Increasing technological plasticity with preserving strength of cold-rolled thin-sheet low-carbon steel

Abstract

At domestic metallurgical plants, the traditional method of softening low-sheet cold-rolled low-carbon steels is long recrystallization annealing of coils in cap furnaces, which has significant disadvantages: the process is very long and energy-consuming. According to the properties of annealed steel, it does not meet the requirements of the consumer for the manufacture of two-layer rolled brazed tubes. In this regard, the question of developing a new method of weakening heat treatment of cold-rolled sheet to improve the set of properties and the quality of the sheet surface is relevant in time and has unconditional practical significance with the prevention of its deformation aging. To achieve this goal the following tasks were solved: research and determination of optimal temperature-time parameters of high-speed contact recrystallization annealing and subsequent aging (which has no analogues) of thin tape blanks to obtain a given set of performance properties and prevention of natural aging. The best mode of contact high-speed (100 0 C / c) recrystallization annealing is established, which provides cold-rolled sheet steel 08 kp with a set of properties that corresponds to GOST 9045-93 category VG, i.e. the ability of steel to cold complex deformation. However, further deformation aging of annealed steel at a speed of 08 kp leads to a sharp drop in ductility and increased strength. Developed a two-stage softening high-speed heat treatment consisting of recrystallization annealing and subsequent aging, increases both the strength and ductility of cold-rolled sheet, stabilizes the properties of steel to prevent its deformation aging. The obtained properties meet the regulated requirements of the consumer to the blanks intended for production of the two-layer rolled up soldered tubes operated in the conditions of the increased pressure. Tubes of small diameter, which were made of steel strips, processed by the recommended technology, have successfully passed 100 % defect-free quality control in the production environment.