Dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing

Abstract

The dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests, using a torsional Kolsky bar, were conducted on four steel specimens, two of which were annealed at 480 °C after ECAP, and then the test data were compared in terms of microstructures, tensile properties, and adiabatic shear-band formation. The equal-channel angular pressed specimen consisted of very fine, equiaxed grains of 0.2 to 0.3 m in size, which were slightly coarsened after annealing. The dynamic torsional test results indicated that maximum shear stress decreased with increasing annealing time, whereas fracture shear strain increased. Some adiabatic shear bands were observed at the gage center of the dynamically deformed torsional specimen. Their width was smaller in the equal-channel angular pressed specimen than in the 1-hour-annealed specimen, but they were not found in the 24-hour-annealed specimen. Ultrafine, equiaxed grains of 0.05 to 0.2 m in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries. These phenomena were explained by dynamic recrystallization due to a highly localized plastic strain and temperature rise during dynamic deformation.

Compressive and Tensile Properties of STS304-Continuous-Fiber-Reinforced Zr-Based Amorphous Alloy Matrix Composite Fabricated by Liquid Pressing Process

“…The band is 20-to 30-lm wide, and its boundaries are not clearly demarked from the nearby region because of severe deformation. At boundaries of the shear band and matrix, some weak plastic striations, observed previously by other researchers, [20][21][22] are found. Inside the shear band, many voids are formed at interfaces between Cr carbides present in STS fibers (white precipitates) and matrix (Figure 8(c)).…”

“…The main cause of the adiabatic shear band formation is the thermomechanical instability occurring during dynamic deformation. [21,22] When the composite is plastically deformed, the plastic work generates some heats as shear bands initiated at the amorphous matrix propagate rapidly, which induces the material to soften because of the lack of time for the heat to be transferred to the outside. This thermal instability further accelerates the localized deformation and causes concentration of the shear deformation to form an adiabatic shear band.…”

Structure and mechanical properties of the low-carbon steel after severe plastic deformation and forging

“…Данный недостаток можно устранить последующей ВК, в процессе которой заготов-ка подвергается многократному повторению операций свободной ковки. Дополнительная об-работка ВК открывает новые перспективы при-менения технологии РКУП, так как существенно расширяется номенклатура изделий, обладаю-щих наносубмикронной структурой с уникаль-ными свойствами, полученными после нано-структурирования [11][12][13][14][15][16][17][18][19].…”

Correlation of Microstructure and Cracking Phenomenon Occurring during Hot Rolling of Lightweight Steel Plates

“…Even when the Mn and Al addition is reduced, e.g., from 15 to 10 wt pct, the cracking occurring during hot rolling can be a serious problem. [7,8] It was reported that this cracking was caused by the following: (1) inhomogeneous microstructures due to the segregation of C and Mn at high temperatures, (2) rolling anisotropy as a result of the formation of dendrite-type microstructures, (3) formation of oxides or nitrides due to the exposure at high temperatures, and (4) void formation arising from oxides fallen off from the friction or impact between rolls and steel plates. Because the lightweight steels containing approximately 10 wt pct Mn and Al are newly developed, their detailed microstructures or deformation and fracture mechanisms are hardly known.…”

“…Furthermore, very few studies have been conducted in order to systematically explain the cracking phenomenon of hot-rolled steel plates in terms of microstructural parameters, except for some studies related to textures and the segregation of precipitates. [7][8][9][10] In the present study, two hot-rolled lightweight steel plates were fabricated, and the cracking phenomenon occurring during hot rolling was clarified in relation to the microstructure. Microstructural analysis, tensile testing, and high-temperature compression testing were conducted to study the cracking behavior and the formation process of high-temperature microstructures.…”