Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ul...Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon （ULC） steel slabs and two low carbon （LC） aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-disper-sive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density （ND） of subsurface inclusions larger than 200μm decreased from 0.02 to 0 cm-2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200μm were concentrated in the region near the slab center （3/8 width-5/8 width）, where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.展开更多
Creep tests of T92/Super304H joints were performed at 923 K under the stress of 85-165 MPa. Microstructure evolution was characterized by light microscopy, scanning electron microcopy and transmission electron microsc...Creep tests of T92/Super304H joints were performed at 923 K under the stress of 85-165 MPa. Microstructure evolution was characterized by light microscopy, scanning electron microcopy and transmission electron microscopy to probe the relationship between creep performance deterioration and microstructure evolution. Results showed that for all the creep tests, failure occurred at fine-grained heat-affected zone of T92, and the joints have lower creep strength than the base metal T92. However, as the stress increased from 85 to 165 MPa, the creep fracture changed from a mixed mode, i.e., intergranular fracture in the center part and transgranular fracture in the edge part to total transgranular fracture. The longer the creep life, the greater is the proportion of the intergranular fracture. The M23C6 coarsened and the Laves phase precipitated along grain boundaries during long-term creep. Vacancies nucleate and propagate at the interface between coarse M23C6, Laves phase and matrix. Finally, cracks forming along grain boundaries are responsible for intergranular fracture.展开更多
文摘Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon （ULC） steel slabs and two low carbon （LC） aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-disper-sive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density （ND） of subsurface inclusions larger than 200μm decreased from 0.02 to 0 cm-2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200μm were concentrated in the region near the slab center （3/8 width-5/8 width）, where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.
文摘Creep tests of T92/Super304H joints were performed at 923 K under the stress of 85-165 MPa. Microstructure evolution was characterized by light microscopy, scanning electron microcopy and transmission electron microscopy to probe the relationship between creep performance deterioration and microstructure evolution. Results showed that for all the creep tests, failure occurred at fine-grained heat-affected zone of T92, and the joints have lower creep strength than the base metal T92. However, as the stress increased from 85 to 165 MPa, the creep fracture changed from a mixed mode, i.e., intergranular fracture in the center part and transgranular fracture in the edge part to total transgranular fracture. The longer the creep life, the greater is the proportion of the intergranular fracture. The M23C6 coarsened and the Laves phase precipitated along grain boundaries during long-term creep. Vacancies nucleate and propagate at the interface between coarse M23C6, Laves phase and matrix. Finally, cracks forming along grain boundaries are responsible for intergranular fracture.
