Cold-rolled Sheet Research Articles

Effects of cold rolling and annealing on the ridging behaviour of ferritic stainless steel

A systematic study was carried out to evaluate the effects of cold rolling and annealing processes on the ridging severity of ferritic stainless steel (FSS). Both microstructural refinement and texture optimisation were achieved with an optimised processing schedule to improve the ridging resistance of FSS. Coarse grain bands comprising of primarily {112} oriented grains were found to form inside cold-rolled and annealed FSS sheets. The effects of annealing schedules and the resultant microstructure and texture on the ridging behaviour of FSS are discussed. The results indicate that the reduction in the fraction of {001} orientation by optimisation of the rolling processes contributes to reduce the ridging height of the FSS during the subsequent forming process. Through extending soaking time and under 880 °C during final annealing step, a maximum of 30% reduction in ridging height can be achieved with a refined microstructure and texture of FSS, improving the surface quality of FSS during subsequent forming processes.

Effects of operation parameters of cold rolling on surface finish of aluminum

The quality of cold-rolled aluminum products is dependent on a low surface roughness and a high surface finish. Accordingly, the present study develops a mixed lubrication model to examine the effects of the main rolling parameters. Cold rolling experiments are then performed on laboratory-scale high-speed cold mill system to evaluate the surface roughness and surface gloss of aluminum sheets processed under different operation conditions. The gloss measurements show that a lower proportion of protrusion of the bearing area ratio leads to a higher gloss of the rolled surface. Overall, the present theoretical and experimental results show that the surface quality of cold-rolled aluminum sheets can be enhanced through the use of a higher reduction rate or a lower roll speed.

Study of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled Micro-Alloyed Sheet Steels (Hsla) of Strength Classes 340–420 for Automobile Building

The effect of microstructure characteristics and also production regimes on corrosion resistance of cold rolled high-strength low-alloy steels (HSLA) grades 340 and 420 is studied. It is shown that the corrosion resistance of cold rolled HSLA steels of strength class 340 (НС340LA) is determined both by aging processes, developing in overageing sections of continuous annealing units (CAU), and also formationm of a considerable amount of nanosize niobium carbonitride precipitates. For rolled product of strength class 420 (НС420LA) with a higher manganese and niobium content after annealing in a CAU average values of corrosion rate are slower than for rolled steel of lower strength classes. Probably, for this steel the aging process does not significantly affect the corrosion resistance. At the same time, an increase inannealing temperature to 750–762°C leads to an increase in corrosion resistance due to the coagulation of nanosize niobium carbonitride precipitates and a reduction in their amount (≈ 1500 to 600 precipitates/ μm2 or less).

Experimental Validation of the Sensitivity-Based Virtual Fields for Identification of Anisotropic Plasticity Models

In this work, the sensitivity-based virtual fields have been applied to identify two anisotropic plasticity models (Hill48, Yld2000-2D) using a deep-notched tensile test performed on flat samples of cold-rolled sheet of DC04 steel. The material was characterised using the standard protocol to obtain the reference sets of parameters. Deformation data was obtained during deep-notched tests using stereo digital image correlation and the virtual fields method was employed to identify material parameters. It was found that the sensitivity-based virtual fields outperform the standard user-defined virtual fields in terms of accuracy.

Phase Transformation Kinetics During Annealing of Cold-Rolled AISI 309Si Stainless Steel

The effects of cold rolling and the subsequent annealing were studied for the AISI 309Si stainless steel. During annealing of cold-rolled sheets, the hardness curve vs temperature showed two regimes of transformations (reversion and recrystallization), where the JMAK analysis revealed that the activation energy of both processes is equal to the lattice diffusion activation energy in austenitic stainless steel. Finally, based on the kinetics analysis, a recrystallization–temperature–time diagram for phase transformations was proposed.

Influence of cold-rolling on incremental sheet forming of polycarbonate

ABSTRACTSince product customization is becoming more and more popular, high process flexibility is required in many industrial sectors. Incremental sheet forming shows versatility and its effectiveness can be improved when coupled with other processes to, for example, change the behavior of the material to be processed. This study combines two technologies, i.e. cold-rolling and incremental sheet forming, for the manufacture of thermoplastic components. Polycarbonate sheets were firstly cold-rolled to reach the desired thickness and then formed incrementally, to study how the first process (which modifies the mechanical behavior of the sheets) influences the second one, e.g. in terms of formability limits and forming forces. To this end, an experimental campaign, covering tensile tests and the manufacture of fixed and variable slope angle frusta by single-point incremental forming, was carried out on parent and cold-rolled sheets. The tests point out the correlation between the tensile behavior and some of the main features of the incremental sheet-forming process, like the maximum formability angle, the forming forces, failures and defects. In conclusion, the study provides a critical interpretation of the results to weight up the pros and cons of this integrated polymer sheet forming process.

Tempering of Cold-Rolled Martensite in Mild Steel and Elucidating the Effects of Alloying Elements

The martensite thermomechanical process was applied to the st37 steel and a modified version of this steel containing micro-addition of Cr and Mo. It was found that the presence of Cr and Mo can result in the retardation of softening during tempering of cold-rolled sheets, where the hardness of the modified steel at each tempering time was much higher compared to that of the st37 steel. Accordingly, the characteristic hardness fall (related to the occurrence of continuous recrystallization) was postponed effectively. The development of fine ferrite/carbide aggregate via martensite process resulted in the enhancement of tensile properties compared to the as-received ferrite/pearlite microstructure. The micro-addition of Cr and Mo was also found to be conducive to grain refinement during tempering of cold-rolled martensite.

Fatigue strength evaluation of self-piercing riveted joints of AZ31 Mg alloy and cold-rolled steel sheets

Abstract The application of magnesium alloys to automobiles is increasing due to their superior specific strength and specific stiffness. In this study, an upper sheet of AZ31 magnesium alloy and a lower sheet of cold-rolled steel were joined by self-piercing riveting (SPR), a method commonly used to join automotive panels. A cross-shaped specimen was fabricated with a punching force of 35 kN, which exhibited the best joint strength for the SPR joint specimen geometry. Monotonic and fatigue strengths were evaluated using cross-shaped specimens at loading angles of 0°, 45°, and 90°. The load amplitude corresponding to the fatigue endurance limit was assumed to be at 106 cycles, and the fatigue ratios (= fatigue endurance limit/static strength) at the loading angles of 0°, 45°, and 90° are 22%, 13%, and 9%, respectively. For all three loading angle specimens, fatigue cracks initiated at the triple point where the rivet shank, the upper sheet and the lower sheet are in contact with each other, with the cracks propagating through the thickness of the upper sheet and ultimately leading to fracture. The fatigue lifetimes were evaluated through the von-Mises stress, maximum principal stress, and equivalent stress intensity factor. It was found that the fatigue lifetimes could be evaluated most appropriately through the maximum principal stress.

High-strength dual-phase steel produced through fast-heating annealing method

Fast-heating annealing method provides a new possibility to produce high-performance dual-phase (DP) steel by controlling austenite decomposition upon cooling. A quenching dilatometer with programmable heating-holding-cooling cycles was employed to stimulate the fast-heating annealing process of a cold-rolled dual-phase steel in the present work. Electron probe microanalysis and X-ray diffraction were conducted to reveal the microstructural evolution and phase transformation behavior in combination with dilatometric measurements. Experimental results showed that in case the cold-rolled DP980 steel sheet was rapidly austenitized just above the full austenitization temperature at a heating rate of 300 ​K/s, ultrafine and discontinuous martensite surrounded by interconnected network ferrite could be obtained after holding at 1073 ​K for 100 ​s. A phase transformation model was established for the cold-rolled dual-phase steel subjected to fast-heating annealing treatment. The produced fast-heating DP980 steel sheet possessed an ultimate tensile strength of about 1200 ​MPa and a fracture elongation up to 16.7%.

Development of a non-contact and non-destructive laser speckle imaging system for remote sensing of anisotropic deformation around fastener holes

Strain sensing around the fastener holes is fundamentally significant in structural health monitoring and failure detections. Conventional non-destructive testing (NDT) techniques typically have limitations in performing reliable and efficient inspections. Here, a laser speckle imaging system (LSIS) has been developed to achieve non-contact, non-destructive and remote strain sensing. Methods for determining optimal laser speckle patterns have been investigated to achieve remote sensing of strain up to a working distance of 5 m. This LSIS was applied to study the anisotropic properties of un-notched and circular notched specimens in cold-rolled aluminium sheet, an important material for the construction of lightweight aircraft structures. The results showed that strain distributions determined by LSIS are consistent with finite element (FE) predictions in which the evolution of strain concentrations not only depends on the notch size but also on material anisotropy. This study demonstrates the potential application of LSIS as an effective NDT technique for full-field, non-contact and remote sensing of anisotropic deformation around fastener holes.

How the Material Thickness Affects 0.08% Carbon Cold-Rolled Sheet Steel

The authors hereof have studied how the thickness of 0.08% carbon cold-rolled sheet steel affects its properties. They experimented with tensioning such sheets and plotted the metal hardening curves. The paper presents comparative analysis of how the material thickness affects the coefficients approximating the hardening curves. A comparison of the hardening curves of control and annealed specimens is given. Experiments have identified the effects that the pre-accumulated plastic strain has on the material properties. It is revealed that lower thickness alters the force parameters of the process and affects the ultimate tensile strain. The paper formulates recommendations on using the estimates obtained by the software simulation of the deformation process. Hardening-curve coefficients approximation functions are proposed in order to predict how changing the thickness would affect the material properties.

Precipitation-induced mitigation of recrystallization in ultra-thin, cold-rolled AlScZrMn(Mg) sheets at brazing temperatures: The critical effect of alloy composition and thermal processing route

Using advanced electron microscopy techniques, statistical analysis and analytical investigation of precipitates/dispersoids evolution, we demonstrate the critical effect of alloy composition (Sc, Mn, and Mg content) and thermal processing route (heating rate and pre-aging) on the recrystallization behavior of AlScZrMn(Mg) alloys. Two major types of second phases, namely Al3(Sc,Zr) precipitates and α-Al(Mn,Fe)Si dispersoids, were identified in the thermally-treated cold-rolled sheets (of 0.3 mm thickness). Both phases were observed to maintain coherency with the Al matrix at abnormally large sizes (>100 nm and >500 nm, respectively), as well as exhibiting unprecedented levels of thermal stability (i.e., high coarsening resistance). The recrystallization behavior and strength evolution were shown to be a strong function of the size and aerial number density evolution of the precipitates/dispersoids which, in turn, are controlled by the alloy composition and thermal history. Particularly, the recrystallization was effectively mitigated at a slow ramp to 590 °C (a typical brazing temperature for AlMn alloys) whereas a full recrystallization occurred during a faster ramp. Such behavior was explained by the competitive kinetics of Al3(Sc,Zr) precipitation and recrystallization phenomenon at intermediate and high-temperature ranges upon heating to 590 °C. The introduction of a pre-aging treatment within the intermediate temperature range (i.e., 250–400 °C), prior to the fast ramp, was shown to prevent recrystallization due to the stabilization effect of a large aerial number density of finely-dispersed Al3(Sc,Zr) precipitates. A higher Sc content in the alloy enhances such a stabilization effect. Mn additions not only enhance the mitigation of recrystallization (through a refinement of Al3(Sc,Zr) precipitates) but also refines the evolution of α-Al(Mn,Fe)Si dispersoids resulting in a higher yield strength. The Mg addition, on the other hand, has no impact on the evolution of Al3(Sc,Zr) precipitates nor on the recrystallization status, though it causes a refinement of α-Al(Mn,Fe)Si dispersoids and thus leads to a higher final yield strength. The extraordinary high-temperature stability of cold-rolled thin sheets, obtained by the alloy and process design in this study, can be effectively utilized for many light-weight applications of AA3xxx Al alloys.

Influence of pre-strain on microstructural characteristics and tensile deformation behaviour of a cold-rolled Al-containing medium Mn steel

Automobile steel sheet parts often experience unavoidable plastic deformation during cold stamping forming and service life. In this study, we explored the microstructure variation and tensile deformation behaviour of a cold-rolled Al-containing medium Mn steel (0.25C–8.67Mn–0.54Si–2.69Al, wt%) subjected to different degrees of pre-straining by tensile testing, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and X-ray diffraction. The cold-rolled steel sheet processed by intercritical annealing at 725 °C for 60 min exhibited a superior combination of strength and ductility [the product of ultimate tensile strength (UTS) and total elongation (TEL), UTS × TEL] as high as 69 GPa% due to the TWIP (twinning-induced plasticity) and TRIP (transformation-induced plasticity) plasticity-enhancing mechanism during tensile deformation. The tensile behaviour, which originally exhibited notable Luders plus Portevin–Le Châtelier (PLC) banding phenomenon, was significantly changed by pre-straining. The strength increased, while the TEL and UTS × TEL decreased linearly with an increase in the pre-strain. A pre-strain equalling to the Luders strain, i.e. 3%, could cause an elimination of the Luders bands, while it had almost no influence on the PLC bands. The increase in the dislocation density, the enhanced stability of retained austenite and the strain-induced martensite and mechanical twins caused the reduction and elimination of the Luders bands with increasing amounts of pre-strain.

Effect of interface bonding process on bending strength in CFRP/metal hybrid composites

Recently, vehicle parts such as center pillars and impact beams used in automobiles have been requiring materials that satisfy both high strength and impact absorption. Therefore, in this study, the applicability of the forming process of CR340 (cold rolled steel sheet)/CFRP Hybrid Composites which are a bonded material of cold rolled steel sheet having excellent formability and carbon fiber prepreg having high strength and high collision absorption in the vehicle parts was investigated. Hybrid composites are fabricated by stacking carbon fiber reinforced plastic (CFRP) prepreg on a cold rolled steel sheet (CR340) with Zn coating. Bonding materials were used at the interface between the CFRP prepreg and steel sheet. In addition, in the case of CR340/CFRP Hybrid composites which are made by bonding CFRP prepreg to the surface of press-formed CR340 material, it is impossible to manufacture complicated shapes due to an interfacial bonding separation phenomenon between the reinforcement and steel sheet. An adhesive agent developed by this research team was applied on the cold rolled sheet between CFRP and CR340 materials to enable the blank production of CR340/CFRP Hybrid composites. The heating time and temperature required for bending test were set similar to the curing curve of the CFRP prepreg. The surface roughness of steel materials is important in terms of their tensile strength and bending strength In this study, the steel sheet used was cold rolled 340 with Zn coating without surface roughness treatment for application to mass production in industry. This study investigates the properties of a CFRP/metal hybrid composite material. The hybrid was fabricated after spreading a developed binder on high-strength steel sheets (CR980) prepared by cold rolling and pressing. During the preparation of the CR980/CFRP hybrid composite, and its mechanical characteristics were investigated through bending, tensile, and lap shear adhesion test experiments.

Study on edge cracking of titanium cold rolled sheet

In this study, to understand oxygen effects on workability of titanium, edge cracking and microstructure changes with the oxygen content variations in the cold rolled sheets were observed carefully and discussed. The higher oxygen content of titanium sheet, the more the edge cracks occurred after cold rolling deformation. While the specimen containing low oxygen became fine grained structures after the cold rolling, the other high oxygen sheets consisted of relatively coarse and elongated grains. The fine-grained structures was assumed to come from an active twinning behavior, meanwhile the other’s elongated structures were due to the twinning suppression by increasing oxygen contents. In addition, distinct shear bands were appeared in the high oxygen sheets after cold rolling. The high oxygen contents may multiply dislocation density by suppression of twinning and promoting dislocation slips. The increased dislocations can also produce a concentration of strain, slip bands thus appears during the cold rolling deformation. These slip bands cause the edge cracking in the higher oxygen sheets.

Microstructure and mechanical properties of high-manganese-containing high-speed twin-roll cast Al-Mn-Si alloy strips and their cold-rolled sheets

Al-Mn based alloys with high-manganese content are expected to have improved mechanical properties due to solid solution hardening and/or dispersion hardening. However, the increase of Mn solubility of the alloy is difficult by using the conventional DC casting. In order to solve this problem, in the present study, we focused on the twin-roll casting method which is characterized by high cooling rates. Several kinds of high Mn-containing Al-Mn-Si alloy strips were fabricated by using a vertical-type high-speed twin-roll caster equipped with a pair of water-cooled copper rolls. Direct temperature measurement of the liquid melt during the casting was also performed. The alloy strips of various compositions containing up to 4 Mn and 2 Si (wt%) were successfully obtained. By observing the microstructure of the cross section of the strip, we found the characteristic solidified structure. The solidified structure consisted of three layers. Two solidified shells with a columnar dendrite structure grew from the roll surfaces toward the strip center. In the mid-thickness region, the band structure consisting of equiaxed dendrites and globular grains was observed between the solidified shells. Very fine primary particles were observed in the matrix near the strip surface, while, relatively coarse particles with blocky and needle-like shape were observed in the central band of the as-cast strip. The electric conductivity measurement was performed for the as-cast strips. Mn solubility in Al matrix was estimated from the obtained values. The estimated Mn solubility in the Al-2Mn-xSi strips was between 1.5 ~ 1.8wt% Mn. It was over 1.43wt%Mn for the Al-4Mn-xSi strips. We found that the Mn solubility of the as-cast strips was considerably high. The strips were cold-rolled to the sheets and then annealed at various conditions. They were subjected to the tensile tests, and the effects of solid solution hardening and dispersion hardening are discussed.

Mechanism of Improved Ductility of 1,500 MPa-class Ultra-high Strength Cold-rolled Steel Sheet Produced by Rolling and Partitioning Method

Mechanism of Improved Ductility of 1,500 MPa-class Ultra-high Strength Cold-rolled Steel Sheet Produced by Rolling and Partitioning Method

Modelling and numerical simulation of steel sheet fine blanking process

The steel sheet metal blanking is widely used for the manufacture of mechanical parts for automotive industry. The general concept of blanking seems a simple one but governing parameters are many and have a complex relation-ship, which directly affects the quality of the produced parts. The latter is assessed using three main criterions: the burr amount, the appearance of the cut edge and dimensional accuracy. However, the optimization of these parts depends on full understanding of the shearing process. The paper presents results of the investigations on numerical computations and experimental verification concerning the influence of selected parameter of the cutting process on the stress state of cold-rolled steel sheets being cut.The commercial code Lsdyna® has been chosen to simulate this process. The material testing and the characterization are carried out in order to fit the constitutive model parameters to the experimental data and to establish the sheet metal constitutive law. The identified model is, then, used for numerical simulations which are performed using LsDyna/Explicit software of various fine blanking tests.The aim of this paper is to predict the shear stress and plastic strain distribution in shearing zone during blanking versus punch-die clearance. The assumption of a deformable punch or not has also been considered. The finite elements predictions have been compared with experimental results. The numerical results of the validation simulations were in agreement with the experimental data with an approximate error margin of 31%, since the springback phenomena after unloading and tools warming up during the cutting procedure have not been considered.

Development and research of the cultivator frame design made of non-standard beams

The paper presents the results of the development and study of the strength of the cultivator frame made of non-standard beams. The term “non-standard beam” refers to a off-sized beam welded from steel strips. As such stripes, both standard hot-rolled strips and strips cut from standard cold-rolled or hot-rolled sheets can be used. The main advantage of the proposed frame design is the relatively low cost and availability of materials for its manufacture, as well as the potential to minimize the weight of the finished product by changing the thickness and dimensions of the strips used. Frame design and calculations were performed by the Autodesk Inventor Professional environment.

Heat treatment strategies for hot-rolled medium-Mn sheet steels

Heat treatment strategies for advanced high-strength medium-Mn sheet steels are addressed. A review of the available thermal cycles for cold-rolled and hot-rolled sheets are presented. The benefits from the intercritical annealing following hot-rolling are emphasized. The examples of intercritical annealing for the hot-rolled sheets of initial martensitic microstructure are provided. The heat treatment was performed in a temperature range of 680-720°C for various times from 1 to 5 hours. The material used in the experiment was a medium-Mn steel containing 0.16% C, 4.7% Mn, 1.6% Al, 0.2% Mo, 0.2% Si. The scope of the research included dilatometer tests, hardness tests and microstructural characterization. The effects of temperature and time on a stabilization of retained austenite are assessed. Intercritical annealing performed at 700 and 680°C allowed forming some stable retained austenite in the microstructure. Moreover, some coiling simulations for hot-rolled strips are described.