Microstructure and microtexture assessment of delamination phenomena in charpy impact tested specimens

Abstract

In this article the delamination phenomena, which occurs in the X70 steel during fracture process from the Charpy impact tests, was investigated. Microstructure, microtexture and Taylor factor map analyses were performed by scanning electron microscopy, light microscopy and electron backscatter diffraction, respectively. In a cross-section of two fractured surface regions namely, in the perpendicular and parallel regions to the propagation fracture direction where delamination occurred, it was possible to notice that delamination showed a key role in the anisotropy of impact toughness between the L-T and T-L orientations. The results also revealed that the cause of the delamination can be attributed to the presence of microstructural banding and elongated ferrite grains aligned in a rolling direction. The presence of (100)[011] and (111)[110] crystallographic orientations, with Taylor factors close to 2.7 and 4.5, respectively, were identified in the delamination region. They contribute to the occurrence of cleavage delamination during the fracture process.

Influences of Thermomechanical Treatment and Nb Micro-alloying on the Hardenability of Ultra-High Strength Steels

“…Steels processed via TMP still are in competition to steels produced via the classical quenching and tempering (Q+T) route, as manufacturers promote the improved impact strength and better isotropy concerning their mechanical properties of Q+T steels. [14,[27][28][29][30] Therefore, we further intend to compare the hardenability of TM steels to that of the steels produced via a traditional Q+T route. In addition, CCT diagrams of the investigated steels will demonstrate the influences of the processing route and the Nb content on the c to a phase transformation and the resulting hardness values.…”

Corrosão Sob Tensão Em Solda Circunferencial De Aço Api 5l X70 Em Contato Com Etanol

“…Na Figura 8, a imagem (a) do MB fraturado por impacto evidencia uma delaminação alongada paralelamente ao progresso da fratura e várias fissuras perpendiculares, decorrentes da anisotropia microestrutural. Ampliações maiores nas imagens (b) e (c) mostram o aspecto misto Trincas e fissuramentos transversais podem ser causados por inclusões não metálicas ou por efeitos de orientações preferenciais de textura associados com alta densidade de grãos ferríticos alongados (como é o presente caso) e influem nos resultados de ensaios de tenacidade e fratura [17,18,21]. Uma observação um pouco mais detalhada revelou que as cavidades de delaminação identificadas nas superfícies de fratura em tração do MB (Figura 4) ocorrem pelo modo de fratura por clivagem, sendo possível identificar tais planos nas paredes dessas cavidades, como já foi observado por outros pesquisadores [19].…”

Effect of Local Crystallographic Texture on the Fissure Formation During Charpy Impact Testing of Low-Carbon Steel

“…[9] Several investigations have been carried out to understand the effect of microstructural constituents on the fissure formation in steel. [2][3][4]12,13,[15][16][17] A list of those studies is given in Table I. Presence of elements like S and P in steel at high level can develop coarse sulfide or phosphide inclusions (such as MnS and FeP) that can weaken the grain boundaries and promote ductile cracking.…”

“…[2,12] Microstructural banding is also reported to be responsible for fissure formation as the strain incompatibility between the adjacent hard and soft phases can generate fissures along the interface. [2,3,12,16] Fissures can also be developed by the decohesion at grain boundaries of the deformed ferrite grains having elongated structure along the rolling direction [4,13] and having high dislocation density. [15] Interaction of dislocations with grain boundaries weakens the grain boundary, which acts as the favorable path for fissure crack propagation.…”

“…Haskel et al demonstrated that the presence of {001}h011i and {111}h110i crystallographic orientations, which have large differences in Taylor factor along with banded microstructure and elongated grain, contribute to the fissure formation. [16] Inoue et al [18] attributed the fissure formation to the presence of a-fiber texture (Rolling Direction (RD)kh110i) developed during the warm caliber rolling of ferritic steel. In contradiction, several studies [2,3,14,15,17,19] also reported that crystallographic texture is not responsible for fissure formation.…”