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

Tae‑Woon Hong,Sang‑In Lee,Jae‑Hyeok Shim,Myoung‑Gyu Lee,Joonho Lee,Byoungchul Hwang 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

An artificial neural network (ANN) model was developed to predict the tensile properties as a function of alloying elementand 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 cementitethickness), while the output parameters of the model were yield strength and tensile strength. Although the ferrite-pearlitesteels have complex relationships among the alloying elements, microstructural factors, and tensile properties, the ANNmodel predictions were found to be more accurate with experimental results than the existing equation model. In the presentstudy the individual effect of input parameters on the tensile properties was quantitatively estimated with the help of theaverage index of the relative importance for alloying elements as well as microstructural factors. The ANN model attemptedfrom the metallurgical points of view is expected to be useful for designing new steels having required mechanical properties.

Mn 및 V 함량이 다른 페라이트-펄라이트 조직강의 강도와 변형능에 미치는 미세조직 인자의 영향

홍태운,이상인,심재혁,이준호,이명규,황병철,Hong, Tae-Woon,Lee, Sang-In,Shim, Jae-Hyeok,Lee, Junho,Lee, Myoung-Gyu,Hwang, Byoungchul 한국재료학회 2018 한국재료학회지 Vol.28 No.10

This study examines the effect of microstructural factors on the strength and deformability of ferrite-pearlite steels. Six kinds of ferrite-pearlite steel specimens are fabricated with the addition of different amounst of Mn and V and with varying the isothermal transformation temperature. The Mn steel specimen with a highest Mn content has the highest pearlite volume fraction because Mn addition inhibits the formation of ferrite. The V steel specimen with a highest V content has the finest ferrite grain size and lowest pearlite volume fraction because a large amount of ferrite forms in fine austenite grain boundaries that are generated by the pinning effect of many VC precipitates. On the other hand, the room-temperature tensile test results show that the V steel specimen has a longer yield point elongation than other specimens due to the highest ferrite volume fraction. The V specimen has the highest yield strength because of a larger amount of VC precipitates and grain refinement strengthening, while the Mn specimen has the highest tensile strength because the highest pearlite volume fraction largely enhances work hardening. Furthermore, the tensile strength increases with a higher transformation temperature because increasing the precipitate fraction with a higher transformation temperature improves work hardening. The results reveal that an increasing transformation temperature decreases the yield ratio. Meanwhile, the yield ratio decreases with an increasing ferrite grain size because ferrite grain size refinement largely increases the yield strength. However, the uniform elongation shows no significant changes of the microstructural factors.

페라이트-펄라이트 조직 아공석강의 강도와 연성에 미치는 미세조직적 인자의 영향

이상인 ( Sang-in Lee ),강준영 ( Jun-young Kang ),이상윤 ( Sang-yoon Lee ),황병철 ( Byoung Chul Hwang ) 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.1

This article presents a study on the tensile properties of hypoeutectoid steels with different ferritepearlite microstructures. Nine kinds of hypoeutectoid steel specimens were fabricated by varying carbon content and isothermal transformation temperature. The microstructural factors such as ferrite & pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured and then tensile tests were carried out on the specimens in order to investigate the correlation of the microstructural factors with strength and ductility. The pearlite volume fraction usually increased with decreasing transformation temperature, while the pearlite interlamellar spacing and cementite thickness decreased mostly with decreasing transformation temperature, irrespective of carbon content. The tensile test results showed that the yield and tensile strengths of all the steel specimens increased and their ductility was also improved as the transformation temperature decreased. For the steel specimens investigated, the difference in the transformation temperature dependence of strength and ductility could be explained by the fact that the variation in pearlite fraction with transformation temperature noticeably affected various microstructural factors such as pearlite interlamellar spacing and cementite thickness associated with pearlite fracture mechanism such as void initiation, cementite necking, and cracking. (Received December 17, 2015; Revised December 24, 2015; Accepted December 30, 2015)

Measurement of the Dynamic Mechanical Properties of High-strength Steel Using Wave Propagation Characteristics

박정원,김도형,김학성,박준홍,유지우 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12

The dynamic mechanical properties of different high-strength steels were measured and comparedbased on their respective microstructures. Beam-shaped test specimens were excited using anelectric shaker while vibration responses were measured using a non-contact laser sensor. Flexuralwave propagation was analyzed to precisely determine material damping. Measured propertieswere compared to those of carbon steels. In addition, the effects of grain size determined by opticalmicrographs on the dynamic properties were investigated. The influence of the tensile strength onthe measured properties was analyzed. The high-strength steels exhibited smaller damping with asimilar Young’s modulus compared to carbon steels, although the tensile strength was much greater.

페라이트-펄라이트 조직 아공석강의 상온 및 저온 충격 인성에 미치는 미세조직적 인자의 영향

이승용,정상우,황병철,Lee, Seung-Yong,Jeong, Sang-Woo,Hwang, Byoungchul 한국재료학회 2015 한국재료학회지 Vol.25 No.11

This paper presents a study on the room- and low-temperature impact toughness of hypoeutectoid steels with ferrite-pearlite structures. Six kinds of hypoeutectoid steel specimens were fabricated by varying the carbon content and austenitizing temperature to investigate the effect of microstructural factors such as pearlite volume fraction, interlamellar spacing, and cementite thickness on the impact toughness. The pearlite volume fraction usually increased with increasing carbon content and austenitizing temperature, while the pearlite interlamellar spacing and cementite thickness mostly decreased with increasing carbon content and austenitizing temperature. The 30C steel with medium pearlite volume fraction and higher manganese content, on the other hand, even though it had a higher volume fraction of pearlite than did the 20C steel, showed a better low-temperature toughness due to its having the lowest ductile-brittle transition temperature. This is because various microstructural factors in addition to the pearlite volume fraction largely affect the ductile-brittle transition temperature and low-temperature toughness of hypoeutectoid steels with ferrite-pearlite structure. In order to improve the room- and low-temperature impact toughness of hypoeutectoid steels with different ferrite-pearlite structures, therefore, more systematic studies are required to understand the effects of various microstructural factors on impact toughness, with a viewpoint of ductile-brittle transition temperature.

다중회귀분석을 이용한 페라이트-펄라이트 조직 아공석강의 충격인성에 미치는 미세조직적 인자의 민감도 해석

이승용 ( Seung-yong Lee ),이상인 ( Sang-in Lee ),황병철 ( Byoung Chul Hwang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9

In this study, the effect of microstructural factors on the impact toughness of hypoeutectoid steels with ferrite-pearlite structure was quantitatively investigated using multiple regression analysis. Microstructural analysis results showed that the pearlite fraction increased with increasing austenitizing temperature and decreasing transformation temperature which substantially decreased the pearlite interlamellar spacing and cementite thickness depending on carbon content. The impact toughness of hypoeutectoid steels usually increased as interlamellar spacing or cementite thickness decreased, although the impact toughness was largely associated with pearlite fraction. Based on these results, multiple regression analysis was performed to understand the individual effect of pearlite fraction, interlamellar spacing, and cementite thickness on the impact toughness. The regression analysis results revealed that pearlite fraction significantly affected impact toughness at room temperature, while cementite thickness did at low temperature.(Received March 2, 2016; Accepted April 8, 2016)

A sandpaper-inspired flexible and stretchable resistive sensor for pressure and strain measurement

Chhetry, Ashok,Das, Partha Sarati,Yoon, Hyosang,Park, Jae Yeong Elsevier 2018 Organic Electronics Vol.62 No.-

<P><B>Abstract</B></P> <P>We report very small shape-factored microstructures developed via a simple and cost-effective approach, enabling a high degree of sensitivity in a low-pressure regime (<2.67 kPa). The surface intertexture on the counter electrode and irregular microstructures with a high surface area developed on the base electrode help reduce the shape factor, allowing the device to deform more easily under pressure. Moreover, the irregular patterns with higher unloaded surface area strengthen the tunneling current sufficiently at low pressure. Furthermore, the fabricated features enable the device to perform as a flexible and stretchable sensing mechanism; the outstanding performance was achieved through a novel and feasible fabrication from a low-surface-energy template without surfactant coating. An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP>, a fast response time of 0.49 s and stability over 6000 cycles were achieved. Finally, the sensing capability was examined by gentle finger tapping and arbitrary movement of the sensor placed on the forefinger. The current platform can be a key component for diverse applications such as muscle movement, speech detection, and health monitoring systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flexible and stretchable resistive sensor for pressure and strain sensing capability. </LI> <LI> Very small shape-factored microstructures were generated from sandpaper template. </LI> <LI> An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP> and stability over 6000 cycles were achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Stress-Rupture Behavior of Diffusion-Welded Alloys for Application in PCSG System

황종배,사인진,김상지 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5

Diffusion welding is one of key technologies for building printed circuit steam generator (PCSG) in small modular reactors (SMRs). Evaluation of mechanical properties, such as tensile, stress-rupture, and fatigue, of the diffusion weldment are essential to employ the PCSG at operating conditions. In this study, microstructural evaluation and stress-rupture test were carried out using diffusion-welded SS 316L and Incoloy 800H(T). The microstructure of the diffusion-welded SS 316L was featured in the grain boundary migration across the welding interfaces. These features account for the comparable stress-to-rupture values of the diffusion-welded SS 316L to the expected minimum stress-to-rupture values presented in ASME Section III. In contrast, the grain boundary migration across the interfaces was limited owing to the presence of secondary precipitates for Incoloy 800H(T). The microstructure explained the degradation of the stress-to-rupture values for diffusion-welded Incoloy 800H(T). The time-temperature dependent reduction factor of the diffusion-welded SS 316L will be covered in detail.

Li을 첨가한 $MgTiO_3$-$CaTiO_3$계 세라믹 유전체의 마이크로파 유전특성

한진우,김동영,전동석,이상석 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.3

The microwave dielectric properties and a sintering behavior of MgTiO$_3$-CaTiO$_3$ ceramics doped with Li were investigated. The main composition was fixed as 0.94MMgTiO$_3$-0.06CaTiO$_3$ and Li$_2$CO$_3$was added excessively in the range of 0~10 mol% (with reference to Li atoms) and the specimens were sintered at 1200~140$0^{\circ}C$ for 4 hours. When the amount of Li was small the quality factor and dielectric constant were reduced, while those tow properties increased if the Li amount was above 1 mol%. But if Li was overly added those dielectric properties decreased again. Li, if added in the composition range of 1.0~3.0 mol%, can increase the quality factor of MgTiO$_3$-CaTiO$_3$ ceramics. The optimum amount of Li was 1.5mol% and sinterign condition was 1275$^{\circ}C$/4hr, at which we cudl obtain following results ; dielectric constant ($\varepsilon$$_{r}$) of f20.0, quality factor(Qxf$_{0}$) of 78,000 GHz and temperature coefficient of resonant frequency($\tau$$_{f}$) of -1.6 ppm/$^{\circ}C$.>.>.>.

Pilot Plant를 이용한 600 MPa급 내진용 철근들의 제조, 미세조직과 기계적 특성 비교

홍태운,황병철,Hong, Tae-Woon,Hwang, Byoungchul 한국재료학회 2019 한국재료학회지 Vol.29 No.6

This study deals with the microstructure and tensile properties of 600 MPa-grade seismic reinforced steel bars fabricated by a pilot plant. The steel bar specimens are composed of a fully ferrite-pearlite structure because they were air-cooled after hot-rolling. The volume fraction and interlamellar spacing of the pearlite and the ferrite grain size decrease from the center region to the surface region because the surface region is more rapidly cooled than the center region. The A steel bar specimenwith a relatively high carbon content generally has a higher pearlite volume fraction and interlamellar spacing of pearlite and a finer ferrite grain size because increasing the carbon content promotes the formation of pearlite. As a result, the A steel bar specimen has a higher hardness than the B steel bar in all the regions. The hardness shows a tendency to decrease from the center region to the surface region due to the decreased pearlite volume fraction. On the other hand, the tensile-to-yield strength ratio and the tensile strength of the A steel bar specimen are higher than those of the B steel bar with a relatively low carbon content because a higher pearlite volume fraction enhances work hardening. In addition, the B steel bar specimen has higher uniform and total elongations because a lower pearlite volume fraction facilitates plastic deformation caused by dislocation slip.