TWIP steels have a fully austenitic structure at room temperatures due to their high manganese content of 17% to 24%. Deformation twins created in these steels drive a large amount of deformation, providing the name to this class of steels. When the microstructure becomes finer, a high value instantaneous hardening rate (n-value) will be the result of the twinning. The resultant twin boundaries increase the strength of the steel by behaving like grain boundaries. The annealed microstructure for a TWIP steel is illustrated in Figure 1.
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Figure 1. Photomicrograph of TWIP steel as annealed.
Key Properties of TWIP Steels
TWIP steels exhibit a unique combination of very high stretchability and high strength. There is an increment in the n-value to 0.4 at 30% engineering strain and then there is no change in the n-value until both total and uniform elongation reach 50%. TWIP steels have a tensile strength more than 1000 MPa (Figure 2).
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Figure 2. The tensile strength-elongation graph for TWIP steel.
The following table summarizes the current TWIP steel production grades and the corresponding automotive applications:
| TWIP 500/900 |
A-Pillar, wheelhouse, front side member |
| TWIP 500/980 |
Wheel, lower control arm, front and rear bumper beams, B-pillar, wheel rim |
| TWIP 600/900 |
Floor cross-member, wheelhouse |
| TWIP 750/1000 |
Door impact beam |
| TWIP 950/1200 |
Door impact beam |
Download the Advanced High-Strength Steels Applications Guidelines free here, to learn more about the metallurgy, forming and joining of these new steels.
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This information has been sourced, reviewed and adapted from materials provided by WorldAutoSteel (World Auto Steel).
For more information on this source, please visit WorldAutoSteel (World Auto Steel).