INFLUENCEOFROLLINGCONDITIONSONTHE
QUALITYOFHOT-ROLLEDSTEELSTRIP
Yu. D.Zheleznov, Yu. A. Mukhin,
S. L.Kotsar',V.F.Usenko,andV.V.Chvilev
The temperature and speed conditions in roiling are a very important factor in determining the geometry and mechanical properties of hot-rolled strip. By maintaining the specified temperature at the end of roiling and by regulating the temperature of the steel during coiling, it is possible to maintain a stable thickness and the required mechanical properties over the length of the coil without further heat treatment. The temperature drop over the length of the strip may be decreased by accelerating the finishing group of the mill with the steel in the rolls.
The building of new hot-rolled strip mills, such as the 2000 mill at Novo-Lipets Plant or the1700 mill at Karaganda Combine,equipped with systems for accelerating the finishing group with the metal in the rolls, requires many-sided study of the influence of acceleration on the temperature conditions of the rolling and on the quality of the sheet.
To study the relationship between accelerating roiling and the quality of hot-rolled strip steel, experimental rollings were made on the 2000 continuous wide-strip mill of Novo-Lipets Metallurgical Plant of 1.2×1050 mm strip of St. 3kp steel and 2.0×1050 strip of St. 2kp steel with varying amounts of acceleration. The strip was rolled from 170×1070×5000 turn slabs, using the method normally used on the mill. Acceleration of the finishing group was started after the strip was grasped by the coilers, at a distance of 230－240m from the finishing stand. As a result, the first half of the strip was rolled without acceleration, and the second, with the specified amount.
To determine the influence of acceleration on the mechanical properties and structure of the strip, six samples -- three longitudinal and three transverse - were taken at the start and finish of the accelerated portion. The samples were tensile-tested according to GOST 1497－61. The tensile strength, yield strength, and elongation were recorded. The experimental data obtained was handled statistically. The relationship of the tensile strength and its spread to the acceleration in rolling the 2.0×1050 strip is as follows:
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