What’s TRIP Steel?

Advanced high-strength steel (AHSS) for automotive application including Dual Phase Steels (DP steel), Complex Phase Steels(CP steel), Transformation Induced Plasticity (TRIP steel Steels), Martensitic Steels(MS steel) and Quenching and Partitioning Steels),Twinning Induced Plasticity Steels (TWIP steel) and, Press Hardening/Boron Steels (PH steel/ B steel). TRIP steel has been more and more widely used in industrial application due to its high yield strength, tensile strength and good stamping performance. TRIP steel is a type of TRansformation Induced Plasticity steel, was first discovered and named by V. F. Zackay, who used the strain-induced martensitic transformation and phase-induced plasticity of residual austenite to improve the plasticity and strength of steel plate and improve the formability of steel plate. It is mainly used for parts with relatively complex structure, such as B-column stiffening plate and front longitudinal beam of auto.

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Residual Austenite is a stable remnant of austenite transformation. When the matrix is transformed into martensite, the residual part can only exist as austenite due to the space limitation, which is called residual Austenite. In the process of deformation of TRIP steel, the residual austenite is transformed into high-strength high-carbon Martensite, and with volume expansion, the instability of plastic deformation is inhibited, and the range of uniform extension is increased, so the strength and plasticity are improved.

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The content and stability of residual Austenite are the keys of TRIP effect. Critical heating and isothermal quenching of lower bainite were used to obtain a large number of residual Austenite. A large amount of residual austenite is obtained by controlling rolling and cooling of TRIP steel. The microstructure of the two TRIP steels is similar, mainly composed of 50%-60% Ferrite, 25%-40% Bainite, and a small amount of Martensite and 5%-15% residual Austenite (as shown in the figure). While TRIP steel has a certain amount ( 0010010 gt; 8%), compare the stability of retained Austenite, it by external produce plastic deformation, the residual austenite increases gradually, strain hardening, phase transformation and transformed into Martensite, making local hardness is improved, it is difficult to continue to deformation, phase change evenly spread to the whole material has a high plasticity.

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Microstructure of trip steel


The advantages of TRIP steel 0010010 nbsp;



1) High strength and ductility, that is, high strong plastic product (Rm×A); The strong plastic product of TRIP steel is generally greater than 20000MPa×%.

2) The working hardening index n value of TRIP steel is high, with an average of more than 0.2;

3) The plane anisotropy is relatively low, and the ears are very small in deep punching;

4) Another reason TRIP steel is used in automobiles is that it has large working hardening and significant baking hardening effect;

5) TRIP steel 0010010 #39;s buckling ratio (Re/Rm) is about 0.6 ~ 0.8, making it easy to process.

6) High forming limit height and tensile properties, especially suitable for bulging parts;

7) High energy absorption during collision, which improves safety. With the increase of strain rate, the rate of transformation from residual austenite to martensite increases, which proves that TRIP steel is very suitable for anti-impact vehicle parts.

8) TRIP steel has high fatigue strength due to high working hardening index and cyclic hardening caused by cyclic stress.

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The chemical composition of TRIP steel


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At present, the low-cost low carbon and low alloy Si-Mn TRIP steel, also known as C-Si-Mn series TRIP steel, has been mass produced. The main chemical composition of C-Si-Mn series TRIP steel is 0.1% ~ 0.2%C, 1.0% ~ 2.0%Si, 1.0% ~ 2.0%Mn. Generally, elements such as Al and P are added to improve the strength.


TRIP chemical composition (Bao steel Q/BQB 312-2009)

C

Si

Mn

P

S

Al

Cu

≤0.3

≤2.2

≤2.5

≤0.090

≤0.015

≥0.010

≤0.20

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TRIP Mechanical property

Material

TRIP600

TRIP800

Grades

BR400/590TR

BR450/780TR

Tensile strength/MPa

705

915.73

Yield strength/MPa

500

585.8

Elongation /%

24.0

17.5

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The application of TRIP steel



At present, TRIP steel is widely used in automobile manufacturing industry.In order to reduce vehicle weight, reduce fuel consumption and reduce environmental pollution, it is necessary to reduce the thickness of automobile plate without sacrificing safety performance. TRIP steel is a good solution for the trend of high strengthening of automobile plate. At the same time, TRIP steel also has a strong energy absorption capacity and can resist the plastic deformation during impact, which significantly improves the safety level of automobiles. 0010010 nbsp;

In addition, TRIP steel can also be used in coal mine bolt, civil engineering, pipelines and cryogenic vessels. Bolt in coal roadway requires the bar body material to have high strength and high bearing capacity to control the deformation of surrounding rock mass of roadway. At the same time, it also requires a certain degree of plasticity to allow the surrounding rock to be decompressed and to redistribute stress, that is, to adapt to the deformation of surrounding rock. Especially under the conditions of soft, broken and expansive surrounding rock and mining, the surrounding rock of roadway has low strength and large deformation. The plasticity of bolt body is more important.


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TRIP steel is often confused with TWIP steel, so you need to know the difference between TRIP and TWIP effects. Simply put, the TWIP effect is stronger than the TRIP effect in terms of improving strength and elongation. TRIP effect is due to the transition of Martensite from Metastable FCC - Austenite to solid - centered cubic (BCC), while TWIP effect is based on mechanical twins, resulting in lower rate of work hardening and greater elongation at break. The TWIP effect can be seen as the dynamic hall-petch reinforcement effect, as the twin faces act as a powerful force to prevent slippage. For more information about TRIP steel, please contact us immediately.