| 摘要 |
PROBLEM TO BE SOLVED: To provide an Ehrhardt piercing process by which a pipe with a bottom in which remaining of internal defects due to shrinkage and cavities is manufactured under the condition of low piercing ratio to high chromium steel. SOLUTION: In the Ehrhardt piercing process which is a method for manufacturing the pipe with a bottom by performing piercing by force-fitting a core bar from the upper surface of a steel ingot housed in a container, the core bar is composed of a cylindrical body part and a contracted diameter part which is connected to the end part of the body part, and the ratio d/D of the outer diameter d of the body part to the inner diameter D of the container is 0.35-0.45. The contracted diameter part of the core bar is gradually reduced in the outer diameter as shifting to the direction of the tip and has a flat part of d1 in the diameter at the tip, the ratio d1/d of the outer diameter d1 of the flat part to the outer diameter of the core bar is 0.70-0.82 and the ratio L/d of the length L of the contracted diameter part of the core bar to the outer diameter d of the body part of the core bar is≥0.90. COPYRIGHT: (C)2011,JPO&INPIT
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