Influence of silicon, aluminium, phosphorus and copper on the phase transformations of low alloyed TRIP‐steels

Traint, S.; Pichler, A.; Hauzenberger, Karl; Stiaszny, Peter; Werner, Ewald

doi:10.1002/srin.200200206

Cited by 57 publications

(41 citation statements)

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“…The two types of low-alloyed TRIP steel sheets chosen are commercially known as TRIP 700 (a C-Mn-Al) and TRIP 800 (C-Mn-Si). While their microstructure and tensile behaviour has been studied, 9,10,24,25) the effects of plastic prestrain on their Young's moduli during loading are less wellknown. 26) This study was undertaken to determine the influence of the dislocation structure on the elastic behaviour of previously deformed materials and the total amount of strain recovery that takes place after the deformation process.…”

Section: Introductionmentioning

confidence: 99%

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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%

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confidence: 99%

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

2005

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“…The TRIP mechanism is based on the deformation-stimulated athermal transformation of metastable austenite (face centered cubic Fe-Mn phase) into martensite (metastable body centered cubic or orthorhombic Fe-Mn phase) and the resulting matrix and martensite plasticity required to accommodate the transformation misfit. [3][4][5][6][7][8][9][10][11] The maraging treatment is based on hardening the heavily strained martensite through the formation of small intermetallic precipitates (of the order of several nanometers). These particles act as highly efficient obstacles against dislocation motion through the Orowan and Fine-Kelly mechanisms enhancing the strength of the material.…”

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confidence: 99%

“…These particles act as highly efficient obstacles against dislocation motion through the Orowan and Fine-Kelly mechanisms enhancing the strength of the material. [12][13][14][15][16][17] While both types of alloys, i.e., TRIP steels [3][4][5][6][7][8][9][10][11] and maraging steels [12][13][14][15][16][17] have been well investigated, the combination of the two mechanisms in the form of a set of simple Fe-Mn alloys as suggested in this work, namely, the precipitation hardening of transformation-induced martensite by intermetallic nanoparticles, opens a novel and lean alloy path to the development of ultrahigh strength steels that has not been much explored in the past. [18,19] We refer to these alloys as maraging TRIP steels.…”

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Designing Ultrahigh Strength Steels with Good Ductility by Combining Transformation Induced Plasticity and Martensite Aging

et al. 2009

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Steels with a high ultimate tensile strength (UTS) above 1 GPa and good ductility [total elongation (TE) of 15-20% in a tensile test] are of paramount relevance for lightweight engineering design strategies and corresponding CO 2 savings, Figure 1. [1,2] In this work, we report about a novel design approach for precipitation hardened ductile high strength martensitic and austenitic-martensitic steels (up to 1.5 GPa strength). The alloys are characterized by a low carbon content (0.01 wt% C), 9-15 wt% Mn to obtain different levels of austenite stability, and minor additions of Ni, Ti, and Mo (1-2 wt%). The latter are required for creating precipitates during aging heat treatment.Hardening in these materials is realized by combining the TRIP effect with a maraging treatment [transformationinduced plasticity (TRIP); maraging: martensite aging through thermally stimulated precipitation of particles]. The TRIP mechanism is based on the deformation-stimulated athermal transformation of metastable austenite (face centered cubic Fe-Mn phase) into martensite (metastable body centered cubic or orthorhombic Fe-Mn phase) and the resulting matrix and martensite plasticity required to accommodate the transformation misfit. [3][4][5][6][7][8][9][10][11] The maraging treatment is based on hardening the heavily strained martensite through the formation of small intermetallic precipitates (of the order of several nanometers). These particles act as highly efficient obstacles against dislocation motion through the Orowan and Fine-Kelly mechanisms enhancing the strength of the material. [12][13][14][15][16][17] While both types of alloys, i.e., TRIP steels [3][4][5][6][7][8][9][10][11] and maraging steels [12][13][14][15][16][17] have been well investigated, the combination of the two mechanisms in the form of a set of simple Fe-Mn alloys as suggested in this work, namely, the precipitation hardening of transformation-induced martensite by intermetallic nanoparticles, opens a novel and lean alloy path to the development of ultrahigh strength steels that has not been much explored in the past. [18,19] We refer to these alloys as maraging TRIP steels.Related steel design trends that are based on small-scaled second phase precipitates are also pursued by using oxide, [20][21][22][23] nitride, [24,25] or Cu nanosized particles. [26] Other pathways to the design of ultrahigh strength steels have been realized in ultra fine grained materials obtained by advanced thermomechanical processing [27][28][29][30][31][32][33][34] or by accumulative roll bonding. [35] The joint maraging TRIP approach justifies a more detailed study since it opens up a new approach to increase the UTS of conventional steels at relatively lean alloying costs, i.e., without large quantities of expensive alloying elements, owing to the small volume fraction of precipitates required in maraging steels. [12][13][14][15][16][17] The negative side of such strategies lies often in the fact that an increase in tensile strength is typically accompanied by a corresponding dro...

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“…However, such substitutions are not straightforward if other effects and interactions among alloying elements are to be taken into account. Therefore, incessant efforts have been taken throughout the development of steels, both by industries and academies, to modify steel with leaner chemistry [9][10][11][12][13] and/or more economical process routes. 14,15) Nevertheless, competing and/or conflicting alloying effects on alloy cost versus alloy properties, make the empirical alloy design approach even more inefficient and hence a system optimization of the performance/price ratio in alloy design become an even more attractive target.…”

Section: Introductionmentioning

confidence: 99%

Property and Cost Optimisation of Novel UHS Stainless Steels via a Genetic Alloy Design Approach

Zwaag

2011

ISIJ Int.

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A computational alloy design approach for precipitation harden Ultra High Strength (UHS) stainless steels is presented. The design methodology is based on thermodynamic and kinetic principles, employing genetic algorithm for optimization. Alloy compositions covering 14 elements are optimized simultaneously together with key heat treatment parameters, i.e., austenitization temperature and ageing temperature, so as to achieve the desired microstructures: strong lath martensite matrix, fine precipitates of particular species for strengthening, adequate Cr concentration in the matrix for corrosion resistance and controlled amounts of undesirable phases throughout the entire heat treatment. Two alloys utilizing MC carbides and Ni3Ti intermetallics, respectively, are designed employing the genetic approach. For the alloys designed, the cost effects of each single element are investigated and both the most and the least cost effective elements are identified. Subsequently the alloy design model was extended to take into account alloying costs by employing the ratio of strengthening contribution to alloying costs as the new optimization factor. Redesigned alloys display significant cost reductions without significantly sacrificing the strength. The extended model is shown to provide valuable guidelines in the industrial practice to design/modify alloy compositions, and optimize strength and cost in an integrated manner.

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Influence of silicon, aluminium, phosphorus and copper on the phase transformations of low alloyed TRIP‐steels

Cited by 57 publications

References 5 publications

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

Study of the Inelastic Response of TRIP Steels after Plastic Deformation

Designing Ultrahigh Strength Steels with Good Ductility by Combining Transformation Induced Plasticity and Martensite Aging

Property and Cost Optimisation of Novel UHS Stainless Steels via a Genetic Alloy Design Approach

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