Effect of alloying elements on the microstructure property relationship in thermomechanically processed C-Mn-Si TRIP steels

Timokhina, Ilana, Hodgson, Peter and Pereloma, Elena 2002, Effect of alloying elements on the microstructure property relationship in thermomechanically processed C-Mn-Si TRIP steels, Steel research, vol. 73, no. 6-7, pp. 274-279.

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Title Effect of alloying elements on the microstructure property relationship in thermomechanically processed C-Mn-Si TRIP steels
Author(s) Timokhina, IlanaORCID iD for Timokhina, Ilana orcid.org/0000-0003-1989-0835
Hodgson, Peter
Pereloma, Elena
Journal name Steel research
Volume number 73
Issue number 6-7
Start page 274
End page 279
Total pages 6
Publisher Verlag Stahleisen
Place of publication Düsseldorf, Germany
Publication date 2002
ISSN 0177-4832
1869-344X
Keyword(s) experimental study
true stress true strain curve
mechanical tests
high-strength steels
steels
thermomechanical treatments
property structure relationship
microstructure
alloying elements
alloying effects
Summary The effect of additions of Nb, Al and Mo to Fe-C-Mn-Si TRIP steel on the final microstructure and mechanical properties after simulated  thermomechanical processing (TMP) has been studied. The laboratory simulations of discontinuous cooling during TMP were performed using a hot rolling mill. All samples were characterised using optical microscopy and image analysis. The volume fraction of retained austenite was ascertained using a heat tinting technique and X-ray diffraction measurements. Room temperature mechanical properties were determined by a tensile test. From this a comprehensive understanding of the structural aspect of the bainite transformation in these types of TRIP steels has been developed. The  results have shown that the final microstructures of thermomechanically processed TRIP steels comprise 50 % of polygonal ferrite, 7 - 12 % of retained austenite, non-carbide bainitic structure and martensite. All steels exhibited a good combination of ultimate tensile strength and total elongation. The microstructure-property examination revealed the relationship between the composition of TRIP steels and their mechanical properties. It has been shown that the addition of Mo to the C-Si-Mn-Nb TRIP steel increases the ultimate tensile strength up to 1020 MPa. The stability of the retained austenite of the Nb-Mo steel was degraded, which led to a decrease in the elongation (24 %). The results have demonstrated that the addition of Al to C-Si-Mn-Nb steel leads to a good combination of strength (∼ 940 MPa) and elongation (∼ 30 %) due to the formation of refined acicular ferrite and granular bainite structure with ∼7 - 8 % of stable retained austenite. Furthermore, it has been found that the addition of Al increases the volume fraction of bainitic ferrite laths. The investigations have shown an interesting result that, in the Nb-Mo-Al steel, Al has a more pronounced effect on the microstructure in comparison with Mo. It has been found that the bainitic structure of the Nb-Mo-Al steel appears to be more granular than in the Nb-Mo steel. Moreover, the volume fraction of the retained austenite increased (12 %) with decreasing bainitic ferrite content. The results have demonstrated that this steel has the best mechanical properties (1100 MPa and 28 % elongation). It has been concluded that the combined effect of Nb, Mo, and Al addition on the dispersion of the bainite, martensite and retained austenite in the ferrite matrix and the morphology of these phases is different than effect of Nb, Mo and Al, separately.
Language eng
Field of Research 091207 Metals and Alloy Materials
Socio Economic Objective 0 Not Applicable
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2002, Verlag Stahleisen
Persistent URL http://hdl.handle.net/10536/DRO/DU:30008569

Document type: Journal Article
Collections: Centre for Material and Fibre Innovation
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