Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

High strength stainless steel (HSS) rebar

As far as the reinforcing steel bars is concerned, the European industrial production of reinforcing stainless steel has developed, in the last decade, products which have good mechanical and corrosion properties. This characteristics, joined to the opportunity to complete or partial avoiding the maintenance and repair actions and to increase the durability and the service life of the buildings, has conferred at the stainless steel a reasonable diffusion especially in critical environment.

In spite of the clear advantages provided by this steel, there is actually a huge problem preventing the construction industries from their wide level use: the cost.

The HIPER Project has achieved a wide set of technical and economical data comparing conventional and innovative stainless steels. The main result achieved is to set up an innovative stainless steel (HSS3) that maintain the same mechanical characteristics and similar corrosion behaviour of the well known stainless steel, but while the last one are affected by an uncontrolled oscillations of costs, the innovative ones, by searching low cost raw materials, maintain a low cost oscillation.

The research has been focused on high tough austenitic stainless steels with a low content of "noble elements" nevertheless the corrosion resistance results are fairly good in respect of the target.

From the application point of view, the innovative stainless steels show an interesting alternative in the seismic structures. Also in structures submitted to high fire risk, like the concrete layers in road or rail tunnels, the innovative stainless steels, on account of its high mechanical properties at very high temperature, can offer a remarkable alternative for designers.

Within the framework of this result, Polito assessed the mechanical properties as well as weldability of all the materials selected. This was done so as to provide the consortium and, later, all the technicians of construction sector a good knowledge about inherent properties of stainless steel (ss) and, in particular, of HSS steels. It is highly necessary to make aware the construction sector technicians of ss and HSS properties (materials which are very different from typical construction steels), so that they can design exploiting their all potential. For Polito, the main point of interest on the new materials is the microstructural modification induced by strain. In austenitic ss the stabilisation of austenite is usually achieved through nickel additions, but to reduce production costs in HSS composition, nickel has been substituted by N and Mn, cheaper but less effective elements. The transformation of austenite into martensite is particularly pronounced in HSS1 which is less stable.

This mechanism has been studied and described with data mainly through tensile test, but in practice, it may occur in any process involving straining. It results in strain hardening, which is in principle positive as it raise tensile properties, but has to be deeply understood to be aware of the behaviour in the preparation phase and in service.

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