Similarity evaluation model for the internal defect detection of strip steel

An internal defect meter is an instrument to detect the internal inclusion defects of cold-rolled strip steel.The detection accuracy of the equipment can be evaluated based on the similarity of the multiple detection data obtained for the same steel coil.Based on the cosine similarity model and eigenvalue matrix model,a comprehensive evaluation method to calculate the weighted average of similarity is proposed.Results show that the new method is consistent with and can even replace artificial evaluation to realize the automatic evaluation of strip defect detection results.

Effect of hot stamping parameters on the mechanical properties and microstructure of cold-rolled 22MnB5 steel strips

Thermomechanical experiments were carried out to reproduce the hot stamping process and to investigate the effects of process parameters on the microstructure and mechanical properties of stamped parts. The process parameters, such as austenitizing temperature, soaking time, initial deformation temperature and cooling rate, are studied. The resulting microstructures of specimens were observed and analyzed. To evaluate the mechanical properties of specimens, tensile and hardness tests were also performed at room temperature. The op-timum parameters to achieve the highest tensile strength and the desired microstructure were acquired by comparing and analyzing the results. It is indicated that hot deformation changes the transformation characteristics of 22MnB5 steel. Austenite deformation promotes the austen-ite-to-ferrite transformation and elevates the critical cooling rate to induce a fully martensitic transformation.

Research on directly cold-rolled AISI 304 stainless steel strip with the twin-roll strip casting process

In order to improve the surface quality and properties of AISI 304 stainless steel strip produced with the twinroll strip casting process,the strip was directly cold-rolled. The results show that cold rolling clearly improves the surface roughness,microstructure and properties. Residual δ ferrite is greatly decreased, anisotropy becomes less obvious and corrosion resistance is greatly improved. These results demonstrate the feasibility of directly cold-rolled AISI 304 stainless steel strip.

Surface rust of cold-rolled bell-type annealing strip steel

This paper offers systematic analysis and in-depth research on the surface rust problem of cold-rolled bell-type annealing strip products.The defect characteristics,occurrence rules,generation mechanism,and influencing factors of surface rust are presented.This research employed a cold-rolled bell-type furnace annealing unit in a coastal steel factory as an example and conducted production process tests,on-site production tests,scanning electron microscopy,energy spectrum analysis,MINITAB statistical analysis,etc.Moreover,six significant influencing factors and their rules were studied:the cooling time of the final cooling table,the storage time of the intermediate storage,the temperature setting of the intermediate storage,the temperature of leveling liquid,the purging pressure of leveling machine,and the dust in the environment.

Effect of water quenching processing parameters on the mechanical properties of a cold-rolled C-Mn-containing steel sheet

Cold-rolled advanced high-strength steel sheets have become the material of choice for the automotive industry because of their unique attributes of high strength and balanced mechanical properties.High-hydrogen gas jet cooling and water quenching are the most commonly used ultrafast cooling technologies for producing martensite-containing high-strength steel sheets.The water quenching technology ensures the fastest industrial cooling rate of 1 000 K/s;therefore,it has the highest potential with respect to saving alloys.In this study,the water quenching of a C-Mn-containing steel sheet is simulated during continuous annealing to investigate the effect of water quenching and tempering parameters on its mechanical properties.The results reveal that at low quenching temperatures,the strength of the steel sheet decreases as the soaking temperature increases.However,at high quenching temperatures,a high soaking temperature corresponds to increased strength after quenching,regardless of whether the material was austenitized in the single austenite zone or the inter-critical zone.Therefore,a high quenching temperature always results in a high strength and a high yield ratio after quenching.Low-temperature overaging(tempering) considerably influences the yield strength and yield ratio,and the extent of this influence is correlated with the soaking temperature.

Development and application of an online pinhole detector for cold-rolled strips

An online pinhole detector based on the photoelectric inspection of cold-rolled steel strips was introduced. Pinhole detection is important to guarantee the quality of cold-rolled steel strips. The detector here was developed independently by Baosteel,and is designed based on the principle of photoelectric transfer. Typically, an inspection light source is installed above the steel strip to be inspected, and a photoelectric receiver is installed beneath the steel strip. The pinhole detector consists of a super-bright LED light source and a photoelectric receiver, which is composed primarily of photomultipliers. The super-bright LED light source illuminates the strip surface, and the light that permeates from pinholes is detected and amplified by a photoelectric receiver. The photomultiplier transforms the detected light into an electrical signal ,which is later recognized and classified by a signal-processing circuit and collected by a data-acquisition card. The detector can accurately track the strip edge and shield the strip edge from outside light. As a result,this system can detect a pinhole in the strip edge with a small blind zone on the edge. Most importantly, the detector exhibits good inspection accuracy and can accurately detect a pinhole with a diameter of 15 μm.

Effect of annealing parameters on mechanical properties of cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets produced on continuous annealing lines with water quenching facility,have advantages of high strength and low alloying element contents.These are in good accordance with the trend of light-weighting and fuel saving for automotive steel.In this article,a cold-rolled martensitic steel is studied to investigate the effect of annealing parameters on its mechanical properties.It is found that the quenching temperature and the slow cooling speed as well as the overageing temperature have significant influence on the strength of the experimental steel.The temperature zone at which the austenite decomposition is slow or has not started may be chosen as the quenching temperature to ensure the steel’s strength stability.The slow cooling speed also influences the steel’s strength greatly.A high cooling rate will lead to significantly higher strength.Tempering would decrease the steel’s tensile strength but would increase its yield strength.

Development and application of Baosteel's cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets are becoming widely applied in the automotive industry because of their ultra-high strength,which may result in satisfactory weight reduction. The grades of martensitic steel sheets are classified based on their tensile strength,which ranges from 980 to 1 700 MPa. The main applications include a series of structural parts of uniform cross-section or simple shape,such as bumper beams,door beams and door sills,etc. The study and development of cold-rolled martensitic steel sheets date back to 2007 in Baosteel,and some grades became commercially available in 2009. By 2015,Baosteel had commercially supplied thousands of tons of these steel sheets with tensile strength up to 1 400 MPa. Currently,1 500 MPa martensitic steel sheet is commercially available and 1 700 MPa martensitic steel sheet has been successfully produced. The process technology and application guides of Basoteel ＇s cold-rolled martensitic steels are summarized and analyzed in order to assist ongoing research and ensure correct applications of these ultra-high strength steel sheets.

Fatigue Response of Cold-Rolled Type-304 Stainless Steel Foil

This study presents the fatigue response of 304 stainless steel foil, cold-rolled to a thickness of 3.2 μm with 87 percent cold work at orientations of 0, 45, and 90 degrees to the direction of rolling. Fatigue specimens were fabricated by laminating a supportive layer of 20-μm polyimide film to one side of the foil and patterning 242 crack initiation features by photolithographic process. Progression of fatigue damage was determined through electrical resistance measurement. The fatigue response was demonstrated to be largely affected by anisotropy existing between the rolling direction and the off-axis orientations. Fatigue cracks that traveled in a direction parallel to the elongated grains (cyclic loads applied at 90-degree orientation to foil rolling direction) had the most fatigue response (undesirable characteristic). The construction of the specimens with thin foil supported by a film backing contributed to high fatigue threshold.

Properties of ultra-low carbon,cold-rolled sheet steels containing titanium or boron for use in enameling

Ultra-low carbon（ULC）,cold-rolled sheet steels for porcelain enameling containing alloys of titanium and boron are studied. The microstructure,mechanical properties,inclusions,and precipitates of the sheet steels are analyzed. The hydrogen permeation time of the sheet steels as-annealed and after skin-passed or cold-rolled at different reductions are measured. It is show n that the sheet steels possess different features of enameling properties in hydrogen permeability,fishscale resistance,and pinhole resistance.

Numerical Simulation of Continuous Tension Leveling Process of Thin Strip Steel and Its Application

Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti-cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were clone with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross-section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti-cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.

Development of Continuous Coating and Plating Strip Steel

The development trend of coated and plated technology for continuous strip steels,which include hot dip plating,electroplating,organic coating and vacuum plating technology,were summarized.

“Quartus scale” of hot-rolled strip steels and its formation mechanism

The types and growth of various oxide scales formed during the different phases of the production of hotrolled strip steel products are reviewed. Similarities and differences between the ＂tertiary scale＂ on the surface of carbon steels at high temperatures and the oxide scale on pure iron are compared. The micro-structural features of the ＂final oxide scale＂ on the surface of strip steels at room temperature as well as the relationship between these features and the position of the steel coil （plate） and the subsequent processes of recoiling, temper rolling and trimming, etc. are summarized. The actual oxide scales retained on the commercial hot-rolled strip steels at room temperature have been proposed to define as ＂ quartus scale＂ for the first time. The micro-structural development and phase transformation of the initial ＂tertiary scale＂ during and after cooling and coiling are described. The reasons for the ＂tertiary scale＂ on carbon steels differing from the oxide scale formed on pure iron, and the major influencing factors in the formation of various types of ＂quartus scales＂ are analyzed from both thermodynamic and dynamic viewpoints. The development mechanism of ＂ quartus scales＂ is discussed and the potential effects of the ＂ quartus scale＂ state （thickness, constitution, structure and defects）, on the rusting and pickling properties of commercial hot-rolled strip steel, as well as on the mechanical properties of oxide scales are analyzed.

Monitor automatic gauge control strategy with a Smith predictor for steel strip rolling

The simplified transfer function diagram block for a monitor automatic gauge control （Mon-AGC） system of strip steel rolling process was investigated. The new notion of strip sample length was given. In this way, the delay time varying with the rolling speed was evaded. After a Smith predictor was used to monitor the AGC system, the control laws were deduced for both proportional and integral regulators. The control strategies showed that by choosing the controller parameter P=∞ for both control algo- rithms each regulator could compensate the whole strip gage error in the first control step. The result shows that the integral algo- rithm is more controllable for the system regulating process and has a better steady-state precision than the proportional regulator. Compared with the traditional control strategy, the new control laws have a faster response speed and a hieher steadv-state precision.

Precipitation characteristic of high strength steels microalloyed with titanium produced by compact strip production

Transmission electron microscopy （TEM） and physics-chemical phase analysis were employed to investigate the precipitates in high strength steels microalloyed with Ti produced by compact strip production （CSP）. It was seen that precipitates in Ti microalloyed steels mainly included TiN, Ti4C2S2, and TiC. The size of TiN particles varied from 50 to 500 nm, and they could precipitate during or before soaking. The Ti4C2S2 with the size of 40-100 nm might precipitate before rolling, and the TiC particles with the size of 5-50 nm precipitated heterogeneously. High Ti content would lead to the presence of bigger TiC particles that precipitated in austenite, and by contrast, TiC particles that precipitated in ferrite and the transformation of austenite to ferrite was smaller. They were less than 30 nm and mainly responsible for precipitate strengthening. It should be noted that the TiC particles in higher Ti content were generally smaller than those in the steel with a lower Ti content.

Seismic responses of the steel-strip reinforced soil retaining wall with full-height rigid facing from shaking table test

To investigate the seismic response of the steel-strip reinforced soil retaining wall with fullheight rigid facing in terms of the acceleration in the backfill, dynamic earth pressure in the backfill, the displacements on the facing and the dynamic reinforcement strain distribution under different peak acceleration, a large 1-g shaking table test was performed on a reduced-scale reinforced-earth retaining wall model. It was observed that the acceleration response in non-strip region is greater than that in potential fracture region which is similar with the stability region under small earthquake,while the acceleration response in potential fracture region is greater than that in stability region in middle-upper of the wall under moderately strong earthquakes. The potential failure model of the rigid wall is rotating around the wall toe. It also was discovered that the Fourier spectra produced by the inputting white noises after seismic wave presents double peaks, rather than original single peak, and the frequency of the second peak trends to increase with increasing the PGA(peak ground amplitude) of the excitation which is greater than 0.4 g. Additionally,the non-liner distribution of strip strain along the strips was observed, and the distribution trend was not constant in different row. Soil pressure peak value in stability region is larger than that in potential fracture region. The wall was effective under 0.1 g-0.3 g seismic wave according to the analyses of the facing displacement and relative density. Also, it was discovered that the potential failure surface is corresponds to that in design code, but the area is larger. The results from the study can provide guidance for a more rational design of reinforced earth retaining walls with full-height rigid facing in the earthquake zone.

Thermodynamic Research on Precipitates in Low Carbon Nb-Microalloyed Steels Produced by Compact Strip Production

Microalloying element Nb in low carbon steels produced by compact strip production （CSP） process plays an important role in inhibiting recrystallization, decreasing the transformation temperature and grain refinement.With decreasing the rolling temperature, dislocations can be pinned by carbonitrides and the strength is increased. Based on the two sublattice model, with metal atom sublattice and interstitial atom sublattice,a thermodynamic model for carbonitride was established to calculate the equilibrium between matrix and carbonitride. In the steel produced by CSP, the calculation results showed that the starting temperature of precipitation of Ti and Nb are 1340℃ and 1040℃, respectively. In the range of 890-950℃, Nb rapidly precipitated. And the maximum of the atomic fraction of Nb in carbonitride was about 0.68. The morphologies and energy spectrum of the precipitates showed that （NbTi） （CN） precipitated near the dislocations. The experiment results show that Nb rapidly precipitated when the temperature was lower than 970℃, and the atomic fraction of Nb in carbonitride was about 60%-80%. The calculation results are in agreement with the experiment data. Therefore the thermodynamic model can be a useful assistant tool in the research on the precipitates in the low carbon steels produced by CSP.

Adaptive illumination light source for online machine vision inspection of tin steel strips

The different reflection characteristics of the surface of tin steel strips and the different speeds of the tinning line demand an adaptive illumination light source for online machine vision inspection. This light source can be integrated with a time delay integration charge-coupled device （TDI CCD ） to capture the images of moving objects and facilitate inspection of the surface quality of tin steel strips. On-site application show the effectiveness of the TDI camera with the adaptive illumination light source in detecting the surface defects on tin steel strips of three different materials and with different tin coating weights.

Microstructure analysis of AISI 304 stainless steel produced by twin-roll thin strip casting process

The microstructure of AISI 304 austenlte stainless steel fabricated by the thin strip casting process were investigated using optical microscope, scanning electron microscope （SEM）, transmission electron microscope （TEM）, and X-ray diffraction （XRD）. The microstructures of the casting strips show a duplex structure consisting of delta ferrite and austenite. The volume fraction of the delta ferrite is about 9.74vo1% at the center and 6.77vo1% at the surface of the casting thin strip, in vermicular and hand shapes. On account of rapid cooling and solidification in the continuous casting process, many kinds of inclusions and precipitates have been found. Most of the inclusions and precipitates are spherical complex compounds consisting of oxides, such as, SiO2, MnO, Al2O3, Cr2O3, and FeO or their multiplicity oxides of MnO.Al2O3, 2FeO.SiO2, and 2MnO.SiO2. Many defects including dislocations and stacking faults have also formed during the rapid cooling and solidification process, which is helpful to improve the mechanical properties of the casting strips.

Microstructure and corrosion resistance of 304 stainless steel electroslag strip cladding

The 304 stainless steel strips were deposited one layer on carbon steel base metal by electroslag strip cladding （ESC） and submerged arc cladding （SAC）, respectively. The solidification microstrueture of ESC metal was analyzed by the optical microscopy, scanning electron microscope and energy dispersive spectroscopy. The corrosion resistance studies of strip cladding metals were carried out in 10% oxalic acid electrolytic etching test. The results showed that the cladding metal obtained by ESC presented low content of C, high content of Cr and enough alloying element of Ni in the chemical composition. The transition zone of ESC with small width was almost parallel with the base metal, leading to a lower dilution. There are three types of solidification modes （ A→AF→FA ） occurred in the ESC metal due to the decrease of cooling rate and degree of dilution from the transition zone to the top of ESC metal. As a result, the microstructure of ESC metal exhibited mainly austenite with a small amount of ferrite, contributing to achievement of better corrosion resistance.