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|1. (WO2017154481) METHOD FOR MANUFACTURING DIFFERENT-THICKNESS STEEL PIPE, AND DIFFERENT-THICKNESS STEEL PIPE|
|Applicants:||NIPPON STEEL & SUMITOMO METAL CORPORATION
|Title:||METHOD FOR MANUFACTURING DIFFERENT-THICKNESS STEEL PIPE, AND DIFFERENT-THICKNESS STEEL PIPE|
This method for manufacturing a different-thickness steel pipe, which manufactures a different-thickness steel pipe from a hollow cylindrical element pipe, has: a locking step, wherein the element pipe is arranged inside a die and a plug is inserted from one end of the element pipe while movement of the element pipe in the lengthwise direction is restricted, thereby enlarging the outer shape of that one end and locking the element pipe in the die; and an ironing step, wherein the restriction of the element pipe is released and, while the locking of the element pipe is maintained, the plug is inserted farther toward the other end of the element pipe, thereby enlarging the inside shape while maintaining the outside shape of the element pipe and forming a thin section.