Hot-rolled Plate Research Articles

Research on the temperature field model of plate hot rolling process based on CUDA

The current temperature field model of plate rolling process is generally based on CPU programming, due to the influence of computer performance, the accuracy and speed of the model can not be improved at the same time. To solve this problem, this paper studies the temperature field model with particle swarm optimization to modify the heat transfer coefficients, and the parallel program of this model is written under CUDA architecture, on premise of ensuring the accuracy of the model, the computation speed of the model is improved. To get the best acceleration, this paper analyzes the factors affecting GPU performance, the accuracy and speed of the temperature field model before and after modification are compared under the best acceleration configuration. Final temperature field model calculation error reduced to an average of 15.57 °C, better than the model based on the empirical formula, the computing speed is also improved, which is 1.78 times that of CPU.

Temperature field modeling of the plate during hot rolling based on inverse heat conduction problem

In the established temperature field model of plate hot rolling process, the heat transfer coefficients of each stage are solved by empirical formula, but due to the complexity of the production environment, temperature field models tend to be less accurate. In order to solve this problem, this paper designs a rolling experiment, collects the actual temperature data, and combines with genetic algorithm, simulated annealing algorithm and particle swarm optimization algorithm to correct the heat transfer coefficients of air-cooling zone, and the three algorithms are compared. Finally, the particle swarm algorithm is selected to establish the temperature field model of the hot rolling process. The average error of the final temperature field model calculation is within 14°C.

Microstructure characteristics and properties of yttrium-bearing 9Cr ferritic-martensitic steel cladding tubes

Thin wall cladding tubes of yttrium-bearing 9Cr ferritic-martensitic steel have been fabricated by cold-rolling process, with the final dimensions of 6 mm outer diameter, 0.5 mm thickness and 3 m length. The changes of microstructure of hot-rolled plate, forged rod and the final tubes were attributed to the cold-rolling process and the intermediate heat treatment. Mechanical properties were tested from room temperature to 600 °C. The final tubes showed the strength level between the traditional ferritic-martensitic steel and the metallurgy alloyed oxide dispersion strengthened steel. It was also found that the degradation of ductility at 400 °C was related to the dynamic strain ageing (DSA) effect. At last, ultra-sound test, flattening test and flaring test were carried out to evaluated the qualities of the final tubes.

Study on cold-formed and hot rolled steel composite panel system

This study on lightweight built-up composite panel comprises of cold-formed profiled steel sheet (CFPSS) built-up with a hot-rolled steel plate (HRSP) connected by bolts. The space between the CFPSS and HRSP was filled with cement mortar as an infill material to study the effect of the composite system's strength and failure behaviour. The testing was carried with eighteen medium scale composite panels under three-point bending tests in two phases. Phase I specimens was fabricated from a single CFPSS and phase II specimens using double (nested) CFPSS, at the bottom. Other parameters include the length of the specimen (700 mm, 1200 mm and 1700 mm) and bolt spacing along the length (L/4, L/6 and L/8). The experimental data were analysed based on idealised load-deflection plots. The results indicate that the shorter and longer length mortar filled specimens experienced higher ultimate load and initial stiffness than the without mortar infill specimens in both the phases. However, infilled mortar specimens in moderate length did not show considerable improvement in ultimate load and initial stiffness values in both the phases. The phase II specimens experienced higher load and ductility in post-debonding failure regime compared to the phase I specimens. Most of the specimens exhibited tearing of CFPSS as a mode of failure at ultimate load. The modified Newmark's analytical expressions using equivalent area method for infilled mortar were derived up to the elastic limit to determine the deflection. The analytical results are in good agreement with the experimental results for both the phases.

The effect of contraction twins and shear bands on the texture evolution during isothermal annealing and its effect on mechanical properties of AZ31 magnesium alloys

Cold-rolling and subsequent annealing were conducted on the commercial AZ31 hot-rolled plates with small (∼5 μm) and large (∼50 μm) grains. After cold-rolling, plenty of shear bands and contraction twins formed in the small grain sample (SG sample) and large grain sample (LG sample), respectively. During annealing, recrystallization firstly occurred in the shear bands and contraction twins due to the local strain concentration. The inclined basal texture with double poles in the cold-rolled SG sample transformed to a strong basal texture after annealing at 500 °C, while the strong basal texture in the cold-rolled LG sample was weakened by the twins related recrystallization. In compression test, the volume fraction of grains favoring for basal slip in the annealed LG sample was much higher than the annealed SG sample, this induced a lower yield strength and higher failure strain in the annealed LG sample. The texture variation also had great effect on the anisotropy and strain hardening behavior.

Centerline inhomogeneity of flat products

Defect free casting requires an excellent accordance between steel properties being cast and the technological parameters, especially from the aspect of inner quality and homogeneity of cast products. Typical serious defects of cast slabs is the centerline segregation (CLS). The centerline segregation in slabs develops in a very complicated way, the main factors influencing the CLS pattern are the macrosegregation and the shrinkage of solidifying melt in the mushy area. The centerline section of the slab can be characterized by different chemical composition compared to the average composition and it can contain shrinkage holes, discontinuities and inclusions. In the hot rolling process the complex shape of interdendritic holes will be modified depending on the strain applied. In chemical composition the difference remains and it can be identified even after the soaking period (over 1050 °C). As an example, the center part of an St52 grade hot rolled heavy plates and strips containing CLS can be characterized by a carbon content of 0,3-0,5 wt% and manganese content of 1,7-1,9 wt%. The segregation level – including the carbon content – can hardly be decreased by post heat treatment or annealing.

Effect of quench and temper on hardness and wear of HRP steel (armor steel candidate)

The need for quenched and tempered steel increased, especially for the manufacture of the combat vehicle components. This steel is classified as high-strength and hardness and is bullet-resistant steel (armor steel). Maintaining the stability of steel hardness is very important because the quality standard for armor steel is hardness. High hardness causes brittleness increase, and tempers are needed to reduce it (residual stress is relieved by temper). Austenite temperature and temper affect steel hardness and wear resistance of quenched and tempered steel. To obtain hardness and wear due to the influence of quench and temper on hot rolled plate steel as the armor steel candidate. The material used in this research is hot rolled plate steel made in Indonesia with a carbon content of 0.29 %. The method used is heating the material to 900 °C, 885 °C and 870 °C (held for 45, 30 and 15 minutes) and cooling in water and quenched steel is produced. Quenched steel is heated to 150 °C (held for 45, 30 and 15 minutes) and cooled in atmospheric air. Optimum heat treatment parameters, the Taguchi and ANOVA methods were used. From the parameters and level of heat treatment chosen, the number of specimens needed can be known. The parameter of heat treatment has a strong influence on hardness, and ANOVA can obtain wear. Optimum hardness and wear are 566.48 HVN (±532 BHN) and 2.01×10 −9 mm 2 /kg, respectively. Both are influenced by austenite and temper temperature.

Testing, numerical modelling and design of S690 high strength steel welded I-section stub columns

This paper describes a comprehensive testing and numerical simulation investigation into the material properties, membrane residual stresses and compression capacities of S690 high strength steel welded I-section stub columns. The testing programme was performed on eight welded I-sections fabricated from 5 mm thick S700MC high strength steel hot-rolled plates by means of gas metal arc welding, and included material tensile coupon tests, membrane residual stress measurements, initial local geometric imperfection measurements, and sixteen concentrically loaded stub column tests. A membrane residual stress distribution model for S690 high strength steel welded I-sections was firstly proposed, based on the experimentally measured results. In conjunction with the structural testing, a numerical modelling study was carried out, in which finite element models were initially developed and validated against the experimental results, and afterwards employed to conduct parametric studies, aiming at generating further structural performance data over a broader range of cross-section sizes. The obtained experimental and numerical data were used to evaluate the accuracy of the slenderness limits (for classifications of plate elements and cross-sections) and design rules for S690 high strength steel welded I-section stub columns, as set out in the European, American and Australian standards. The results of the evaluation revealed that the codified slenderness limits are accurate for the plate element and cross-section classifications of S690 welded I-sections in compression, and the established local buckling design provisions in the considered three codes result in precise and consistent cross-section compression resistance predictions for both non-slender and slender S690 welded I-section stub columns.

Utilizing inclusion data in characterization of oxide-sulfide stringers in hot-rolled plates

The targets of this study were to determine the effect of vertical location and the composition of inclusions to the occurrence of oxide–sulfide stringers, and to determine the calcium aluminate phases most prone to form stringers during hot rolling of aluminium killed, calcium treated steel. The phases present in the inclusions have a significant effect on the deformation of inclusions during hot rolling, and consequently, on mechanical properties of the steel. A MATLAB script is utilized to identify and locate detrimental stringers from the hot rolled plates. Inclusion analysis data gathered with a scanning electron microscope and exported from IncaFeature software is analyzed. The following properties are presented for each stringer: the number of inclusions and length of stringer, phase fractions and compositions, and the composition of the unfragmented inclusion before hot rolling. According to the results, the longest stringers have total lengths over 200 µm, with almost 20 inclusions. The overall composition of the longest stringers is between C12A7 and C3A calcium aluminates with minor MgO contents. The diameters of the unfragmented inclusions in the slabs, forming stringers during hot rolling, were estimated to be around 20 µm for the longest stringers. From the dataset, plenty of CaO–CaS stringers were also characterized, obviously a result of excess calcium treatment.

Microstructural Evolution, Precipitation and Mechanical Properties of 27Cr-4Mo-2Ni Super-Ferritic Stainless Steels

Good mechanical properties and excellent pitting corrosion resistance for 0.8 mm-thick 27Cr-4Mo-2Ni super-ferritic stainless steels produced by one-stage cold rolling or two-stage cold rolling together with intermediate annealing processes are achieved. The microstructural evolution, precipitation and their effects on mechanical properties and corrosion resistance are investigated in terms of optical microscopy, scanning electron microscopy, electron backscattered diffraction pattern and transmission electron microscopy. The results demonstrated that the as-received hot-rolled plates consist of single ferrite grains characterized by α-fiber and γ-fiber orientations. A few Laves phases close to Nb(C, N) are formed in the recrystallized sheets solution-treated at 1050°C. After cold-rolling and finally annealing, fine recrystallized grains characterized by weaken γ-fiber orientation, are accomplished. The formation of Laves phases near the spherical Nb(C, N) makes large Nb(C, N) particles change into small granules. Corrosion resistance is more sensitive to Laves phases than mechanical properties. Small grain size improves strength and ductility, while it has a negative influence on resistance to pitting corrosion. Finer grains and a few more Laves phases are gained in steels processed by a one-stage cold-rolling process. The percentage elongation, yield strength (0.2% proof stress), ultimate tensile strength and average corrosion rate of final sheets produced by a one-stage cold-rolling process are 27.3%, 520 MPa, 641 MPa and 0.033 mm/a, respectively, and the values for two-stage cold-rolling process are 24.4%, 494 MPa, 610 MPa and 0.022 mm/a, respectively.

Interface formation and bonding mechanisms of hot-rolled stainless steel clad plate

Since the 1980s, vacuum hot rolling has been developed to fabricate the stainless steel clad plates by the Iron and Steel Institute of Japan. Herein, hot rolling is a widely used solid-state bonding process to join the carbon steel substrate and stainless steel cladding. In this paper, we provide a brief overview of the vacuum hot rolling process and effective parameters on the interface characteristics and shear strength of stainless steel clad plate. The effects of surface preparation condition, atmosphere condition, vacuum degree, rolling temperature, rolling reduction ratio, interlayer, heat treatment on the microstructure, interface characteristics and mechanical properties of stainless steel clad plate have been analyzed in detail. It is shown that the interface transition zone is formed due to the carbon diffusion, and the strong interface bonding is attributed to the sufficient alloy elements diffusion of Fe, Cr and Ni. Moreover, the interface shear strength and toughness are also affected by interfacial precipitation phase and multiple oxides. Finally, the present work concluded the bonding mechanism of hot-rolled stainless steel clad based on the oxide film theory, diffusion theory, recrystallization theory and three stage theory.

Influence of metallurgical texture on the abrasive wear of hot-rolled wear resistant carbon steels

Hot-rolled wear resistant carbon steel sheets are commonly applied in mining equipment as abrasive wear-resistant material for front loaders, chutes, etc. The rolling process can induce metallurgical texture in the form of alternating bands of ferrite and pearlite known as "banding" which affect the mechanical properties of the material. The goal of this work was to verify the impact of metallurgical texture on the abrasion resistance of hot-rolled wear resistant carbon steels. SEM images of the field specimens showed that the prevailing wear mechanism was parallel scratches. This wear mechanism was replicated in the laboratory using a dry sand-rubber wheel wear tester. The particle size used in the abrasive wear test (0.15–0.30 mm) was defined by the topographical analysis of the field sample. In addition, linear scratch tests were conducted to determine the specific scratch energy. The block specimens used in the abrasion wear tests were cut from hot rolled plates with and without metallurgical texture taking into account the rolling direction. Metallographic analysis of these samples showed an anisotropic microstructure related to the lateral and transversal surfaces of the plates. The wear rate of the lateral surface was up to 40% lower than that of the upper surface. This result was attributed to the presence of metallurgical texture that increased hardness. In addition, the wear rate presented a linear relationship to the scratch specific energy. In this case, samples without metallurgical texture were more difficult to scratch. The analysis of the specific energy and wear rate parameters clearly showed the anisotropy of the samples presenting metallurgical texture, which corresponded to the highest abrasive wear rate.

Dynamic Phase Transformation Behavior of a Nb-microalloyed Steel during Roughing Passes at Temperatures above the Ae3

A five-pass torsion simulation of the roughing passes applied during hot plate rolling was performed in the single-phase austenite region of a Nb-microalloyed steel under continuous cooling conditions. The deformation temperatures were approximately half-way between the Ae3 and the delta ferrite formation temperature (i.e., 250 °C above the Ae3) in which the free energy difference of austenite and ferrite is at maximum. The microstructures in-between passes were analyzed to characterize and quantify the occurrence of deformation-induced dynamic phase transformation. It was observed that about 7% of austenite transforms into ferrite right after the final pass. The results are consistent with the calculated critical strains and driving forces which indicate that dynamic transformation (DT) can take place at any temperature above the Ae3. This mechanism occurs even with the presence of high Nb in the material, which is known to retard and hinder the occurrence of DT by means of pinning and solute drag effects. The calculated cooling rate during quenching and the time–temperature–transformation curves of the present material further verified the existence of dynamically transformed ferrite.

Microstructure and Tensile Elongation Enhancement of 1.6 wt% B stainless Steel Plates Fabricated by Composite Rolling

A 3‐layered composite plate is innovatively fabricated via composite rolling of 1.6 wt% B stainless steel surrounded by two layers of boron‐free steels. The tensile properties of composite and non‐composite plates are comparatively tested and analyzed. Besides, the microstructure evolution of the investigated plates is characterized in detail. It is found that the composite specimens exhibit higher tensile elongation comparing with that of non‐composite specimens. Specifically, the engineering strain of the 1050 °C × 30 min solution‐treated specimens reaches to 12.5 ± 0.8% which is 2.5–3.0 times as high as that of non‐composite specimens. In addition, the as‐cast lamellar borides break into bar‐shaped structures in hot rolled plates, however, their morphology and distribution hardly change after solution treatment. Besides, the transition regions between the core and clad layers are formed and characterized by medium‐sized recrystallized grains and fine borides in the solution‐treated composite specimens. The enhancement mechanism of tensile elongation is mainly analyzed in term of the geometrical restriction of necking in the composite plate during tensile deformation. This paper provides a promising method to effectively enhance the tensile fracture elongation for these metallic materials with poor plasticity like high borated stainless steels.

Surface defect classification of steels with a new semi-supervised learning method

Defect inspection is extremely crucial to ensure the quality of steel surface. It affects not only the subsequent production, but also the quality of the end-products. However, due to the rare occurrence and appearance variations of defects, surface defect identification of steels has always been a challenging task. Recently, deep learning methods have shown outstanding performance in image classification, especially when there are enough training samples. Since most sample images of steel surface are unlabeled, a new semi-supervised learning method is proposed to classify surface defects of steels. The new method is named CAE-SGAN, as it is based on Convolutional Autoencoder (CAE) and semi-supervised Generative Adversarial Networks (SGAN). CAE-SGAN first trains a stacked CAE through massive unlabeled data. Considering the appearance variations of defects, the passthrough layer is used to help CAE extract fine-grained features. After CAE is trained, the encoder network of CAE is reserved as the feature extractor and fed into a softmax layer to form a new classifier. SGAN is introduced for semi-supervised learning to further improve the generalization ability of the new method. The classifier is trained with images collected from real production lines and images randomly generated by SGAN. Extensive experiments are carried out with samples captured from different steel production lines, and the results indicate that CAE-SGAN had yielded best performances compared with traditional methods. Especially for hot rolled plates, the classification rate is improved by around 16%.

Embrittlement Due to Excess Heat Input into Friction Stir Processed 7075 Alloy.

The grain size of high strength 7075 hot-rolled aluminum plates was refined by a friction stir process (FSP) to improve their mechanical properties. The results of the tensile ductility tests, which were conducted at various tool rotational speeds, in the friction stir zone indicate significant tensile ductility loss, which even resulted in a ductile-to-brittle transition (DBT). DBT depends on the tool rotational speed. Our 1450 rpm specimens showed large data fluctuation in the tensile ductility and the location of the fracture controlled the formation of friction stir induced bands (FSIB). The crack initiation site located at FSIB was due to the tool rotational speed (1670 rpm). A higher heat-input causes the formation of FSIB, which is accompanied with micro-voids. This contributes significantly to tensile cracking within the stir zone after the application of the aging treatment. This investigation aimed to determine the dominant factor causing tensile ductility loss at the stir zone, which is the major restriction preventing further applications.

High-Precision Section Control Technology for High-Strength Yoke Steel Strip

The hot-rolled yoke steel plate is used in the manufacture of motor rotors for core components of large generators, which is required to ensure high strength and high-precision plate profile, especially the control of the thickness difference. High-precision cross-section control technology from rough rolling to finishing rolling for high-strength yoke steel is designed. First, through the varying contact backup roll technology and optimization of load distribution in the roughing stand, the profile of transfer bar is improved, which provides the basis for the strip shape control in the finishing mills. Secondly, the approximate rectangular section of a hot strip is obtained by high-precision shape setting and control model for finishing rolling, symmetrical variable taper work roll technology and smart shifting technology in the downstream stands. These methods solve the problem that the shape of the high-strength strip is difficult to control, and significantly enhance the shape regulation ability and control accuracy of the hot-rolled yoke. In addition, this technology has been applied to hot rolling mills with remarkable results and economic benefits.

Microstructure and Mechanical Properties of Ferritic Rolling Low Carbon Steel

The microstructure and mechanical properties of ferritic rolling low carbon steel are investigated by metallurgical microscope, thermal simulation testing machine, electron backscattered diffraction (EBSD) and universal tensile test machine. The finishing temperature of the transition from austenite to ferrite changed from 680°C to740 °C with different cooling rates, which was obvious lower than that of the interstitial free steel. The deformation stress of low carbon steel was larger than that of interstitial free steel. In addition, the deformation stress of the low carbon steel was more sensitive to the deformation rate than that of the interstitial free steel. The microstructure at the surface layer of the hot rolling plate was composed of fully recrystallized grains while the microstructure in the center was composed of fibrous deformed grains. The ferritic rolling low carbon steel has lower yield ratio and higher elongation than that of normal rolling low carbon steel.

Modeling and Investigation of the Process of Hot Rolling of Large-Sized Ingots from Aluminum Alloy of the Al-Mg System, Economically Alloyed by Scandium

Results of researches of process of hot rolling of ingots from the experimental aluminum alloy which is economically alloyed by scandium are given. The computer model of process of hot rolling with the use of which the straining, temperature and speed processing modes conditions is calculated and also power parameters of processing is calculated in applied to industrial conditions. It is shown that the use in the model of a certain shape of the ingot faces (Petrov's lock) and indirect rolling action in the edging stand is made it possible to reduce the likelihood of the formation and further development of micro cracks on the edges of rolled metal. The adequacy of results of modeling was confirmed by carrying out pilot-industrial tests when rolling large-size ingots from the experimental alloy and obtaining batches of hot-rolled plates and sheets of various sizes. The tensile test was used to study deformed samples after rolling and samples obtained on five regimes of heat treatment with varying heating temperatures of 300, 350 and 380 oС and holding time in the furnace for 1 and 3 hours. The results of the studies on samples of hot-rolled sheets 10 mm thick showed that, compared with the initial state, the strength characteristics of the metal after heat treatment are reduced by an average of 12-20%, and plastic characteristics increase by 50-65%. In this case, the heat treatment regimes 1 - 3 give a good ratio of the ductility and plastic properties of the metal.

Thixoforming of Semisolid Slurry with High Fraction Solid Fabricated by Partial Melting of Commerical Wrought Aluminum Alloys

Semisolid slurries of four wrought alloys were fabricated via partial melting of commerical wrought aluminum alloy. Thixoforming experiments of four typical parts were performed. The results showed that a large amount of equiaxed grains before soaking in semisolid state were created due to recrystallization occurred in the continuous heating from room temperature to a given temperature above recrystallization temperature. It provides a desirable microstructure to form spheroidal grains during the next soaking process in semisolid state. The microstructure of the 2A12,7A04 and 7075 semisolid slurry consisted of fine and spheroidal grains. The elongation of the thixoformed parts were higher those of the hot-rolled plate. The UTS of the thixoformed parts were close or ever higher than those of the hot-rolled plate. Although the grain size and roundness of the 5A06 semisolid slurry are not very desirable, the mechanical properties of the thixoformed part are close or ever than those of the hot-rolled plate. The high mechanical properties of the thixoformed parts further confirmed the feasibility of short-process thixoforming route