Hot-rolled Steel Sheets Research Articles

Ensuring the quality indicators of the surface layer of parts made of 30KhGSA steel by laser microstructuring

The purpose of the work was to study the influence of laser microstructuring modes on the formation of qualitative indicators (the length of the laser exposure zone, microhardness) of the surface layer of parts made of hot-rolled sheet steel grade 30KhGSA.Methods. The structural medium-alloy steel of the 30KhGSA grade in the hot-rolled state (sheet 6 mm thick) was chosen as the object of research. Special samples were produced by laser cutting to study changes in the structure, structure and microhardness of the laser exposure zone. After laser cutting, one of the sides of the sample was subjected to mechanical milling in order to remove a layer with a modified structure of the material obtained during laser cutting. Next, laser microstructuring of the sample surfaces was performed using a continuous fiber laser. Metallographic and durometric studies were carried out to study the effect of laser microstructuring on changes in the structure and quality of the surface layer.Results. The peculiarities of changing the microstructure of the laser exposure zone depending on the type of laser treatment are considered. It is shown that, regardless of the type of laser treatment, a "white layer" is formed on the heat-strengthened surface, the thickness of which depends on the parameters of laser radiation: power, speed, spot diameter, focal length. It has been revealed that when milling operations are used as a preliminary mechanical treatment of the cutting edge surface, in the vast majority of cases a white layer is not formed.Conclusion. The results obtained can be used to create resource-saving material processing processes using highly concentrated energy flows.

Effect of Welding Parameters on Pull-through Load in Projection Welding of M4 Nut to Hot Rolled Low Carbon Steel Sheet

Projection welding is frequently used in automotive industry for its practicality in application and also help complex parts to be welded fast enough to reduce labour intensive processing. This study investigates the effect of parameters of projection welding on the weldability performance of dissimilar steels of hot rolled Low Carbon steel (WSS-M1A365-A22) sheet to M4 steel nuts in the projection welding operation. The aim of this study was to improve product quality by examining the fracture load within the minimum and maximum value range specified by the automotive industry. In this study, the effect of welding parameters on the quality of the projection weld of M4 weld nut on steel sheet was investigated using a 100 kVA projection welding machine with UNIS brand MFDC (Mid Frequency Direct Current) transformer. The samples underwent a tensile snap force test using a fully destructive testing device. The tests used a 3 mm WSS-M1A365-A22 steel sheet and M4 DIN 928 welding nut. The current value, welding time, and electrode compression force were varied to determine the optimal conditions. The results showed that a current value of 14.5 kA, welding time of 23 ms, and electrode compression force of 480 dAN met the pull-through load conditions.

Forming quality and static properties of self-piercing riveted joints of hot-rolled steel and aluminum alloy sheets

The self-piercing riveting (SPR) Forming and tensile tests of hot-rolled steel sheet BR1200HS and aluminum alloy sheet AA 6082-T6 were simulated by Simufact Forming software. The test results show that the diameter of the rivet leg opening, which is the most important parameter affecting the mechanical properties of the joints, shows a first increase and a second decrease with the increase of rivet length, and the Max. tensile loads of the joints have the same variation law. The larger the diameter of the rivet leg opening, the greater the Max. tensile load of the joint, and the greater the effective plastic strain of the rivet of the joint. The rivet length of the joints in the five preferred SPR formation schemes obtained were all 6.5 mm, and only one scheme had a rivet hardness of H4, the rest were H5. The SPR experiment is used to verify the current finite element simulation data can get the final research conclusion. The finite element simulation (FEM) would greatly reduce the test times of the SPR test, save the test consumables and save the test cost.

Characteristic analysis of mold level fluctuation during continuous casting of Ti-bearing IF steel

Mold level fluctuation has always been one of the key factors in slab quality control. Abnormal fluctuations can easily cause slag entrainment and form surface defects of hot-rolled and cold-rolled steel sheets, thus reducing the product qualification rate. In this study, mold level fluctuation data was collected during Ti-bearing Interstitial Free (IF) steel in a stable state for a complete casting sequence in a certain factory. The mold level fluctuation is analyzed using the discrete wavelet transform (DWT) method, and its characteristic values are classified based on frequency. Combined with the corresponding process parameters, the causes were traced during abnormal fluctuation characteristic values. It was found that the formation of abnormal mold level fluctuation mainly comes from two aspects. On the one hand, there are random fluctuations in the low-frequency band, and on the other, there are clustered fluctuations in the relatively high-frequency band. There is always a rising trend in mold liquid levels when there are random abnormal fluctuations in the low-frequency band. There is a delay of approximately 0.1412 s in the feedback of the stopper rod to the mold level fluctuation. The major causes of the low-frequency random fluctuations include variations in the tundish weight, casting speed, and mold width, and the clogs peeling. The clogging of the side hole at the submerged entry nozzle (SEN) is the primary cause of abnormal clustered fluctuations in the high-frequency band. These are certain relationships with clogging, whether it is high-frequency clustered or low-frequency random abnormal fluctuations. Without a doubt, this is a crucial link that limits the slab quality.

The effect of thickness of the hot-rolled sheet on the magnetic properties of non-oriented electrical steel

Non-oriented (NO) electrical steel sheets with a thin thickness are drawing interest as potential materials for electric vehicle drive motor cores due to their ability to reduce high-frequency core loss. To produce electrical steel sheets with a thickness of 0.25 mm or less, it is beneficial to minimize the thickness of the hot-rolled sheets. However, it is well known that it is difficult to achieve hot-rolled coils with a thickness of 1.4 mm or less with a conventional hot rolling process. Therefore, the thin slab casting and rolling (TSCR) process is now used to produce thin hot-rolled coils that cannot be produced by conventional methods.In this study, we investigated the effects of hot-rolled sheet thickness produced by the TSCR process and cold-rolling reduction ratio on the crystallographic texture, microstructure, and magnetic characteristics of 3% Si NO steel. The results showed that the textures of the hot-rolled sheet and the annealed hot-rolled sheet are virtually unaffected by the hot-rolling reduction ratio. However, the cold-rolling reduction ratio substantially affects many aspects of NO electrical steels. The recrystallized grain size after the final annealing process decreases as the cold reduction ratio increases, while the magnetic flux density decreases with increasing cold reduction ratio, especially for reductions exceeding 82.8 %.In conclusion, the thickness of hot-rolled steel sheets manufactured by the TSCR process has little effect on the microstructure and texture of hot-rolled sheet. Therefore, reducing the cold rolling reduction ratio, which can be achieved by using thin hot-rolled sheets manufactured by the TSCR process, is a promising method for enhancing the magnetic characteristics of thin-gauge NO electrical steel sheets.

A New Phenomenological Model to Predict Forming Limit Curves from Tensile Properties for Hot-Rolled Steel Sheets

A phenomenological model for the prediction of the forming limit curve (FLC) based on basic mechanical properties through a uniaxial tensile test can tremendously shorten the design time of the forming process and reduce the measuring costs. In this paper, a novel phenomenological model named the IMR-Baosteel model (abbreviated as the IB model) is proposed for efficient and accurate FLC prediction of hot-rolled steel sheets featuring distinct variations in thickness and mechanical properties. With a systematic test of the plane strain forming limit (FLC0), it was found that a higher regression correlation exists between the FLC0 and the total elongation under different sheet thicknesses. For accurate assessment of the FLC0 from tensile properties, compared using experiments, the error of FLC0 calculated with the proposed model is within 10%. In the IB model, the left side of FLC can be calculated using a line with a slope of −1 while the right side of the FLC is obtained via a modified Keeler model with the exponent (p) determined as 0.45 for hot-rolled steels. Complete experimental FLCs of hot-rolled steels from measurements and the literature were used to validate the reliability of the proposed model. Resultantly, the prediction of FLCs with the proposed IB model is greatly improved, and agrees much better with the experimental FLCs than the predictions of the well-known Keeler model, Arcelor model and Tata Steel model.

Experimental investigation and numerical optimization of sheet metal forming limits during deep drawing process of DD14 steel

This work aims to experimentally study the deep drawability of DD14 hot-rolled steel sheets and to optimize numerically the material formability. The material anisotropy was confirmed by metallographic analysis of the material and tensile tests on specimens taken in three orientations with respect to the sheet rolling direction. Where the stress-strain curves show a sensitivity of material to the Piobert-Lüders phenomenon. The die pressure and the blank holder were considered as controlling factors on plastic instability and the success of the deep drawing operation. The forming limit curves (FLC) were plotted to highlight the different deformation modes that the sheet metal underwent during the deep drawing process. The collected deep-drawn parts observation shows severe plastic instability, until fracture. The initial plastic anisotropy is determined by the Hill48 quadratic criterion and the work hardening by the Hollomon power law. It results, during the experimental tests, that the front bottom corners of the deep drawn part are the areas at high risk of damage. The various numerical simulation scenarios followed by comparisons with the experimental results, allowed us to confirm the optimum conditions that minimize the material's plastic instability risks, forming operation “Step” and BHP “Amplitude”.

PREDICTION OF RESIDUAL STRESS AFTER HOT ROLLING AND COILING PROCESSES

Residual stresses are a subject of great industrial and academic interest. Detection and prediction methods can be experimental, analytical and numerical furthermore there is a substantial amount of developed techniques. In this context, this manuscript intends to propose an analytical methodology for predicting residual stresses in the thickness of hot-rolled steel sheets, followed or not by coiling/uncoiling, by developing the basic differential equation of deflections, aided by a numerical prediction of the temperature profile throughout the cooling process. Basically, the sources of residual stresses are considered to be the austenite/products phase transformation, the evolution of the temperature gradient and the deformation/relief caused by coiling and uncoiling. Prediction results were compared to experimental own results and that from a reference. There was a good coincidence of values when the profile raised was the one caused by the temperature gradient. Other sources found no support for the cases analyzed. New experimental results are needed for conclusions to mature.

Thermodynamic Analysis of Precipitation Behaviors in Hot-Rolled Ti-stabilized Interstitial-Free Steel Sheets

Thermodynamic Analysis of Precipitation Behaviors in Hot-Rolled Ti-stabilized Interstitial-Free Steel Sheets

Predicting the Product Classification of Hot Rolled Steel Sheets Using Machine Learning Algorithms

Predicting the Product Classification of Hot Rolled Steel Sheets Using Machine Learning Algorithms

Controlled Coil Chilling As Backbone Link in Hot-Rolled Sheet and Plate Steel Production

Controlled Coil Chilling As Backbone Link in Hot-Rolled Sheet and Plate Steel Production

Commodity market profiling methodology

The article considers the methodology of commodity markets research, which includes the assessment of the volume and structure of supply and demand according to a wide range of indicators. The information on formation of system representations of markets on the basis of segmentation of markets, marketing profiling of markets and their clients is generalized. The market profiling approach is discussed in depth. This approach consists in the representation of the market as a multidimensional array of data on the type of goods, price ranges, the distribution of buyers and sellers by region, industry and other characteristics on the basis of available reliable, but incomplete data. The article considers the problem of obtaining reliable data to determine their reliable sources and organization of data collection in the framework of consulting services. The relevance of the task of forming the correct sample for consulting markets research, which provides in conjunction with data from public sources, a representative representation of the commodity market. Specific features of commodity markets, which causes the variability of approaches to the market dependence on imports, the share of direct deliveries, transport channels of supply and other factors have been considered; features of profiling in the express-analysis of commodity markets have been determined. As an example of practical realization of commodity markets profiling methodology, the market of hot-rolled stainless steel sheets with thickness of 2.0–13.0 mm and width up to 1600 mm is considered. This market is characterized by high import dependence and, therefore, the Federal Customs Service database was used as a source of information for it. Market profiling, performed in accordance with the proposed methodology, provided detailed information on the distribution of imports and consumption of individual groups of stainless steel sheets. Estimates of the commodity market obtained as a result of the study using market profiling have been verified by independent consulting studies.

Investigation of Production Technology for Hot-Rolled High-Strength Low-Alloy Automobile Sheet Steels to Improve Properties and Quality Indices at Reduced Cost

Investigation of Production Technology for Hot-Rolled High-Strength Low-Alloy Automobile Sheet Steels to Improve Properties and Quality Indices at Reduced Cost

Experimental investigation on anisotropic fatigue crack growth characteristics of Q420C steel

The hot-rolled steel sheets often exhibit anisotropy in their mechanical characteristics due to the grain’s elongation along the rolling orientation. The anisotropy characteristic also appears in the fatigue crack growth behaviour. However, it has not been thoroughly studied for some types of steel materials although they have been widely used for wind turbine towers. In this study, the longitudinal fatigue crack growth behaviour of the hot-rolled steel sheet (Q420C) is investigated by an experimental programme. A total of six specimens were tested under constant amplitude loading cases with different load ratios. It was found that longitudinal cracks are approximately 15% faster than transverse cracks at the load ratio of 0.1; at the load ratio of 0.3, they are approximately 22% faster. The anisotropy of crack growth rates is attributed to differences in the microstructure of the material. A comparison of the crack growth rate is carried out for Q420C steel and some widely used American-made steel materials. Furthermore, the applicability of design curves in the British Standard BS 7910 is explored, the crack closure phenomenon is analysed and the fatigue crack growth mechanism is discussed.

Effect of Cut-Off Side Stiffness on Stretch Flangeability in High-Strength Steel

In high-strength steel (HSS), shear edge failure due to stretch-flange formability is a serious problem. Shear edge failure is strongly affected by cutting methods. As countermeasures, cut-off punching and double punching of the entire circumference have conventionally been considered. However, it has not been shown whether these processes can be applied to the stretch-flange forming part of the outer circumference of automotive parts. In this study, the effect of the punching allowance and the method of improving the double punching process on the outer circumferences of automotive parts were investigated using high-strength hot-rolled steel sheets. The results of hole expansion tests and observations of shear edge faces and metal flow show that partial double punching reduces the rigidity of the cut-off side and increases the collapse probability. Also, the crack propagation caused by high tensile stress near the upper blade is accelerated. In comparison with double punching of the entire circumference of a 590 MPa or 780 MPa-class high-strength steel sheet, the effect of improving the stretch-flange formability is approximately 1.5 times the hole expansion test value, as indicated by the index, up to the area where the punching exceeds the size of the sheet thickness. However, it is considered that the stiffness of the cut-off side varies depending on the curvature and the thickness of the plane, and the effect of such variations will be confirmed in a wide range of the curvature and the thickness in the future.

Analysis of surface blackening defects on hot-rolled pickled steel

There are many blackening defects on the steel surface after the pickling of the hot-rolled strip. The microstructure and roughness of the picked steel surface were analyzed using SEM and LEXT OLS4000 laser scanning confocal microscope, XPS, and surface roughness measure. The experiment result shows that the blackening defects of the hot-rolled pickled steel sheet surface are aging of anti-rust oil film to the strip steel surface. In order to improve the surface quality of the hot rolling pickled sheet, the anti-rust oil coating process is improved, the thickness and uniformity of the oil film are controlled, and the management in the course of packing, storage and transportation are strengthened.

Surface Defects on Semicoherent and Incoherent NaCl-Type Carbides Dispersed in Hot-Rolled Ferritic Steel

The interface structure of semicoherent titanium carbide (TiC) nanoparticles and incoherent micron-sized TiC precipitates in Fe–C–Ti alloy hot-rolled steel sheets was studied by transmission electron microscopy (TEM) and positron annihilation spectrometry (PAS). The TiC nanoparticles were formed by interphase precipitation during the γ-to-α transformation, and the coarse micron-sized TiC precipitates remained in the matrix as undissolved carbides in the slab reheating process before hot rolling. The semicoherent TiC nanoparticles have coherent planes with the Baker–Nutting orientation relationship and incoherent surface almost parallel to {001}α planes. The present investigation revealed that positrons are not annihilated inside TiC particles but rather are trapped at open volume misfit defects located at the incoherent interface between TiC particles and the matrix. The positron lifetime related to misfit defects associated with the semicoherent TiC nanoparticles and incoherent micron-sized TiC precipitates was around 240 ps and 500 ps, respectively. Considering the results of TEM observations and the theoretical positron lifetime, it can be concluded that the positron annihilation site related to TiC nanoparticles is located at the incoherent interface and consists of some vacancies.

Causes and Prevention Measures of Bright Pitting Defects on Surface of Hot-Rolled Galvalume Steel Sheets

Causes and Prevention Measures of Bright Pitting Defects on Surface of Hot-Rolled Galvalume Steel Sheets

Effect of initial solidification characteristics on longitudinal crack formation in thin slab caster

ABSTRACT Longitudinal surface crack has been one of the serious problems of thin slab casting (TSC). The present study was undertaken to comprehend the characteristics of longitudinal facial crack (LFC) and minimise the same in hot rolled low carbon steel sheets produced through thin slab casting and rolling (TSCR). Macro-structural characteristics of solidified shell has been investigated and correlated with plant observations. The centre and edges of funnel region showed maximum propensity of LFCs. TSC solidification is initiated with fine columnar dendrites which gradually coarsened towards the slab centre. This has been attributed to the characteristics of liquid steel flow instability in the upper mould region. Meniscus flow instability may lead to non-uniform heat transfer besides mould flux entrapment in the solidifying shell. Examination revealed that the mould hot faces ware covered with brass containing voids and cracks. Brass formation was found to be the most prominent around the meniscus of the wide hot face, which gradually faded out towards the mould exit. Tramp elements (zinc and lead) in liquid steel were found to be responsible for harmful brass formation during casting. The present findings were implemented in plant operation to minimise its concentration.

APPLICATION OF MARKOV’S CHAIN THEORY TO PREDICT PROPERTIES OF HOT ROLLED STEEL SHEET

The multivariance and multistage nature of manufacturing technological processes of a wide range metal products of different purposes requires the use of special approaches for their formalization in order to find optimal solutions to ensure obtaining the products with the required level of properties. Under conditions of wide variability of the raw materials used, possibility to change the technological modes of processing, use of technological operations of various physical nature, possibility to provide the given level of metal products properties has the probabilistic nature. The theory of Markov processes is used to determine the probability of an object to appear in one of the process states for a certain time or time interval. In the example of the hot rolling process, a graph of the states of rolled steel properties, which are possible during the operation of this technological system, is constructed. It is shown that in this system there is a probability of transition from one state to the next in a finite number of steps, which means the existence of limiting probabilities. Matrices have been constructed to calculate the transition probabilities of the technological system “hot rolled steel sheet” for possible states: compliance of rolled metal with specified properties, partial compliance with specified properties, partial non-compliance with specified properties, and non-compliance with specified properties. Based on the calculations performed, it can be concluded that it is possible to ensure the probability to form the properties of hot rolled steel sheet. The obtained results can be used to improve existing technological processes for the production of hot rolled steel sheet with the required level of properties.