Mechanical requirements of martensitic steel pipes for OCTG applications are becoming more demanding, particularly in relation to the appearance of narrow yield strength ranges specified for several products. For this reason, a clear understanding of the effects of different microalloying additions on softening rates during tempering is needed. In the case of Ti microalloyed steels, this element is often added with several objectives not related to strengthening. Being in concentrations close to the stoichiometric ratio with Nitrogen, Titanium helps to control grain growth at high temperature (toughness effect) and to protect Boron from precipitation, thus obtaining its optimum effect on hardenability. However, when Ti is over-stoichiometric it can precipitate as carbides during different stages of the industrial process. The hardening effect of this precipitation may be negligible, for example if it takes place during hot rolling, or important if it proceeds during tempering, where it may result in a fine distribution of particles.
In this work the effect of different Ti additions on strength of carbon steels is analyzed it terms of its dependence on chemistry and processing conditions. Simulations of heat treatments were performed in a Gleeble® 3500 machine starting from distinct as rolled conditions. Metallographic studies were performed on resulting samples. For some cases TEM analysis was carried out to confirm the presence of fine nanometric TiC precipitates. The results obtained were used to fit an empirical model for tempering of medium-carbon martensitic steels, which is used as a tool to fine tune heat treatment conditions.