Analysis of internal crack in a six-ton P91 ingot

P91 is a new kind of heat-resistant and high-tensile steel. It can be extruded after ingot casting and can be widely used for different pipes in power plants. However, due to its mushy freezing characteristics, a lack of feeding in the ingot center often generates many defects, such as porosity and crack. A six-ton P91 ingot was cast and sliced, and a representative part of the longitudinal section was inspected in more detail. The morphology of crack-like defects was examined by X-ray high energy industrial CT and reconstructed by 3D software. There are f ive main portions of defects larger than 200 mm^3, four of which are interconnected. These initiated from continuous liquid f ilm, and then were torn apart by excessive tensile stress within the brittle temperature range(BTR). The 3D FEM analysis of thermo-mechanical simulation was carried out to analyze the formation of porosity and internal crack defects. The results of shrinkage porosity and Niyama values revealed that the center of the ingot suffers from inadequate feeding. Several criteria based on thermal and mechanical models were used to evaluate the susceptibility of hot crack formation. The Clyne and Davies' criterion and Katgerman's criterion successfully predicted the high hot crack susceptibility in the ingot center. Six typical locations in the longitudinal section had been chosen for analysis of the stresses and strains evolution during the BTR. Locations in the defects region showed the highest tensile stresses and relative high strain values, while other locations showed either low tensile stresses or low strain values. In conclusion, hot crack develops only when stress and strain exceed a threshold value at the same time during the BTR.

Bilateral retrocorneal hyaline scrolls secondary to asymptomatic congenital syphilis: A case report

BACKGROUND Retrocorneal hyaline scrolls are a rare phenomenon.We report a case of bilateral retrocorneal hyaline scrolls that were likely induced by asymptomatic congenital syphilis.CASE SUMMARY A 71-year-old woman presented with blurred vision due to cataracts.Slit-lamp microscopy revealed bilateral hyaline scrolls with a dichotomous branching pattern extending to the anterior chamber or rods attaching to the rough posterior surface of the cornea.The patient was positive for syphilis-specific antibodies,with no ocular or systemic evidence of congenital or acquired syphilis.Binocular cataract,retrocorneal scroll,and corneal endothelial gutta were considered.The scroll of the right eye was removed during cataract surgery and further observed using hematoxylin–eosin staining and scanning electron microscopy.The cornea of the right eye remained transparent,and the residual scroll seemed stable,however,the corneal endothelial density declined at 13 mo after surgery.In vivo confocal microscopy revealed coalescence of corneal guttae at the level of the corneal endothelium or adhesion to the posterior surface of the endothelium,with enlarged endothelial cells in both eyes.Activated keratocytes in the stroma and a highly reflective acellular structure at the level of the Descemet’s membrane were observed.The removed scroll had a cartilage-like hardness and a circularly arranged fiber-like acellular structure.CONCLUSION Occult congenital syphilis could induce corneal endothelial gutta and theformation of retrocorneal scrolls without other signs of ocular syphilis.