The deformation microstructure of various warm (ferritic) rolled steels was characterized and its influence upon the subsequent annealing behavior determined. The materials investigated included three interstitialfree (IF) steels (stabilized with either titanium or niobium), an extra low carbon (ELC) steel, and four experimental low carbon chromium steels with varying levels of boron, nitrogen and phosphorus. Single pass rolling experiments were conducted in a pilot mill at temperatures between 440 and 850°C and the asrolled microstructures were examined using optical microscopy. Particular attention was paid to the nature and intensity of the in-grain shear bands produced. Partial annealing was conducted to examine the nucleation of recrystallization in the deformed microstructure. Shear bands of moderate intensity were usually formed in the IF steels, which tended to be insensitive to rolling temperature. For the ELC steel, intense shear bands were formed at low rolling temperatures, but at higher temperatures this intensity was found to be drastically reduced. The development of shear bands at the higher rolling temperatures was significantly enhanced by alloying with chromium. The differences in shear band frequency and intensity are explained in terms of the dynamic strain aging behaviors of the various materials. Recrystallized grains were found to nucleate preferentially on the shear bands during annealing, regardless of their morphology or intensity.
Warm (ferritic) rolling can be a low cost method of producing sheet steel products. However, for steels containing solute carbon, microstructural development during processing is affected by dynamic strain aging (DSA). This can signi cantly weaken the {111} texture formed during annealing, thus resulting in products with poor formabilities. It is known that the DSA behaviour can be modi ed by the addition of elements such as boron and chromium. Experimental low carbon (LC) steels with various additions of chromium, boron and phosphorus were warm rolled and their behaviour compared with that of a standard LC material. It was found that these additions promote the formation of shear bands under warm rolling conditions, thus resulting in a stronger {111} recrystallisation texture than that of the unmodi ed LC steel.MST/5629
Warm-rolling trials were carried out on three interstitial-free (IF) steels (stabilized with either niobium or titanium), an extralow-carbon (ELC) steel, and an experimental low-carbon chromium (LC Cr) material at temperatures between 440 °C and 850 °C. The influence of rolling temperature on their as-rolled microstructures and deformation and recrystallization textures was investigated. Also, the effect of coiling simulation and degree of rolling reduction on the r values of some of these materials was examined. In-grain shear bands were evident in all as-rolled microstructures, but their sensitivity to deformation temperature varied between steels. Shear bands of moderate intensity were formed in the IF steels across all temperatures. In the ELC material, intense shear bands were formed at low rolling temperatures, but at higher temperatures, this intensity was drastically reduced. The development of shear bands at the higher rolling temperatures was significantly enhanced by alloying with chromium. The deformation textures produced were typical of rolled ferrite materials. The intensity of this texture increased markedly with temperature for the ELC grade. Conversely, the intensity of the recrystallization texture decreased with increasing temperature. The addition of chromium was found to strengthen the {111} component and, hence, the formability. The sharpness of both the deformation and recrystallization textures of the IF steels was relatively unaffected by rolling temperature. These differences are attributed to the intensity and frequency of shear-band formation and the dynamic strain-aging (DSA) behaviors of the various materials.
The effect of Si addition on the interaction between recrystallization and precipitation was investigated in terms of the no-recrystallization temperature (T nr ) on three microalloyed steels containing about 0.035 mass% Nb. The T nr was measured using torsion testing over the Si concentration range from 0.01 to 0.48 mass%. It was observed that the T nr increased with Si level, but appeared to saturate at long interpass times. In addition, high strains reduced the influence of Si on the T nr . This behaviour is attributed to the acceleration of Nb(C, N) precipitation by the addition of Si.
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