Method for producing thermo-mechanically produced profiled hot-rolled strip products

Patent metadata

Field	Value
Publication number	US-12258648-B2
Application number	US-201917413364-A
Country	US
Kind code	B2
Filing date	Dec 18, 2019
Priority date	Dec 19, 2018
Publication date	Mar 25, 2025
Grant date	Mar 25, 2025

Abstract

A method for producing thermomechanically produced hot strip products having improved mechanical properties is provided. A steel alloy is melted and adjusted so that a recrystallization during hot rolling at greater than 800° C. is suppressed. The melted steel alloy is cast into slab ingots and after being heated to a temperature above Ac 3 , the slab ingots are hot rolled until they reach a desired degree of deformation and strip thickness. The strip is then cooled to room temperature and is hardened by briefly reheating to a temperature above Ac 3 and cooling again. The reheating takes place with a rapid temperature increase of more than 5 K/s and is maintained at the targeted temperature for a period of 0.5 to 60 seconds before cooling to yield the improved mechanical properties.

First claim

The invention claimed is:

1. A method for producing thermomechanically produced profiled hot-rolled strip products, comprising the steps of:
providing a steel alloy including the following elements, in percent by weight:
0.03 to 0.22% carbon,
0.0 to 2.0% silicon,
0.5 to 3.0% manganese,
0.02 to 1.2% aluminum,
0 to 2.0% chromium,
0 to 2.0% nickel,
0.0 to 1.0% molybdenum,
0.0 to 1.5% copper,
0 to 0.02% phosphorus,
0 to 0.01% sulfur,
0 to 0.008% nitrogen,
0 to 0.005% boron,
0.0 to 0.2% niobium,
0.0 to 0.3% titanium,
0.0 to 0.5% vanadium,
the remainder being comprised of iron and smelting-related impurities;
melting the steel alloy;
adjusting the steel alloy so that a recrystallization during hot rolling is suppressed;
casting the melted steel alloy into slab ingots;
heating the slab ingots to a temperature above Ac 3 ;
thermomechanically hot rolling the slab ingots using a final rolling temperature greater than 800° C. until the slab ingots reach a desired degree of deformation and a desired strip thickness to form hot-rolled steel strips having a non-recrystallized elongated austenite structure;
cooling the hot-rolled steel strips to room temperature;
after the cooling, hardening the hot-rolled steel strips by heating the hot-rolled steel strips to a target temperature above Ac 3 and cooling the hot-rolled steel strips again to form hardened steel strips; and
before or after the hardening, profiling the hot-rolled steel strips in a forming process to form the profiled hot-rolled strip products;
wherein the heating of the hot-rolled steel strips is performed using a temperature increase of more than 5 K/s and the hot-rolled steel strips are kept at the target temperature for a holding period of about 0.5 to about 60 seconds prior to cooling the hot-rolled steel strips again; and
the hardened steel strips have a crystal structure that comprises up to 90% martensite and a remainder of austenite and bainite.

2. The method according to claim 1 , wherein the steel alloy comprises the following elements in percent by weight:
0.055 to 0.195 carbon,
0.0 to 0.3% silicon,
1.4 to 2.3% manganese,
0.02 to 0.6% aluminum,
0 to 2% chromium, 0 to 2% nickel,
0.0 to 0.42% molybdenum,
0.0 to 0.5% copper,
0 to 0.008% phosphorus,
0 to 0.0015% sulfur,
0 to 0.007% nitrogen
0 to 0.005% boron,
0.0 to 0.2% niobium,
0.0 to 0.3% titanium,
0.0 to 0.5% vanadium,
the remainder being comprised of iron and smelting-related impurities.

3. The method according to claim 1 , wherein the heating of the hot-rolled steel strips comprises inductive heating.

4. The method according to claim 1 , wherein the heating of the hot-rolled steel strips to a temperature above Ac 3 comprises heating the hot-rolled steel strips to between about 800° C. and about 1000° C.

5. The method according to claim 1 , further comprising annealing the hardened steel strips at a temperature of about 300° C. to about 700° C.

6. The method according to claim 1 , wherein the holding period is about 0.5 to about 10 seconds.

7. The method according to claim 1 , wherein the step of cooling the hot-rolled steel strips again takes place at a cooling rate of >10° K/s.

8. The method according to claim 7 , wherein the cooling rate is >30 K/s.

9. The method according to claim 1 , wherein the heating of the hot-rolled steel strips is performed using rolling heat.

10. The method according to claim 1 , wherein the hot-rolled steel strips are subjected to the hardening before the profiling.

11. The method according to claim 1 , further comprising the steps of welding the hardened steel strips by forming a weld seam, and heat treating the welded steel strips to homogenize the weld seam.

12. The method according to claim 1 , wherein the hardened steel strips have a sheet thickness of about 1.5 mm to about 20 mm.

13. The method according to claim 1 , wherein the step of hardening the hot-rolled steel strips is performed using a Hollomon-Jaffee parameter of about 18000 to about 23000.

14. The method according to claim 1 , wherein the profiled hot-rolled strip products comprise a tensile strength (Rm) and a notched bar impact bending work (Kv) satisfying at least one of the following mechanical properties:
tensile strength (Rm)>=900 MPa,
notched bar impact bending work (KV)>=70 J, measured at −40° C.,
and the following condition is satisfied:
Rm×KV >=75000 MPa J.

15. A method for producing thermomechanically produced profiled hot-rolled strip products, comprising the steps of:
providing a steel alloy including the following elements, in percent by weight:
0.03 to 0.22% carbon,
0.0 to 2.0% silicon,
1.4 to 2.3% manganese,
0.02 to 1.2% aluminum,
0 to 2.0% chromium,
0 to 2.0% nickel,
0.0 to 1.0% molybdenum,
0.0 to 1.5% copper,
0 to 0.04% total of phosphorus, sulfur, nitrogen and boron,
0.0 to 1.0% total of niobium, titanium and vanadium,
the remainder being comprised of iron and smelting-related impurities;
melting the steel alloy;
adjusting the steel alloy so that a recrystallization during hot rolling is suppressed;
casting the melted steel alloy into slab ingots;
heating the slab ingots to a temperature above Ac 3 ;
thermomechanically hot rolling the slab ingots using a final rolling temperature greater than 800° C. until the slab ingots reach a desired degree of deformation and a desired strip thickness to form hot-rolled steel strips having a non-recrystallized elongated austenite structure;
cooling the hot-rolled steel strips to room temperature;
after the cooling, hardening the hot-rolled steel strips by heating the hot-rolled steel strips to a target temperature above Ac3 and cooling the hot-rolled steel strips again to form hardened steel strips; and
before or after the hardening, profiling the hot-rolled steel strips in a forming process to form the profiled hot-rolled strip products;
wherein the heating of the hot-rolled steel strips is performed using a temperature increase of more than 10 K/s and the hot-rolled steel strips are kept at the target temperature for a holding period of about 0.5 to about 60 seconds prior to cooling the hot-rolled steel strips again; and
the hardened steel strips have a crystal structure that comprises up to 90% martensite and a remainder of austenite and bainite.

16. The method of claim 15 , wherein the profiled hot-rolled strip products comprise a tensile strength (Rm) and a notched bar impact bending work (Kv) satisfying at least one of the following mechanical properties:
tensile strength (Rm)>=900 MPa,
notched bar impact bending work (KV)>=70 J, measured at −40° C.,
and the following condition is satisfied:
Rm×KV >=75000 MPa J.

17. The method of claim 16 , wherein the Rm multiplied by the notched bar impact bending work (KV) is at least about 165,000 MPa-J.

18. The method of claim 15 , wherein the steel alloy comprises the following elements in percent by weight:
0.055 to 0.195 carbon,
0.0 to 0.3% silicon,
1.4 to 2.3% manganese,
0.02 to 0.6% aluminum,
0 to 2% chromium,
0 to 2% nickel,
0.0 to 0.42% molybdenum,
0.0 to 0.5% copper,
0 to 0.008% phosphorus,
0 to 0.0015% sulfur,
0 to 0.007% nitrogen
0 to 0.005% boron,
0.0 to 0.2% niobium,
0.0 to 0.3% titanium,
0.0 to 0.5% vanadium
the remainder being comprised of iron and smelting-related impurities.

19. A method for producing thermomechanically produced profiled hot-rolled strip products, comprising the steps of:
providing a steel alloy including the following elements, in perc

Assignees

• Voestalpine Stahl Gmbh
• voestapline Stahl GmbH

Inventors

• Ernst Wolfgang
• Spindler Helmut

Classifications

• C21D8/02

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

• C21D8/10

  during manufacturing of tubular bodies · CPC title

• C22C38/58

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

• C22C38/54

  with boron · CPC title

• C22C38/50

  with titanium or zirconium · CPC title