Weathering steel

Patent metadata

Field	Value
Publication number	US-10174398-B2
Application number	US-201615049461-A
Country	US
Kind code	B2
Filing date	Feb 22, 2016
Priority date	Feb 22, 2016
Publication date	Jan 8, 2019
Grant date	Jan 8, 2019

Abstract

A method of making weathering steel by preparing a molten melt producing an as-cast carbon alloy steel strip with a corrosion index of at least 6.0 comprising, by weight, 0.02%-0.08% carbon, <0.6% silicon, 0.2%-2.0% manganese, <0.03% phosphorus, <0.01% sulfur, <0.01% nitrogen, 0.2%-0.5% copper, 0.01%-0.2% niobium, 0.01%-0.2% vanadium, 0.1%-0.4% chromium, 0.08%-0.25% nickel, <0.01% aluminum, and the remainder iron and impurities. The molten melt is solidified and cooled into a cast strip ≤4 mm in thickness in a non-oxidizing atmosphere. The strip is hot rolled in an austenitic temperature range above Ar 3 to between 10% and 50% reduction, cooled at above 20° C./s and coiled below 700° C. to form a steel strip with a microstructure comprising bainite and acicular ferrite with more than 70% niobium in solid solution. Then, age hardening the strip resulting in a yield strength of at least 550 MPa and a total elongation of at least 8%.

First claim

What is claimed:

1. The method of making weathering steel comprising the steps of:
a. preparing a molten melt producing an as-cast carbon alloy steel strip less or equal to 4 mm in thickness with a corrosion index of at least 6.0 comprising, by weight, between 0.02% and 0.08% carbon, less than 0.6% silicon, between 0.2% and 2.0% manganese, less than 0.03% phosphorus, less than 0.01% sulfur, less than 0.01% nitrogen, between 0.2% and 0.5% copper, between 0.01% and 0.2% niobium, between 0.01% and 0.2% vanadium, between 0.1% and 0.4% chromium, between 0.08% and 0.25% nickel, less than 0.01% aluminum, and the remainder iron and impurities from making the molten melt;
b. solidifying and cooling the molten melt into a cast strip less than or equal to 4 mm in thickness in a non-oxidizing atmosphere;
c. hot rolling the cast strip in an austenitic temperature range above Ar 3 to between 10% and 50% reduction;
d. cooling the hot rolled cast strip at above 20° C. per second and coiling the cast strip below 700° C. to form a steel strip with a microstructure comprising bainite and acicular ferrite with more than 70% niobium in solid solution; and
e. age hardening the steel strip forming an age hardened steel strip having a yield strength of at least 550 MPa and a total elongation of at least 8%.

2. The method of making a weathering steel as claimed in claim 1 where the age hardened steel strip is batch annealed at a temperature greater than 450° C. between 15 and 50 hours.

3. The method of making a weathering steel as claimed in claim 2 where the age hardened steel strip has a yield strength of at least 700 MPa and a total elongation of at least 8%.

4. The method of making a weathering steel as claimed in claim 1 where the age hardened cast strip is in-line annealed at a temperature between 450° C. and 800° C. for less than 30 minutes.

5. The method of making a weathering steel as claimed in claim 4 where the age hardened steel strip has a yield strength of at least 700 MPa and a total elongation of at least 8%.

6. A method of continuously casting weathering steel comprising the steps of:
a. assembling a pair of counter-rotatable casting rolls to form a nip there between through which a thin strip can be casted, and capable of supporting a casting pool of molten metal formed on casting surfaces of the casting rolls above the nip with a pair of confining side dams adjacent the ends of the casting rolls;
b. assembling a delivery system with metal delivery nozzle or nozzles disposed axially above the nip and capable of discharging molten metal to form the casting pool supported on the casting rolls;
c. solidifying the molten metal delivered from the casting pool on the casting surfaces of the casting rolls in a non-oxidizing atmosphere and forming at the nip between the casting rolls a cast strip delivered downwardly that is less than 4 mm in thickness with a corrosion index of at least 6.0 comprising, by weight, of between 0.02% and 0.08% carbon, less than 0.6% silicon, between 0.2% and 2.0% manganese, less than 0.03% phosphorus, less than 0.01% sulfur, less than 0.01% nitrogen, between 0.2% and 0.5% copper, between 0.01% and 0.2% niobium, between 0.01% and 0.2% vanadium, between 0.1% and 0.4% chromium, between 0.08% and 0.25% nickel, less than 0.01% aluminum, and the remainder iron and impurities from melting;
d. hot rolling the cast strip in an austenitic temperature range above Ar 3 to between 10% and 50% reduction;
e. cooling the hot rolled cast strip at above 20° C. per second and coiling the cast strip below 700° C. to form a steel strip with a microstructure comprising bainite and acicular ferrite with more than 70% niobium in solid solution; and
f. age hardening the steel strip forming an age hardened steel strip having a yield strength of at least 550 MPa and a total elongation of at least 8%.

7. The method of continuously casting weathering steel as claimed in claim 6 where the age hardened steel strip is batch annealed at a temperature greater than 450° C. between 15 and 50 hours.

8. The method of continuously casting weathering steel as claimed in claim 7 where the age hardened steel strip has a yield strength of 700 MPa and a total elongation of at least 8%.

9. The method of continuously casting weathering steel as claimed in claim 6 where the age hardened cast strip is in line annealed at a temperature between 450° C. and 800° C. for less than 30 minutes.

10. The method of continuously casting weathering steel as claimed in claim 9 where the age hardened steel strip has a yield strength of 700 MPa and a total elongation of at least 8%.

11. A weathering steel made by steps comprising:
a. preparing a molten melt producing an as-cast carbon alloy steel strip less or equal to 4 mm in thickness with a corrosion index of at least 6.0 comprising by weight, between 0.02% and 0.08% carbon, less than 0.6% silicon, between 0.2% and 2.0% manganese, less than 0.03% phosphorus, less than 0.01% sulfur, less than 0.01% nitrogen, between 0.2% and 0.5% copper, between 0.01% and 0.2% niobium, between 0.01% and 0.2% vanadium, between 0.1% and 0.4% chromium, between 0.08% and 0.25% nickel, less than 0.01% aluminum, and the remainder iron and impurities from making the molten melt;
b. solidifying and cooling the molten melt into a cast strip less than or equal to 4 mm in thickness in a non-oxidizing atmosphere;
c. hot rolling the cast strip in an austenitic temperature range above Ar 3 to between 10% and 50% reduction;
d. cooling the hot rolled cast strip at above 20° C. per second and coiling the cast strip below 700° C. to form a steel strip with a microstructure comprising bainite and acicular ferrite with more than 70% niobium in solid solution; and
e. age hardening the steel strip forming an age hardened steel strip having a yield strength of at least 550 MPa and a total elongation of at least 8%.

12. The weathering steel as claimed in claim 11 where the age hardened steel strip is batch annealed at a temperature greater than 450° C. between 15 and 50 hours.

13. The weathering steel as claimed in claim 12 where the age hardened steel strip has a yield strength of at least 700 MPa and a total elongation of at least 8%.

14. The weathering steel as claimed in claim 11 where the age hardened steel strip is in line annealed at a temperature between 450° C. and 800° C. for less than 30 minutes.

15. The weathering steel as claimed in claim 14 where the age hardened steel strip has a yield strength of at least 700 MPa and a total elongation of at least 8%.

16. A weathering steel made by steps comprising:
a. assembling a pair of counter-rotatable casting rolls to form a nip there between through which thin strip can be casted, and capable of supporting a casting pool of molten metal formed on casting surfaces of the casting rolls above the nip with a pair of confining side dams adjacent the ends of the casting rolls,
b. assembling a metal delivery system with a metal delivery nozzle or nozzles disposed axially above the nip and capable of discharging molten metal to form the casting pool supported on the casting rolls;
c. solidifying molten metal delivered from the casting pool on the casting surfaces of the casting rolls in a non-oxidizing atmosphere and forming at the nip between the casting rolls a cast strip delivered downwardly that is less or equal to 4 mm in thickness with a corrosion index of at least 6.0 comprising by weight, of between 0.02% and 0.08% carbon, less than 0.6% silicon, between 0.2% and 2.0% manganese, less than 0.03% phosphorus, less than 0.01% sulfur, less than 0.01% nitrogen

Assignees

• Nucor Corp

Inventors

• Watson James W
• Wang Tao
• Young Eric
• Baudendistel Chad

Classifications

• C21D8/02

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

• C21D8/0205

  Chemistry & Metallurgy · mapped topic

• C21D1/18

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• B22D11/0651

  Casting wheels (B22D11/0682 takes precedence) · CPC title

• B22D11/0622

  formed by two casting wheels · CPC title