Method of annealing steel sheets

Patent metadata

Field	Value
Publication number	US-2016304980-A1
Application number	US-201315102118-A
Country	US
Kind code	A1
Filing date	Dec 10, 2013
Priority date	Dec 10, 2013
Publication date	Oct 20, 2016
Grant date	—

Abstract

A method of annealing of steel sheets is provided which includes a first step consisting in fully oxidizing the surface of such steel sheet thus creating a fully oxided surface layer, a second step consisting in selectively oxidizing elements other than iron of such steel, in an area extending under said fully oxided layer, thus creating a selectively oxided internal layer and a third step consisting in fully reducing said fully oxided surface layer.

First claim

1 - 12 . (canceled)

13 . A method of annealing steel sheets comprising:
a first step consisting of fully oxidizing a surface of a steel sheet thereby creating a fully oxided surface layer; a second step consisting of selectively oxidizing elements other than iron in said steel sheet, in an area extending under said fully oxided layer, thereby creating a selectively oxided internal layer; and a third step consisting of fully reducing said fully oxided surface layer.

14 . A method of annealing steel sheets according to claim 13 ,
wherein said method is performed in a facility comprising a direct flame heating zone, a radiant tubes heating zone and a radiant tubes soaking zone; and wherein said first step is performed in the direct flame heating zone, said second step is performed at least in the radiant tubes heating zone, and said third step is performed at least in the radiant tubes soaking zone.

15 . A method of annealing steel sheets according to claim 14 , wherein said first step comprises regulating said direct flame heating zone atmosphere to an air/gas ratio above 1.

16 . A method of annealing steel sheets according to claim 13 ,
wherein said method is performed in a facility comprising a radiant tubes preheating zone, a radiant tubes heating zone, and a radiant tubes soaking zone; and wherein said first step is performed in the radiant tubes preheating zone, said second step is performed at least in the radiant tubes heating zone, and said third step is performed at least in the radiant tubes soaking zone.

17 . A method of annealing steel sheets according to claim 16 , wherein said first step is performed in an oxidizing chamber containing an amount of O2 of 0.1 to 10 vol. %.

18 . A method of annealing steel sheets according to claim 14 , wherein said second step is performed by setting a dew point of such radiant tubes heating zone above a critical value depending on the H2 content of the atmosphere of such zone.

19 . A method of annealing steel sheets according to claim 18 , wherein said dew point is regulated through injection of water vapor.

20 . A method of annealing steel sheets according to claim 17 , wherein said second step is performed by setting a dew point of such radiant tubes heating zone above a critical value depending on the H2 content of the atmosphere of such zone.

21 . A method of annealing steel sheets according to claim 20 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

22 . A method of annealing steel sheets according to claim 13 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

23 . A method of annealing steel sheets according to claim 13 , wherein said steel comprises up to 4 wt % of manganese, up to 3 wt % of silicon, up to 3 wt % of aluminium and up to 1 wt % of chromium.

24 . A method of production of a galvanized steel sheet wherein an annealed steel sheet obtained according to claim 13 is hot dip coated by dipping in a zinc bath.

25 . A method of production of a galvannealed steel sheet wherein a galvanized steel sheet obtained according to claim 25 is further heat treated at a temperature from 450° C. to 580° C. during 10 to 30 seconds.

26 . A method of production of a galvannealed steel sheet according to claim 27 wherein said heat treatment is performed under 490° C.

27 . A method of annealing steel sheets according to claim 16 , wherein said second step is performed by setting a dew point of such radiant tubes heating zone above a critical value depending on the H2 content of the atmosphere of such zone.

28 . A method of annealing steel sheets according to claim 14 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

29 . A method of annealing of steel sheets according to claim 16 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

30 . A method of annealing of steel sheets according to claim 15 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

31 . A method of annealing of steel sheets according to claim 17 , wherein said third step of reduction is performed by using an atmosphere containing at least 2% H2, balance being N2.

Assignees

• Arcelormittal

Inventors

• Rotole John
• Staudte Jonas
• Mataigne Jean-Michel

Classifications

• C23C8/80

  After-treatment · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/38

  with more than 1.5% by weight of manganese · CPC title

• C23C2/40

  Plates; Strips · CPC title

• C21D6/005

  containing Mn · CPC title