Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

Microstructure based modeling for the mechanical behavior of ferrite–pearlite steels suitable to capture isotropic and kinematic hardening

Abstract: This study proposes a new microstructure based model for the mechanical behavior of non-microalloyed ferrite–pearlite steels. Its main originality consists in estimating the internal stresses evolving with strain. It takes into account two contributions corresponding to two different scales of the microstructure: the huge internal stresses generated in pearlite all along the deformation and the mesoscopic strain incompatibility between ferrite and pearlite. This estimation allows the distinction to be made between the isotropic and kinematical components of work-hardening. The parameters of the model have been adjusted on numerous results from the literature concerning fully ferritic or pearlitic steels. The performance of the model is then demonstrated on datasets from the literature concerning steels with different fractions of pearlite. The predictions of the model are excellent concerning both tensile behavior and Bauschinger effects. The size effects of lamellar pearlite have been reviewed in this paper, i.e., the impact of interlamellar spacing on mechanical properties. In pearlite, the yield strength scales with s −1 , the internal stress with s −1/2 and the macroscopic strain-hardening (i.e., slope of the tensile curve) do not depend on interlamellar spacing. This review gives new perspectives for the understanding of the mechanical behavior of lamellar structures, such as pearlite or bainite.

Stress affected bainitic transformation in a FeCSiMn alloy

Abstract: Isothermal transformation experiments are reported in which the formation of bainitic ferrite occurs under the influences of stresses below the yield strength of the austenite. The response of the transformation was monitored by simultaneously measuring the longitudinal and radial transformation strains. This enabled the dilatational and deviatoric strain components to be deconvoluted from the total transformation strain. The data have been analysed by comparison with a theoretical model for the stress-assisted growth of bainite. The results confirm that the microstructure readily responds to stresses well below the yield strength of the parent phase. Furthermore, those crystallographic variants which are favoured by the stress grow first in the sequence of transformation. Experiments where the stress just exceeds the yield strength are also reported.

Thermal stability of retained austenite in bainitic steel: an in situ study

Abstract: The tempering of two-phase mixtures of bainitic ferrite and carbon-enriched retained austenite has been investigated in an effort to separate the reactions that occur at elevated temperatures from any transformation during cooling to ambient conditions. It is demonstrated using synchrotron X-radiation measurements that the residue of austenite left at the tempering temperature partly decomposes by martensitic transformation when the sample is cooled. It is well established in the published literature that films of retained austenite are better able to resist stress or strain-induced martensitic transformation than any coarser particles of austenite. In contrast, the coarser austenite is more resistant to the precipitation of cementite during tempering than the film form because of its lower carbon concentration.

Dual phase structure formed by partial reversion of cold-deformed martensite

Abstract: Effect of prior deformation and heating rate on the dual phase (DP) structure formed by partial reversion of cold-rolled martensite was investigated in a low carbon steel (0.15%C–1.0%Mn). The steel plate was quenched after austenitization to obtain full martensitic structure and then cold-rolled with varying reductions. The cold-rolled specimens were continuously heated at a slow (0.083 K/s) or fast (100 K/s) heating rate up to a temperature above A1 point to partially form reversed austenite. Increasing rolling reduction rate or lowering heating rate enhanced recrystallization on heating before the onset of reversion, while the undeformed martensite never caused recrystallization irrespective of heating rate. The matrix of DP structure was changed from tempered martensite to equiaxed ferrite through the recrystallization, which resulted in a large difference in the distribution of fresh martensite (reversed austenite). Tensile testing revealed that the excellent strength-elongation balance was obtained in the DP steel produced from undeformed martensite, while higher strength was realized in the steel with prior deformation. With increasing the rolling reduction and the heating rates, the grain size of recrystallized ferrite becomes finer and the tensile strength is more increased. It was also suggested that the competition between recrystallization and reversion during continuous heating could be predicted by the modified tempering parameter.