Continuous annealing system and continuous annealing method

Patent metadata

Field	Value
Publication number	US-2016265079-A1
Application number	US-201415034340-A
Country	US
Kind code	A1
Filing date	Oct 30, 2014
Priority date	Nov 7, 2013
Publication date	Sep 15, 2016
Grant date	—

Abstract

A continuous annealing system and a continuous annealing method with which it is possible to achieve an annealing atmosphere having a low dew point which is suitable for annealing a steel strip containing easily oxidizable metals such as Si and Mn at low cost and with stability by preventing easily oxidizable metals such as Si and Mn in steel from being concentrated in a surface portion of a steel strip and preventing the formation of oxides of easily oxidizable metals such as Si and Mn.

First claim

1 . A continuous annealing system comprising:
a vertical annealing furnace comprising upper rolls, lower rolls, a heating zone, and a soaking zone, the upper rolls and lower rolls configured to wind a steel strip; gas suction ports configured to suction a part of a gas inside the vertical annealing furnace; a refiner configured to remove water and oxygen from the gas suctioned through the gas suction ports; and gas delivery ports configured to return the gas treated in the refiner to the vertical annealing furnace and to blow the gas to the steel strip, wherein the gas delivery ports are provided at positions where (i) the gas is blown to a portion of the steel strip that is descending in the vertical annealing furnace and (ii) the portion of the steel strip is at a temperature in the range of 300° C. to 700° C.

2 . The continuous annealing system according to claim 1 , wherein one or more of the gas delivery ports are placed at a position in the vertical annealing furnace expressed by the relational expression:
L≧ 0.7× L 0 ,
where L is distance from the center of a lower roll to a delivery port and L 0 is distance between the centers of an upper roll and a lower roll on which the steel strip travels next to the upper roll.

3 . The continuous annealing system according to claim 1 , wherein one or more of the gas delivery ports are placed on a side wall of the vertical annealing furnace so that the gas from the one or more of the gas delivery ports is blown in a direction at an angle in the range of −30° to +10°, where + indicates an upward direction and − indicates a downward direction to a horizontal direction of the vertical annealing furnace.

4 . The continuous annealing system according to claim 1 , wherein the gas is blown in a direction from a same side wall of the vertical annealing furnace through all of the gas delivery ports.

5 . The continuous annealing system according to claim 1 , wherein the vertical annealing furnace further comprises a first flow-straightening plate, a second flow-straightening plate, and a third flow-straightening plate,
the first flow-straightening plate is a convex body extending from a bottom of the vertical annealing furnace and faces the lower roll on which a part of the steel strip is wound first in a direction in which the gas is blown from one of the gas delivery port, or in a vicinity of the direction, after the gas has been blown, the second flow-straightening plate and the third flow-straightening plate are convex bodies extending from side walls of the vertical annealing furnace and face each other at positions immediately before a position where the part of the steel strip is wound on the lower roll, the distance between the lower roll and the first flow-straightening plate is in the range of 40 mm to 200 mm, and the second flow-straightening plate and the third flow-straightening plate have a length in the range of 200 mm to ((Wf−Ws)/2−50) mm or less in a width direction of the steel strip and a length of 100 mm to (Px−300) mm in a traveling direction of the steel strip, where Wf is furnace width, Ws is width of the steel strip, and Px is distance between a top of the furnace and a top surface of the lower roll.

6 . A continuous annealing method for continuously annealing a steel strip by using a vertical annealing furnace comprising upper rolls and lower rolls on which a steel strip is wound, a heating zone, and a soaking zone, the method comprising:
suctioning with gas suction ports a part of a gas inside the vertical annealing furnace; removing with a refiner water and oxygen from the as suctioned through the gas suction ports; and returning via gas delivery ports the gas treated in the refiner to the vertical annealing furnace and blowing the gas to the steel strip, wherein the gas delivery ports are provided at positions where (i) the gas is blown to a portion of the steel strip that is descending in the vertical annealing furnace and (ii) the portion of the steel strip is at a temperature in the range of 300° C. to 700° C.

7 . The continuous annealing method according to claim 6 , wherein one or more of the gas delivery ports are placed at a position expressed by the relational expression:
L≧ 0.7 ×L 0 , where L is distance from the center of a lower roll to a delivery port and L 0 is distance between the centers of an upper roll and a lower roll on which the steel strip travels next to the upper roll.

8 . The continuous annealing method according to claim 6 , wherein one or more of the gas delivery ports are placed on a side wall of the vertical annealing furnace so that gas from the one or more of the gas delivery ports is blown in a direction at an angle in the range of −30° to +10°, where + indicates an upward direction and − indicates a downward direction to the horizontal direction of the vertical annealing furnace.

9 . The continuous annealing method according to claim 6 , wherein the gas is blown in a direction from a same side wall of the vertical annealing furnace through all of the gas delivery ports.

10 . The continuous annealing method according to claim 6 , wherein the vertical annealing furnace further comprises a first flow-straightening plate, a second flow-straightening plate, and a third flow-straightening plate,
the first flow-straightening plate is a convex body extending from a bottom of the vertical annealing furnace and faces the lower roll on which a part of the steel strip is wound first in a direction in which the gas is blown from one of the gas delivery ports, or in a vicinity of the direction, after the gas has been blown, the second flow-straightening plate and the third flow-straightening plate are convex bodies extending from side walls of the vertical annealing furnace and face each other at positions immediately before a position where the part of the steel strip is wound on the lower roll, the distance between the lower roll and the first flow-straightening plate is in the range of 40 mm to 200 mm, and the second flow-straightening plate and the third flow-straightening plate have a length in the range of 200 mm to ((Wf−Ws)/2−50) mm or in a width direction of the steel strip and a length of 100 mm to (Px−300) mm in a traveling direction of the steel strip, where Wf is furnace width, Ws is width of the steel strip, and Px is distance between a top of the furnace top and a top surface of the lower roll.

11 . The continuous annealing system according to claim 2 , wherein one or more of the gas delivery ports are placed on a side wall of the vertical annealing furnace so that the gas from the one or more of the gas delivery ports is blown in a direction at an angle in the range of −30° to +10°, where + indicates an upward direction and − indicates a downward direction to a horizontal direction of the vertical annealing furnace.

12 . The continuous annealing system according to claim 2 , wherein the gas is blown in a direction from a same side wall of the vertical annealing furnace through all of the gas delivery ports.

13 . The continuous annealing system according to claim 3 , wherein the gas is blown in a direction from a same side wall of the vertical annealing furnace through all of the gas delivery ports.

14 . The continuous annealing system according to claim 2 , wherein the vertical annealing furnace further comprises a first flow-straightening plate, a second flow-straightening plate, and a third flow-straightening plate,
the first flow-straightening plate is a convex body extending from a bottom of the vertical annealing furnace and faces the lower roll on which a part of the steel strip is wound firs

Assignees

• Jfe Steel Corp

Inventors

• Takahashi Hideyuki
• Sato Nobuyuki
• Yokoyama Hiroyuki

Classifications

• C21D1/74

  Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material · CPC title

• C21D9/56 Primary

  Continuous furnaces for strip or wire · CPC title

• C21D9/562

  Details · CPC title

• C21D1/76

  Adjusting the composition of the atmosphere · CPC title

• C21D6/005

  containing Mn · CPC title