Penny-shaped Central Bursting Defect in the Cold Drawing of High Chromium Ferritic Stainless Steel

Abstract

The phenomenon of central bursting during cold drawing of a high-purity high-chromium ferritic stainless steel has been investigated, and it is well established that the defect forms periodically in the drawing direction and does not have the usual chevron or arrow shape but a penny shape. The defect is generated by cleavage fracture at the centerline of the billet, depending on the stress state when plastically deformed during drawing. In drawing the hydrostatic stresses are most tensile in the slipline field analysis, and the damage at a critical tensile stress is most severe at the centerline despite the small amounts of deformation and strain-hardening. The growth of defects takes places in a direction perpendicular to the highest tensile stress by discontinuous cleavage propagation to form the penny shape. Blunting of the crack tip occurs in the region directly under the die and then the crack propagation rate is retarded to stop. Mechanical properties of the high-purity highchromium stainless steel play a very important role in the damage formation process.

Transmission detection of internal defects in billets using shear ultrasonic waves

“…2,3) In the casting process, gases such as carbon dioxide and nonmetallic inclusions remain inside the billets as defects. 4,5) These defects can be stretched during processing and cause cracks, which will affect the quality of the final product. [6][7][8] Defects with a diameter of 2-3 mm are called pinholes, while larger defects are called blowholes.…”

Interval of Observation Plane in Visualization of Region near Defects in Billets Using Ultrasonic Computerized Tomography Method

“…They might include defects caused by inclusions mixed in the molten steel or gas bubbles remaining at the time of solidification. [1][2][3] Since defects affect the production efficiency of steel products and the quality of the final products, it is necessary to detect defects nondestructively. Although there are various inspection methods, [4][5][6][7][8][9][10] for the nondestructive testing of defects in billets, the most effective is the use of ultrasound.…”

Speeding Up of Nondestructive Inspection for Shape-Distorted Billet by Simultaneous Measurement of Time of Flight

“…A steel billet sometimes contains residual gas, such as CO 2 , during manufacturing processes. [1][2][3] An inner defect owing to remaining gas reduces the production efficiency because a billet with an inner defect must be remelted. Additionally, such defects degrade the final product quality.…”