Process for hot rolling steel strips and hot rolling train

Abstract

The invention relates to an apparatus and a process for hot rolling steel strips (3) in a plurality of successive roll stands (F1-F5), wherein the steel strips are finish-rolled to the end thickness in one or more roll stands firstly in the austenitic state and then, after liquid cooling, in the ferritic state. In order to ensure that the steel strip actually reaches the ferritic state after cooling, it is provided that the end thickness of the steel strip (3) is less than 3 mm, that the difference between the outlet temperature of the steel strip from the last roll stand (F3) before liquid cooling and the equilibrium austenite boundary temperature is set by the pilot control or regulation of the outlet temperature to no more than 70 K, preferably no more than 50 K, preferably less than 25 K, and that the liquid cooling takes place between two roll stands depending on the length (Lc) of a cooling section (1) by the application, in the cooling section and on both sides of the steel strip (3), of at least in each case a quantity of liquid Qu > 284 / (Lc1.42) litres per minute and per metre of strip width, in particular Qu > 2*284 / (Lc1.42) litres per minute and per metre of strip width, but not more than Qu = 7*284 / (Lc1.42) litres per minute and per metre of strip width, preferably Qu < 4*284 / (Lc1.42) litres per minute and per metre of strip width.

Description

technical field [0001] The invention relates to a method for hot rolling a steel strip in a plurality of successive rolling stands first in the austenitic state and then in the ferritic state after forced intermediate stand liquid cooling Finish rolling to final thickness in one or more rolling stands and a corresponding hot-rolling train. Background technique [0002] When the rolled piece has a temperature higher than its recrystallization temperature when it is rolled, it is called hot rolling. For steel the temperature is in the range above about 780°C, typically hot rolling is performed at temperatures up to 1200°C. [0003] When hot rolling steel, the metal is mostly in the austenitic state in which the iron atoms are arranged in a face-centered cubic manner. In this case, the degree of deformation, ie the ratio of output thickness to input thickness, can be as high as 1:200: for example, a slab thickness of typically 240 mm can be reached to a final thickness of 1.2...

AI Technical Summary

Problems solved by technology

[0007] However, these measures alone do not guarantee a controlled cooling of the steel strip which, depending on the strip width, thickness, temperature before cooling, etc., actually reaches the ferrite state after cooling

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