Why Do Secondary Cracks Preferentially Form in Hot-Rolled ODS Steels in Comparison with Hot-Extruded ODS Steels?

Abstract

Secondary cracks are known to absorb energy, retard primary crack propagation and initiate at lower loads than primary cracks. They are observed more often in hot-rolled than in hot-extruded ODS steels. In this work, the microstructural factors responsible for this observation are investigated. Better understanding of these factors can lead to tailoring of improved ODS steels. Fracture toughness testing of two batches of 13Cr ODS steel, one hot-rolled and the other hot-extruded, was carried out. The fracture behaviour of secondary cracks was investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Crystallographic texture and grain morphology play a predominant role in preventing secondary cracks in hot-extruded ODS steels. At lower temperatures, secondary cracks occur predominantly via transgranular cleavage. The fracture mode changes to ductile and intergranular at higher temperatures.

Analysis of Ductile Fracture Obtained by Charpy Impact Test of a Steel Structure Created by Robot-Assisted GMAW-Based Additive Manufacturing

“…The secondary cracks might also have been generated due to the stacked layers, which act as a crack divider, as depicted in Figure 13. This delamination phenomenon can occur even without a substantial difference between the interlayer and intralayer microstructures [35]. Another important factor responsible for the high absorbed energy is the formation of secondary cracks.…”

“…The secondary cracks might also have been generated due to the stacked layers, which act as a crack divider, as depicted in Figure 13. This delamination phenomenon can occur even without a substantial difference between the interlayer and intralayer microstructures [35]. As the fracture was purely in the upper shelf region and was ductile in nature, fracture toughness can be estimated using the relation [36,37]: K IC = 0.804 σ ys (CVN/σ ys − 0.0098) 0.5 (1) where K IC is the fracture toughness in MPa•m 1/2 , σ ys is the yield strength in MPa, and CVN is the Charpy impact absorbed energy in J.…”

Fundamental Improvement of Creep Resistance of New-Generation Nano-Oxide Strengthened Alloys via Hot Rotary Swaging Consolidation

“…Special care must be taken to avoid significant inhomogeneities in the grain size, as this may cause secondary cracking or delamination, as described in [ 51 , 52 ]. Thus, complete secondary recrystallization is required to proceed in the samples.…”