Deformation Behavior and Damage Evaluation in a New Titanium Diboride (TiB 2 ) Steel-Based Composite Zehoua Hadjem-Hamouche,  Jean-Pierre Chevalier, Yiting Cui, and Fre ´de ´ric Bonnet Deformation behavior and damage evaluation of a new composite steel has been investigated by means of in situ three-point bend tests in the scanning electron microscope. The titanium diboride (TiB 2 )-reinforced steel composite is produced by in situ precipitation of the TiB 2 particles during eutectic solidification. This production process developed by ArcelorMittal leads to a steel composite with a significant increase in specific stiffness (>20%), and good strength/ductility compromise. The microstructures obtained consist of primary TiB 2 crystals surrounded by a eutectic mixture of ferrite and TiB 2 particles. The primary mode of damage is particle fracture and inhomogeneous plastic deformation in the matrix. In contrast with other production process, particle fracture was more common than interfacial debonding indicating that interfacial strength is not the limiting factor in damage accumulation and fracture in this composite. Crack growth occurred by particle fracture ahead of the crack tip, producing large microvoids, which then link up to the growing crack by ductile failure of the remaining matrix ligaments. The results suggest also that the cracks tended to avoid direct particle interactions. 1. Introduction Automotive weight reduction is a primary and necessary way to reduce energy and fuel consumption, since 57 kg weight reduction is equivalent to 0.09–0.21 km L 1 fuel economy. [1] Structural components can be designed with either strength or stiffness as primary design criterion. The wide range of available high to ultra high strength steels can provide appropriate solutions, within a strength/form- ability compromise, when strength is the principal design criterion. However, the metallurgical mechanisms used to reach high strength have little or no effect on Young’s modulus, since this will be essentially governed by the Fe–Fe bonds. As such, all steels display values of Young’s modulus around 210 GPa. In order to increase stiffness, Young’s modulus has to be increased. Here, there are very few possibilities. For iron, Young’s modulus is anisotropic, and hence the use of strong textures could lead to significant increases in stiffness in specific direc- tions. Another route, more easily manageable, is to use a composite effect, with high stiffness particles. Metal matrix composites (MMCs) have received con- siderable interest for their enhanced specific proper- ties. [2,3] Although, most of the work on MMCs is directed toward lighter structural metals (Ti, Al, and Mg), [4–6] there is also significant interest in developing Fe matrix compo- sites. Most of these composite materials are designed using TiC [7–10] or TiB 2 [11–14] as a reinforcing particulate phase. Indeed, compared to other reinforcement materials, these ceramic phases are particularly efficient in improving not only the specific stiffness but also hardness and wear resistance of the materials. [3] Moreover, TiB 2 is relatively stable in liquid Fe. [15,16] As a result, TiB 2 reinforced iron or steel matrix composites are particularly interesting for structural components with stiffness as the design criteria such as chassis-parts in the automotive industry. So far available steel/ceramic composites on the market are mainly produced through the powder metallurgy route. Other processing routes such as endogenous precipi- tation [17–21] or supply of exogenous particles have already been tested at the laboratory level. The literature is rather abundant on this subject, but no lasting extrapolation on an industrial scale has yet been achieved. Recently, ArcelorMittal has successfully developed a new composite steel family by in situ precipitation of the ceramic particles during eutectic solidification. [22] The alloy design criteria for such composite steel were a very high Young’s modulus for the particulate phase and as [  ] Dr. Z. Hadjem-Hamouche, J.-P. Chevalier, Y. Cui P-2AM, CNAM, Case 2D7P20, 292 rue Saint-Martin, 75141 Paris Cedex 03, France Email: zehoua.hamouche@cnam.fr F. Bonnet ArcelorMittal Research, Voie Romaine-BP30320, 57283 Maizie `res-le `s- Metz Cedex, France DOI: 10.1002/srin.201100255 www.steel-research.de 538 steel research int. 83 (2012) No. 6 ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim FULL PAPER