Method for hot dip coating a flat steel product

Patent metadata

Field	Value
Publication number	US-9279175-B2
Application number	US-201113819481-A
Country	US
Kind code	B2
Filing date	Aug 18, 2011
Priority date	Aug 31, 2010
Publication date	Mar 8, 2016
Grant date	Mar 8, 2016

Abstract

A method for hot dip coating a flat stainless steel product with more than 5 wt. % Cr with a protective metallic coating by: heating the flat steel product under an oxygen-free heating atmosphere to 100° C.-600° C. within 1-30 seconds; continuing heating to a holding temperature of 750° C.-950° C., by heating to 550° C.-800° C. under an inert or reducing atmosphere, holding within this temperature window for 1 to 15 seconds under an oxidizing atmosphere, and continuing heating under an inert or reducing atmosphere, until the holding temperature is reached; holding at the holding temperature for 10-120 seconds under a reducing atmosphere; and passing the flat steel product through a nozzle area under an inert or reducing atmosphere at 430°-780° C. and into a molten bath in which the flat steel product is coated with the metallic coating.

First claim

The invention claimed is:

1. A method for hot dip coating of a flat steel product comprising a stainless steel comprising more than 5 wt. % Cr with a protective metallic coating which protects against corrosion, comprising the following work steps carried out in sequential order:
a) within 1-30 seconds, heating of the flat steel product to a heating temperature of 100-600° C. under a heating atmosphere which is oxygen-free with the exception of operation-related impurities preventing the oxidation of the surface of the flat steel product, the heating atmosphere comprising 1-50% by volume H 2 in addition to N 2 and technically unavoidable impurities;
b) continuation of the heating of the flat steel product up to a holding temperature of 750-950° C., wherein the heating is carried out
up to a pre-oxidation temperature window of 550-800° C. in an inert or reducing heating atmosphere,
for 1-15 seconds within the pre-oxidation temperature window the heating is carried out in an oxidising pre-oxidation atmosphere in order to cause a pre-oxidation of the surface of the flat steel product, the pre-oxidation atmosphere comprising 0.1-3.0% by volume O 2 and optionally 1-50% by volume H 2 in addition to N 2 and technically unavoidable impurities and having a dew point of −20° C. to +25° C., and
after leaving the pre-oxidation window under an inert or reducing atmosphere until the holding temperature is reached;
c) holding the pre-oxidised flat steel product at the holding temperature for 10-120 seconds under a reducing holding atmosphere, the holding atmosphere comprising 1.0-50.0% by volume H 2 in addition to N 2 and technically unavoidable impurities and having a dew point of −30° C. to +25° C.;
d) optionally: ageing the flat steel product for 1-30 seconds under an inert or reducing ageing atmosphere at an ageing temperature of 430-780°, the ageing atmosphere comprising 1.0-50.0% by volume H 2 in addition to N 2 and technically unavoidable impurities and having a dew point of −30° C. to +25° C.;
e) passing the flat steel product through a nozzle area and then through a molten bath in which the flat steel product is hot dip coated with the metallic coating, wherein the flat steel product is held in the nozzle area under an inert or reducing nozzle atmosphere until it enters the molten bath, the nozzle atmosphere having a dew point of −80° C. to −25° C. and comprising 1-50% by volume H 2 in addition to N 2 and technically unavoidable impurities or completely consisting of H 2 and technically unavoidable impurities, and the temperature of the flat steel product as it passes through the nozzle area is 430-780° C.

2. The method according to claim 1 , wherein the work step a) is completed within 1-5 seconds.

3. The method according to claim 1 , wherein the heating temperature in the work step a) is 200° C.-500° C.

4. The method according to claim 1 , wherein the flat steel, product is subjected to recrystallising annealing before the work step a) and the holding temperature is 750° C.-850° C.

5. The method according to claim 1 , wherein the flat steel product enters the work step a) in an as-rolled state and the holding temperature is 800° C.-850° C.

6. The method according to claim 1 , wherein the hot dip coating is carried out as hot dip galvanising and the ageing temperature set during the optionally carried out ageing is 430° C.-650° C.

7. The method according to claim 1 , wherein the hot dip coating is carried out as hot dip aluminising and the ageing temperature set during the optionally carried out ageing is 650° C.-780° C.

8. The method according to claim 1 , wherein the hot dip coating of the flat steel product is carried out as hot dip galvanising and the molten bath temperature is 420° C.-600° C.

9. The method according to claim 1 , wherein the hot dip coating of the flat steel product is carried out as hot dip aluminising and the molten bath temperature is 650° C.-780° C.

10. The method according to claim 1 , wherein the stainless steel comprises, in addition to iron and unavoidable impurities (in % by weight):
Cr: 5.0-30.0%,
Mn: <6.0%,
Mo: <5.0%,
Ni: <30.0%,
Si: <2.0%,
Cu: <2.0%,
Ti: <1.0%,
Nb: <1.0%,
V: <0.5%,
N: <0.2%,
Al: <0.2%, and
C: <0.1%.

11. The method according to claim 10 , wherein the steel (in % by weight) comprises: Cr: 10.0-13.0%, Ni: <3.0%, Mn: <1.0%, Ti: <1.0%, and C: <0.03%.

Assignees

• Blumenau Marc
• Heiler Hans-Joachim
• Jindra Fred
• Schoenenberg Rudolf
• Krautschick Hans-Joachim
• Thyssenkrupp Steel Europe Ag

Inventors

• Blumenau Marc
• Heiler Hans-Joachim
• Jindra Fred
• Schoenenberg Rudolf
• Krautschick Hans-Joachim

Classifications

• C23C2/40

  Plates; Strips · CPC title

• C23C2/02 Primary

  Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) · CPC title

• C23C2/12 Primary

  Aluminium or alloys based thereon · CPC title

• C23C2/06

  Zinc or cadmium or alloys based thereon · CPC title

• C23C2/004

  Snouts · CPC title