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The indentation response of cold rolled strip steel was studied to advance the understanding of surface scratch resistance by instrumented indentation technique. The effect of radial stress on indentation response was analyzed using numerical simulation and dimensional analysis method. It was revealed that the indentation plastic work of strip steel inlayed in epoxy resin remained unchanged roughly at the load of 200 mN, and the instrumented indentation hardness could be calculated with small error using a work approach. It was found that the reverse analysis algorithm proposed by Dao et al. (Acta Mater 49:3899–3918, 2001) for extracting elasto-plastic properties from indentation data was inapplicable to strip steel. The computation results showed that the indentation curvature $$C$$ first decreased and then increased with the increase in radial tensile stress. And $$C$$ first increased slowly and then rapidly with the increase in radial compressive stress. The turning point was about $$\sigma_{{{\text{add}}}} /\sigma_{{\text{r}}} = - 0.5$$ in compression, and it would be $$\sigma_{{{\text{add}}}} /\sigma_{{\text{r}}} > 0.5$$ in tension. The research results are valuable for controlling surface quality.

Alloy development on a commercial scale in recent years has become much more costly and as such has adopted a more iterative approach, making small refinements while keeping within known limits. Laboratory-based rapid alloy development is therefore a key in pushing new grade boundaries. This work shows the rapid alloy development (RAP) facilities at WMG, including capability, sizes and time required for each stage of the process, which have been mapped against the relevant industrial process. A case study of a dual-phase steel grade DP800 has been used for this work. It has been shown that through knowledge of the strengthening mechanism of the alloy (2nd phase distribution for DP800) is critical with respect to mechanical properties and that specific changes and optimisation to the laboratory production casting and subsequent reduction allows for the final product microstructure and mechanical properties to match the production product. This gives confidence in upscalability.

Impurity elements of Cu, Ni, Sn and Cr have been added to a model low-carbon strip steel to mimic the levels that could arise due to increased scrap recycling during steel production. The microstructure and tensile properties of the base composition and impurity added compositions after thermomechanical processing, consisting of hot rolling and simulated coil cooling, have been investigated. The addition of impurities results in a lower bainite fraction, a smaller effective grain size and the precipitation of Cu-rich particles. Meanwhile, higher strength and lower ductility are found in the steel with impurities.

Hot-rolled strip steel is widely used in automotive manufacturing, chemical and home appliance industries, and its surface quality has a great impact on the quality of the final product. In the manufacturing process of strip steel, due to the rolling process and many other reasons, the surface of hot rolled strip steel will inevitably produce slag, scratches and other surface defects. These defects not only affect the quality of the product, but may even lead to broken strips in the subsequent process, seriously affecting the continuation of production. Therefore, it is important to study the surface defects of strip steel and identify the types of defects in strip steel. In this paper, a scheme based on ResNet50 with the addition of FcaNet and Convolutional Block Attention Module (CBAM) is proposed for strip defect classification and validated on the X-SDD strip defect dataset. Our solution achieves a classification accuracy of 94.11%, higher than more than a dozen other compared deep learning models. Moreover, to adress the problem of low accuracy of the algorithm in classifying individual defects, we use ensemble learning to optimize. By integrating the original solution with VGG16 and SqueezeNet, the recognition rate of oxide scale of plate system defects improved by 21.05 percentage points, and the overall defect classification accuracy improved to 94.85%.

The blank is prone to wrinkles and spring-back in multi-point forming, seriously affecting the quality and forming accuracy of the formed part. To improve this state, a sandwich structure constructed from a strip steel pad and blank was presented. The deformation behaviour and forming accuracy using three forming processes, namely, without a cushion, using a polyurethane elastic pad and using a strip steel pad, were analysed by numerical simulation and experimentation. The results showed that the use of the strip steel pad in multi-point forming can effectively increase the deformation resistance of the sheet bending; make the material evenly thinned during forming; suppress defects such as wrinkles, spring-back, dimples and straight edges; and improve the forming accuracy.

A novel self-excited oscillating mixer is developed for the descaling of strip steel, which synthesizes the post-mixed abrasive water jet and self-excited oscillation. The realizable k-ɛ model is selected to investigate the effects of different abrasive entrance, inlet pressure, mixing chamber diameter, and length on the jet characteristics. Meanwhile, the effects of different inlet pressure and target distance on the outlet velocities for two kinds of mixers (including the developed mixer and conventional post-mixing mixer) with or without abrasive jet are investigated through simulation. Experiment as well as simulation results exhibited: (1) The oblique abrasive entrance can accelerate the mixture of water and abrasive due to its larger turbulent kinetic energy, and its outlet velocity is larger than that of radial and axial abrasive entrances. (2) For the developed mixer, the outlet velocity is preferable when the mixing chamber diameter is about 40–50 mm and the mixing chamber length is 20 mm. (3) The descaling efficiency of the developed mixer is superior to that of conventional post-mixing mixer. The research will lay foundation to optimize the structure of self-excited oscillating mixer for the descaling of rusty steel.

An auger flighting is a helical-shaped circular product used to transfer bulk materials in broad applications. Continuous auger flightings are formed from straight steel strips by a specialty rolling mill. Because of the geometry and configuration of auger flightings, the rolling process is more complex than the ordinary longitudinal rolling. However, there is little published literature on the theoretical features of auger flighting rolling. In this article, the fundamental kinematics and mechanics of auger flighting rolling are mathematically developed. From these mathematical models, the contact area, rolling force, and torque are calculated and the affecting factors are evaluated. The slip characteristics between the strip and forming rolls and the effects of roll offset are studied. The article also provides design considerations, primarily for the main roll shafts and required rolling mill power. Finally, the application results are compared to the actual rolling readings and satisfactory agreement is obtained.

A strip steel pad with a polyurethane board pad is suggested to improve the quality of multi-point die forming. In this work, the formability of four different forming processes, namely without a cushion, using a polyurethane pad, using a strip steel pad, and using a strip steel pad with a polyurethane board, was compared via numerical simulations and experiments. The results show that using a strip steel pad with a polyurethane board in multi-point die forming can effectively improve the stress and strain of the blank and suppress the defects of dimpling, straight edge, and wrinkling. This work demonstrates that the use of the strip steel pad with a polyurethane board in the multi-point forming process can improve the sheet forming conditions and quality.

The present paper focuses on asperity contact during cold rolling at a microscopic level. As analyses of such a contact are not practical with experimental facilities, a three-dimensional finite element method (FEM) is adopted to simulate the indentation and furrow behaviors of a single asperity on work roll surface in mixed lubrication. The effects of the tensile stress, the hydrodynamic pressure and the plastic deformation of steel strip are considered comprehensively. Most calculations are done for parabolic asperities, but for comparison purposes, some results are presented for sinusoidal and elliptical asperities. The indentation behaviors including uplift height of edges and plastic deformations of strip steel are calculated and analyzed. The friction during furrow behaviors is also considered. It reveals that the reduction and lubrication condition has a significant effect on the uplift height of strip steel edges around the asperity. Furthermore, long-term repeated effects of mixed lubrication contact are liable to spark asperity wear and decrease the roughness of rolls and even cause the failure of rolls in strip rolling mills.

Recent results in the literature have shown that subsurface properties play a key role during the bending of steel plates. Now, for the first time, surface microstructure, surface texture, subsurface hardness and dislocation density have been studied to reveal the effect of tempering and thermomechanical treatment on the bendability of a direct-quenched strip steel. In the experiments, different thermomechanical treatments as well as non-isothermal tempering treatments were performed with slow heating to 570 °C and slow cooling to simulate the tempering of large steel coils in a batch annealing furnace. The results show that in addition to the improved production efficiency obtained through direct quenching and a single tempering process, tempering improves bendability by reducing subsurface dislocation density and hardness without a significant loss of strip yield strength. The subsurface microstructure and texture of the strip are the result of thermo-mechanical processing and transformation behaviour. Upper bainite containing elongated Martensite-Austenite (MA) islands in addition to an intense shear texture component {112}〈111〉α leads to shear band formation, and therefore poorer bendability when the bend axis is perpendicular to the rolling direction. This texture is not affected by tempering. Therefore, tempering does not improve the bendability of steels with an unfavourable texture. When the subsurface layers comprise a softer ferritic microstructure, good bendability is obtained in the untempered direct-quenched condition with a modest improvement caused by tempering.

According to the “Hill rolling force formula”, taking particular account of the influence from horizontal vibration of rolled piece in roll gap, a dynamic rolling force model is analyzed. Considering the interaction between vibration of strip and roll, the dynamic vibration model of rolling mill is established. On this basis, the time delayed feedback is introduced to control the vibration of the roll system. The amplitude frequency response of the coupled vibration control equation is obtained by using the multiple scales method. Different time delay parameters are selected to test the control effect. Research results show that the unstable vibration of the roll system can be suppressed with appropriate time delay feedback parameters. Because it is simpler and has good control effect in solving nonlinear mechanical vibration, so these results will make a difference for the research of strip mill vibration, and provide theoretical basis for strip steel production.

This laboratory study utilised a dilatometer to simulate the run-out table cooling rate and the coiling temperature to investigate the effect of the cooling rate and simulated coiling conditions on the age hardening response of a niobium microalloyed Ultra-thin Cast Strip (UCS®) steel, produced by the CASTRIP® Process. Three cooling rates of 1, 5 and 40 °C/s, covering very slow (1 °C/s) to typical run-out table cooling rates (40 °C/s), down to two coiling temperatures of 500 and 675 °C were used. Dilatation curves were used to determine the temperature range over which the γ-α phase transformations occurred and the final microstructures were characterized using an optical microscope equipped with an image analysis software. The subsequent age hardening response, which previous studies have shown, results from the retention of Nb in solid solution, was assessed by the hardness changes after a post heat treatment at 700 °C for 60 s. A range of age hardening responses were obtained, depending on cooling rates and cooling stop (coiling) temperatures, which indicate a different degree of Nb retention. At the same cooling rate, the lower coiling temperature of 500 °C resulted in higher Nb retention compared to the higher coiling temperature of 675 °C. As the coiling temperature of 675 °C was within the austenite to ferrite transformation range, the simulated slow cooling of the coil impacted the precipitation behaviour of Nb rendering the interpretation more complex and this will be discussed in this paper. For the 500 °C simulated coiling temperature, the higher cooling rate resulted in a higher age hardening increment thus more Nb retention.

The study described here focuses on toughening and crack-arrest mechanism in a 560 MPa microalloyed pipeline strip steel processed by combination of thermo-mechanical controlled processing and ultra-fast cooling (TMCP-UFC) and compared with the strip processed at low cooling rate and high cooling interrupt temperature (TMCP-LC). Furthermore, delamination mechanisms involved in drop weight tear test (DWTT) were also studied from the perspective of microstructure, crystallographic orientation, and stress field ahead of the crack. The TMCP-UFC processed strip was primarily composed of acicular ferrite (AF), bainitic ferrite (BF), and small-sized martensite/austenite (M/A) constituent, and the microstructure was homogeneous across the thickness. While the TMCP-LC processed strip mainly consisted of quasi-polygonal ferrite (QPF), degenerate pearlite (DP), and small fraction of BF. The TMCP-UFC processed strip exhibited excellent low-temperature toughness with upper shelf energy (USE) of ∼302 J and transition temperature (TT) of ∼−75 °C in relation to TMCP-LC processed strip with USE of ∼273 J and TT of ∼−30 °C. Significant consumption of crack-propagation energy during ductile fracture and smaller effective grain size of ∼2.4 μm were responsible for higher USE and lower TT of TMCP-UFC processed strip compared to TMCP-LC processed strip with effective grain size of ∼4.0 μm. The smaller effective grain size with respect to TMCP-UFC processed strip contributed to excellent crack-arrest property by deflecting the propagated crack. In the TMPC-UFC processed strip, delamination occurred along the crystallographic cleavage plane of {001} under plane strain condition at mid-thickness. In contrast, besides delamination mechanism along the cleavage plane, delamination also occurred along the macro-segregation band under plane strain condition at mid-thickness in the TMCP-LC processed strip, which led to severe delamination.

The effect of red scale on the bendability of a thermomechanically rolled and direct quenched pilot-scale strip steel has been studied by comparing the bending behaviour of adjacent areas with and without red scale. The yield strength of the studied 8 mm thick strip was 960 MPa. The local microstructure and texture below the different scale surfaces were characterized using FESEM and FESEM-EBSD, chemical compositions were determined using GDOES, microhardness profiles were measured and bendability was determined using three-point brake press bending. Red scale was found to significantly affect bendability especially when the bend axis is transverse to the rolling direction. The minimum usable punch radius for defect-free bends in the absence of red scale was 12 mm (1.5 x thickness) while under red scale it was 30 mm (3.75 x thickness). Beneath the red scale the microstructure 50 to 400 μm below the surface was clearly different to that in the absence of red scale. Without the red scale the microstructure was mainly granular bainite with small fraction of upper bainite and polygonal ferrite. Below the red scale the microstructure was a mixture of upper bainite and granular bainite. As a result of the microstructural differences, the subsurface hardness changed substantially from 360 HV in the absence of red scale to 410 HV with red scale. The chemical composition did not change as a result of the presence or absence of red scale, which rules this factor out as possible cause of differences in bendability or final microstructure. Possible explanations for the observed effects of red scale on subsurface microstructure, and microstructure on bendability, are discussed in the paper.

The influence of oxide scales on the corrosion behaviors of B510L hot-rolled steel strips was investigated in this study. Focused ion beams and scanning electron microscopy were used to observe the morphologies of oxide scales on the surface and cross sections of the hot-rolled steel. Raman spectroscopy and X-ray diffraction were used for the phase analysis of the oxide scales and corrosion products. The corrosion potential and impedance were measured by anodic polarization and electrochemical impedance spectroscopy. According to the results, oxide scales on the hot-rolled strips mainly comprise iron and iron oxides. The correlation between mass gain and test time follows a power exponential rule in the damp-heat test. The corrosion products are found to be mainly composed of γ-FeOOH, Fe3O4, α-FeOOH, and γ-Fe2O3. The contents of the corrosion products are different on the surfaces of the steels with and without oxide scales. The steel with oxide scales is found to show a higher corrosion resistance and lower corrosion rate.

For the cold-rolled silicon steel strip lubricated with emulsion, the typical oil spot defects always can be found on the surface of rolled strip. The oil spot are parallel to the rolling direction. In the present study the micro-structure of oil spot defects was investigated by several surface analysis techniques, including LEXT ols4000 laser scanning confocal microscope, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS). The chemical compositions of the oil spot defects were analyzed by EDS. The results showed that the surface quality of the rolled non-oriented silicon steel was affected strongly by emulsion stability. The emulsion stability decreased with the increasing content of CL-. When the particle size of emulsion was larger, the lubricity of the emulsion deteriorated. Furthermore, there were some emulsions which contain miscella on the strip steel surface. The emulsions existed in the confined areas where the plate shape defects formed. The majority of its water was evaporated with the increasing of temperature and time. The oxides and residual emulsions could be found on the surface strip steel, which originated from the oxidation reaction between vapors and silicon steel surface. Eventually, the reaction produced some oxides (Fe3O4, FeO, Fe2O3, SiO2, CoCr2O4, NiCr2O4, Fe-Cr) and other by-products. In addition, the emulsion spots area were easier to suffer corrosion than the normal area under the same conditions.

Surface defect detection of strip steel is still a challenging task for its complex variances, e.g., intra-class defects exist large differences in appearance while inter-class defects contain similar parts. To address these issues, we regard the defect object as the salient part of the image and propose a novel, effective saliency propagation algorithm based on multiple constraints and improved texture features (MCITF). Firstly, we deliberately design 83-dim texture features that are used to generate label matrix (among which the label information viewed as the important basis of diffusion process) in the framework of multiple-instance learning. Then we resort to Laplacian regularization viewed as smoothness constraint for enlarging the gap between defect objects and background, and high-level prior (background, object, and mid-level feature) constraints for constraining the label information propagation process locally in order to uniformly highlight the complete defect objects while effectively suppress the non-salient background. Finally, we observe that the superpixel segmentation algorithm based on spectral clustering can adequately capture the edge information of defects, thus promoting to yield high-quality pixel-level saliency maps. Experimental results implemented on the real challenging strip steel benchmark database demonstrate that our MCITF model outperforms state-of-the-art methods with large margins and strong robustness in terms of eight evaluation metrics.

Roll surface wear morphology directly affects the surface quality of steel plates and even affects the texture composition of plates and strip steel products. Using image processing methods to judge the wear state of a roll is low cost, easy to operate, and easy to realize an automatic smart data processing system. In this paper, we propose a Smart Roll Wear Check (SRWC) scheme for ensuring the rolling quality of steel plates. In the SRWC scheme, roll surface images in different wear stages are analyzed, from which seventeen dimension features are extracted. At the same time, the fractal theory is introduced to explore the relationship between fractal dimensions and roll wear degree. The results show that four characteristic parameters, such as roundness, equivalent area circle radius, second moment and texture entropy, and the fractal dimension can be used as effective parameters to quantitatively judge roll wear state. Lastly, a back-propagation (BP) neural network model for recognition and judgment for roll wear is established. It provides an experimental test to show that the five parameters as a quantitative evaluation for roll wear morphology are effective. By processing the data on the images, the SRWC scheme can demonstrate whether the roll needs to get off mill in time, so as to avoid the hidden danger of safety and ensure the rolling quality of the steel plate.

The control of surface roughness is of great significance for measuring the quality characteristics of cold-rolled steel strip. At present, the conventional method is used to monitor the surface roughness of steel strip by random sample inspection, off-line analysis and test, and on-line adjustment of production process, but the method is of some hysteretic nature and discontinuity. To this end, the paper presents an on-line intelligent control method for surface roughness of the cold-rolled steel strip, adjusting parameters of the skin-pass process in real time and reducing the fluctuation of surface roughness of strip steel. To establish the fuzzy neural network control model of the corresponding relationship between the parameters of the skin -pass process and the surface roughness of steel strip, the deviation between the online detection value and the target value of the surface roughness is taken as the input of the model, so is the differential value of deviation. In addition, the skin -pass rolling force is used as the output. Learning and training fuzzy neural network to get a fuzzy neural network online prediction control model that is applied to continuous treatment unit for cold rolling strip steel. By measuring the surface roughness of steel strip, the system adjusts the skin-pass rolling force in real time. At the same time, to keep the mechanical properties of the steel strip and the strip shape, the system optimizes skin -pass rolling tension and bending force accordingly to realize on -line intelligent control for the surface roughness of steel strip. The proposed system can improve the control accuracy of surface roughness, which can even better satisfy the requirements of downstream users.

The bendability of thermomechanically rolled and direct-quenched martensitic – bainitic ultrahigh-strength steels can be very anisotropic. Unlike in most steels, it can be good when the bend axis is parallel to the rolling direction but poor when the bend axis is perpendicular to the rolling direction as a result of shear band formation. This paper shows how bendability can be significantly improved and made more isotropic by modifying the subsurface microstructure to include a relatively soft polygonal ferrite and granular bainite layer. It is shown that the thickness of this layer should be at least 300 μm to prevent shear band formation and thereby improve bendability during transverse bending. The results are interpreted in terms of the opposing effects of geometric softening and the strain hardening of the different subsurface microstructures. The role of subsurface shear texture in explaining the anisotropic nature of geometric softening and shear band formation is discussed.

Hot rolled coil after winding cooled to room temperature in the storage room often takes 4 to 5 days. The process of coil cooling sometimes produces collapse defects in industrial applications. In this research, the cooling process after coiling of Shougang Group 72AU2 hot-rolled strip steel was taken as the research material. We used finite element method (FEM) software ABAQUS to analyze the temperature field of coil after coiling. At first, a temperature field model of hot-rolled coil during cooling was established by the finite element method. The simulation results show that, the maximum temperature difference is 206°C, when the cooling-time is about 50th min. The highest temperature node was about at 44% apart from inside diameter distance position in the thickness direction, and finally moved to the node which is at 26% apart from inside diameter distance position. Temperature field calculation considered the anisotropy of the heat transfer. The temperature of each node can be obtained by this simulation, which cannot be obtained from field measurements and experiments. Thereby this research has a significant impact on further research on the causes of the contraction and collapse.

Microstructure and properties of DP590 steel in overaging process of continuous annealing were investigated in the laboratory. Effects of the overaging temperature (OT) in conventional process (Process A) and reheated overaging temperature (ROT) of the proposed process (Process B) on microstructure and mechanical properties were analyzed. The results showed that, in process A, with the increase of the OT from 280 °C to 400 °C, the amount of granular retained austenite increases, the tensile strength decreases, the yield strength and elongation both increase. In process B, with the increase of the ROT from 310 °C to 400 °C, the tensile strength decreases, whereas the yield strength changes little. Compared with the conventional process, the tensile strength of the experimental steel increases obviously and the ratio of yield-to-tensile strength decreases in process B. The variation of instantaneous work hardening index ( n ⁎ ) with tensile strain can be divided into three stages. The increase in the OT or ROT leads to the continuous increase of n ⁎ in the third stage.

In this paper, the deformation behaviors of elastic–plastic asperity on rough roll surface in a strip steel mill were simulated by a three-dimensional finite element (FE) model. The asperity characterized a sinusoidal profile and all objects in the FE model were elastic–plastic with linear strain hardening. The deformation behaviors including contact stresses, strains (including elastic and plastic strains), and contact radii of different rolling force densities and different geometrical shapes and sizes were calculated and analyzed. It revealed that the tall-thin type asperity caused larger plastic strain in the asperity itself and larger Von Mises stress in the mating roll subsurface. Long-term repeated effects of large cyclic strain and stress were liable to spark subsurface cracks and increased the risk of fatigue failure of rolls in strip rolling mills.

The tempering of re-austenized, quenched and tempered (RAQT) martensitic steels is an extensively studied and well understood field of metallurgy. However, a similar understanding of the effect of tempering on direct-quenched (DQ) high-strength steels has been lacking. Now, for the first time, the effect of tempering in the range of 250–650 °C on the strength, toughness, bendability, microstructure, crystallography and dislocation density of a DQ steel is reported. In the case of tempering at 570 °C, the effects of having a RAQ or DQ starting condition are compared. For the composition and thermal cycles studied, it was found that a peak tempering temperature in the range of 570–600 °C resulted in a DQT steel with an optimal balance of strength, bendability and toughness, i.e. a yield strength greater than 960 MPa, a minimum usable bending radius of 2 times the sheet thickness and T28J of − 50 to − 75 °C depending on the test direction. Crystallographic texture, dislocation density and the distribution of carbides are important factors affecting the bendability of DQT strip. Tempering had no effect on texture, but strongly influenced the size and distribution of carbides thereby resulting in differences in bendability and impact toughness transition temperature.

A kind of new hot strip steel temperature measuring device has been designed. The mathematical model and the geometric model of the nozzle flow field have been established based on computational fluid dynamics theory. The impact of equalizing groove and nozzle structure on the nozzle system characteristics is researched in detail using fluid dynamics software FLUENT. The research results show that: the nozzle pressure groove can improve the gas flow properties of the nozzle and the nozzle can meet the design requirements. The nozzle gap, the inlet pressure of nozzle, the lower edge diameter of the nozzle, nozzle diameter and chamfer structure have different effects on flow field characteristics and nozzle flow. The study provides a theoretical basis for designing hot strip steel temperature measurement devices and the nozzle of purge.

Intertwined automobile generator stator core is made from twisted Strip steel with teeth. This winding process is different from the method of traditional laminated machining. Intertwined technique is a new method that for the manufacturing of stator cores in automotive alternators. The productive process include such key steps: Leveling of the bar-typed materials, stamping, enwinding, soldering and plastic. This methods has raised the production efficiency and used ratio of the materials, and even make a cost reduction compared with the traditional ways of strap-typed stator core manufacturing. They are able to make a substitution to the imported products by most automotive alternator enterprises as well as complete the blanks of domestic market and have a large extent of social and economic benefits.

This paper firstly analyzes the problems that exist in the cold rolling of steel industry. Secondly, a new approach is proposed to temper and straighten the strip steel based on the temper leveling mill, shortly, TLM. The required high quality of the wave, surface and mechanical properties can be achieved only with TLM. TLM holds the functions of both temper machine and straightening mill and can produce good quality strip steel, no only the waviness, mechanical properties, but also the surface quality. The usage of TLM can lower the cost of the production of tempering, straightening and equipment investment.Finally, the experiments are done and verify the validity of the approach.

The microstructures and impact absorbed energies at various temperatures were investigated for steel strips hot rolled to thickness reductions of 95.5%, 96.0%, 96.5%, 97.0%, and 97.5%. Results indicate that grain refinement can be realized with an increase in hot rolling reduction. Besides, finer precipitates can be achieved with an increase in hot rolling reduction from 95.5% to 97.0%. The impact absorbed energy decreases with a decrease in testing temperature for steel strips hot rolled to 95.5%, 96.0%, and 96.5% reductions in thickness. However, in the case of steel strips hot rolled to 97.0% and 97.5% reductions in thickness, the impact absorbed energy remained almost constant with a decrease in testing temperature.

Use of ultra-high-strength steels (UHSS) in weight critical constructions is an effective way to save energy and minimize carbon footprint in the end use. On the other hand, the demands for reducing manufacturing costs and energy consumption of the steelmaker are increasing. This has led to development of energy efficient direct quenching (DQ) steelmaking process as an alternative to the conventional quenched and tempered or thermomechanical rolling and accelerate cooled processes. Ruukki has employed thermomechanical rolling and direct quenching process (TM + DQ) for a novel type of ultra-high-strength strip and plate steels since 2001. Advantages of the ultra-high-strength level (>900MPa) can be fully utilized only if fabricated properties are on a sufficient level. Bending is one of the most important workshop processes and a good bendability is essential for a structural steel. Hence, the metallurgy and bendability of Ruukki ́s TM + DQ strip steel Optim® 960QC have been investigated closely. It was found that by optimizing process parameters and chemical composition, a good combination of strength and ductility can be achieved by a modification of martensitic-bainitic microstructure. Despite of smaller total elongation, the bendability of Optim® 960QC is at least on the same level as on conventionally manufactured 960MPa steels. However, it is important to pay special attention to bending process (tool parameters, springback, bending force, material handling) when bending UHSS. It was also found that the bendability of Optim® 960QC can be significantly enhanced by local laser heat treatments or roll forming.

For strip steel with the thickness of 1.6 mm, the yield and tensile strengths as high as 760 and 850 MPa, respectively, were achieved using the compact strip production technology. Precipitates in the steel were characterized by scanning and transmission electron microscopy to elucidate the strengthening mechanism. In addition, intragranular misorientation, Kernel average misorientation, and stored energy were measured using electron backscatter diffraction for crystallographic analysis of ferrite grains containing precipitates and their neighbors without precipitates. It is found that precipitates in specimens primarily consist of TiC and Ti4C2S2. Ferrite grains containing precipitates exhibit the high Taylor factor as well as the crystallographic orientations with {012}, {011}, {112}, or {221} plane parallel to the rolling plane. Compared with the intragranular orientation of adjoining grains, the intragranular misorientation of grains containing precipitates fluctuates more frequently and more mildly as a function of distance. Moreover, the precipitates can induce ferrite grains to store a relatively large amount of energy. These results suggest that a correlation exists between precipitation in ferrite grains and grain crystallographic properties.

The strip steel surface defect classification belongs to multi-class classification. It demands high classification accuracy and efficiency. However, traditional methods are not fit for abnormal datasets, such as the large-scale, sparse, unbalanced and corrupted dataset. So a novel classification method is proposed in this paper based on enhanced twin support vector machine (TWSVM) and binary tree. According to the density information, the large-scale dataset is pruned, the sparse dataset is added with unlabeled samples, and TWSVM is improved to multi-density TWSVM (MDTWSVM) which has efficient successive overrelaxation (SOR) algorithm. Finally, MDTWSVM and binary tree are combined together to realize multiclass classification. Some experiments are done on the strip steel surface defect datasets with the proposed algorithm. Experimental results show that MDTWSVM has higher accuracy and efficiency than the other methods of multi-class classification for the strip steel surface defect.

Hot rolled strips having a minimum yield stress of 700 MPa have been produced in full scale processing. Alloy additions (1·5%Mn, 1%Cr and 0·3%Mo) together with rapid cooling on the run-out table produce fully bainitic microstructures which confer strength and toughness. Microalloying with 0·08%V has been shown to be essential for achieving stable strength levels that are independent of the coiling temperature since the necessary low coiling temperatures are difficult to reproduce accurately under steelworks conditions. The products have excellent bendability and HAZ toughness. Typical microstructures and textures of the hot rolled strips are also presented.

A separation phenomenon occurring during the drop weight tear test of commercial thick-walled API (American Petroleum Institute) X80 strip steel was investigated in this work. Microstructural analysis showed that the band structure of bainite elongated along the rolling direction works as the initiation sites of separation. The propagation of separation can be promoted not only by the occurrence of the band structure of martensite/austenite constituent, prior austenite grain boundaries, and elongated bainite, but also by fine acicular ferrite and bainite. Wide separation formed in the former case, while the narrow one appeared in the latter case. Some methods were proposed to obtain fine and homogeneous acicular ferrite in thick-walled X80 pipeline steel in order to minimize the occurrence of separation.

This paper introduced the application of the loop on the hot strip mill. The loop mainly support the strip steel, form the loop variable which can adjust the dynamic speed of the mill, keep the pulling force of the strip steel between the framework, participate the speed control of the framework of the finishing rolling and the quality of the strip steel is ensured.

This paper introduced the control of the electric loop on the hot strip mill. The loop mainly support the strip steel, form the loop variable which can adjust the dynamic speed of the mill, keep the pulling force of the strip steel between the framework, participate the speed control of the framework of the finishing rolling and the quality of the strip steel is ensured.

This paper presents an investigation on the impact fatigue characteristics of valve leaves that are prevalently used in hermetic reciprocating compressors especially for the household type refrigerators. A unique automated impact fatigue test system has been designed and produced, which enables to carry out impact fatigue tests of the compressor valve leaves under the desired impact velocities. The test system serves investigations on the impact fatigue characteristics with the ability of crack detection and as the subsequent step of automatically terminating the test. The crack detection technique incorporates a non-contact actuation, a data acquisition system and a microphone. The investigation relates the impact fatigue lifetime of the valve leaves with the impact velocity, asymmetrical impact, operation temperature, material type (carbon strip steel, stainless strip steel and new stainless strip steel grade) and tumbling operation duration. Microscopic and metallographic observations were performed on the specimens. It was observed that the crack initiated at the edge of the valve leaves on the contact surface of valve leaf and vale plate and a particle is torn away from the edge before propagation. As the crack propagates, branching along the crack path is caused by the geometrical shape and stress waves on the valve leaves. The investigation and introduced test system guide the design optimization of valve leaves in terms of compressor performance due to energy consumption and lifetime of the valve leaf.

We demonstrate that a Nb-microalloyed ultra-thin cast strip steel can be strengthened substantially without compromising ductility by performing a simple heat treatment at 700 °C for 4 min. The strengthening was attributed to a fine dispersion of Nb-rich solute atom clusters. These clusters had an average size of ∼60 atoms at peak hardness and resembled Guinier–Preston zones in Al–Cu alloys. The application of the Ashby–Orowan equation indicates that these clusters are potent strengthening agents when compared to conventional Nb(C,N) precipitation strengthening.

Dual-phase (DP) steels are generally characterized by the combination of high strength with good ductility, but some formability characteristics of these steels are low compared to other steel classes. In particular, stretched edge ductility and bendability are poor by comparison with other less ductile strip steel classes such as complex-phase (CP) steels. This paper describes the effect of short time tempering of the order of few seconds to few minutes on the mechanical properties of two cold rolled and hot-dip galvanised dual-phase (DP) steels. The uni-axial tensile characteristics, hole-expansivity, Erichsen cupping height and bendability were assessed after tempering at temperatures between 200 and 450 °C for relatively short time scales up to 10 min. The short tempering treatments significantly changed the character of the DP steel leading to a decrease in tensile elongation and an increase in hole-expansitivity and bendability. The properties observed in tempered DP steels where found to be closely comparable to those expected for CP steels. Microstructural analyses using the SEM showed carbide precipitation within the martensite and ferrite that increased with tempering.

Laminar Cooling is an indispensable part of hot strip steel mill. Based on the devices, instruments and control requirements of 1150mm hot strip steel mill in a certain actual Iron & Steel Co., the laminar cooling control system is designed, including hardware figuration, network framework, software functions, mathematical model, etc. The engineering practice proves that the control system is steady and reliable, and it has the value being popularized in the other similar production line.

A fast Bortz–Kalos–Lebowitz kinetic Monte Carlo model for the prediction of rates of strain ageing in ultra-low-carbon strip steel is presented. The new model is shown to accurately predict rates of ageing over the temperature range 50–100 °C and to display t 2/3 kinetics.

Twin roll casting (TRC) of low-carbon ultra-thin cast strip (UCS) steel has the potential to deliver significant economic advantages over steels made by conventional processes. Novel microstructures containing intragranularly nucleated acicular ferrite may be produced in UCS products manufactured by the CASTRIP®* process, however, their mechanical property performance has yet to be fully evaluated. This study compared the mechanical properties and edge formability of UCS steel produced by the CASTRIP process to steel produced by conventional hot rolled (HR) and cold rolled and continuously annealed (CR & CA) process routes. The results revealed an apparent paradox, where recent UCS steel produced by the CASTRIP process was shown to have lower total tensile elongation values, yet higher edge formability than products manufactured by the conventional process routes. The discrepancy was largely attributable to the influence of acicular ferrite microstructure on steel plasticity. Acicular ferrite decreased macro-plasticity by reducing the contribution of yield point elongation (lower volume fraction of pro-eutectoid ferrite) and post uniform elongation (strain localisation to softer pro-eutectoid ferrite) components of the total tensile elongation value. Conversely, the high homogeneity of the acicular ferrite microstructure enhanced micro-plasticity of the UCS steel produced by improving resistance to void initiation and propagation during forming. This study also showed that plastic anisotropy can significantly influence the edge formability of low-carbon sheet steel, with failure occurring along the direction where the resistance to through thickness thinning was the least.* CASTRIP is a registered trademark of Castrip LLC