A good selection of the thermomechanical processing parameters will optimize the function of alloying elements to get the most of mechanical properties in Advanced High-Strength Steels for automotive components, where high resistance is required for passenger safety. As such, critical processing temperatures must be defined taking into account alloy composition, in order for effective thermomechanical processing schedules to be designed. These critical temperatures mainly include the recrystallization stop temperature (T5%) and the transformation temperatures (Ar1, Ar3, Bs, etc.). These critical processing temperatures were characterized using different thermomechanical conditions. T5% was determined through the softening evaluation on double hit tests and the observation of prior austenite grain boundaries on the microstructure. Phase transformation temperatures were measured by dilatometry experiments at different cooling rates. The results indicate that the strain per pass and the interpass time will influence the most on the determination of T5%. The range of temperatures between the recrystallized and non-recrystallized regions can be as narrow as 30 °C at a higher amount of strain. The proposed controlled thermomechanical processing schedule involves getting a severely deformed austenite with a high dislocation density and deformation bands to increase the nucleation sites to start the transformation products. This microstructure along with a proper cooling strategy will lead to an enhancement in the final mechanical properties of a particular steel composition.

A simulation model has been used to calculate temperature distribution and internal stresses of steel ingots. The aim of this study is to optimize the heating cycles without compromising the mechanical integrity of the ingots, which ideally will result in a reduction in energy consumption and an increase in furnace productivity. The heating cycles of three ingots of different materials (ASTM A105, AISI 4330, and AISI 8630) and sizes (1.60, 1.75 and 1.32 m) are optimized. The optimization procedure of the heating cycle is based on a time reduction at each step of the set point. The phase transformation temperature at the ingot center was taken as a reference because this is where the higher stresses are developed. A sample of a 1 m ∅ AISI 8630 ingot was characterized with a Scanning Electron Microscope, Energy-dispersive X-ray Spectroscopy, X-Ray Diffraction, and Differential Scanning Calorimetry. Results show precipitates in the as-cast condition, which will eventually be dissolved after a complete heating cycle.

A modification to picric acid solutions has been undertaken to reveal the prior-austenite grain boundaries in microalloyed steels as a result of elemental segregation. It has been found the maximum addition of sodium dodecyl sulphate plus hydrochloric acid to fully reveal both the prior austenite grain boundaries and the final post-processed structures in these steels.

A simulation model is presented, where temperature, phases and internal stresses can be predicted as a function of time during the heating of large steel ingots for forging. Heating cycle measurements and computer simulations are compared for an A105 steel grade 34-Ton tapered ingot. A study of the heat transfer inside a natural gas-fired furnace was carried out to make an estimation of internal stresses due to thermal expansion and phase transformation from α ferrite and pearlite to γ austenite during heating. The model was validated with a second test of an AISI 4330 steel grade 35.4-Ton ingot. The simulation model described can calculate internal stresses in any ingot in order to optimize its heating cycle without compromising ingot internal quality, reducing energy consumption and increasing productivity of the furnace.