Microstructural characterization and production of high yield strength rebar

Abstract

Various technical standards from all over the world set out the mechanical and chemical characteristics for high
yield strength rebar. High yield strength rebar - as defined in this study – is applied to all concrete reinforcement
steel grades which require a minimum yield strength of 600MPa. The standards concerning rebar production were
reviewed in order to select all the possible grades that come under the above-mentioned definition.
This research project aims to determine if by applying an in-line quenching and self-tempering process, the
technological requirements for high yield strength rebar, as specified in the standards, can be met, in order to
optimize the chemical composition and save on alloying elements. The work can be divided into two different
phases. The preliminary phase took place in the metallurgical laboratory of Danieli’s research center and the
second phase in an industrial plant. Tests done in the laboratory set out to evaluate the effect of quenching
and chemical composition on the rebar’s final mechanical properties and microstructure. The purpose of the
industrial-scale tests was to evaluate the potential of DANIELI’s in-line quenching and self-tempering process,
referred to as QTB (Quenching and Tempering Bar process), applied to high-strength steels. At the end of the
lab tests, three different chemical compositions were selected, deemed suitable for the production of high yield
strength rebar. In the industrial-scale tests it was then possible to evaluate the performance of the QTB process
in the production of high yield strength rebar in terms of operating flow rates / pressures, optimized chemical
compositions, productivity and process stability.