Effect of Isothermal Temperature on Microstructure and Mechanical Properties of High Al–Low Si TRIP Steel

doi:10.1007/s40195-014-0068-9

Abstract

Abstract:

In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al–low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 °C and austempering temperature is 400 °C, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.

Key words: TRIP steel, Microstructure, Mechanical properties, Isothermal temperature, Retained austenite

Yang Zhao, Qiangjun Yan, Liqing Chen, Xiaoyun Yuan. Effect of Isothermal Temperature on Microstructure and Mechanical Properties of High Al–Low Si TRIP Steel[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(3): 389-394.

Figures/Tables 9

Table 1 Chemical composition of the experimental steel (wt%)

C	Si	Mn	Al	Cr	P	S	Fe
0.18	0.30	1.56	1.44	0.077	0.008	0.008	Bal.

Fig. 1 Schematic of the heat treatment process for experimental steel

Fig. 2 SEM photo showing microstructures of experimental steel treated at different isothermal temperatures: a 400 °C, b 450 °C, c 500 °C

Fig. 3 XRD patterns of the samples after isothermal treated at different temperatures for 5 min

Fig. 4 TEM images of blocky and film-like retained austenite in experimental steel: a bright field image of blocky retained austenite; b dark field image of blocky retained austenite; c SAEDP of blocky retained austenite as marked by the circle in a; d bright field image of film-like retained austenite; e dark field image of film-like retained austenite; f SAEDP of film-like retained austenite as marked by the circle in d

Fig. 5 Engineering stress–strain curves of experimental steel treated at different isothermal temperatures

Fig. 6 Mechanical properties of experimental steel treated at different isothermal temperatures

Fig. 7 EBSD analysis of retained austenite distribution in the experimental steel before tensile deformation a and after tensile deformation b

Fig. 8 TEM images of retained austenite after tensile deformation: a bright field image, b dark field image, c SAEDP of the area marked by circle in Fig. 8a

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