Bainite steel: structure and work hardening

Abstract

Using the methods of transmission electron diffraction microscopy, a quantitative evolution analysis of defective and carbide subsystems of medium-carbon steel with a bainite structure under a compression strain up to 36% has been performed. A quantitative analysis of carbon redistribution has been carried out, as well as the dependence established of the concentration of carbon atoms arranged in a crystal lattice of-and-iron on structural defects in cementite particles lying in a number of bainite plates and intra-phase boundaries, and on the degree of deformation. It has been demonstrated that scalar dislocation density, material volume with deformation twins, a number of stress concentrators, the amplitude of crystal lattice curvature-torsion, the disorientation degree of fragments are increased with the growth of the degree of deformation and average longitudinal fragment sizes are decreased. The long-range stress fields have been estimated. The possible causes of the different stages of parameter changes of the carbide phase and dislocation substructure with deformation have been discussed. Strengthening mechanisms with the boundaries of the plates and fragments, scalar dislocation density, long-range stress fields, and cementite particles, the interstitial atoms have been estimated. It has been shown that the largest contribution to the amount of work hardening of the steel examined leads to substructural hardening (hardening due to long-range internal stress fields and structure fragmentation) and solid-solution hardening, due to the introduction of carbon atoms into the crystal lattice of the ferrite. It has been suggested that the cause of softening of steel with a bainite structure at high (over 15%) degrees of deformation is the activation of the process of deformation fine-scale twinning.

Analysis of stress distribution in a rail by electromagnetic-acoustic method

“…Rails undergo heat treatment in the manufacturing process [6]. Quenching is a basic step of heat treatment.…”

Experimental Consideration of Conditions for Measuring Residual Stresses of Rails Using Magnetic Barkhausen Noise Method

“…The residual stresses remain inside materials after manufacture, processing, and heat treatment, which condition is known to cause destruction of structural materials [2]. Rails Materials 2021, 14, 5374 2 of 13 undergo a heat treatment process and a roller straightening process during manufacture, and at these times, residual stresses form inside [3,4]. In addition, the rails are subjected to vertical loads due to wheel rolling, to shear loads caused by train braking and traction during train driving, and to fatigue conditions due to repetitive loads [5,6].…”