Papers by Keyword: Dual Phase

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Authors: Taher El-Bitar, Eman El-Shenawy, Maha El-Meligy
Abstract: The proposed Ferrite-Bainite Dual Phase (FBDP) steel is suitable for automotive industries. The steel satisfies high specific strength (strength/weight ratio), which is positively reflected on both fuel consumption and crashing resistance.
Authors: Kai Liu, Jin Jin Zhang, Kai Ming Wu
Abstract: A high strength low alloy wear-resistant steel was quenched at 900°C and tempered at varying temperatures. The microstructures were observed utilizing optical and electron microscope. Results show that microstructures consist of predominantly martensite and lots of bainite in the as-quenched specimens. When the specimen was tempered at 250°C, no obvious change in the microstructure was observed. It has an optimized strength and elongation in this condition of heat treatment. With the increase of tempering temperature, the lath or plate of martensite were coalescenced. The strength of the steel is thus greatly reduced and the elongation was accordingly increased.
Authors: Y. Suwa, T. Matsuno, S. Hirose, N. Fujita, A. Seto
Abstract: In the present study, the effects of inclusions on the local ductility of DP steel are investigated using finite element analysis (FEA). In order to evaluate local ductility, a continuum damage mechanics (CDM) model has been incorporated into the Abaqus/Explicit® commercial finite element code. Furthermore, three-dimensional representative volume elements (RVEs) with ferrite, martensite, and inclusion phases have been used to evaluate the stress-strain response. Simulation results show that the volume fraction of the martensite as well as the difference in hardness between the ferrite and the martensite phases dominates the effect of inclusions on local ductility.
Authors: Nan Qiao Xu, Mei Li, Yi Xi Zhao, Xing Hu
Abstract: In this paper, experimental and numerical analysis is used to investigate the failure modes of dual phase steels under different loading paths. Numerical models are established for uniaxial tensile tests and stretch flanging tests. Special attention has been paid to the behavior of DP780 in stretch flanging tests with small die radius. The occurrence of shear fracture is identified by comparing numerical simulation results with test data. The study suggests that traditional theory of localized necking is feasible for DP780 under uniaxial tensile condition but invalid when it is undergoing stretch flanging tests with small radius.
Authors: Mohamed A. Gebril, M.S. Aldlemey, Farag I. Haider
Abstract: In this work, the investigations were carried out to study the effect of heat treatment at dual phase of austenite and ferrite on mechanical properties , microstructure and corrosion rate of low alloyed medium carbon steel. The specimens were divided into five groups, first group, specimens were heated to the duel phase region at temperature of 740°C soaked for 30 minutes and quenched in water. The second group, The specimens were heated to 740°C soaked for 30 minutes and quenched in water, then tempered to 480°C soaked for 20 minutes. The third group the specimens were heated to austenizing temperature of 840°C soaked for 30 minutes and quenched in water, then the specimens reheated to the dual phase region at 740°C, soaked for 30 minutes and quenched in water, then the specimens were tempered at temperature 480°C for 30 minutes. The forth group, the specimens were heated to austenizing temperature of 840°C soaked for 30 minutes and quenched in water, this process were repeated again before the specimens were thereafter heated to the dual phase region at temperature of 740°C, soaked for 20 minutes and quenched in water, then the specimens were tempered at temperature 480°C for 20 minutes. The fifth group, the specimens were heated to austenizing temperature of 840°C soaked for 20 minutes and quenched in water, this process were repeated two times again before the specimens were thereafter heated to the dual phase region at temperature of 740°C, soaked for 20 minutes and quenched in water, then the specimens finally tempered at temperature 480°C for 20 minutes. The results proved the hardness increase after heat treatment at first and second group, at third group the highest hardness value was due to formation of martensite and ferrite, but at fourth and fifth groups hardness decreases due to appearance of carbides particles, also corrosion rate usually increases with two phase at microstructure than stable one phase, third group have less corrosion rate than fourth and fifth due to carbides particles formation which lead to more corrosion rate due to three phases presents.
Authors: Marek Vojtko, Ján Balko, Martin Fides, Liudmila Vojtkova
Abstract: The aim of this work is indentation study of local mechanical properties of Cu-22Zn-4.6Al alloy, which has significant shape memory effect after quenching from dual α + β phase region. The study was carried out on the samples with thermoelastic and non-thermoelastic martensite in the structure, which were obtained by quenching from various temperatures. A different behavior concerning mechanical properties measurements of α phase and β phase transformed to martensite after quenching from various temperatures was found out. It was observed almost no change of mechanical properties of α phase, whereas indentation hardness HIT and indentation modulus EIT raised with increasing quenching temperature. Also some serious differences were observed at indentation test of thermoelastic and non-thermoelastic martensite.
Authors: Frank Hisker, Richard Thiessen, Thomas Heller
Abstract: AHSS (Advanced High Strength Steels) combine high strength and good ductility. Their outstanding forming and work-hardening behavior predestines these steels for fabrication of strength relevant structural elements and automobile body parts. To characterize a material, not only tensile, but also hole-expansion and bending behavior are important and help predict the stretch-flange-formability. In this study, detailed analyses of the correlation between these three tests and the damage mechanisms during forming have been performed for selected steels. The results show that for AHSS one should differentiate between “local” and “global” failure. Furthermore, not only are certain materials more sensitive to local or global damage, but also various testing methods tend to provoke either local or global damage. Tensile testing provokes global failure whereas hole-expansion tends to induce local failure. A specimen fails during bending with a mixture of local and global modes. These failure modes are strongly attributed to the microstructure. DP-steels yield high elongation during tensile testing and poorer hole-expansion values. High-resolution EBSD has revealed that the microstructure of DP-steels is sensitive to localized damage, which is compensated by work-hardening around damaged regions and thus shifts the loading to un-hardened regions. This makes DP-microstructures well-suited to tensile loading but sensitive to hole-expansion. CP-steels of comparable strength show poorer tensile elongation and higher hole-expansion ratios due to a microstructure which is not sensitive to localized failure (but has limited capacity for work-hardening). The failure mode in TRIP-steels exhibits a similar character as in DP-steels, but only after the martensitic transformation of retained austenite.
Authors: C. Elgoyhen, Annick De Paepe, A. Lucas, Y. Hardy
Abstract: Nowadays, it is not evident to produce in a robust way cold rolled and annealed/galvanised high strength steels based on lean chemistries and with consistent mechanical properties over the coil length. The reasons behind this are first the low cooling rates available on the lines which require the use of a large amount of alloying elements for avoiding the unwanted phases such as the pearlite and secondly the difficult control of soaking temperature and time in a narrow range, resulting in a variable austenite content at the end of the soaking and then in a dispersion of the obtained mechanical properties. By considering high speed cooling technologies on a compact annealing/galvanizing line, this production becomes possible. After rapid heating by means of induction heating and short holding at a high soaking temperature, the strip is cooled down to an intermediate temperature, where it is held for a short period for obtaining a stable ferrite-austenite structure. Then it is rapidly cooled by means of cold water (Twice) in the case of a continuous annealing line or by the zinc quench process in the case of the galvanizing line. These rapid cooling equipments allow reaching high tensile strength levels with a significant reduction of the addition of expensive elements (Mn, Cr and Mo).
Authors: Ohjoon Kwon, Kyoo Young Lee, Gyo Sung Kim, Kwang Geun Chin
Abstract: The body design with light weight and enhanced safety is a key issue in the car industry. Corresponding to this trend, POSCO is developing various automotive steel products with advanced performance. Conventional advanced high strength steels such as DP and TRIP steels are now expanding their application since the steels exhibit higher strength and ductility than those of conventional solution and precipitation strengthened high strength steels. Efforts have been made to enhance the mechanical performance of these steels such as ductility, hole expansion ratio, deep drawability, etc. Current research is focused on development of extra- and ultra-AHSS. Extra-AHSS are designed to utilize nano-scale retained austenite embedded in fine bainite and martensite. Ultra-AHSS are designed to have austenite as the major phase, and the ductility is enhanced primarily by continuous strain hardening generated during forming. These steels including extra- and ultra-AHSS are believed to be the next generation automotive steels which will replace the existing high strength steels due to their extremely high strength and ductility combinations.
Authors: Lukasz Madej, Norbert Kwiaton, Roman Kuziak, Mateusz Sitko, Maciej Pietrzyk
Abstract: Development of fast and efficient finite element model for rolling industrial grades of two DP steels was the subject of the present paper. Basis of the finite element framework, as well as material model development stages, are presented first. Model validation with experimental measurements is shown next. Finally, selected examples of multi scale modelling including microstructure level are presented to complement presented investigation and show possibilities of future developments.
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