Development of Ultra Fine Grain Steel Tube with High Strength and Excellent Formability

摘要

Kawasaki Steel Corporation developed the HISTORY process and the HISTORY tube. This new tubes are manufactured by the newly developed warm-reducing process which consists of a new thermo-mechanical control process. The HISTORY tube has following new superior features which can not be obtained in the conventional ERW tubes and steel sheets. The HISTORY tube can contribute to 20～30% of body weight reduction for automobile parts. (1) The HISTORY tube has uniform hardness distribution in the welded portion compared with the ERW tube. (2) The HISTORY tube has high strength and excellent formability. The high strength is obtained due to the ultra fine grain micro structure. The excellent formability is attributed to the suppression of work-hardening, dispersion of secondary phase, development of rolling texture and formation of dual phase structure. (3) The warm-reduced process of tubes can produce high carbon steel tubes with excellent formability with high productivity. (4) In the stretch bending, the HISTORY tube can be bent with smaller wall thickness reduction than that of the ERW tube. (5) In the three points bending, the HISTORY tube can be bent into U-shape without buckling on condition of two times diameter bend radius. (6) Fatigue limit of the HISTORY tube is higher than that of the ERW tube due to the higher tensile strength of the warm-reduced tube in the same materials.