abrasion), the depth of wear zone of Zn-Al-Mg coating product is 9% shallower than that of pure zinc coating product, and the width of wear zone is 15.4% smaller. Both products still meet the requirements of use after corrosion. The corrosion resistance of two products after degreasing treatment was significantly reduced. The Mg and Al in the Zn-Al-Mg coating can hinder the progress of corrosion, so it has better corrosion resistance.

Experimental Inwestigation of Compressed Beams / Columns Using Optical Methods

The cold-formed thin-walled channel beams/columns with non-standard cross sections are the subject of researches (Fig. 1). The columns are thin-walled members made of cold-rolled steel sheets. Thin-walled, cold-formed structural members, such as beams and columns, are popular constructional elements due to their many advantages. They are made of single steel sheet that may be protected against corrosion. The cross-section of channel beams/columns have evolved over the last years. New shapes have been looked for in order to increase their strength, stability and load capacity.

How the skin-pass rolling reduction ratio affects the strain aging behaviour of low-carbon steel sheets

ABSTRACT When producing cold-rolled steel sheets, the penultimate annealing process is followed by a final skin-pass rolling (or temper rolling) whose purpose is to eliminate any discontinuous yielding which creates stretcher–strain markings when the steel sheets are formed. To find out the critical reduction ratio eliminating the discontinuous yield phenomenon, the samples were annealed at 820°C for 3 min and then subjected to the temper rolling at various thickness reductions at room temperature. Results showed that the discontinuous yield phenomenon could not be eliminated in the case of a thickness reduction less than 0.5%, that a certain reduction ratio should be exceeded to eliminate the discontinuous yielding, and that the aging time varied depending on the reduction ratio. In addition, while the low-carbon steels did not undergo strain aging in three months with a 1% thickness reduction, they underwent strain aging in at least four months with higher thickness reductions.

Recrystallisation before austenitization for improved microstructure and properties in automotive steel sheets with high product of strength and elongation

This study investigated the effect of recrystallization before austenitizing transformation (i.e., pre-recrystallization) on the microstructure and properties of 22Mn2Cr cold-rolled automotive steel sheets based on continuous annealing at 700 °C for various holding times. Subsequently, the samples were heated to an austenitizing temperature of ∼850 °C, which led to the formation of a fine austenite grains via nucleation at the dislocations during reheating. The austenite grain size was more refined when samples were pre-recrystallized at 700 °C for several minutes compared to those directly heated to 850 °C, which was attributed to combined grain refinement from recrystallization and austenite phase transformation. This refined austenite grain size led to a finer bainite grain size in the cooled final product. The strength of the steel decreased slightly (∼1200 MPa), but the elongation (∼19%) and product of strength and elongation (∼23 GPa%) were significantly enhanced by the pre-recrystallization treatment.

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.

Some Formability Aspects of High Strength Steel and of Consisting Tailor Welded Blanks

Abstract In recent years, the demand for a reduction in pollutant emission has become extremely important in the vehicle industry. It can be achieved through fuel consumption reduction, which is a direct function of the vehicle’s weight. nowadays weight is widely controlled by the use of advanced- and ultra-high strength steels (AHSS and UHSS) in vehicle body construction. With the application of such steel sheets as chassis elements, crashworthiness can be maintained next to reduced sheet thicknesses, too. In this paper, the deep-drawability and springback after V-die bending is monitored for three types of AHSS grades, namely DP600, DP800 and DP1000 materials. The investigations are extended to tailor welded blanks (TWBs), made by the aforementioned steels coupled with a cold rolled steel sheet (DC04). Our results show that deep-drawability reduces with both the increase in strength and the increase in strength difference between the components in the TWBs. Furthermore, the higher strength is shown to cause higher spring-back. The TWBs have unique spring-back behavior around the weld line.

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.

Recrystallization behaviour of IF steel at the interface of Al junction

The recrystallization behavior of an IF steel was investigated at the interface with aluminum junction, using cold-rolled IF steel sheets with high recrystallization temperature. In the region surrounded by the tongue-like η phase, recrystallization of the steel was fast at first glance, and the equiaxed structure was formed, but actually, it had a subgrain structure. The η phase grew preferentially to the c axis, and the growth of the η-Fe2Al5 phase distorted the surrounding iron due to the difference in the molar volume; compressive deformation was expected in the a-axis and b-axis directions, and tensile deformation was expected in the c-axis. The growth of η phase obviously changed the recrystallization behavior of the IF steel. The development of γ-fiber crystalline texture (<111>/ND), which was a typical recrystallization texture of IF steel, was not observed in the region surrounded by η phase.

Preparation of superhydrophobic coating films using silica nanoparticles and trimethylethoxysilane

Superhydrophobic coating solutions were prepared using fumed silica nanoparticles and trimethylethoxysilane (TMES) as precursors. At this time, the surface of silica nanoparticles was modified by TMES from hydrophilic to hydrophobic in various types of catalysts and organic solvents. The prepared coating solutions were coated on a cold rolled steel sheet by using a spin coater, and then superhydrophobic coating films were prepared by thermal curing. In this process, the effects of the amount of silica nanoparticles added, the type of catalysts, and the type of organic solvents were observed on the hydrophobicity of the coating films. As the content of silica nanoparticles added increased from 0 g to 0.08 g, the contact angle of the coating films increased from 93o to 151o, and when 0.08 g of silica nanoparticle was added, it showed superhydrophobicity of 151o. On the other hand, when nitric acid and hydrochloric acid, strong acids, were used as catalysts, the coating films showed low hydrophobicity of 73o and 86o, respectively. However, when oxalic acid, a weak acid, was used, the coating film showed superhydrophobicity of 151o. In addition, with methanol as an organic solvent, the coating film showed superhydrophobicity of 151o, while when i-propanol and n-butanol were used, the coating films exhibited low hydrophobicity of 97o and 91o.

Study of wear particles formation at single asperity contact: An experimental and numerical approach

Wear particles generated due to the relative sliding of the roll and the sheet metal in the roll bite are one of the main factors that contaminate the surface of a cold rolled steel sheet. The details of the wear mechanisms in the contact of individual roll-sheet asperities define the total amount of wear particles generated. In this paper, a micro-mechanical experimental approach is coupled with material point method (MPM) scratch simulations to study the friction and wear behavior of a single roll asperity sliding through a sheet metal. Micro-tribology experiments in the form of single asperity scratch testing showed that ploughing is the dominant wear mechanism in lubricated conditions, while wedge forming was the main wear mechanism in the absence of lubricant. The beneficial influence of chrome plating the rolls on wear particles formation is found to stem from its interaction with the lubricant as the same influence was not observed in non-lubricated test conditions. MPM single asperity simulations revealed that almost all the frictional resistance arises from deforming the substrate in the case of an interfacial shear strength corresponding to the lubricated contact. In contrast, MPM showed that, in unlubricated sliding, the frictional resistance is primarily due to shearing of the adhesion junction and tearing the deforming body. Furthermore, using the degree of wear of the scratch experiments as a benchmark, a critical plastic strain needed to produce wear particles was found to be between 3 to 4 for the investigated interstitial-free steel.

Modeling plastic anisotropy evolution of AISI 304 steel sheets by a polynomial yield function

In this study, a numerical model for the evolution of plastic anisotropy is investigated for the purpose of stamping method design by Finite Element (FE) analysis and proved experimentally via process simulations of a cold-rolled austenitic stainless steel (AISI 304) sheet. The plastic anisotropy of the sheets is described with a fourth-order homogenous polynomial yield function and this modelling approach is enhanced by plastic strain dependent material coefficients. Tensile tests of coupon specimens taken along the different directions from rolling direction, and flow strength and deformation anisotropies are described with the planar variations of yield stress and plastic strain ratio computed at four plastic strain levels (0.002, 0.02, 0.05 and 0.18). A new numerical approach is, then, applied to identify polynomial coefficients ensuring an orthotropic positive-definite, convex yield surface with a well-defined stress gradient at every loading point on plane stress subspace. The developed computational model is implemented into general purpose explicit FE analysis software Ls-Dyna by a user-defined material model subroutine (UMAT) and applied in the stamping simulation of AISI 304 steel rectangular cups for the house-hold applications. The computed thickness distributions and the flange geometries were compared with measurements and it was observed that the best predictions were done with material parameters at %5 plastic strain level.

Increasing technological plasticity with preserving strength of cold-rolled thin-sheet low-carbon steel

At domestic metallurgical plants, the traditional method of softening low-sheet cold-rolled low-carbon steels is long recrystallization annealing of coils in cap furnaces, which has significant disadvantages: the process is very long and energy-consuming. According to the properties of annealed steel, it does not meet the requirements of the consumer for the manufacture of two-layer rolled brazed tubes. In this regard, the question of developing a new method of weakening heat treatment of cold-rolled sheet to improve the set of properties and the quality of the sheet surface is relevant in time and has unconditional practical significance with the prevention of its deformation aging. To achieve this goal the following tasks were solved: research and determination of optimal temperature-time parameters of high-speed contact recrystallization annealing and subsequent aging (which has no analogues) of thin tape blanks to obtain a given set of performance properties and prevention of natural aging. The best mode of contact high-speed (100 0 C / c) recrystallization annealing is established, which provides cold-rolled sheet steel 08 kp with a set of properties that corresponds to GOST 9045-93 category VG, i.e. the ability of steel to cold complex deformation. However, further deformation aging of annealed steel at a speed of 08 kp leads to a sharp drop in ductility and increased strength. Developed a two-stage softening high-speed heat treatment consisting of recrystallization annealing and subsequent aging, increases both the strength and ductility of cold-rolled sheet, stabilizes the properties of steel to prevent its deformation aging. The obtained properties meet the regulated requirements of the consumer to the blanks intended for production of the two-layer rolled up soldered tubes operated in the conditions of the increased pressure. Tubes of small diameter, which were made of steel strips, processed by the recommended technology, have successfully passed 100 % defect-free quality control in the production environment.

Modelling of the Guillotine Cutting Process by Means of a Symmetrical Blade with the Defined Geometry.

This paper modelled the cutting process of a bundle consisted of ultra-thin cold-rolled steel sheets using a guillotine. The geometry of a cutting tool with given dimensions was assumed. A bundle of sheets being cut was modelled as deformable, the cutting tool was rigid, and the finite element method along with computer system LS-DYNA was employed. Numerical simulations of the complex state of stress and of the corresponding complex state of strain were carried out. Cutting processes belong to fast changing physical phenomena, and therefore, highly nonlinear dynamical algorithms were applied in order to solve this particular problem. Experimental investigations were also conducted by means of the scanning electron microscopy. It was found that the fracture region consisted of two distinct zones: brittle and ductile separated from each other by the interfacial transition. Morphological features of the brittle, ductile, and the transition regions were identified. The ductile and brittle zones were separated at the depth of ca. 1/5 thickness of the cut steel sheet. Finally, the numerical results obtained by usage of the finite element method as well as experimental ones in the form of microscopic images were compared, showing quite good agreement.

Measurements of lattice strain in cold-rolled CR4 steel sheets using X-ray diffraction

In this study, the effect of orientation and bending has been investigated on CR4 steel for lattice constant, crystallite size and lattice strain. The one mm thick sheet of CR4 steel was bent through air-bending. The samples were prepared by using wire electric discharge machining (WEDM) followed by polishing for X-ray diffraction study. The peaks were analysed using QualX 2.1 software and lattice constant was analysed using Bragg’s law and lattice strain using Williamson-Hall’s method. Result shows, lattice constant is smallest on rolled face and after bending it increases along thickness. Whereas, the lattice strain is compressive in nature for all three orientations. However, for 0°orientation lattice strain (0.5%) is more across the thickness as compared to 90°orientation lattice strain (0.34%). Crystallite size was analysed by Scherrer’s method and Williamson-Hall’s method. Williamson-Hall’s crystallite size is observed to be smaller than Scherrer’s crystallite size. Further, crystallite size is observed to be the smallest on the rolled face. Moreover, after bending force application, enhancement in the lattice strain is observed while the size of the crystallite is reduced noticeably.