Microstructure and Mechanical Properties of Ferritic Rolling Low Carbon Steel

The microstructure and mechanical properties of ferritic rolling low carbon steel are investigated by metallurgical microscope, thermal simulation testing machine, electron backscattered diffraction (EBSD) and universal tensile test machine. The finishing temperature of the transition from austenite to ferrite changed from 680°C to740 °C with different cooling rates, which was obvious lower than that of the interstitial free steel. The deformation stress of low carbon steel was larger than that of interstitial free steel. In addition, the deformation stress of the low carbon steel was more sensitive to the deformation rate than that of the interstitial free steel. The microstructure at the surface layer of the hot rolling plate was composed of fully recrystallized grains while the microstructure in the center was composed of fibrous deformed grains. The ferritic rolling low carbon steel has lower yield ratio and higher elongation than that of normal rolling low carbon steel.

Mechanical Properties and Microstructures of Ferritic-Rolled Ultra-Low Carbon (ULC) and Ti-Stabilized Interstitial-Free (Ti-IF) Steels

In this paper, effects of ferritic rolling process on microstructures and mechanical properties especially drawability of ultra-low carbon (ULC) and Ti-stabilized interstitial-free (Ti-IF) steels were investigated and the precipitates of ferritic-rolled Ti-IF steels were also analyzed. The results show that good deep drawability are achieved as IF steels are ferritic rolled in good lubricant condition; on the contrary, lubricant condition has less influence on the deep drawability of ULC steels. And with the decrease of rolling temperature in ferrite region, deep drawability of Ti-IF steels are improved, but for ULC steels, when ferritic rolled at low temperature, the r-value is still less than one, which means insignificant deep drawability.

Recrystallisation Texture of Cold Rolled and Annealed IF Steel Produced from Ferritic Rolled Hot Strip

The ferritic rolling strategy allows for the production of two different hot strip grades, a "soft" and a "hard" hot strip. The "soft" hot strip is rolled in the upper ferrite region and a sufficiently high coiling temperature ensures direct recrystallisation in the coil. The "hard" hot strip is rolled at relatively lower temperatures in the ferrite temperature region and exhibits a strained microstructure with a desirable rolling texture. Furthermore, these ferritic rolled hot strips can be used as initial strip for subsequent cold rolling. The current investigation focuses on the development of the recrystallisation texture of cold rolled and annealed ferritic rolled hot strip for different cold reductions. For this purpose "soft" and "hard" hot strips were produced on a laboratory hot rolling mill. These strips were cold rolled with a total reduction of 40 to 80% to a final thickness of 0.5mm. Subsequently the strips were subjected to simulated continuous annealing, using a salt bath furnace. The macro texture of both types of specimens was measured and correlated to the mechanical properties, including the Lankford values. A very different development of the recrystallisation texture and hence mechanical properties has been observed. However, both grades yielded improved deep-drawing properties.