The role of deformed rail microstructure on rolling contact fatigue initiation

A detailed qualitative and quantitative examination of the microstructure and mechanical properties of three different classes of DP600 and DP450 dual-phase (DP) steels was carried out. The tested DP steels are characterized by different alloying elements: aluminum, boron, and phosphorus. Among them, aluminum DP steels showed the lowest percentages of hard phases, while phosphorus DP steels exhibited the highest resistance values. The Hollomon, Pickering, Crussard–Jaoul (CJ), and Bergstrom models were used to reproduce the strain hardening behavior of DP steels. Relationships that correlate the fitting parameters with the chemical composition and the thermal cycle parameters were found, and the predictive abilities of different models were evaluated. The Pickering equation, among the tested models, is the best one in the reproduction of the experimental stress-strain data.

Strain Hardening Behavior of Dual-Phase Steels

A new 3D multiphase FE model for micro cutting ferritic–pearlitic carbon steels

https://profdoc.um.ac.ir/articles/a/1029226.pdf

FEM modeling of the flow curves and failure modes of dual phase steels with different martensite volume fractions using actual microstructure as the representative volume

A model of plastic strain accumulation, wear, and rolling contact fatigue (RCF) crack initiation in rail steel has been developed. Local to the contact zone, material is subject to severe cyclic stresses taking it beyond yield and leading to incremental accumulation of plastic deformation (ratcheting). This model is based on a ratcheting law derived from twin-disc, rolling-sliding contact experiments and can simulate thousands of ratcheting cycles with corresponding strain hardening.The model is being further refined to account for detailed microstructural changes. Sections of worn and fatigued rail, removed from service, have been metallurgically analysed. To obtain further data on rail-steel deformation and RCF crack initiation, twin-disc tests have been performed using discs cut from across a railhead and wheel rim. Two heat treatments were applied to some rail discs to investigate the effect of pro-eutectoid ferrite phase distributions and volume fractions. Tests were run to failure (defined b...

Predicting the life of steel rails

Flow curves of ferrite/pearlite two-phase steels were simulated using finite element method (FEM) with regression equations for flow curves of each ferrite and pearlite phase proposed by Hiramatsu et al. and Furukawa et al. The calculated flow strength of ferrite/pearlite two-phase steel was lower than the experimentally measured one mainly due to the underestimation of flow strength of ferrite phase according to the yield elongation. To improve the simulation, the flow curves in homogeneous deformation range were considered. Microscopic observations revealed that most deformation was accumulated in the ferrite phase during yield elongation. Flow curves of ferrite phase were re-evaluated based on this observation and flow curves of ferrite/pearlite steels were also re-calculated. Re-calculated yield strength of ferrite/pearlite steels showed good agreement with measured ones, however the work hardening rate of re-calculated flow curves is still lower than that of measured one. The simplicity of pearlite morphology for FEM analysis is thought to be responsible for lower work hardening behavior of calculated flow curve by FEM than that of measured one.

FEM Modeling of Flow Curves for Ferrite/Pearlite Two-Phase Steels

The Quantitative Analysis of Composite Materials by the RIETVELD Method with Texture Correction

The effect of shape and volume fraction of retained austenite on the uniaxial behavior of transformation induced plasticity(TRIP) steels was studied by using the numerical and experimental methods. 0.16%C-1.4%Si-1.4%Mn TRIP steels were intercritically annealed at 800 o C and 840 o C, and isothermally transformed at 450 o C (Banite Transformation) during 1, 5 and 10 min. As the bainite isothermal transformation time increased, the volume fraction of retained austenite, tensile stress and total elongation decreased, and 0.2% yield stress increased. Finite element method calculations were carried out by using ABAQUS user subroutine UMAT based on the finite deformation theory and self-consistent method. Numerical results were in good agreement with experimental data.

Jin Ho Bae

Papers

FEM Modeling of Flow Curves for Ferrite/Pearlite Two-Phase Steels

The Quantitative Analysis of Composite Materials by the RIETVELD Method with Texture Correction

Prediction of Mechanical Properties of TRIP Steels by FEM and Micromechanics