Improving the Strength of Prestressed Steel ASTM A633 Grade C by Combination of the Cr-Ti Alloying and Heat Treatment

Laboratory-scale experiments were carried out to improve the strength of prestressed steel by combination of the Cr-Ti alloying and heat treatment. A predetermined amount of the scrap and some ferrous alloys (such as FeMn, FeSi, FeCr and FeTi) was melted in the induction furnace to obtain the aimed compositions of the steel ASTM A633 grade C and the modified steel with Cr-Ti alloying. The molten steel was cast into the 45 mm ingot which was then hot forged into the 25 mm, subsequently prepared the tensile specimens that were heat-treated by quenching and tempering. After that, the hot forged and heat-treated specimens were subjected to the composition analysis, the tensile test and microstructural observation by optical and scanning electron microscopy. It has been concluded that the strengths of the prestressed steel strongly increased when the martensitic microstructure was obtained through the proper heat treatment. All the prepared steel exhibited high strength and adequate elongation, especially the UTS/YS of the Cr-Ti alloyed steel had increased from the value of 961/702 to 1611/1217 MPa and the elongation decreased from 15 to 10% corresponding to the deformed and heat-treated sample. These increasing strengths were attributed to the hardenability of the Cr element as well as the formation of the TiN precipitates which hindered the movement of the dislocation. The results suggested that further research must be conducted for the practical production of prestressed steel that is used in construction applications.