JPWO2021105486A5

JPWO2021105486A5 -

Info

Publication number: JPWO2021105486A5
Application number: JP2022531073A
Authority: JP
Publication date: 2023-12-04

Claims

A method of hot press forming a steel article from zinc or zinc alloy coated steel strip, the method comprising:
The steel strip has the following composition in weight%:
C: 0.05-0.3;
Mn: 3.0-12.0;
Al: 0.04-3.0;
Optionally, additional alloying elements:
One or more of the following: Si: less than 1.5 Cr: less than 2.0 V: less than 0.1 Nb: less than 0.1 Ti: less than 0.1 Mo: less than 0.5;
unavoidable impurities (for example, S: less than 30 ppm by weight, P: less than 0.04); and Fe: having the remainder,
The method of manufacturing zinc or zinc alloy coated steel strip includes the following steps:
The process of casting molten steel into slabs;
reheating the slab to a temperature above 1150°C and holding it at that temperature for at least 60 minutes;
hot rolling the steel into strip, preferably at an exit finishing hot rolling temperature FRT above a temperature Ar3, where Ar3 denotes the temperature at which ferritic transformation begins in the steel during cooling;
The process of winding hot rolled steel strip;
pickling hot rolled steel strip;
optionally cold rolling the pickled hot rolled steel strip into cold rolled steel strip, comprising:
In the case of cold rolling, the hot rolled strip after winding and pickling is subjected to batch annealing at a temperature TB for a time PB;
Temperature TB and time PB are selected such that the microstructure in the steel after cooling to room temperature exhibits more than 60% ferrite by volume, and in a preferred embodiment, temperature TB and time PB are selected such that when temperature TB is below 650 °C Yes, and the time PB is selected to be 24 hours or more;
successively annealing the strip according to an annealing thermal cycle, where:
The temperature of the steel strip increases in the heating section, preferably at a rate of 1 to 15 °C/sec in the heating section, and then remains at a relatively stable level due to soaking in the soaking section;
The soaking atmosphere is maintained at a temperature between TMIN and TMAX,
TMIN is (TMAX-100℃),
Continuous annealing is considered to end when the temperature of the steel strip is reduced in the annealing thermal cycle, preferably at a rate of 0.5 to 10° C./sec;
TMAX is below the lowest temperature of (Ac3-100°C) and 700°C,
The dew point of the soaking atmosphere is -40°C to -10°C,
continuous annealing comprises pre-oxidizing the steel strip in a heating section in an annealing atmosphere with an oxygen content of 500 to 3000 ppm by volume;
The soaking atmosphere is a reducing atmosphere, preferably a reducing atmosphere containing 1 to 15% by volume of hydrogen in nitrogen,
The continuous annealing time, consisting of the heating section time and the soaking section time, is 150 seconds or more, preferably 180 seconds or more;
A process of hot-dip galvanizing steel strip with zinc or zinc alloy, wherein:
The immersion time is 3 seconds or more,
The bath temperature is maintained at 420°C to 500°C in the melt bath;
The zinc bath comprises essentially zinc and at least 0.1% by weight Al, optionally up to 5% by weight Al, and optionally up to 4% by weight Mg, with the remainder of the bath contains additional elements and unavoidable impurities, each additional element independently less than 0.3% by weight;
including;
The method of hot press forming into steel articles involves the following steps:
preparing a blank cut from molten zinc or zinc alloy coated steel strip;
reheating the blank to a blank temperature TRH of (Ac3-300°C) to 750°C;
Soaking the blank in TRH for 3 to 15 minutes;
Transferring the blank to the press within 30 seconds;
forming into a steel article in a press and then cooling the steel article;
A method comprising removing a steel article from a press.

The method according to claim 1, wherein the Mn content is 6.0% by weight or more.

3. A method according to claim 1 or 2, wherein the slab is reheated to a temperature above 1200<0>C, preferably above 1250<0>C and held at that temperature for more than 60 minutes.

A method according to any one of claims 1 to 3, wherein the slab is reheated to a constant temperature and held at that temperature for at least 120 minutes.

The method according to any one of claims 1 to 4, wherein the TRH is (Ac3-300°C) to 700°C.

Method according to any one of claims 1 to 5, characterized in that the blank is transferred to the press within 10 to 15 seconds.

A hot-pressed hot-dip zinc or zinc alloy coated steel article obtainable by the method according to any one of claims 1 to 6, comprising in % by volume:
Ferrite: 30% or more, preferably 40% or more;
Retained austenite: 20% or more, preferably 30% or more;
Martensite: A hot press formed hot dip zinc or zinc alloy coated steel article containing up to 40% (inclusive), preferably up to 30% (inclusive).

8. The hot press formed molten zinc or zinc alloy coated steel article of claim 7, wherein the ferrite content of the microstructure is 40% or more.

9. A hot press formed hot dip zinc or zinc alloy coated steel article according to claim 7 or 8, wherein the retained austenite content of the microstructure is 30% or more.

The following characteristics:
Yield strength: 800 MPa or more, preferably 850 MPa or more, more preferably 900 MPa or more;
Tensile strength: 820 MPa or more, preferably 1000 MPa or more;
Total elongation: 10% or more, preferably 15% or more, more preferably 25% or more;
Hot press formed hot dip zinc or zinc alloy coated steel article according to any one of claims 7 to 9, having a minimum bending angle at a thickness of 1.0 mm: 80° or more, more preferably 90° or more.

Claims 7 to 7, wherein the hot press-formed molten zinc or zinc alloy coated steel article is comprised of a steel substrate provided with a molten zinc coating layer, and the length of microcracks in the steel substrate is 5 μm or less. 11. A hot press formed molten zinc or zinc alloy coated steel article according to any one of 10 .