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Acta Metall Sin  2019, Vol. 55 Issue (8): 951-957    DOI: 10.11900/0412.1961.2019.00014
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Effects of C Content on Microstructure and Properties ofFe-Mn-Al-C Low-Density Steels
Xingpin CHEN1(),Wenjia LI1,Ping REN1,Wenquan CAO2,Qing LIU1
1. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
2. Special Steel Department of Central Iron & Steel Research Institute, Beijing 100081, China
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Abstract  

The lightweight Fe-Mn-Al-C steels (so-called low-density steels) have received great attentions as promising candidate for automobile structure applications due to their excellent combination of density reduction, mechanical properties and corrosion resistance. In previous studies, most examinations of the Fe-Mn-Al-C alloys focused on the deformation mechanisms and the relationship between the microstructure and mechanical properties. It is well known that chemical composition, especially C content, which enhances strength as the interstitial element and reduces the density of steels, plays an important role in the control of microstructure and performance. However, the influence of C element in the alloy with high Mn content is barely studied. In this work, the effects of C content on microstructure and mechanical properties of four Fe-30Mn-10Al-xC (x=0.53, 0.72, 1.21, 1.68, mass fraction, %) alloys were studied by EBSD, TEM, XRD and universal testing machine. The results show that with the increase of C content, the amount of austenite gradually increases and the ferrite/austenite dual-phase microstructure transforms into single phase austenite. In addition, the strength increases monotonously, while the elongation increases and then decreases ultimately with increasing C content. Statistical analysis reveals that the strain coordination capacity of austenite is higher than that of ferrite. Therefore, with the increase of austenite content, the ductility of the dual-phase steel remarkably increases, while the strength increases slightly. For single austenite steels, the yield strength increases but the elongation and work hardening ability decrease with increasing C content, which is related to the precipitation of κ′ carbides.

Key words:  low-density steel      Fe-Mn-Al-C alloy      mechanical property      austenite      ferrite     
Received:  17 January 2019     
ZTFLH:  TG142.1  
Fund: National Natural Science Foundation of China((Nos.51871062 and 51421001));and Fundamental Research Funds for the Central Universities(No.2018CDJDCL0019)
Corresponding Authors:  Xingpin CHEN     E-mail:  xpchen@cqu.edu.cn

Cite this article: 

Xingpin CHEN,Wenjia LI,Ping REN,Wenquan CAO,Qing LIU. Effects of C Content on Microstructure and Properties ofFe-Mn-Al-C Low-Density Steels. Acta Metall Sin, 2019, 55(8): 951-957.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2019.00014     OR     https://www.ams.org.cn/EN/Y2019/V55/I8/951

Fig.1  EBSD showing microstructure of the experimental steels with different C contents(a) 0.53%C (b) 0.72%C (c) 1.21%C (d) 1.68%CColor online

C content

%

γ phase

%

α phase

%

Grain size

μm

0.5352.844.313.3
0.7272.326.011.3
1.2199.70.28.9
1.6899.70.19.5
Table 1  Phase fraction and grain size of the experimental steels
Fig.2  TEM image (a) and corresponding selected area electron diffraction pattern (b) of 1.68%C steel
Fig.3  XRD spectra (a) and a partial enlarged figure (b) of the experimental steels with different C contents

C content

%

2θ

(°)

Lattice parameter

nm

γαaγaα
0.5342.8644.290.3660.290
0.7242.7944.270.3660.290
1.2142.69-0.367-
1.6842.52-0.368-
Table 2  Experimental data obtained from the X-ray diffraction profiles of the present four steels
Fig.4  Tensile test results of the experimental steels with different C contents (a) engineering stress-strain curves (b) true stress-strain (σ-ε) curves and the corres-ponding strain hardening rate (dσ/dε-ε) curves (c) mechanical properties of the four steels
Fig.5  EBSD maps of austenite (a, c) and ferrite (b, d) in the 0.53%C steel before (a, b) and after (c, d) deformation (The numbers 1~5 indicate the aspect ratios of the grains)
Fig.6  Distributions of true strain in each grain of 0.53%C steel before (a) and after (b) deformation
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