THERMOMECHANICAL PROCESSING OF ADVANCED HIGH STRENGTH STEELS IN PRODUCTION HOT STRIP ROLLING

Hot strip rolling of low carbon Advanced High Strength Sheet Steels (AHSS) is challenging due to non-traditionalchemical compositions required to attain the unique mechanical properties in AHSS products. In hotstrip rolling, TMP implies various types of controlled rolling where temperature, strain rate and rollingreductions are carefully selected to produce the target austenite microstructure, which is either fullyrecrystallized or fully pancaked austenite before starting cooling. Microalloying of HSLA in combinationwith suitable TMP provides an efficient tool to control austenite recrystallization prior to the beginningof cooling. However, the existing TMP routes cannot be easily applied to AHSS that have much more sophisticatedalloying and lower level of microalloying. TMP of AHSS in the finishing train of hot strip mill shouldbe designed so as to ensure controlled type and extent of transformation on run-out table by precise control ofstrip temperature and rolling speed with account for mill configuration and capabilities, product dimensions,gauge and shape tolerances. Further complications can be brought about by high sensitivity ofAHSS to various aspects of hot strip rolling and cooling parameters. These aspects are discussed in the paperalong with various practical implications

Model Fe-Al Steel with Exceptional Resistance to High Temperature Coarsening. Part II: Experimental Validation and Applications

In order to achieve a fine uniform grain-size distribution using the process of thin slab casting and directing rolling (TSCDR), it is necessary to control the grain-size prior to the onset of thermomechanical processing. In the companion paper, Model Fe-Al Steel with Exceptional Resistance to High Temperature Coarsening. Part I: Coarsening Mechanism and Particle Pinning Effects, a new steel composition which uses a small volume fraction of austenite particles to pin the growth of delta-ferrite grains at high temperature was proposed and grain growth was studied in reheated samples. This paper will focus on the development of a simple laboratory-scale setup to simulate thin-slab casting of the newly developed steel and demonstrate the potential for grain size control under industrial conditions. Steel bars with different diameters are briefly dipped into the molten steel to create a shell of solidified material. These are then cooled down to room temperature at different cooling rates. During cooling, the austenite particles nucleate along the delta-ferrite grain boundaries and greatly retard grain growth. With decreasing temperature, more austenite particles precipitate, and grain growth can be completely arrested in the holding furnace. Additional applications of the model alloy are discussed including grain-size control in the heat affected zone in welds and grain-growth resistance at high temperature