Effects of heat treatment and alloying elements on the microstructures and mechanical properties of 0.15 wt pct C transformation-induced plasticity-aided cold-rolled steel sheets

Kim, Sung-Joon; Lee, Chang Gjl; Choi, In Soo; Lee, Sunghak

doi:10.1007/s11661-001-0067-0

Cited by 98 publications

(51 citation statements)

References 15 publications

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“…The mechanical properties of these steels have been determined mainly by using uniaxial tensile tests, which yield strength and ductility values. [7][8][9][10] In the automotive industry TRIP steels sheets are typically formed by stamping, and one of the problems associated with deep drawing processes is the difference between the final shape of formed parts before and after the removal of tools. These variations are caused mainly by springback and the Finite Element Method (FEM) has been used to correct these part shape errors.…”

Section: Introductionmentioning

confidence: 99%

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

2005

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A study of the elastic response before and after tensile plastic strain was undertaken for two commercial low-alloyed TRIP steels. These steels, TRIP 700 (C-Mn-Al alloy) and TRIP 800 (C-Mn-Si) are commercial alloys used in sheet metal stamping. The behaviour of the instantaneous tangent modulus (E T ) versus stress during loading and unloading was measured for each degree of prestrain. Loading curves show a decrease in the E T of the deformed samples as compared with the undeformed state. Though at low stresses a highly linear response was measured for both steels, a decrease was obtained for TRIP 700 as strain increased, whereas TRIP 800 remained unchanged. During unloading, a progressive decrease in E T was obtained in all deformed states, with lower chord modulus values as the tensile plastic prestrain increased. The inelastic response observed is attributed mainly to microplastic strain caused by the displacement of mobile dislocations. Thus, the differences between the two TRIP steels studied are related to the microstructure and the different dislocation structures observed in them. A notable consequence of this study is a better accuracy in the prediction of springback passes due to a better understanding of these inelastic effects that stems from going beyond mere use of traditional Young's modulus values.KEY WORDS: TRIP steels; springback; Young's modulus; dislocation structure. This microplastic deformation results firstly from the short range of motion of mobile dislocations, 19) and secondly from the bowing of the dislocation line between pinning points following models proposed by Mott and Friedel,20,21) and by Granato and Lücke. 22) This extra deformation, which occurs below the internal strength level of the material, is recoverable, and is affected by the dislocation density and the total length of dislocation line that is able to move or bow out. Thus, when e mp grows, a decrease in E is expected. The following Eq. (2), proposed by Granato and Lücke,22) summarizes this idea:where b is the magnitude of the Burgers vector, r is the density of the mobile dislocations and x is the average displacement of a dislocation line of length l.As springback appears after tools have been removed, it is the behaviour of Young's modulus 'during unloading' that should be investigated to obtain a more accurate prediction of the recovery from strain after forming. Ghosh et al. 13,23) used uniaxial tensile tests to study strain recovery after plastic prestrain for a type of steel used in sheet metal stamping, and demonstrated the nonlinearity of the unloading part of the stress-strain curve. This "inelastic behaviour" results in an extra deformation that is not predicted by the usual values of Young's modulus, and again is resumed as microplastic strain. This deformation must be accounted for in FEM simulations in order to better predict the final shape of the pieces stamped. The nature of microplastic strain during unloading is mainly associated with the backward movement of the dislocations that pile up during...

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Section: Introductionmentioning

confidence: 99%

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

2005

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“…There has been a focus on the suitable annealing temperature and the volume fraction of retained austenite on moderate cold rolled strips (65-75%) of TRIP steels. 20,29,30) Effect of this parameter is discussed here.…”

Section: Volume Fraction Of Retained Austenitementioning

confidence: 96%

“…Many researches have been performed to identify the effect of some mentioned parameters on retained austenite characteristics and resulted properties of the product. 4,[14][15][16][17][18][19][20][21][22][23] Although, Kim et al [18][19][20] and Lee et al 4,[15][16][17] have conducted many experiments on the effect of heat treatment and alloying elements, however, they have not discussed about the initial cold rolling conditions. Srivastava et al 22) focused on retained austenite feature and its effect on formability and mechanical properties which are obtained at different annealing and austempering times.…”

Section: Introductionmentioning

confidence: 99%

Effect of Cold Rolling on Annealing Behavior and Retained Austenite Characteristics of Multiphase CMnSi Steel

Emadoddin

2013

ISIJ Int.

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The newly developed multiphase transformation-induced plasticity (TRIP) steels are of interest for industrial applications because of their excellent combination of high strength and ductility. Retained austenite as a key constituent in final microstructure plays an important role in TRIP steels. The volume fraction, carbon concentration, size and morphology of this phase are the well known parameters which effects on the rate of transformation of retained austenite to martensite and the properties of steel. The performance of steel can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite.Against this background, in this research the effect of initial cold-rolling reduction and intercritical annealing temperature on the final microstructure and retained austenite characteristics has been studied on a silicon-containing TRIP steel by electron backscattered diffraction (EBSD) method. The results show that moderate percent of cold rolling followed by intermediate annealing temperature would provide optimum condition for desirable retained austenite characteristics with proper adjacent phase.

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“…The interest for high strength Dual-phase (DP) steel sheets having excellent ductility has increased significantly in recent years in various industries and in the automotive industry in particular [1]. Obviously, the potential that has encouraged the development and adoption of these steels in the industry are mainly motivated by their possibilities to improve productivity and reduce auto body weight, and to increase the passenger safety at a competitive price often equal or lower than that of conventional material solutions of similar strength level [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…Obviously, the potential that has encouraged the development and adoption of these steels in the industry are mainly motivated by their possibilities to improve productivity and reduce auto body weight, and to increase the passenger safety at a competitive price often equal or lower than that of conventional material solutions of similar strength level [1,2].…”

Section: Introductionmentioning

confidence: 99%