Claims
- 1. In or for use in an in-line rolling mill for producing steel, said mill having a continuous caster for producing a cast strand of steel, severing means for cutting the cast strand transversely into a series of slabs, a reheat furnace downstream of the caster for bringing slabs to a substantially uniform pre-rolling temperature, and a Steckel mill downstream of the reheat furnace for rolling the castings in sequence; the apparatus combination comprising;
(a) an in-line upstream quench station located downstream of the caster and upstream of the reheat furnace and having a plurality of spray nozzles directed at the cast steel for applying cooling sprays onto the cast steel that quench a surface layer of the cast steel to a selected depth so that the surface layer is transformed from an austentitic to a substantially non-austentitic microstructure; (b) a shear located downstream of the Steckel mill for transversely severing and trimming the leading edge of the rolled steel to provide a precise transverse vertical face thereon and for optionally cutting the steel to a series of portions of selected length; and (C) a temperature reduction station downstream of the shear for applying a controlled flow of cooling fluid to the rolled steel so as to obtain a preferred microstructure of the steel; wherein (d) the reheat furnace heats the slabs to a suitable pre-rolling temperature above the temperature Tnr, and transforms the quenched surface layer to fine-grained austenite; and (e) the Steckel mill rolls and reduces the thickness of the slab first in a temperature range above the temperature Tnr and then at a decreasing temperature between the temperatures Tnr and Ar3 to obtain first a controlled recrystailization of austenite and then a pancaking of the austenite.
- 2. The apparatus of claim 1, wherein the temperature reduction station comprises a controlled cooling station for cooling the rolled steel at a rate of about 12 C to 20 C per second and to a temperature of about 200 C to about 350 C below the temperature Ar3, thereby obtaining in the rolled steel a preferred microstructure including a substantial portion of fine-grained bainite.
- 3. The apparatus of claim 1, wherein the temperature s reduction station comprises a downstream quench station immediately followed by a controlled cooling station, the quench station applying cooling fluid to the rolled steel at a rate and in a quantity sufficient to quench the rolled steel rapidly and intensely to obtain a preferred microstructure including a substantial portion of fine-grained martensite, and the controlled cooling station applying additional cooling fluid sufficient to maintain the cooling of the steel at a high rate so as to obtain a relatively high portion of fine-grained martensite in the quenched steel.
- 4. The apparatus of claim 3, additionally including a tempering furnace receiving the rolled steel from the controlled cooling station and tempering same.
- 5. In or for use in an in-line rolling mill for producing steel plate of a selected target length and thickness, said mill having a continuous caster for producing a cast strand of steel, severing means for cutting the cast strand transversely into a series of slabs, a reheat furnace downstream of the severance means for bringing slabs to a substantially uniform pre-rolling temperature, and a Steckel rolling mill downstream of the reheat furnace for rolling the castings in sequence; the apparatus combination comprising:
- 6. The apparatus of claim 5, including a transverse shear in line with and proximate to the temperature reduction station.
- 7. The apparatus of claim 5, including a transverse shear upstream of the temperature reduction station for transversely severing and trimming the leading edge of the rolled steel to provide a precise transverse vertical face thereon.
- 8. The apparatus of claim 6, additionally including a transverse shear downstream of the temperature reduction station for cutting the steel to a series of portions of selected length.
- 9. The apparatus of any of claims 5-8, wherein the temperature reduction station comprises a controlled cooling station for cooling the rolled steel at a rate of about 12 C to 20 C per second and to a temperature of about 200 C to about 350 C below the temperature Ar3, thereby obtaining in the rolled steel a preferred microstructure including a substantial portion of fine-grained bainite.
- 10. The apparatus of any of claims 5-8, wherein the temperature reduction station comprises a downstream quench station immediately followed by a controlled cooling station, the quench station applying cooling fluid to the rolled steel at a rate and in a quantity sufficient to quench the rolled steel rapidly and intensely to obtain a preferred microstructure including a substantial portion of fine-grained martensite, and the controlled cooling station applying additional cooling fluid sufficient to maintain the cooling of the steel at a high rate sufficient to substantially maintain and preferably to increase the portion of fine-grained martensite obtained in the rolled steel.
- 11. The apparatus of claim 10, additionally including a tempering furnace receiving the rolled steel from the controlled cooling station and tempering same.
- 12. The apparatus of any of the preceding claims, wherein the Steckel mill is provided with coiler furnaces immediately upstream and downstream thereof, each said coiler furnace including pinch rolls in the vicinity of the entrance port thereof for facilitating near-complete retraction into the coiler furnace of coilable steel undergoing rolling.
- 13. The apparatus of any of the preceding claims, wherein the controlled cooling station provides laminar flow cooling for the upper surface of the rolled steel and quasi-laminar flow cooling for the undersurface of the rolled steel.
- 14. The apparatus of any of the preceding claims, wherein said upstream quench station comprises:
(a) an array of spray nozzles arranged in transversely separated spray groups above and below the cast steel as the cast steel passes through the upstream quench station; (b) at least one valve for each spray group for controlling the amount of spray provided by each group to the cast steel; (c) a control unit for controlling the valves thereby to regulate the amount of spray provided by each spray group, in response to selected parameters including casting width and casting speed; thereby to provide transversely differential spray to the cast steel being quenched.
- 15. The apparatus of claim 14, wherein the selected parameters include a post-quench surface temperature profile of the cast steel.
- 16. The apparatus of claim 14 or 15, wherein the selected parameters include a pre-quench surface temperature profile of the cast steel.
- 17. The apparatus of any of claims 14-16, wherein the upstream quench station is located upstream of the severing means.
- 18. The apparatus of any of claims 14-16, wherein the upstream quench station is located downstream of the severing means.
- 19. The apparatus of any of claims 14-18, wherein the array of nozzles underneath the cast steel is substantially the mirror image of the array of nozzles above the cast steel.
- 20. The apparatus of any of claims 14-19, wherein the array of nozzles underneath the cast steel provides a greater amount of spray to the cast steel than is provided by the nozzles above the cast steel.
- 21. The apparatus of any of claims 14-20, additionally including spray nozzles arrayed in longitudinally spaced transversely extending groups, said last mentioned groups being controlled by the control unit to provide longitudinally differential spraying of the cast steel.
- 22. An in-line method for producing a rolled steel product, including continuously casting a strand of steel, severing the cast strand transversely into a series of slabs, reheating the slabs to a substantially uniform pre-rolling temperature, and reversingly reduction-rolling the reheated steel slabs; characterized by:
(a) applying to the cast steel an upstream quench prior to reheating so as to quench a surface layer of the cast steel to a selected depth so that the surface layer is transformed from an austentitic to a substantially non-austentitic microstructure; (b) shearing the leading edge of the rolled steel immediately after completion of rolling to crop the steel so as to provide a precise transverse vertical face on the leading edge of the rolled steel; and (c) applying to the cropped rolled steel a controlled temperature reduction so as to obtain a preferred microstructure of the steel; and further characterized in that (d) the slabs are reheated to a suitable pre-rolling temperature above the temperature Tnr sufficient to transform the quenched surface layer to fine-grained austenite; and (e) the slabs are reduction rolled first in a temperature range above the temperature Tnr and then at a decreasing temperature between the temperatures Tnr and Ar3 to obtain first a controlled recrystallization of austenite and then a pancaking of the austenite.
- 23. The method of claim 22, wherein the controlled temperature reduction comprises cooling the rolled steel at a rate of about 12 C to 20 C per second and to a temperature of about 200 C to about 350 C below the temperature Ar3, thereby obtaining in the rolled steel a preferred microstructure including a substantial portion of fine-grained bainite.
- 24. The method of claim 22, wherein the controlled temperature reduction comprises a downstream quench immediately followed by a martensite sustaining cooling, the quench being sufficient to obtain a preferred microstructure including a substantial portion of fine-grained martensite, and the sustaining cooling being sufficient to substantially maintain and preferably to increase the portion of fine-grained martensite obtained in the rolled steel.
- 25. The method of claim 24, additionally including tempering the rolled steel following the sustaining cooling step
- 26. The method of any of claims 22-25, wherein the controlled temperature reduction is effected at least in part by laminar flow cooling.
- 27. The method of any of claims 22-26, wherein the upstream quench is applied transversely differentially to compensate for the transverse surface temperature profile of the cast steel.
- 28. The method any of claims 22-27, wherein the reduction rolling comprises
(i) a selected number of flat-pass rolling passes above Tnr to achieve a selected flat-pass reduction of the thickness of the steel and recrystallization of the austentite in the steel being rolled, then (ii) a selected number of initial coiler passes performed while the steel is of coilable thickness and the temperature of the steel is above the Tnr, each said initial coiler pass comprising reducing the steel and then coiling the product in a heated environment at a temperature above the Ar3, then (iii) a selected number of final coiler passes performed while the temperature of the steel is above the Ar3, each said final coiler pass comprising reducing the steel and then coiling the product in a heated environment at a temperature above the Ar3.
- 29. The method defined in claim 22-28, wherein the reduction rolling prior to the final coiler passes reduces the thickness of the steel by a factor in the order of at least 1.5:1 and wherein the final coiler passes reduce the thickness of the steel by a factor in the order of at least 2:1 so that the overall combined reduction of the steel is at least about 3:1.
- 30. The method defined in any of claims 22-29, for optimizing the production of steel products in circumstances in which the rolling mill is limited at least in part by coiler furnace capacity and by the inability of the coiler furnaces to coil steel above a maximum coilable thickness;
characterized by rolling a maximum-weight slab exceeding the coiler furnace capacity and severing 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 coiler furnace capacity; and further characterized by (a) flat-pass reduction rolling the maximum-weight slab from a pre-rolled thickness to produce an interim steel product of a severable thickness exceeding the maximum coilable thickness; 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 capacity, and a residual surplus portion; (c) flat-pass rolling the target portion to further reduce the target portion from the severable thickness to a thickness not exceeding the maximum coilable thickness; (d) coaling the target portion an one of the coiler furnaces; (e) flat-pass rolling the surplus portion from the severable thickness to a desired end-product thickness; then (f) transferring the surplus portion downstream for further processing to obtain a surplus end product.
- 31. The method as claimed in claim 30, additionally including, after completion of step (f),
(g) flat-pass rolling the target portion to a plate of desired end-product thickness, then directing the target portion downstream for processing as plate end-product.
- 32. Apparatus as claimed in claim 1, wherein the temperature reduction station is selectably operable to apply cooling to provide an end-product that is bainite-rich or martensite-rich.
- 33. Apparatus as claimed in claim 32, wherein the temperature reduction station comprises a downstream quench station and immediately downstream thereof a controlled cooling facility, wherein both the quench station and controlled cooling station are operated to produce martensite-rich steel, and wherein the quench station is idle and the controlled cooling station is operated to produce bainite-rich steel.
- 34. Apparatus as claimed in claim 33, wherein the controlled cooling station is a laminar flow cooling station.
- 35. Apparatus as claimed in claim 33 or 34, wherein the quench station comprises RPQ quench apparatus.
RELATED APPLICATIONS
[0001] This is a divisional application of (1) U.S. application Ser. No. 09/350,314, filed Jul. 9, 1999, which is a continuation-in-part of (2) U.S. application Ser. No. 09/157,075, which is a continuation of U.S. application Ser. No. 08/594,704, now issued as U.S. Pat. No. 5,810,951, and (3) U.S. application Ser. No. 08,870,470, which is a continuation of U.S. application Ser. No. 08/481,614, now issued as U.S. Pat. No. 5,706,688, and (4) U.S. application Ser. No. 09/113,428. This application also claims priority from U.S. application Ser. No. 09/113,428, filed Jul. 10, 1998.
Divisions (1)
|
Number |
Date |
Country |
Parent |
09350314 |
Jul 1999 |
US |
Child |
09910176 |
Jul 2001 |
US |