Abstract: A preforming method for a high-strength steel variable-diameter tubular part is provided, which belongs to the technical field of metal forming process. The preforming method for a high-strength steel variable-diameter tubular part includes: selecting a tubular blank; and preparing a tubular blank forming mold, where the tubular blank forming mold includes a preforming mold and a final forming mold; sealing and pressurizing the tubular blank; heating the tubular blank by using electrodes; preforming the tubular part at a constant temperature; maintaining a temperature T1 and moving the preformed tubular part to the final forming mold;finally forming the tubular part. Through two steps of operation of preforming and final forming, and maintaining a temperature during moving the tubular blank between the two steps, so that the conversion of intrametallic structure between the two steps is improved, and the performance of the tubular part is improved.

Abstract: Disclosed is a mold for partially shortening the circumference of a tube billet and a using method of the mold. The mold comprises an upper mold, a lower mold and a mold core used for being inserted into a tube cavity of the tube billet, wherein the upper mold is provided with an upper mold cavity, the lower mold is provided with a lower mold cavity, and the upper mold cavity and the lower mold cavity are matched to form a mold cavity. After the mold core is placed in the mold cavity, a tube billet deformation cavity is formed in the mold cavity; and the upper mold cavity and/or the lower mold cavity are/is in the shape of a flaring, the two sides of the flaring are arc-shaped, and included angles are formed between the two sides of the flaring and the moving direction of a movable mold.