US 6,309,482 B1 · Steckel mill/on-line controlled cooling combination

Abstract

The in-line combination of a reversing rolling mill (Steckel mill) and its coiler furnaces with accelerated controlled cooling apparatus immediately downstream thereof and associated method permits steel to be sequentially reversingly rolled to achieve an overall reduction of at least about 3:1, imparted by a first reduction while the steel is kept at a temperature above the Tnr by the coiler furnaces so as to preserve an optimum opportunity for controlled recrystallization of the steel after each rolling pass, and a second reduction while the temperature of the steel drops from about the Tnr to about the Ar3. The second reduction is preferably of the order of 2:1 as a result of which the steel reaches a final plate thickness. The steel product then passes through the accelerated controlled cooling apparatus, preferably applying laminar flow cooling at least to the upper surface of the steel passing therethrough so as to reduce the temperature of the steel from about the Ar3 to a temperature at least about 250° C. to about 300° C. or more below the Ar3 at a cooling rate of at about 12° C. to about 20° C. and preferably about 15° C. per second, thereby to achieve a preferred fine-grained predominantly bainite structure affording enhanced strength and toughness in the final steel product.

Claims44

Dependent claims

In a steel rolling mill, the in-line combination of

(a) a Steckel mill for reversingly rolling a steel product above Tnr to an interim reduced thickness and to obtain a controlled austenite recrystallization of the steel microstructure, and between Tnr and Ar3 to a target end-product thickness and to pancake the austentite microstructure, the Steckel mill having associated upstream and downstream coiler furnaces for coiling steel product of a suitable thickness and maintaining the temperature of the steel product above Tnr to obtain a controlled recrystallization of the steel;
(b) a flying shear in the vicinity of the Steckel mill, for severing the leading edge of the steel product;
and for steel product having a weight exceeding the capacity of a limiting apparatus in the combination, also for severing the steel product into a target portion having a weight within the capacity of the limiting apparatus, and a surplus portion;
and
(c) a controlled cooling apparatus downstream of the Steckel mill and the shear, the controlled cooling apparatus being operational to, in a single pass of the steel product therethrough following the rolling in the Steckel mill, reduce the temperature of the steel product from an entry temperature of about the Ar3 to an exit temperature of at least about 200° C. lower than the Ar3, at a cooling rate of about 12° C. to about 20° C. per second, in order to obtain a product having a relatively large amount of bainite and being relatively free of marsenite.

2 more elements

A method of optimizing the production of a steel rolling mill that includes a Steckel mill,

the operation of said rolling mill being limited at least in part by an applicable limiting flow-through parameter being one of (i) at least one strip flow-through capacity parameter for a strip end-product, and (ii) at least one plate flow-through capacity parameter for a plate end-product;
the method including the rolling of a maximum-weight slab exceeding the applicable flow-through capacity parameter and the severing of the slab to obtain an end-product of a target weight and target dimensions, the target weight of the particular end-product of target dimensions being limited by the applicable limiting flow-through capacity parameter;
the Steckel mill having associated therewith upstream and downstream coiler furnaces capable of coiling plate up to coiler furnace thickness and weight limitations and downstream equipment for further processing and handling of the steel following its rolling;
the method comprising the steps of:
(a) flat-pass rolling the maximum-weight slab in the Steckel mill from a pre-rolled thickness to produce an interim steel product of a severable thickness exceeding the coiler furnace thickness limitation;
then
(b) transversely severing the interim steel product into two portions, viz a pre-determined target portion having a target weight selected to be within the coiler furnace weight capacity, and a residual surplus portion;
(c) flat-pass rolling the target portion in the Steckel mill to further reduce the target portion from the severable thickness to a thickness not exceeding the coiler furnace thickness limitation;
(d) coiling the target portion in one of the coiler furnaces;
(e) flat-pass rolling the surplus portion from the severable thickness to a desired surplus portion end-product thickness;
then
(f) transferring the surplus portion downstream for further processing to obtain a surplus end-product.

9 more elements

A method of processing steel, comprising:

in a recrystallization stage,
(a) sequentially reversingly rolling a steel product in a Steckel mill for a selected number of flat-pass rolling passes performed while the steel is above the Tnr in order to achieve a selected flat-pass reduction of the thickness of the steel product and to enable controlled austenite recrystallization of the steel during at least one of the flat-pass rolling passes;
(b) reversingly rolling the steel product in the Steckel mill for a selected number of recrystallization coiler passes performed while the steel is above the Tnr in order to reduce the steel product to an interim thickness and to enable controlled austenite recrystallization, each said recrystallization coiler pass comprising reducing the steel product and then coiling and uncoiling the steel product in at least one of an upstream coiler furnace and a downstream coiler furnace,
the total length of time of the recrystallization stage being dependent on the chemistry of the steel and being selected to enable suitably substantial austenite recrystallization of the steel;
(c) heating the coiler furnaces sufficiently to maintain the temperature of the steel product above the Tnr while the steel product is being coiled and retained in the coiler furnaces during the initial recrystallization coiler passes;
in a pancaking stage, after the last of said recrystallization coiler passes,
(d) reversingly rolling the steel product in the Steckel mill for a selected number of pancaking coiler passes performed while the steel is undergoing a declining temperature from about the Tnr to about the Ar3, in order to achieve a selected further reduction of the steel product to reach substantially the end-product thickness of the steel product, and to pancake the steel microstructure, each said pancaking coiler pass comprising reducing the steel product and then coiling and uncoiling the steel product in at least one of the coiler furnaces, then,
in a cooling stage, immediately following completion of the coiler passes,
(e) subjecting the steel product to controlled cooling during a single pass to reduce the temperature of the steel from a controlled entry temperature of about the Ar3 to an exit temperature of at least about 200° C. lower than the Ar3, at a cooling rate of about 12° C. to about 20° C. per second, thereby to obtain a steel product of enhanced strength and toughness, having a composition including a substantial portion of fine-grained bainite.

6 more elements

A method of processing steel, comprising:

in a recrystallization stage,
(a) sequentially reversingly rolling a steel product in a Steckel mill for a selected number of flat-pass rolling passes performed while the steel product is above the Tnr, in order to achieve a selected flat-pass reduction of the thickness of the steel product and to enable a controlled recrystallization of the steel product during at least one of the flat-pass rolling passes,
(b) maintaining the temperature of the steel product above Tnr for a period of time sufficient to perform the selected number of flat-pass rolling passes, by applying heat to the steel product from an induction furnace located in-line and in the vicinity of the Steckel mill,
the total length of time of the recrystallization stage being dependent on the chemistry of the steel and being selected to enable suitably substantial austenite recrystallization of the steel;
then, in a pancaking stage, immediately following completion of the recrystallization stage,
(c) further reversingly rolling the steel product in the Steckel mill for a selected number of pancaking passes performed while the steel is undergoing a declining temperature from about the Tnr to about the Ar3, in order to pancake the steel microstructure and to achieve a selected further reduction of the steel product to reach substantially the end-product thickness of the steel product, then, in a cooling stage, immediately following completion of the pancaking stage,
(d) subjecting the steel product to controlled cooling during a single pass to reduce the temperature of the steel from a controlled entry temperature of about the Ar3 to an exit temperature of at least about 200° C. lower than the Ar3, at a cooling rate of about 12° C. to about 20° C. per second, thereby to obtain a steel product of enhanced strength and toughness, having a composition including a substantial portion of fine-grained bainite.

4 more elements

Dependencies are inferred from the claim text.

Steckel mill/on-line controlled cooling combination

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Steckel mill/on-line controlled cooling combination

Life of this patent

Abstract

Claims44