Influence of Niobium on the Beginning of the Plastic Flow of Material during Cold Deformation

Abstract

Investigations were conducted on low-carbon steel and the steel with same chemical composition with addition of microalloying element niobium. While tensile testing was carried out, the thermographic measurement was tacking place simultaneously. A specific behavior of niobium microalloyed steel was noticed. Test results have shown that, in the elastic deformation region, thermoelastic effect occurs, which is more pronounced in niobium microalloyed steel. Start of plastic flow in steel which is not microalloyed with niobium begins later in comparison to the microalloyed steel, and it is conducted so that, at the point of maximum stress, deformation zone is formed within which stresses grow. In steel microalloyed with niobium after proportionality limit, comes the occurrence of the localized increase in temperature and the occurrence of Lüders band, which propagate along the sample forming a deformation zone.

The Impact of Hot Rolling Temperature after Reheating in the New Generation Strip Casting Process on Structure‐Property Relationship in Extra‐Low Carbon Steel

“…In a number of low carbon steels, the yield point and Lüders elongation usually appear at the beginning of tensile deformation . It is considered that the main reason for the occurrence of Lüders bands is pinning of dislocations induced by dissolved C and N atoms, which form the so‐called Cottrell atmosphere .…”

Dependence of thermoelastic effect on volume change by elastic deformation

“…By using digital image correlation it is possible to measure small deformations and calculate the mentioned changes in volume during the elastic deformation. The earlier studies on niobium microalloyed steel have shown the presence of thermo-elastic effect during elastic deformation of these steel [10].…”

“…have an additional impact on this effect. Thus, delaying the onset of plastic deformation, as is the case in niobium microalloyed steels, due to the dislocation blocking precipitates [10] the temperature drop is further pronounced. Foreign atoms and crystal lattice faults can, depending on their nature, increase or decrease the amount of volume change during the elastic stretching.…”

The Application of a Factorial Experiment with Repeated Measurements in the Investigation of Parameters Influencing the Properties of Niobium Microalloyed Cold Drawn Welded Steel Tubes

“…Tests have shown that the subsequent cold deformation results in significant hardening [5]. Inhomogeneous deformations at the beginning of the plastic material flow were observed during the cold drawing of niobium microalloyed steel tubes [6,7]. These inhomogeneous deformations are associated with the appearance and propagation of Lüders bands.…”