Influence of Niobium on the Beginning of the Plastic Flow of Material during Cold Deformation
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.
Lüders bands at the beginning of the plastic flow of materials
Intensive research into inhomogeneous deformations at the beginning of the plastic flow on different metal materials has been carried out during the last few years. Luders bands are detected using methods of static tensile testing, thermography and visioplasticity with digital image correlation. This paper is a review of insights into the mechanism of formation and parameters influencing the occurrence and propagation of Luders bands. Current knowledge indicates that there is not a full explanation of the cause of the Luders bands formation. There are also certain differences in the way some parameters influence the occurrence of Luders bands, primarily in different materials. Therefore, modern methods are used to explain the formation of Luders bands.
Effect of Initial Solidified Structure on Ridging Phenomenon and Texture in Type 430 Ferritic Stainless Steel Sheets
This study investigated the effect of the initial solidified structure on the ridging phenomenon and the texture in type 430 ferritic stainless steel sheets that have α+γ two-phases at high temperature. The initial solidified structure with equiaxed or columnar grains was used and the effect of annealing of hot-rolled sheet on the texture formation during cold rolling and annealing was investigated. The effect of the initial solidified structure on the ridging phenomenon differed depending on annealing of hot-rolled sheet. With annealing of hot-rolled sheet, the columnar grain specimen exhibited severer ridging than the equiaxed grain specimen. On the other hand, without annealing of hot-rolled sheet, there was no effect of the initial solidified structure, and both specimens showed slight ridging. The columnar grain specimen with {001}‹uv0› initial texture had strong {001}‹110› texture after hot rolling and annealing, and the grain colonies with {001}‹110› and {112}‹110› orientations were identified after cold rolling and annealing. However, without annealing of hot-rolled sheet, the equiaxed and columnar grain specimens showed roughly random textures. In the case without annealing of hot-rolled sheet, the deformation zone forming around the hard α′ phase during cold rolling was effective for no influence of the initial solidified structure and the microstructure before cold rolling.