A Novel Approach for Controlling the Band Formation in Medium Mn Steels

Abstract

Formation of the microstructural ferrite/pearlite bands in medium Mn steels is an undesirable phenomenon commonly addressed through fast cooling treatments. In this study, a novel approach using the cyclic partial phase transformation concept is applied successfully to prevent microstructural band formation in a micro-chemically banded Fe-C-Mn-Si steel. The effectiveness of the new approach is assessed using the ASTM E1268-01 standard. The cyclic intercritical treatments lead to formation of isotropic microstructures even for cooling rates far below the critical one determined in conventional continuous cooling. In contrast, isothermal intercritical experiments have no effect on the critical cooling rate to suppress microstructural band formation. The origin of the suppression of band formation either by means of fast cooling or a cyclic partial phase transformation is investigated in detail. Theoretical modeling and microstructural observations confirm that band formation is suppressed only if the intercritical annealing treatment leads to partial reversion of the austenite-ferrite interfaces. The resulting interfacial Mn enrichment is responsible for suppression of the band formation upon final cooling at low cooling rates.

Effects of Microstructural Morphology on Formability, Strain Localization, and Damage of Ferrite-Pearlite Steels: Experimental and Micromechanical Approaches

“…The simulation results also indicate that the tensile properties including tensile strength and ductility are weaker in the banded microstructure with the banding direction perpendicular to the tensile axis, as mentioned in previous studies. [7,10] Local micromechanical deformation behavior resulted from the RVE simulations has been investigated for the non-banded and banded microstructures with the banding direction parallel to the tensile axis during uniaxial tension. Figures 5(a 1 ) and (b 1 ) show the evolution of equivalent strain in the non-banded microstructure at two deformation steps (e eq ¼ 0:04; 0:08).…”

“…When the steel temperature reaches the eutectoid temperature, pearlite is nucleated by simultaneous precipitation of ferrite and cementite in the segregated regions. [7] Previous investigations have shown that the occurrence of ferrite-pearlite banding strongly depends on the cooling rate after austenitization of steels. No ferrite-pearlite banding can occur at high cooling rates such as air-cooling, while low cooling rates lead to an intense microstructural banding.…”

“…In general, ferrite-pearlite banding in ferritic-pearlitic steels results in an undesirable decrease of the mechanical properties perpendicular to the banding direction. [7] Additionally the influences of microstructural banding on the bendability have been studied in several works. [11][12][13] It was shown that banded structures have potentially deleterious effects on the bendability.…”

Effects of Alloying Elements (C, Mo) on Hydrogen Assisted Cracking Behaviors of A516-65 Steels in Sour Environments

“…There were also differences between Steel B and C with relatively low fractions of pearlite. Compared to Steel B, Steel C showed a high degree of pearlite dispersion in the microstructure, meaning that the pearlite banding index, defined previously [39,40], of Steel C was lower. A high degree of pearlite dispersion in Steel C is closely associated with the addition of Mo in the steel.…”

Effect of the Initial Microstructure and Thermal Path on the Final Microstructure and Bendability of a High Strength Ferrite-martensite Dual Phase Steel

“…It should be pointed out that the inhomogeneous Mn distribution causing the banded microstructure in the FP steel is still present in the homogeneous B steel. 23)…”