Papers by Keyword: TRIP Steel

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Authors: Roumen H. Petrov, Orlando León-García, Hemant Sharma, Kyoo Young Lee, S. Eric Offerman, Leo Kestens
Abstract: Texture formation during an austempering treatment of a TRIP-assisted steel was studied by in-situ texture measurements with a high energy source (synchrotron). Samples from a cold rolled sheet were subjected to a complete heat treatment cycle for TRIP steels including reheating to the intercritical (α+γ) temperature region, isothermal soaking and bainitic holding (austempering) at 400°C for 600s. At specific points of the thermal cycle {200}γ, {220}γ {222}γ, {331}γ and {200}α, {211}α and {220}α Debye rings were recorded and the corresponding incomplete pole figures were calculated. The latter were used to derive the orientation distribution functions (ODFs) of BCC and FCC phases at specific steps of the annealing process after assuming the orthotropic sample symmetry. The acquired data for the texture evolution during the α–γ–α phase transformation showed that during the reheating for intercritical annealing the gamma phase with {011} orientation is among the first to nucleate from the recrystallized α phase during heating and the Goss and Cube orientations are among the principal gamma phase components which transform to BCC phase after cooling.
Authors: Hang Thi Pham, Takeshi Iwamoto
Abstract: It is considered that fracture toughness of TRIP steel can be evaluated by means of the small punch (SP) test. However, a mechanism of improving fracture toughness in the SP test for TRIP steel under the impact condition might not be clarified through merely experimental works because the effect of strain-induced martensitic transformation (SIMT) coupled with temperature in TRIP steel becomes quite complicated at high deformation rate. Therefore, a computational simulation on the SP test for an evaluation of the mechanism is indispensable. Since the specimen in the SP test will be fractured at a certain level of deformation, it is necessary to express the fracture by incorporating damage model into constitutive equation of the material in simulation of the SP test. In the present study, a finite element analysis is performed for the SP test with a specimen made of type-304 austenitic stainless steel by an inclusion of damage parameter and its evolution equation. After showing the validity of the computation, the effects of deformation rate, temperature, and SIMT on the force-deflection curve and deformation behavior are examined. Then, the mechanism of rate-sensitive fracture toughness in TRIP steel is challenged to be clarified.
Authors: Ti Kun Shan, Li Liu
Abstract: An enhanced elastic-plastic constitutive equation taking into account strain induced transformation and its effect on work hardening of TRIP steel during deformation are investigated. The transformation rate relies on the stress triaxiality. The strain hardening of the TRIP steel takes on parabola shape because of the austenite changed to the martensite during straining. The physical model is verified by comparing with the stress-strain relation of the uniaxial tension experiment. The results showed that the steel keeps a high hardening potential which retards the onset of necking and a good formability thanks to the martensitic strain-induced transformation and the subsequent austenite hardening.
Authors: Anthony J. DeArdo, J.E. Garcia, Ming Jian Hua, C. Isaac Garcia
Abstract: TRIP steels containing Mn, Si, Al, Mo, and Nb have been examined using a laboratory simulation of a continuous hot dipped galvanizing line. The evolution of microstructure has been studied as the steel passes through the various stages of CG line processing. Tensile strengths approaching 800 MPa and ductilities approaching 30% have been achieved in the 1.5Mn-0.5Si- 1.0Al-0.015Mo-0.03Nb system.
Authors: W.J. Dan, Z.G. Hu, W.G. Zhang
Abstract: TRIP-assisted steels are ideal for lightweight automotive applications due to not only its high strength and ductility but also the fatigue resistance, which result from the special strengthening mechanism of phase transformation in deformation processes. In this paper, a kinematic transformation model is developed, based on shear-band intersections, to reasonably evaluate the transformation from austenite into martensite with cyclic loading. The transformation process is controlled by parameters, such as, increase temperature, transformation driving force, shear-band formation rate and shear-band intersection volume fraction, by which the influences of cyclic loading variables (such as, number of cycles, strain amplitude and frequency) on transformation from austenite into martensite are predicted. The microstructure volume fraction is tested by X-Ray to verify the model.
Authors: You Liang He, Stéphane Godet, Pascal J. Jacques, John J. Jonas
Abstract: The crystallographic relationship between the g and a phases in samples of the Gibeon meteorite and a TRIP steel was investigated by means of EBSD techniques. The orientations of the two phases were measured and are represented in pole figures. The results are compared to predictions made on the basis of the Bain, Kurdjumov-Sachs (K-S), Nishiyama-Wassermann (NW), Greninger-Troiano (G-T) and Pitsch orientation relationships. The local misorientation between individual fcc and bcc crystals along their common interface was measured to demonstrate the way in which the exact orientation relationship varies along the boundary. The local orientations within lamellae and laths of kamacite and bainite are compared to that in recrystallised ferrite polygons. The occurrence of variant selection during the transformation of deformed austenite is analyzed using a recent dislocation-based model.
Authors: Emil Spišák, Janka Majerníková
Abstract: The article deals with the comparison of thickness change of spherical cup made from TRIP steel RAK40/70 after hydraulic bulge test. The thickness has been measured by timing gauge and by apparatus Argus. Experimental material thickness has been 0.75 mm. From measured values of thickness of experimental material has been calculated the dependence stress-strain by models of several authors.
Authors: Can Sheng Yu, Zhi Wang Zheng, Min Li Wang, Gong Ting Zhang
Abstract: The hot-rolling deformation resistances of a TRIP Steel were studied by using a Gleeble-3500 thermal simulator. The true stress-true strain curves of the TRIP steel is determined under different hot-rolling deformation conditions, and the effect of deformation temperature, strain rate and deformation amount on the deformation resistance was evaluated. Based on experimental results, the mathematic model for the calculation of the deformation resistance of the TRIP Steel has been set up by the regression analysis by means of the origin software. It is found that the simulated stress-strain curves have good curve-fitting performance.
Authors: Daiki Inoshita, Takeshi Iwamoto
Abstract: TRIP steel possesses excellent mechanical properties dominated by strain-induced martensitic transformation (SIMT). For automotive industries, if TRIP steel can be applied to shock absorption members, it can be considered that the weight of automobile can be reduced. However, the strain rate sensitivity of TRIP steels has not been fully understood because the strain rate sensitivity and the deformation mode dependency of SIMT are still unclear. Therefore, it is important to reveal these sensitivity and dependency for confirming a reliability of TRIP steel. Therefore, in this study, it is attempted to estimate the amount of produced martensite in TRIP steel by measuring the inductance of TRIP steel. The specimen made of TRIP steel is used as a core of a prototype coil manufactured in this study. Then, the compressive and tensile tests are conducted by using a material testing machine and a drop weight testing machine using the specimen inside the coil. The inductance of the coil with the deformed specimen are measured continuously during the tests.
Authors: Gabor Por, Balazs Fekete, Peter Trampus
Abstract: Carrying out fatigue testing of reactor vessel material 15H2MFA acoustic emission sensors were applied to follow changes. It is shown, that observed bursts can be explained only with appearance of acoustic Barkhausen Effect (ABE). Interesting source localization is shown during heat treatment and consecutive stress test, which can be explained acoustic emission due to material transition from martenzit phase to bainite phase. Observed ABE opens the way to apply it in industry using magnetic stresses to provoke acoustic response for characterization of the state of the magnetic materials.
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