Method for producing a nitrided packaging steel

Patent metadata

Field	Value
Publication number	US-10920309-B2
Application number	US-201515506911-A
Country	US
Kind code	B2
Filing date	Jul 2, 2015
Priority date	Aug 27, 2014
Publication date	Feb 16, 2021
Grant date	Feb 16, 2021

Abstract

A nitrided packaging steel in the form of a flat steel product and method for producing a nitrided packaging steel with a carbon content of 10-1000 ppm and uncombined nitrogen, dissolved in the steel, of more than 100 ppm. The nitriding is performed in two stages: a first stage, in which a molten steel is nitrided to a nitrogen content of at most 160 ppm by introducing a nitrogen-containing gas and/or a nitrogen-containing solid into the molten steel, and a second stage, in which a flat steel product produced from the nitrided molten steel by cold rolling is treated with a nitrogen-containing gas in order to increase further the amount of uncombined nitrogen in the flat steel product.

First claim

The invention claimed is:

1. A method for producing a nitrided packaging steel having a carbon content of 10 to 1000 ppm by weight and a quantity of uncombined nitrogen dissolved therein of at least 150 ppm by weight, the method comprising:
nitriding a molten steel to a nitrogen content of a maximum 160 ppm by weight by feeding nitrogen into the molten steel in a form of a nitrogen-containing gas or a nitrogen-containing solid to form a nitrided molten steel;
casting a slab from the nitrided molten steel;
hot-rolling the slab to form to a hot-rolled strip;
cold-rolling the hot-rolled strip to form a flat steel product; and
recrystallization annealing and nitriding the flat steel product in a continuous annealing furnace, the recrystallization annealing and nitriding including;
passing the flat steel product through the continuous annealing furnace; and
introducing a nitrogen-containing gas into the continuous annealing furnace, directing the nitrogen-containing gas onto the flat steel product while passing the flat steel product through the continuous annealing furnace at a strip speed of at least 200 m/min, and increasing a quantity of uncombined nitrogen in the flat steel product to at least 150 ppm by weight, thereby producing the nitrided packaging steel, the nitrided packaging steel produced having a tensile strength of more than 600 MPa and an elongation at fracture of at least 5%.

2. The method according to claim 1 , wherein nitriding a molten steel includes feeding nitrogen gas (N 2 ), calcium cyanamide (CaCN 2 ), manganese nitride (MnN), or combinations thereof into the molten steel.

3. The method according to claim 1 , wherein introducing a nitrogen-containing gas into the continuous annealing furnace includes introducing ammonia gas (NH 3 ) into the continuous annealing furnace.

4. The method according to claim 3 , wherein introducing ammonia gas (NH 3 ) includes directing the ammonia gas onto the flat steel product through one spray nozzle or through a plurality of spray nozzles.

5. The method according to claim 3 , wherein introducing the ammonia gas includes establishing an ammonia equilibrium with an ammonia-equilibrium concentration in a range of 0.05 to 1.5% in the continuous annealing furnace.

6. The method according to claim 5 , further comprising measuring a value of the ammonia-equilibrium concentration using an ammonia sensor.

7. The method according to claim 6 , further comprising using the value of the ammonia-equilibrium concentration measured to control a quantity of ammonia gas fed per unit of time into the continuous annealing furnace.

8. The method according to claim 3 , further comprising, in addition to the ammonia gas, introducing an inert gas into the continuous annealing furnace.

9. The method according to claim 1 , wherein recrystallization annealing includes heating the flat steel product to a temperature of more than 600° C.

10. The method according to claim 1 , wherein the nitrided packaging steel produced has a carbon content in a range of 100 to 1000 ppm by weight.

11. The method according to claim 1 , wherein the nitrided packaging steel produced has a thickness of less than 0.5 mm.

12. The method according to claim 11 , wherein, after nitriding the flat steel product in the continuous annealing furnace, the uncombined nitrogen has a mean concentration value of 150 ppm or more by weight and a concentration distribution of the uncombined nitrogen varies from the mean concentration value by less than ±10 ppm by weight throughout the thickness of the nitrided packaging steel.

13. A method for producing a nitrided packaging steel having a carbon content of 10 to 1000 ppm by weight and a quantity of uncombined nitrogen dissolved therein of 150 ppm or more by weight, the method comprising:
forming a nitrided molten steel having a carbon content of 10 to 1000 ppm by weight by nitriding a molten steel to a nitrogen content of a maximum 160 ppm by weight by feeding nitrogen into the molten steel in a form of a nitrogen-containing gas or a nitrogen-containing solid;
casting a slab from the nitrided molten steel;
hot-rolling the slab to form to a hot-rolled strip;
cold-rolling the hot-rolled strip to form a flat steel product having a thickness of less than 0.5 mm;
recrystallization annealing and nitriding the flat steel product in a continuous annealing furnace by passing the flat steel product through the continuous annealing furnace and heating the flat steel product to a temperature in a range of 620° C. to 660° C.;
feeding ammonia gas (NH 3 ) into the continuous annealing furnace to produce a nitrogen gas containing atmosphere in the continuous annealing furnace having an ammonia equilibrium concentration in a range of 0.05% to1.5%; and
directing the ammonia gas onto surfaces of the flat steel product using a spray nozzle or a plurality of spray nozzles to increase the quantity of uncombined nitrogen in the flat steel product to 150 ppm or more by weight, thereby producing the nitrided packaging steel, the nitrided packaging steel produced having a homogenous concentration distribution of the quantity of uncombined nitrogen throughout thickness thereof and lacking a nitride layer on surfaces thereof.

14. The method according to claim 13 , wherein the nitrided packaging steel produced has a tensile strength of more than 600 MPa and an elongation at fracture of at least 5%.

15. The method according to claim 13 , wherein nitriding a molten steel includes feeding nitrogen gas (N 2 ), calcium cyanamide (CaCN 2 ), manganese nitride (MnN), or combinations thereof into the molten steel.

16. The method according to claim 13 , further comprising measuring a value of the ammonia-equilibrium concentration using an ammonia sensor.

17. The method according to claim 16 , further comprising using the value of the ammonia-equilibrium concentration measured to control a quantity of ammonia gas fed per unit of time into the continuous annealing furnace.

18. The method according to claim 13 , further comprising, in addition to the ammonia gas, introducing an inert gas into the continuous annealing furnace.

19. A method for producing a nitrided packaging steel having a carbon content of 10 to 1000 ppm by weight and a quantity of uncombined nitrogen dissolved therein in a range of 150 ppm to 500 ppm by weight, the method comprising:
a first nitriding step including forming a nitrided molten steel having a carbon content of 10 to 1000 ppm by weight by nitriding a molten steel to a nitrogen content of a maximum 160 ppm by weight by feeding nitrogen into the molten steel in a form of a nitrogen-containing gas or a nitrogen-containing solid;
casting a slab from the nitrided molten steel;
hot-rolling the slab to form to a hot-rolled strip;
cold-rolling the hot-rolled strip to form a flat steel product;
a second nitriding step including recrystallization annealing and nitriding the flat steel product in a continuous annealing furnace by passing the flat steel product through the continuous annealing furnace and heating the flat steel product to a temperature in a range of 620° C. to 660° C.;
feeding ammonia gas (NH 3 ) into the continuous annealing furnace to produce a nitrogen gas containing atmosphere in the continuous annealing furnace having an ammonia equilibrium concentration in a range of 0.05% to 1.5%;
directing the ammonia gas onto surfaces of the flat steel product using a spray nozzle or a plurality of spray nozzles, thereby increasing the quantity of uncombined nitrogen in the flat steel product achieved

Assignees

• Thyssenkrupp Rasselstein Gmbh
• Thyssenkrupp Ag

Inventors

• Kaup Burkhard
• Massicot Blaise
• Matusch Dirk

Classifications

• C21D8/02 Primary

  during manufacturing of plates or strips (C21D8/12 takes precedence) · CPC title

• C21D8/04

  to produce plates or strips for drawing, e.g. for deep-drawing · CPC title

• C22C38/004

  Very low carbon steels, i.e. having a carbon content of less than 0,01% · CPC title

• C22C38/001

  containing N · CPC title

• C21D9/48

  deep-drawing sheets · CPC title