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Brittle intermetallic compound makes ultrastrong low-density steel with large ductility


Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density3,4,5. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

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Figure 1: Precipitation of B2 particles during annealing of cold rolled Fe–10%Al–15%Mn–0.8%C–5%Ni (weight per cent) high-specific-strength steel.
Figure 2: Room-temperature tensile properties of HSSS compared with selected metallic alloys of high specific strength6,7,22,23,24,25,26,27.
Figure 3: Scanning TEM images of HSSS after tensile deformation (0.5% strained) showing interaction of dislocations and B2 particles.


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We thank J.-S. Lee and Y.-U. Heo for discussions. The press hardening steel was obtained from POSCO. This work was supported by the Steel Innovation Program of POSCO.

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Authors and Affiliations



N.J.K. and H.K. designed the study; S.-H.K. and H.K. performed the research; S.-H.K., N.J.K. and H.K. analysed the data; and N.J.K and H.K. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Hansoo Kim.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Change of X-ray diffraction pattern during annealing at 900 °C.

With the increase in annealing time, the (100) peak of B2 becomes more pronounced owing to its precipitation (samples were water-quenched after annealing). au, arbitrary units.

Extended Data Table 1 Composition of the present HSSS and reference materials
Extended Data Table 2 Thermal treatment condition and properties of the present HSSS and reference materials

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Kim, SH., Kim, H. & Kim, N. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility. Nature 518, 77–79 (2015).

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