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The aim of the present research project was to identify steel compositions and process conditions for in line head hardened rails, able to develop a uniform fine grained pearlitic microstructure with small interlamellar spacing, characterised by tensile strength values up to 1250 MPa and good ductility. The chemical composition and the flash welding process of hardened rails also need to be optimized in order to prevent the softening of the heat affected zone (HAZ). The influence of hot rolling variables on the austenitic grain size of steel rails was evaluated by laboratory tests using a quench-deformation dilatometer and by industrial trials run at Piombino's rail mill. Mathematical models were also applied to predict austenite evolution during hot rolling and accelerated cooling of rails. Steels of different compositions (0.60-0.82C, 0.60-1.1Mn, 0.25-0.50Si, 0.04-0.50Cr, V<0.10, all in wt-%) were investigated. A compressed-air cooling device was designed, built and applied on rail specimens of length up to 500 mm to relate the operating parameters to cooling rates at various positions in the rail head. The experiments were carried out dipping rail samples, instrumented with thermocouples, into aqueous synthetic polymer media. Results in terms of temperature evolution and hardness were compared with those obtained on rails cooled by still and forced air. Various steels were submitted to cooling conditions simulating the in line accelerated cooling of the head of a rail. The cooling pattern and the transformation characteristics were measured and related to the hardness levels obtained. Fine austenitic grains with less than 40 micron were obtained lowering the finishing rolling temperature (FRT) to less than 900 deg C. Hot compression tests performed by the dilatometer and calculations by mathematical modelling showed that the application of low strains (epsilon = 0.05-0.1) results in recrystallisation induced grain growth. Ti microaddition and increased rolling speed were effective in slowing the growth of recrystallised grains, preserving grain refinement at high FRT (> 900 deg C). The reduction of area was increased from 30 to 40 % when reducing the grain growth from 70 to 20 micron.