비만아 부모의 돌봄 경험: q 방법론

An artificial neural network (ANN) model was developed to predict the tensile properties as a function of alloying element and microstructural factor of ferrite-pearlite steels. The input parameters of the model were composed of alloying elements (Mn, Si, Al, Nb, Ti, and V) and microstructural factors (pearlite fraction, ferrite grain size, interlamellar spacing, and cementite thickness), while the output parameters of the model were yield strength and tensile strength. Although the ferrite-pearlite steels have complex relationships among the alloying elements, microstructural factors, and tensile properties, the ANN model predictions were found to be more accurate with experimental results than the existing equation model. In the present study the individual effect of input parameters on the tensile properties was quantitatively estimated with the help of the average index of the relative importance for alloying elements as well as microstructural factors. The ANN model attempted from the metallurgical points of view is expected to be useful for designing new steels having required mechanical properties.

Artificial Neural Network for Modeling the Tensile Properties of Ferrite-Pearlite Steels: Relative Importance of Alloying Elements and Microstructural Factors

In this work, actual production data from a rolling mill has been analyzed through the concept of Self Organizing Maps (SOM) for understanding various correlations and patterns in the production data set. SOM is an unsupervised machine learning approach, thus all the process parameters and desired properties can be analyzed simultaneously. Yield Strength (YS), Ultimate tensile strength (UTS) and elongation percent properties have been chosen as the metrics on the basis of which the coil can be utilized for a specific application. This production data contains many missing parameters. Additionally, parameters like different carbon equivalents (CE) and grain size of ferrite GS are dependent of other input parameters (composition of the coils, processing temperature, etc). Therefore, it is important to understand correlations between compositions, processing parameters, structure (GS), and macroscopic properties. Through SOM approach, several correlations have been determined in the production data set which are in accordance with the findings reported in the open literature. SOM predictions have been tabulated. These predictions will be helpful in achieving the optimum properties for various AHSS grades in the industry. 

AHSS applications in Industry 4.0: Determination of optimum processing parameters during coiling process through unsupervised machine learning approach

The Kanbara reactor (KR) process is a mechanical stirring method that reacts hot metal with desulfurization flux; it is a widely implemented desulfurization method in contemporary steel production. This study aimed to develop a new impeller profile for improving the desulfurization efficiency of the KR process. We implemented operational data analysis, a computational fluid dynamics simulation based on the operational data and performed testing and analysis with impeller models on-site a production facility. Operational data from the production facility was gathered over a 3-year period. Seven impeller models with varying impeller blade width (top and bottom), height, inclination, and curvature (curved, straight, and combination) were simulated. The results were analyzed to determine the optimal conditions. A new impeller design was selected for on-site operational testing to investigate the in situ desulfurization efficiency over 350 charges, and the results corroborated the predictions by the numerical simulations. It is expected that the proposed process modification can be successfully used for improving industrial desulfurization efficiency.

Improvement of Desulfurization Efficiency via Numerical Simulation Analysis of Transport Phenomena of Kanbara Reactor Process

Flattened plates often show the lower or higher yield strength than initial leveled plates because tensile and compressive strains are repeatedly experienced at outer and inner walls during the pipe-forming and flattening, but reasons for the yield-strength variation after the pipe-forming are not sufficiently verified yet. In this study, ten line-pipe steels were fabricated by controlling alloying elements and finish rolling temperatures (FRTs), and the yield strength of pipe-flattened steel plates was predicted by using cyclic simulation tests, based on competing contributions of Bauschinger effect (BE) and strain hardening (SH) effect quantified from yield drop (YD) and yield rise (YR) parameters, respectively. High-FRT-treated steels (H steels) showed the lower BE and the higher SH than low-FRT-treated steels (L steels), thereby resulting in the smaller yield-strength reduction. This lower BE in the H steels was caused by the lower total boundary density, while the higher SH was caused by the higher fraction of granular bainite. According to the SH analyses between the YR parameters obtained from cyclic simulation tests and the yield ratios obtained from ordinary tensile tests, the decrease in yield-strength reduction with decreasing yield ratio was not attributed to the increase in ordinary tensile SH but to the increase in YR parameter.

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Effects of finish rolling temperature and yield ratio on variations in yield strength after pipe-forming of API-X65 line-pipe steels.

Oil country tubular goods (OCTG) steels with a low yield ratio (yield strength/tensile strength) and excellent impact toughness have recently been demanded to ensure mining performance and safety. From this viewpoint, the optimization of the manufacturing conditions is important because they influence the microstructure and mechanical properties of the steels; in particular, in the case of OCTG steels with carbon contents greater than 0.2 wt%, the finishing mill temperature (FMT) and coiling temperature (CT) strongly affect the microstructure of the final products, which are generally composed of ferrite and pearlite phases. In this study, 0.39C-0.23Si-1.56Mn-0.11Cr steel plates were fabricated under various FMT and CT conditions and their yield strength, tensile strength, and impact energy were investigated. In addition, pipes with diameters of 244 and 508 mm were manufactured via an electric resistance welding method using two of these strips fabricated under two different optimized conditions [(1) FMT = 880 °C and CT = 630 °C and (2) FMT = 800 °C and CT = 690 °C] to analyze the change in mechanical properties induced by the work-hardening effect during the piping process. The results revealed that the FMT and CT are closely related to the volume fraction of the ferrite phase, the grain size and lamellar spacing of the pearlite phase, and the tensile and impact properties of the steel strips; the variations in the microstructure and mechanical properties with the FMT and CT were also discussed in detail.

Effect of Rolling and Coiling Temperatures on Microstructure and Mechanical Properties of Medium-Carbon Pipeline Steel

In this study, variations in the tensile behavior and Bauschinger effect with the applied loading direction in an American Petroleum Institute (API) X70 steel sheet are investigated by conducting tensile and strain-reversal tests along the rolling direction (RD), the transverse direction (TD), and a direction inclined at an angle of 45° from the RD to the TD (45D). The microstructure of the rolled steel sheet consists of polygonal ferrite and acicular ferrite, and it has a rolling texture that is typical of body-centered cubic metal materials. During tensile deformation, the yield-point phenomenon, which involves occurrence of discontinuous yielding and development of Luders strain, occurs in all the loading directions. However, the material shows a lower yield strength and larger Luders strain under tension along the 45D than under tension along the RD and TD. The Bauschinger effect, which occurs under subsequent reversal tension after compression, is also more pronounced under loading along the 45D. These results are attributed to the fact that dislocation slips are activated more easily under deformation along the 45D, which is evidenced by the lower Taylor factor and larger number of active slip systems under loading along the 45D. Furthermore, results of viscoplastic self-consistent simulation reveal that along all the directions, the {112}   slip system is vigorously activated during tensile and compressive deformations and that its activation plays an important role in the deformation behavior and yield strength of the material.

Loading Direction Dependence of Yield-Point Phenomenon and Bauschinger Effect in API X70 Steel Sheet

In this study, the deoxidation behavior of Zr powder with the use of a Mg reductant is discussed. The original Zr powder was produced by the hydride-dehydride (HDH) method. The raw Zr powder has a thick surface oxide layer of 43 nm as well as high oxygen concentration in the inner part of the powder. The raw Zr powder carries out the reduction reaction with the Mg agent, which maintains self-propagating high-temperature synthesis (SHS) by releasing significant exothermic heat, thereby decreasing the oxygen content. The surface oxide layer of the deoxidized Zr powder is thinner than that of the raw Zr powder, as observed by transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). Furthermore, the oxygen atoms in the inner part of the Zr powder are easily released by a bcc structure providing more active migration of interstitial atoms induced by the open structure at high temperature, and the emitted oxygen atoms readily react with the Mg agent. The lattice parameters of the deoxidized Zr powders, therefore, are decreased with the reduction of oxygen content in comparison with the raw Zr powder because of shrinkage by the decrease of the excess oxygen interstitial atoms. These results are consistent with the observation that the oxygen content in the raw and deoxidized Zr powder was reduced from 0.595 to 0.338 wt pct due to the decreased surface oxide layer and oxygen content in the inner part of the Zr powder, respectively. It is, thus, confirmed that the Mg agent is capable of playing an important role in the deoxidation behavior in Zr powder to obtain high-purity Zr powder.

Hyung Lae Kim

Papers

Effect of Rolling and Coiling Temperatures on Microstructure and Mechanical Properties of Medium-Carbon Pipeline Steel

Loading Direction Dependence of Yield-Point Phenomenon and Bauschinger Effect in API X70 Steel Sheet

Deoxidation Behavior of Zr Powder Manufactured by Using Self-Propagating High-Temperature Synthesis with Mg Reducing Agent